Selecting the correct tire pressure; How airing down motorcycle tires affects contact patch

[@wanderlpnw]

As an engineer, I love these experiment videos. A lot of common motorcycle beliefs aren't rooted in science, so it's great to see people like Bret get down and dirty with real data.

[@nickthequick]

Beliefs aren't rooted in science. A basic definition of belief is the absence of knowledge; it is a worldview that is chosen due to the social environment a person happens to find himself in. A prime example is religion.

[@PP-wz7mp]

@@nickthequick utter bullshit

[@MrDavidfuchser]

@@nickthequick Beliefs can be rooted in truth, lies, science, or ignorance. I believe in good science, but then by your definition science is the absence of knowledge from my perspective.

[@Wintersdark]

Not gonna get into the semantic argument, but for sure it's GREAT to see some science done because as you said, a LOT of common knowledge for motorcycles is not at all rooted in science, just random explanations that people guessed at then told other people until everyone is repeating the same "seems plausible" but totally unfounded stuff. This is the motorcycle content I want more than anything else.

[@CarnevalOne]

@@nickthequick Most belief is absolutely based in science, or some kind of systematic observation, like belief in God is based in philosophical inquiry and observation of our universe. Whether that belief corresponds to truth, is another matter, which is why more scientific inquiry is employed to try to get closer to truth. Science should never really answer all of our questions absolutely, apart from the basic stuff, like how long an object is, thus ot can never really "be settled", a statement that is profoundly unscientific. So, more scientific experiments are needed to try to better answer the questions this man here thinks he did. For example, he observed what he deems to be a small change in contact patch area. Cool. How much does that actually affect traction or floatation over a given type of surface? There was no attempt to test this scientifically, yet I feel like an attempt to draw such conclusions was made, which IMO was pseudoscientific. A 10% contact patch change could have a 50% impact on traction, if that could be measured. Another factor that was never considered here was the type of tire casing, sidewall thickness, compound, tread. What other unbeknown to us factors could there be? The more we know, the more questions we have. That is true science IMO.

[@gmrecneps]

Folks. Find a bit of technical (hill, rocky, or deep sand/gravel) terrain that you can barely ride without crashing at street tire pressures. Then lower your pressure to 17-20 psi and ride it again. You won't need to do anything else. The difference will be unbelievable. The reason Brett isn't seeing much difference in the length and width of the contact patch is that he is not airing down by a lot, and contact patch (surface area) is a function of length TIMES width. If you air down by 10% your contact patch will only be 11% bigger. And the length and width of it will only each only be about 5.4% bigger. That won't seem like a lot. I run about 45 on the street and air down to about 18 off road. That gives me a contact patch that is 2.5 times bigger, but still is only 1.6 times longer and wider. It won't look like that much if you look at a footprint. Now imagine going to the beach and having a 2 by 4 piece of lumber. Press it end wise into the sand and it will have an 8 inch contact patch (2 x 4 = 8). If you press down on it with 144 lbs that will be 18 pounds per square inch. Imagine how deep into the sand it would go. That's how deep my GS will dig with tires at 18 psi. Now press down on that two by four with 360 pounds. That's how deep my GS (and yours) will go with tires inflated to 45 psi. All you have to do to decide which pressure is best for you is ask yourself how deep you would like your tires to dig. It's huge pain in the ass to air back up, and Brett is an incredible rider, so he doesn't need the help and hence doesn't bother. If he rode right at the edge of his ability and frequently ran into terrain he couldn't handle I bet he would be airing down too.

[@BigRockMoto]

Thank you for doing this, this must have been a lot of work and we all appreciate it.

[@adstryker5084]

Yep. The test tires were a roughly 70% pavement / 30% dirt design, with small grooves between large blocks, such that the surface of the tire is unlikely to shift around much when the internal pressure is reduced. I'd be interested in seeing a test with a more dirt-worthy tire, like a RallZ or Dual Venture. I've noticed that dropping the front tire pressure on a RallZ (from the KTM recommended solo 22 psi down to about 16-to-18 psi) made the front end of my 640 Adventure a lot less skittish on hard-pack single-track (hard-pack with a thin layer of dust on top). Given the marginal gains in footprint area, I wonder if the significant difference in "skittishness" (which is just the "feel" of losing traction) is primarily in the tire's ability to conform to small surface irregularities.

[@6226superhurricane]

a couple of things i feel the need to pull you up on being an experience trail bike rider and 4wdriver. airing down isn't about width of the tyre it's about length, it's about changing the tyre from more of a fixed round shape to turning the bottom section of the tyre into a tank track (figuratively) where the leading edge is placed on the ground stays in situ until it moves past the centreline of the rim and is lifted up. this does happen at road pressure too but your analysis of the increased length from airing down being basically insignificant is flawed. small changes can have big effects. tyre conformity increases both traction and puncture resistance, if a tyre can mould around a sharp object some of the pressure on the point is spread onto the sides of that object or onto the ground. you can visualize this by getting two party balloons and inflating one as much as you can and half inflating the other make a pyramid out of blue tack or something similar with a toothpick sticking out of the top and then push the balloons onto it. the hard one won't deflect and will pop the half inflated one will take much more force before popping if it does. so too much pressure = punctures, too little pressure = pinch flats. the right pressure ultimately comes down to weight, tyre stiffness, speed and terrain. more weight = more pressure stiffer sidewall = less pressure required to achieve sidewall flex high speed = high pressure or sidewall flex can overheat the tyre terrain is variable square edged rocks require pressures or speeds that prevent pinch flats sand requires low pressures for flotation (the figurative tank tread) tar roads have good traction and high speeds, high pressures allow maximum handling and braking. there's no set answer for tyre pressure, but there is benefits to airing down and times where it is necessary.

[@danmoore6195]

What I'm getting from your video and then the comments below is that the science is telling us that while the actual change in footprint and/or flex is small, most comments show that airing down gives the rider a better "feel", and more confidence. I think I have heard you and other top experts teach that confidence is one of the main things a rider needs to become competent on a motorcycle. So if that tiny growth footprint and miniscule amount of flex result in a huge boost in confidence and feel - then airing down a bit is probably well worth it for many. And for competitive riders, every tiny bit of advantage can make a difference. Thanks for clarifying the science behind this, but the placebo effect seems to be much stronger than the science in this case.

[@BikerGirlTraveler]

May be, but riders get a boost in confidence because they have been brained washed to believe that they have more traction. It’s all in their mind. I am one who when ai bought my Tenere 700 about a year and a half ago started airing down my tires when riding in the rain. Until a couple of months ago I realized that I’ve been riding for 34 years, rain or shine, and I never aired down my tires on any of my sport bikes and never had any problems at all with traction in the rain. So I started asking myself why I was doing that now. I realized that I developed that mentality from watching videos about ADV bikes. It’s amazing how much others can influence us when you when we are hungry for knowledge. Which is the problem with social media, any fool can make himself or herself sound like an expert when they are not. Sadly someone will always be willing to believe them, I did. What I like about Bret is that he practices what he teaches and his skills are far what I see from others.

[@4LowRocks]

Seems like a good case of confirmation bias is at work here and potentially being confused as better "feel" and confidence.

[@monunyabidness5949]

As somebody who's sold tires for a long time, I can guarantee you, most people can't tell the difference in air pressure. The "confidence" comes from believing they have done something that aids them.

[@monunyabidness5949]

@@4LowRocks YUP!

[@edwindol3597]

i think we also need to factor in that the low tire pressure is making the tire work like a suspension system, suspension systems keep the tire in contact with whats ridden on, therefore contact surface does not matter so much?

[@Alaska_MD]

I'm an engineer [retired] and I've been saying this for years. The critical parameter in a tire is the sidewall. The engineers set the tire pressure recommendations to achieve a certain sidewall profile. When you mess with that, bad things happen [pinch flat]. But, Bret, the science won't matter... the engineering won't matter. They all watched Travis do it once.... once... and after that they won't listen to any calculations.

[@rider65]

Absolutely. Suppleness. Compliance.

[@Alaska_MD]

@@rider65 Yep, so is the bead where the rubber meets the frame. Instead of being ridid that slips now ... oh wait, let's invent rim locks for that. So smart.

[@abcusa123mich]

I struggle with this topic, for me there is a major difference in "feel" on sand when I air down about 50%. I can't say if its a larger foot print or what, but it makes the bike much easier for me to ride at low speeds on sand. R1200gs w/ 50/50 tires.

[@ReverendBill1]

Although not measurable by any criteria discussed, my anecdotal experience is about FEEL. When I air down the bikes feel planted, stable, and confident in marginal off-road surfaces. The difference in sand is remarkable. Nice analysis, thanks Brett.

[@rydedaworld]

Agreed. Try both and draw your own conclusions. I'm not going to run 8psi dirt bike pressures on my 600 lb tubeless ADV, but I'm also not going to run the manufacturer suggested *STREET* 36/42 pressures in the gnarly stuff either. I like Brett's conclusion of no more than 20% lower. 28/33 sounds about right, though I have gone down to 25/32.

[@JohnnyFuelMotorcycleAdventures]

I can't say for sure if I"m truly feeling a difference or if it's the placebo effect. After watching this video, I have no doubt Bret is right about the contact patch changes being minimal (like 1-3 mm) but there are many times when a few millimeters here and there make a meaningful change. Examples include seat height, handlebar height, rake & trail, preload, etc. So maybe a tiny change in contact patch is still substantial?

[@stevestowell-virtue3781]

Sand, gravel, and mud are reasons to air down. You will have much better feel. These are 3 dimensional surfaces the tires sink into. The channel host's analysis was done on a hard 2 dimensional surface.

[@JW-jh7zv]

@@JohnnyFuelMotorcycleAdventures I don't think it's a placebo effect. When I had E10 front on my R1200 GSA it was better all the way around off road at 28psi than my road pressure. The front suspension wasn't as rough over obstacles, and the front was planted in corners.

[@MKlukowski]

​@@stevestowell-virtue3781 Rob Pepper's analysis (on 4x4's) has similar conclusions as Bret's. Perhaps in terms of feel it *may* be different up to a certain pressure (as Bret noted) but the traction/surface area argument is near insignificant.

[@ridingluna]

I guess it is VERY important, after reading many comments, to keep this in mind and read well the video title. This air down test its for ADV Bikes, and NOT for enduro, motocross or trial bikes. Great job as always Bret, thank you so much for your effort and time.

[@BretTkacs]

Details matter

[@RetiredAdventureRider]

I think the small increased surface area of my tire when airing down pales in comparison to the massive increase in my skills that I get by some proper training. I always like to put my effort into where I get the best payback. Thanks for these videos.

[@monunyabidness5949]

The way you started that statement, ... I was getting ready to post "YOU CAN"T ARGUE WITH FACTS"

[@igi20031]

Thanks! You creating extremely useful content. As your proud supporter on patreon, adding some here too.

[@BretTkacs]

I am currently in CA lining up to shoot a trail braking video that is only possible because of Patreon funds... Thank you

[@pinnacleroofing9841]

I'm torn. Data is good and generally king. The problem is what do I do with the actual experience of fighting to get up a gravel hill for 3 hours. The bike falls over, I try and pick it up and we both slide 30 ft back down the hill, only after airing down was I able to get up, and fairly easily

[@YangCalgary]

Your videos actually influence my decisions. (Sorry, it's Canadian $$)

[@YangCalgary]

Bret, I thought I’d get a bit more reaction than a like for my donation. At least a heart ….

[@LostInADV]

Please, someone correct me because I’m not a math dude, I’m just trying to make sense for myself and what I feel when on the bike, because there is certainly a difference. Anyway, looking at the quarter and dime representation with the tire and pressures he used, I’m showing about a 13% increase in surface area when dropping 10%psi and 20% increase in surface area when dropping 20% psi on his front tire. Of course this isn’t exact. To me a 13-20% increase in surface area seems rather large. Again, please fix my numbers. I agree with others saying the feel is better. Grip and control is truly noticeable. Also want to mention that a massive obstacle for new riders on dirt is the mental barrier of feeling like their tires will slide out and not hold. They have a hard time focusing on training because “I felt my tire start to slip”. Airing down tends to fix that real quick. Let them ride stock psi for some time, then, when they go use the restroom you air their tires down a bit and watch them ride with more confidence and not no why. However, I can’t prove this to be caused by airing down, it could be because they left the restroom much lighter than before.

[@MujoNovak]

I ride 1.9 bar front and 2.0 bar rear, on my cb500x for TET. I do belive that a little less pressure is better for off and on road. So dont exactly understand why Bret says it not...

[@progammler]

very interesting! On our 300cc dirt bikes we go from ~14psi on dry rocks down to ~9psi in wet/muddy terrain (on mousse) and it makes a huge difference because the carcasse is so soft that it basically wraps around rocks. In comparison on my 790 the carcasse is much more rigid, the compound is harder and the knobs larger and shallower. That's why airing down doesn't have that much of an effect. And indeed: in mudddy terrain no matter the pressure the grip is always terrible :D

[@danmiezejeski7735]

This lines up with my experiences too. I have a KTM 500 Dual sport and decided to try to ride my local trails at street pressures. It was mostly OK but the steep loose climbs were much more difficult to keep the rear from spinning up, and the front was much less stable.

[@philipraposo8324]

On a 300lbs or less bike even 10psi is a huge difference. Not only in feel but performance. This video doesn't apply to actual off-road bikes and only for large adv bikes with road focused tires.

[@ExpatonTwoWheels]

Same here. I run Tubliss on my WR450F and it's amazing the increase in traction from dropping from 15 psi normal trail pressures to 8-10 psi. I only do that in the rear. Found low pressures in the front just kill my steering feel with no gain. I can't place the bike precisely with low pressure in the front.

[@philipraposo8324]

@@ExpatonTwoWheels yeah front tire I run it a little higher forsure.

[@edwindol3597]

i think we also need to factor in that the low tire pressure is making the tire work like a suspension system, suspension systems keep the tire in contact with whats ridden on, therefore contact surface does not matter so much?

[@musicwithmr.yvellez3583]

I don’t ride the big heavy bikes. I reserve judgment on the “science” of this experiment. One problem I see, however, is that the video does not discuss methodology. It does not state under what conditions the footprint was measured. But I get the feeling it was measured under static (stand still) conditions rather than specific dynamic conditions. For example, I sometimes ride up or down a steep rock surface. When going down, I believe there is considerable advantage to having low pressure and weighting the front end by moving all the way forward. As the brake is applied, the suspension compresses and I believe the tire flattens giving me a substantially bigger patch to slow the bike and prevent skid. Similarly, when riding up the face, the weight is shifted to the rear. The lower pressure allows the tire to flatten more and provide the greater contact, giving one more traction. The video shows the tire will flatten more easily with lower pressure in a dynamic situation (going over obstacle), but only discusses this as a disadvantage (hitting the obstacle harder with the rim because the tire folded more). This is true in that situation, but this is why you would deweight the front of the bike going over such an obstacle. But he states they just ran over it. So I suggest this may be a case where the author just does not recognize the weakness of his testing methodology. 17:33

[@jrdepew]

And a pinch flat avoided is worth any real or imagined gain! Thanks for such in-depth analysis.

[@thomassowinski6765]

Thanks for the years of great content Bret! I appreciate the effort you put into these videos, and I'm looking forward to taking one of your classes in person at some point in the future!

[@BretTkacs]

Awesome, thank you!

[@frank_jk]

Thanks Bret! Insightful as always. In my limited experience, I have found that whatever traction issues I encounter are most likely due to a lack of riding skills, and not due to tire pressure.

[@royandtracyboling5969]

I am appreciating the concept of "ride your ride" more as I watch different instructors. We ride based on experience, bike type, bike setup, and terrain.

[@sanjosejeff]

All I know are dirt bikes. I have the “tubliss” system in the front and rear allowing me to run 4psi in the rear and 6-8 in the front. The most noticeable upgrade I’ve done on the bike. We call it cheating. Traction and control over wet, angled roots in the trail is amazing. Plus, the 110 psi core keeps the rim protected while hitting obstacles like in this video. It’s not a myth. On this, I absolutely know of what I speak. I ordered a 23 890 r that’s not here yet. I know nothing about adventure bikes. Thx for the info although if “tubliss” ever makes a system for bigger bikes, I’m all in

[@scudrunneradv3269]

Left my home in eastern nc on brand new Dunlop trailmax mission tires on my 2017 f 800 gs. Rode the entire Trans American trail coast to coast and back on the same tires. Kept them at the operators manual recommended TP the entire trip. Tires performed magnificently on and off road. Tires held up even on big rocks etc. No damage to my rims or tires. Was comfortable riding at the recommended pressure.

[@ecalzo]

Wow... i've taken for granted that airing down my tires won't give me a lot of benefits based on your words.. And now you came out with this video supporting your words with experimental testing .. Well done .... you rock !! Hi from italy Bret..

[@ADHDiy_Guy]

I really appreciate that you included how the tires form around obstacles in addition to surface area only. I would have thought it had a bigger difference, but this was great to see.

[@gaucho1937]

Thanks Bret for all the hard work and reasonsble explanations. It is no surprise that the Contact patch variation in size is neglectible when airing down about 10 to 20 %. The tire manufacturer of a 50/50 street legal tire must comply with a series of safety requs and warrant road performance even for fools like me forgetting to check the tire pressure regularly. Off road lower pressure reduces vibrations caused by rough surface better than the suspension is able to do in the first 3 mil of travel. Thats why it feels better. 20 % down is a good starting point for self testing. Contact patch shape is an underrated topic. The longe the patch the more straight you go. A shorter patch shape will steer more sensitive resp. deflect much easier on rough terrain. The size of the patch

[@MujoNovak]

I ride 1.9 bar front and 2.0 bar rear, on my cb500x for TET. I do belive that a little less pressure is better for off and on road. So dont exactly understand why Bret says it not...

[@PetrolJunkie]

As always I love the way Bret breaks down everything in his videos and shows his work. That's how you make an argument that should convince all but the stubborn idiots in a room. This issue is about scale. The reason it works on a 4x4 is weight and size which is substantially more than a motorcycle. (I've built and tuned professional-level competition machines.) That is really important. Motorcyclists are trying to apply that effect to their motorcycles and it just doesn't scale the way they imagine. I don't air down at all unless I'm on really rough ground and that is specifically to reduce deflection. A rock garden can bounce a fully aired-up tire all over the place, but at 20% less air the bike is much more controllable. It's not a lot but sometimes not a lot is what you want. The suspension setup is more critical to bike performance than air pressure, air pressure is more like the fine-tuning knob after you get the suspension right. Suspension is more like a course adjustment. Anyone that tunes anything with an engine can tell you that is dead true at any scale. Sidewall and tread section construction matter more when it comes to tire flex and contact patch than air pressure even on a monster truck, air pressure is still a fine adjustment. There is little surprise that all the tires have similar contact patch sizes. That's a matter of physics. They are balancing rolling resistance and grip and that formula only has so much give. If you have a narrower tire you need a longer contact patch to get the same surface area. What matters more when you are talking about contact patch size is surface area, not so much the shape. The shape is more about rolling resistance as a wider tire has more resistance than a narrow tire with the exact same surface area. Softer tires have more rolling resistance than harder tires, but the softer tire has more traction given the same surface area. If you want more grip you actually want a softer tire with a more appropriate tread pattern. I run 70/30s on everything but soft and loose soil, when I know there is going to be sandy river bottom soil I switch to knobbies with large and deep voids. The 70/30s work well on compacted soil, river rock, and whatnot. But, there is something else to this discussion. The size of the tire matters. Taller tires climb more easily. Narrow tires dig more, and wide tires float more. Ask anyone how a 300 or 350 tire feels on a wet road versus a standard-size tire. It's why they make giant agricultural tires and very narrow tires, each has its purpose. But in the motorcycle world there is more to it than just float vs dig. Width also affects turn-in rate a long with some other geometry of the forks and wheelbase, and weight, it's complicated, but just know that tire width affects how the bike turns into a corner. That doesn't seem as obvious as to why off-road people should care, it matters when you put that same bike on pavement. That tire has to keep you on the road at 70 MPH and keep you from eating dirt on a trail. Believe it or not, there is a magic formula most tire companies use to arrive at that point. That is the real reason why the tires are so closely matched in performance, they don't have a lot of room to work with while designing a tire that can do both as well as they can.

[@rivernet62]

Thanks for fixing the title. My OCD was triggered.

[@christopherrowley7506]

This has been experimented with for decades with 4wd vehicles, and the resounding answer is that airing down helps a bunch in many different offroad situations: stuck in the sand, you air down and you get out; slipping on the mud and can't get up the hill, you air down and crawl up the hill; the road is washboardy and rough as hell, you air down now your ride is smooth; your wheel are skidding on a boulder step up, you air down and crawl over the boulder. So I'd be surprised if the nature of motorcycle tires were so different that they wouldn't reap any of those benefits. I'm not sure what the mechanism is, but definitely airing down objectively helps 4wds at least. I'm more inclined to think that the methodology is flawed than to think it disproves reality. So then footprint on a hard flat surface doesn't mean much. Maybe it's the tautness of the rubber which impacts grip, whether or not it translates to a bigger contact patch? I'm thinking about the difference between summer and winter tires, where subtle differences in the rubber compound end up making a huge impact on how that rubber grips on different surfaces and in different temperature ranges.

[@dave-d]

Damn dude - there you have it. Excellent work Bret. I always thought the air down was for greater tread flexion to increase grip off road - not increased contact patch but I may be wrong. A deep subject indeed. Thank you.

[@Trialgubben]

Comin from trials riding where we are running with almost no air in the tires, going to a 2005 model 1200GS with TKC-80`s going a lot gravel and also real offroad, i think I have some experience to share. For "normal" gravel riding reducing slightly from road pressure - lets say from 32PSI to 25PSI - makes the ride noticeable more smooth and noticeable more grip on loose surface. Its not only the tires that works better, but it also takes some of the load off the suspension. For "real off road" riding in slow speed (im a trials rider. Trials riders dont need speed to have fun ;) ) i go even lower to around 20PSI and this really makes a difference in grip over rocks, diagonal roots and so on.

[@BretTkacs]

20 PSI is around 45% below the pressure for the OEM tires. Of course if you are running an ADV knobbie then rise often have lower pressures by design including the pressure for max load

[@Ironhawx]

Thanks Bret! This video is a must for new riders.

[@BretTkacs]

Not necessarily

[@cadaunoensumoto]

If gaining width of the tire were the main reason, then to use a bigger tire would be the ultimate solution, but that is negligible, I mean the real reason of airing down is that the tire do not bounce a lot and the tire surround the irregularities to gain grip and increase the security.

[@luismokdeci]

Valeu! thanks so much for the hard work all those years you have been putting content on your channel!

[@marcclarke01]

Thanks! Oh look! Actual data. 👍🥳

[@henrygerwien186]

Compared to the myriad of motorbike videos flooding the world, I am very grateful for such factual posts with sensible content. The comparison of the different surfaces between 90/90 and 120/80 (as an example) was very amazing, how little difference it makes. But I am even more thrilled to learn that more than 20% less air actually makes all driving characteristics worse. Thanks, Bret, for this valuable work. Regards, Henry

[@rickparliament4525]

To analyze properly, in my opinion , the contact area of the tread should be compared while in a rock bed, sand, or other obstacle, not on a flat surface. It has to be taken into consideration of how the power and control is different if say, the rear tire of a GSA was dropped to 4 lbs and how that would allow for slower speed manoeuvres through and over rough terrain. Hitting a curb with low tire pressure in the front tire is obvious that it will be jarring, but over a rock bed of 4-6” round rocks it would be a different result. Having said this, I don’t air down my tires. There has been some challenging hill climbs and challenge courses that I wish I had thought of airing down. The individual who did air his rear tire to 4 lbs did win the challenge course over 40+ other participants.

[@BretTkacs]

The challenge is how to isolate each effect.

[@rider65]

@@BretTkacs Of course it is. Actual Comparative Analysis. Otherwise the data is not credible.

[@mosa4688]

Good to see the firmly held age old "truths" being looked at rationally rather than hearsay.

[@brantfurr986]

Great insight. I appreciate the scientific presentation... It does have me wondering about my Dual Sport motorcycle, with tubes and rimlocks, where I sometimes run as low as 8 PSI, where we are seeing a 70% decrease in tire pressure... Because as you demonstrated, tire response to deflation isn't linear... I know that your channel is largely focused on the adventure rider, on an adventure bike, but I thought it was worth sharing that you have sparked curiosity.

[@philipraposo8324]

This doesn't apply to smaller dual sports with actual off-road tires

[@brantfurr986]

@@philipraposo8324 Yes, I know this was a video about bigger adventure bikes, however, I was stating that I was curious what the results for smaller dual sports would be.

[@philipraposo8324]

@@brantfurr986 i ride a klx300 and its a huge difference with tire pressures. we run dot knobbies that have soft sidewalls the tires flex far more and have lugs. its not comparable and his tests are extremely flawed and misleading.

[@brantfurr986]

@@philipraposo8324 How are they flawed and misleading?

[@philipraposo8324]

@@brantfurr986 because dirt riding is not done on flat yard ground. Contact patch is completely different when considering a small rock on a hard tire vs same rock on a soft tire. A half inch stone will literally take the tire off the ground if it's pumped to street psi. If your running 8-10psi which I do all the time on my dual sport the rock does nothing because the tire conforms around it and doesn't leave the ground.the difference in area is huge. He is testing a street tire when most people who actually ride off-road ride some kind of knobby tire. Trying to validate his beliefs but it's only applies to a tiny portion of the off-road motorcycles. Yet he doesn't mention any of this in the video. Hard Enduro guys don't even run any air. Many keep 0 psi. Small dual sports run sub 14 psi all the time. Only large adv bikes run stupid high pressures because of the weight of the rider and bike plus gear. They are not designed to conform to terrain in the same way that off-road focused tires will.

[@therealturbofanisme]

The purpose of airing down is to keep more tire in contact with the ground when the ground is uneven. If you have a tire at 35 psi and it hits a little rock, that rock is going to make the rest of the tread lift off the surface. If you hit that same little rock with that same tire at 25 psi, the tire will give and allow the rest of the tire to stay in contact with the surface. Not talking about big obstacles like in your example, but small rocks and surface imperfections. It's a balance between protecting your wheel/avoiding flats, and improved grip. You can sit here all day and explain why it doesn't make a significant difference in grip, but if you ride a bike down a trail at full pressure, then go again at lower pressure, there's a *clear* difference in the stability and grip of the motorcycle. It won't make up for rider skill or training. It's usually not *required* to get down a trail. But ride down a road that's hardpack with little marbles on top of it, airing down makes a monumental difference in available grip. cool to debunk the surface area myth, though.

[@philipraposo8324]

100% agree. This presentation is not a true representation of what actually happens on the trails.

[@rider65]

@@philipraposo8324 BINGO

[@rider65]

He mentions zero about Hysteresis losses.

[@constantinosschinas4503]

I happen to ride a small KLX250s this period, very fast on tarmac and fast on trails and using very low pressures makes the bike skid on tarmac, when riden hard. You can feel the tyre deforming and front and back slides become very often especially when driving supermoto style. Controlable but very frequent and rather pronounced. I guess tyre works as a spring but with less dampening, which bumps the type up till it looses grip. It is very exciting to end up drifting with 27hp front end back at the same time going 60km/h, but definetely shows low pressure does not always give more grip. The other funny thing is that with very low pressure at the dront the bike is easier to turn and more responsive, whereas in street bikes it is usually the opposite.

[@pieroo900ng]

thanks Bret

[@hughhawley3169]

One of the things that fascinates me about motorcycles is how seemingly small "inputs" create relatively dramatic "outputs." Push on the right grip just a few millimeters while traveling at 30 mph, and that 500 pounds of metal and plastic suddenly leans and wants to turn! Just a few clicks on an adjustment in the front suspension, which is moving very small parts inside the tube, can cause a noticeable change in the bike's handling. A one-degree change in rake, a one-inch change in trail, can make it seem like a different motorcycle. So I wonder if a few millimeters of difference in the area of the contact patch results in a noticeable change in the way the bike feels to the rider?

[@BretTkacs]

Possibly but not because of surface area. It's more about flex and heat.

[@cameronbrown8757]

Great content. Coming from a mountain bike background, we air down primarily for increased traction in cornering off-road. I know from experience that the amount of "G"s you can pull on a corner goes up significantly at lower pressures. We basically air down until you risk a pinch flat, or until it feels too squirrelly. I would like to suggest a follow-on video, again, data-driven: perhaps record max speed on a fixed turn radius before slipping vs. air pressure.

[@jessicafryer4258]

I too am curious about the contact patch footprint and cornering; more challenging to collect the data. Thank you for this data-driven study.

[@elconquistador7363]

Airing down doesn't necessarily increase the contact patch much. But, it does spread the contact patch weight distribution. A contact patch (not withstanding a buckled tire) will always have a higher pressure point in its center area vs the surrounding area. Lower air pressure allows the contact patch to not have such a higher focused pressure point in the middle... This is why a lower pressurized tire has a tendency to sit on sand vs plow into it.

[@haroldshull6848]

As a retired mechanic, I didn't have all the materials of measurement listed here, but I'd bought a 2020 Ducati Desert Sled, changed the front rim to 21" with an appropriate tire and slid the fork tubes up the triple clamps (head and crown if you will) and needed a system for initial setup. Having a 10 acre back yard of sand and mesquite and a (usually) dry creek bed with motorcycle trails well beat in through all of it I proceeded to testing. With front and rear at max suggested pressure it didn't take long to decide it was rolling like a rock. Those tire pressures were within 2 psi of each other and stayed at that difference for the whole test. Starting at suggested mfg. pressures I rode the track at an increasing pace until things were sliding around and the suspension was working vigorously. Back to the garage, let out 2psi, and ride to test parameters. 2 psi lower and test. Repeat. Eventually it was just wallowing around with little response to steering input. At that point I started adding pressure at the 2psi rate unti all responses were midrange acceptable. It was a well spent afternoon and I learned a lot. The Duc is running at expectations.

[@joancarles6740]

Good job Bret.

[@hdjnfirnfnhdhdjjdkdk9349]

The tire acts multidimensionally, and your explanation with footprints, in that way, is only applicable on asphalt. The hardness of the tire as a result of a high pressure will only generate the effect of removing the loose terrain, while a soft tire will compact the contact surface on a micro level, generating a pushing force. Everything is add up. Of course, too little pressure creates danger for the rim.

[@IRLtrolls]

Years back after watching one of your tire videos I went from a 130 rear on my Dualsports to a 120 rear (Dunlop D606 always) and the 120 is so so much better off-road. The thinner tire is lighter and spins up faster and it seems to dig into the mud and bite better instead of floating on top. Proper pressure and a thinner tire help me a lot

[@MotoAdventurer]

Solid work Bret. I was pretty convinced you were going to completely stone wall airing down. I was pleasantly surprised. We’re racing adventure bikes in Kentucky and have been doing “research” in this area with low Pressures, rim locks, and even mousses. It’s interesting to compare our notes to yours. Thanks again!

[@dandersonjr]

I've never aired down but not because of scientific reason it has more to do with laziness but now I'm glad to know my laziness has scientific backing. Thanks. This video was worth the wait.

[@BretTkacs]

🤣

[@matt_kelly]

Thanks for all the research on this! I still rarely air down, especially since the time I hit a pothole and blew the bead on my cast rim, necessitating a tube to keep going. Lesson learned.

[@Garzatron-ue3cp]

Great video. Coming from mountain biking I’ve realized moto tires are a different beast. In mtb there’s a fine line between traction and compliance vs pinch flats. Dual sport/adv tires are much much stiffer and I don’t think you’ll ever get the compliance without walking the line of pinch flatting. I’ve ridden some rocky trails at recommended single rider psi recently and it felt totally fine for traction….id rather lose a wee bit of traction than deal with a flat. You have a great channel. I watched it before I swapped out my new DOT tires and it went pretty well. Thanks for the content.

[@DavidODonnell-Breck]

I come from a motorcycle and 4x4 Jeep background. The one factor you're not talking about here is speed which makes a huge difference. In the Jeep world I typically air down to 12-14 PSI on a 35" tire. When you do that you've entered a different world to what the tire was typically designed for. At those pressures the tire can no longer absorb the impacts or protect the rim at higher speeds, but at crawl speeds it's fine and the tire deforms significantly giving you better traction particularly on wet hard surfaces. The other main advantage is the ride quality inside the Jeep is night and day compared to street pressures. If you try to duplicate this in the motorcycle world, it just doesn't work out because you can't go slow enough. The tire has to have enough inflation to absorb an impact at the speed you're going. The faster you're going the more inflation required. The suspension and load play a big part too. If you try to go slow with significantly less tire pressure you may go outside the sweet spot of the suspension which will become harsh compared to higher speeds. If you're loaded up with adventure gear then the tires have more load and require more pressure. When I air down on the motorcycle it is almost exclusively to minimize deflection and I tend to stick to around 15% of regular pressures.

[@whitedrguy6503]

Tyre construction plays a big part in how much flex you get from the tyre, stiffer side walls give less flex as opposed to softer side walls for the same air pressure. Most tyres designed for overweight motorcycles have stiff side walls so will flex less than say a tyre designed for a mid weight bike, the difference is quite noticeable on an enduro bike like a KTM 450, 16 PSI on a stiff construction is a world away from that of a soft construction tyre when it comes to traction. The best way to test if a tyre has a stiff side wall is, one, try and fit it to a rim or Two, let the air out and sit on the bike, a tyre with a stiff side wall will feel almost the same to reach the ground when seated, a soft side wall the bike will sit a lot lower. I guess there is a reason why enduro riders and Paris/ Dakar riders run a mouse equivalent to around 14/16 PSI in the tyres and their bikes don’t weigh 250 Kg. To get the tyre to flex more on a stiff side wall you need a fair pressure drop then one with a softer side wall but a stiffer side wall is needed as the weight gets higher.

[@stitch3163]

Thanks, Brett. A lot of work and analysis went into this, which is greatly appreciated. Looking forward to comments from the tire and bike manufacturers.

[@coq7716]

Thank you for your great work and reporting. Awesome knowledge 💪

[@onerider808]

Interesting video, and spot on, IMO. I’ve always stuck with recommended pressure, and got where I was going just fine, on or off road. Tire type and rider skill trump pressure tweaks every time.

[@docimastic]

Love it! Thanks for a great, informative, and well done video. I know every motorcyclist has wondered about contact patch variations, both with regard tire cross-section/width and also with regard air pressure and you covered them both. Thanks again, David

[@abubakarhussein5197]

I love your approach Bret and look forward to meeting you. Your effort, and straight forward explanation even in tutorial videos is another level. Much appreciated

[@RedRupert64]

Thanks very much. Very interesting. I know from experience that the 90/90 21" front wheel on my KTM 950 offers plenty of grip on-road, even compared with bikes that have traditionally sized road or track tyres. Normally 17". I never air down when riding off-road; I dont think it's worth the faff. The biggest advantage is to learn to ride better.

[@Mark-rv5dd]

A static print doesn't prove everything. When you ride fast on a complex surface(like rocky and slippery) airing down can help tires a lot in "grabbing and pawing" the obstacles

[@hibob841]

Interesting! I'm learning to ride off-road, recently got a light dual-sport, and the whole concept of airing-down (along with much else) is new to me. My recommended highway pressures are 22/22, but I've been dropping to 10-12 off-road at an instructor's recommendation. At my level, I'm sure I can't perceive any difference, but I thought I was giving myself a little help-and I need all of that I can get. In fact I just got Tubliss installed, in part, so that I could experiment with _really_ low pressures in relative safety. Now I'm wondering if it's worth the bother, haha...maybe I should just leave them at 22.

[@philipraposo8324]

Try this test and see for yourself if the information you're being given in this video is valid. Pump your tire to the recommended tire pressure, take a rock about 3/8-1/2" and place it on the driveway. Roll your bike on top and sit on it. Have someone get low and take a photo of the tire standing ON TOP of the rock. Now lower the pressure to a true off-road pressure. Example 22 psi dual sport tire, dropped to 8-10psi with rimlock. Do the same test and photo. You will clearly see that the difference is substantial. In one case the tire will sit on top and the other case the tire will eat up the rock and the rest on the driveway.

[@RogierYou]

Wow you put a substantial amount of work into this one!

[@BretTkacs]

A stupid amount, I could have made a 2 hr documentary on the process and controls to isolate accurate results.

[@stevewiley3539]

I agree completely on everything thing that you stated. I consistently run 25 psi on my Africa Twin in our SoCal desert and mountains specifically for puncture resistance over severe rocky terrain. In my experience airing down in the rocks, gives the tires just enough give to resist punctures versus 33 - 38 psi. If you have a chance, test for puncture resistance at different tire pressures.

[@discoveror9576]

Based on the 'riding on air', rather than 'riding on the tire', principle, I calculated the ratio of running load (i.e. wet bike + me + space suite + luggage) TO maximum tire load. I multiplied that ratio times the oem (for KTM 390 Adventure) recommended psi. The result (22 psi front & 18 psi rear) was a more comfortable, less 'squirrely' ride - both on and off pavement. For challenging off-pavement riding, I found that BELOW 15 psi the bike got 'squirrely', again; BUT, 17 psi front and 15 psi rear felt very nice i.e. confidence inspiring. Also, I noticed that KTM recommends 15 psi for MOST of their off-road bikes! All this was predicated on the assumption that tire manufacturer 'maximum load psi' is carefully (and conservatively?) calculated tor each specific tire model and size.

[@davidwood974]

This is a great format for discussion, thank you Bret!

[@treybenavides9138]

And the science is correct. Absolutely proper observations.

[@ParklandTKD]

Thanks so much Bret. we had a chance to spent some time talking about this topic before and I firmly believe airing down the tires change the BIKE HANDLING... but , nothing is absolute and the surface changes very dramatically often... finding the right air pressure is the key ... relying in airing down to increase BIKE HANDLING is not the "one size fits all" solution.

[@bytesandbikes]

That is a super interesting video. I'm not experienced with off road bikes, but I've done a fair bit of 4×4 offroading. There's two big effects there with air down, and I'd like to know how much they apply to bikes: 1. paddling- the tyre distortion gives you large scale dishing of the contact patch, which helps in sand and mud. 2. lug flex- the gap between the lugs opens at the edge and closes in the middle, giving grip edges, and clearing out some mud.

[@BretTkacs]

Lugs are shorter and tightly gapped, there is less area to allow distortion and bikes travel at higher speeds than those of 4x4's when they are aired down

[@danmanthe9335]

Wow. Thanks Bret! As if I needed another reason to listen to his knowledge

[@OnTheHonda]

Outstanding data! Quite comprehensive study.

[@TheUnsungVil]

I feel reminded of a simplified math assignment in high school: From a predefined diameter -> Calculating the pressure inside a rubber tube with given outside pressure and contact patch surface - or calculating the contact patch surface from the difference between inner and outer pressure - or calculating the outer pressure from contact patch surface and inner pressure. In essence: Apart from the diameter (basically flattening/prolonguing the curvature segment touching the ground, and therefore the length) the tube width and height had only neglectable impact (at least in that simplified assignment scope)

[@tshansen]

Ooohhh the cruelty in destroying good myths and discussions with facts. This will video will shake the foundations in some communities 😆 Great work Bret, once again you deliver high quality content. Cheers ☕🇳🇴

[@AboutaMileAdventures]

One thing I might have missed and i apologize if it was mentioned, but your tire is the first part of your suspension, and a tire with lower tire pressure will be on the ground longer and more often than one with higher pressure, so that marginal footprint really adds up over the course of a tough section of trail. On adv bikes, I agree with bret, a lot of effort for little to no reward, on dirtbikes it makes a HUGE difference.

[@demezon6572]

Longer and more often on the ground? - Use good suspension and adjust its good damping characteristics properly. Then you'll have it. Tire pressure won't change what you are postulating much. A lil' bit yes, but not at all much. BTW. Dirt bikes are all sus, with just a bare minimum of other parts. I am an engineer.

[@AboutaMileAdventures]

@@demezon6572 Everyone on youtube is an engineer, Then you should know that tires and tire pressure are also part of your suspension, and adjusting the tire pressure is also adjusting your suspension.

[@morganmullins7559]

I’m always afraid of pinch flats that my biggest reason for not airing down. Great video!!

[@ChooseBrian]

I just run 30-33 all the time. Never an issue on or off road (with knobby Motoz Rallz). This video is fantastic.

[@MujoNovak]

thats good, but on what bike?

[@cyclopathic998]

.. the other aspect of airing down is the temperature. Under-inflated will generate heat and change rubber properties. This mostly impacts riding at higher speed on high grip surfaces. Most likely the changes in behavior and between 140 vs 170 and 21 vs 19 are related to specific tire construction and there are substantial differences between different brands/models of tires

[@AT2021Rocker]

You are the best motorcycling video instructor/informational teacher out there! I have learned so much from your videos!

[@BretTkacs]

Wow, thanks!

[@backcountry4life]

I’m a believer in 15% air down for off-road riding then back up to normal when on street. It’s about feel, control and confidence. Also, anymore than that I see riders getting pinch flats on their ADVs (500+ lbs). Thanks for the detailed analysis.

[@yukonpeter]

Super interesting. As a very average adv rider on a T7 what I am most interested in is how I smooth out my ride on dirt roads, when riding over wash-board and potholes (I hate standing up!), when going between 30-50 kmh. I've sometimes convinced myself that by airing down 10-15 percent that my ride is a little smoother, that the lower pressure is magically eating some of those little bumps. But it -- the smoother ride -- could very well be in my imagination! Adjusting preload, rebound and air pressure seems like a voodoo art to me!

[@enduromotorradtouren]

I love your myth busting, Bret, done with data. Your episode also confirms that "feeling" is important, that a combined team of rider-bike has a certain "window" a feeling well. A bit like cooks - they don't weigh their spices exactly to the milligram ;-) Thanks a lot, much appreciated, Günter/Nürnberg, Germany

[@rickwheeler6811]

Great information... I have personally never aired down

[@Loiczzr]

On a drz400s, so not a big bike, I would air down to 12 psi on technical (SLOW RIDING) sharp rock area in the desert. It does make a difference and prevent your tires been destroyed by the sharp rocks.

[@BretTkacs]

The DRz 400 came in an off-road, duel sport and SM versions. The wheels were proper narrow rims on a light bike with wheel locks. 12 psi is fine on dirt.

[@rodrigofabregas7756]

Thank you Bret....nice and serious analysis!

[@exparrot9074]

Great video Brett, the minimal change in surface areas was pretty surprising to me. I would be curious to see if you could measure the changes in static friction between different pressures on various surfaces such as mud, sand, and hard pack dirt, by putting a rider on the bike and then side loading the front and rear wheel with a scale and seeing when deflection happens. Anecdotally, I started out riding the NEBDR with my pressures at 32/35 with Bridgestone AX41s on my 1290 Super Adventure R (max pressure for the tires was 35, tried to keep the same ratio F/R that KTM recommended (38/42). The front end grip was like a light switch at these pressures, the front end would slide and wash out in any type of soft mud or clay. When I backed pressures off further to 25/27 the motorcycle was far more controllable in soft terrain.

[@danmiezejeski7735]

I have similar anecdotal evidence as you. I have a 790 ADV and the factory tires weren't great. I dropped the pressures from 35/35 to 28/30 and felt much better. At the time I was living close to a offroad riding area, so I was riding about 70/30 offroad vs on. I took the bike in for service, and the next time I rode in the dirt I washed the front end and dropped the bike 3 times. The dealer had reset the pressures to 35/35. I was riding the same trails and the same conditions as before, and I had never dropped the bike until that day. The difference was the tire pressures. I think that a healthy part of that problem was the Karoo's that came on that bike, I switched to Dunlop TrailMax Missions and don't have issues with front end grip, even when I don't air down.

[@exparrot9074]

@@danmiezejeski7735 I ran the Trailmax Missions for a season and a half, loved them in firm conditions, but they were awful in mud and clay. Granted, I did not play around with airing down at all. I hope Dunlop brings the Trailmax Raid over this season.

[@ride4adventure]

Great investigation Brett.

[@ChuckButtercup]

Thanks for this study. Just a small observation on the OEM recommendation sheet, the KLR loaded numbers do not look correct against my 2022's manual. Rear tire loaded should be at 36.

[@themightylui9632]

Great video - looking forward to the follow up video(s)

[@Wintersdark]

Fascinating! It's good to see some explanation to things I've experienced, but lacked the knowledge to really understand. I found dropping 3-6 psi (Tenere 700, 300lb rider) maybe helped a little, but going beyond that (despite people telling me it should help) made the bike wallow and felt *bad* at high speed on dirt and gravel. Maybe that matters less when bike+rider isn't 750lbs, but it certainly mattered for me. Not gonna lie. I REALLY thought there'd be a bigger contact patch size delta. While I already understood bigger contact patch doesn't inherently mean more traction (see fingertip vs whole hand on table traction experiment) I thought the conformance/give would do more... But it clearly doesn't until pressures are so low as to cause other problems. Yeah. Fascinating. Thank you for this incredibly informative video!

[@Getting-On]

Another great video, professionally produced with great scientific data to back it up.

[@Snowhite808]

As a suspension workshop - we greet the interesting video. As a biker - it is quite subjective, what air pressure You like to ride. But! There is a "correct" pressure for the tyres. Has been so for the cars and is so also for bikes. It usually is a range of about 20percent of the overall pressure. It depends on so many things and will be different from rider to rider and place to place. But in any case - the manufacturers are running the so-called safe numbers on the bikes. Ktm 690 with a 65kg beginner rider will have a different pressure for good off-road characteristics than the same bike with 100kg pro agressive rider. But the pressure will not be more than 10-15% different. As a workshop - AIR DOWN - but not too much. Rebuilding wheels is not cheap. air still is.

[@rc51bigdaddy]

Great informative video. Thank you! I am pretty lazy so run my 890r at around 30 psi. On road is 35. Off road is 26. So kind of splitting the difference. Sounds OK after watching your video.

[@qwerty-er1cy]

ありがとうございます！

[@matthewtomaszewski3269]

Great lecture. I learned a lot, but I hope the midterm will be multiple choice.

[@BretTkacs]

Yes it will

[@TexasTacoKiller]

Excellent information Professor, as a beginner on the off road, glad I’m getting good info as I def would prefer a possible fall as to a bent rim

[@mattdelcomyn8012]

Nice job Bret! Very scientific.

[@mikhailm4594]

Hi Bret. I admire your determination with all these tire footprints and measurements to 1 mm. However, there is a more straightforward explanation using a simple formula for… pressure: P=m/S, where P is pressure (yep, inflation pressure), m - mass and S - surface area. Since we are interested in the surface area of the footprint (a.k.a. contact patch), let’s transform the formula: S=m/P. Here you have it, the contact patch is inversely proportional to inflation pressure: the larger the inflation pressure, the smaller the contact patch and vice versa. As you noticed, the tire size is out of the picture. A wider tire will have the same contact patch area as a narrower tire, just different in shape. Of cause, it is a bit of simplification, as the contact patch area is affected by the tire geometry and stiffness. However, it gives you a pretty good idea.

[@mikemills5144]

Very detailed info, that must have taken a long time to put all of that together.

[@MotorDanko]

I thought i was crazy feeling much harsher suspension when i aired down my tires from 36 to about 26, then, without seein this video, i realized that maybe, airing down made part of my suspension useless because the primary "suspension" element being the tire, wasn't doing its job and it was compressing all to the rim, transfering that harshness to the bike directly... i found after a lot of tires, that rubber on the knob and its design was much more important on the riding confort more than the pressure they are inflated... after that i never deflate my tires, i set up the suspension in order to be confortable and apply the "weightless rider" technique learned here to improve the absortion of the terrain... also, i'm completely decided to go down from a 150-70-17, to a 140-80-17 on my TRK... but i'm still wondering if going 100-90-19, in opose of 110-80-19. Thank you for this video Bret, you are the best on youtube, by far.

[@constantinosschinas4503]

I always drove fast street bikes. Now i somehow ended up with a low power KLX 250s, but much fun!, and noticed that with very low front pressure steering becomes faster, the reverse from street bikes.

[@williambanzhof9739]

EXCELLENT! Thanks for presenting!