Unsprung weight & Suspension performance (MTB Rear Ep. 22)

Heavy unsprung weight can affect the suspension performance by reducing the contact between tires and ground over bumpy surfaces. Learn more in this video with intuitive and visual dynamic simulations.
Learn also how rebound speed can affect the suspension performance:
• Rebound speed vs Suspe...
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[@o8thman812]

Now I get it. Terrific vid. Hey from New South Wales 🦘

[@xXETouXx]

I think I would also add normal forces at the point of contact in your explanation! As you said, light unsprung mass means more time spent in contact to the ground... But it also means higher normal force, which in turns means higher friction forces (handling). For example, at 4:55, the 6kg wheels seems to follow the road just as the 4kg does... But in reality, it's "about to" lift up so it has less normal force on the ground! By the way, thanks for your videos! 👌👌

[@cryalowicki]

Thank you for the new video! Glad to see you back :)

[@kyleroxasphoto]

Thanks for the videos man. I have learned so much about suspension from your videos. Keep the videos coming!

[@shadowdove3250]

Absolutely brilliant. Well done.

[@willmoua1]

Andre, you are the best!

[@activelives]

Thanks for sharing your knowledge!

[@SudoChuckwalla]

Great video as usual thank you!

[@syifahasyim1522]

Great engineering analysis..

[@bbens999]

in the last year or so of casually looking up how to dynamically explain this, this is by far the best video

[@ryanmb21]

Very informative, thanks!

[@justinwbohner]

Very interesting. Thank you!

[@mikkop9238]

Quality content!

[@ISpiksterI]

Great video.

[@user-xk1xx8es9l]

Nice job!

[@bike_somm]

Awesomely Cool 🦸🏻‍♂️🚲💨 Thank you for this

[@alekosty]

Thank you for the explanation! The unsprung mass is pretty much the reason why I'm still on 26-inch wheels with 2x10 transmission.

[@andrextr]

26 ain't dead !! eheh I'am also an old school guy... My trail bike is a 26-inch with 2x9 and my DH bike is also 26-inch :) Both of them 2009 models eheh

[@BrynAtkinsonmtb]

Love your vid's mate 🤙

[@andrextr]

Thanks Bryn! :)

[@Chewwsky]

Bring this back!!!

[@moonmuscle3332]

Please make more videos, we love you

[@andrextr]

Thank bro 😅 Maybe one day. Cheers 🍻

[@kennethtomawis6956]

Very usefull.

[@paultimmer1223]

Hi man, thanks for your nice videos. Dont you miss the effect less unsprung mass has on comfort in this video? In the early simulations in this video you already see less movement of the sprung weight with a lower unsprung mass. I think its a big advantage you especially notice in light jeeps. They are terribly bouncy ride because of the big weels on a simple light car. Secondly, a gearbox on a MTB shifts the weight (of a derailler) from the unsprung weight to the spung weight. (so it works in your advantage twice) I disagree that this change is just a placebo effect.

[@ryanmb21]

You have skill in explaining these concepts! I’d love to learn how best a regular rider can set up their suspension and test changes. For example the common way to set rebound on a rear shock, I’ve seen ride off a curb. Well, that pretty hard to test and measure. Just a thought.

[@andrextr]

I have some videos about that. See the episode 5 and 7 vídeos. Cheers 🍻

[@maxwestenberg6409]

interesting concept. it seems that a heavier unsprung mass would be a smoother ride on a track with negative depressions, although that's not a very realistic situation as most riding is over bumps.

[@phenax1144]

The ratio should be equally important for bumps

[@xyz12334567898]

Super insightful simulation! Would be interesting to see the small spring generated by the tire @ ~24 PSI layered in below the wheel weight

[@MRTNPRODUX]

Thanks for sharing your knowledge, can you make a video about the norco aurum/commençal supreme? 👍🏻

[@justsayin3600]

I usually go on long rides and carry all my tools and combined 4 litres of hydration. I have to adjust my rear suspension 2 times during my rides to compensate for weight. It's kind of a hassle but necessary. Thanks for the video!

[@andrextr]

In that case you are increasing only the sprung mass (suspended mass) and therefore you might need to adjust the SAG. Nevertheless, you are not increasing the UNsprung mass. Unless you store the hydration in the rear triangle of the bike eheheh :) Cheers

[@justsayin3600]

@@andrextr The motorcycle company Buell made a motorcycle, the Firebolt where the frame doubled as the fuel tank. I always enjoy your videos and content! I personally wouldn't mind if you recycled your old videos and content. 🤙

[@LongLiveEnduro]

Interesting video as always. One can also invert what you said. You won't feel a difference of a 500g reduction, so you won't feel a difference in a 500g addition. I notice no drawbacks on my DH Ebike with DH tires and wheelset and thick tubes.

[@andrextr]

Yes, I also think that 500gr does not have a big impact. I mean, it's always better to have less, in particular on rocky bumpy tracks, but I'm not sure whether you can feel that difference or if it is only placebo effect (probably you can, who knows... it would be interesting to do some real-world experiments with a shaking test-rig platform, under the bike)

[@andrextr]

PS: I also ride 500gr maxxis DH tubes on my DH bike eheheh

[@bhimanipradip4604]

it is nice but i have one request... we cant feel displacement however we feel acceleration so i hope you will make video about variable unsprung mass vs body acceleration.. at the end you will find unrealistic result

[@jeromeweite5333]

Hello Andre, Thank you very much for this nice and interesting video. The question of hydraulic is still complexe because shock absorbers have hydraulic to slow down the mouvement and itwould seem to be logical that a lower hydraulic braking balances a little bit heavier unsprung mass, in compression and in rebound.

[@andrextr]

Hi! Yes, its complex. I think that more unsprung mass requires more compression damping to slow down the wheel movement. The problem is that this also affects the sprung mass (rider + frame) and makes the riding stiffer (the wheel moving up or the chassi + rider moving down, they both cause compression in the shock). Theoretically, with zero unsprung mass you don't need hydraulics to control and dampen the wheel movements :) Cheers.

[@romanjoly2109]

nice

[@Rippy211]

Thank you for the video, it's really interesting. So the important factor here is the ratio between sprung and unsprung mass, correct? Meaning a heavier rider/bike can afford to put on more unsprung mass. Two things come to mind, as you increase the sprung weight you exert more force on the ground, meaning that you sometimes need heavy casing tires and or inserts (depending on the terrain of course) to compensate for an increased chance of punctures or sidewall instability. You don't want to just keep adding air pressure in the tire because it will cause other problems. Also, your suspension setting is more aggressive compensate (unless this is proportional). So essentially not taking everything in isolation but as a whole system, as you change the sprung weight you also want to adjust the unsprung weight to keep everything performing correctly in the real world. It's not just about keeping the wheels on the ground but also having them perform correctly when they are on the ground, giving you grip, traction, and security. Another interesting factor, the Shimano 12 speed cassette range comes to mind. While the Deore or SLX might perform exactly the same as the much more expensive but lighter XTR. The lighter one won't only make you climb up hills faster but provide marginally better tire tracking performance too.

[@andrextr]

Hi. Yes the ratio is what matters, because an heavy rider needs a stronger springrate in the shock that will push the wheel faster against the ground. So the wheel is less prone to get “airborne” after bump crests or in holes. However, an heavier rider also has disadvantages because due to increased inertia it wont brake / decelerate / turn as fast... this is common sense and its why racing cars need to be as light as possible (both sprung and unsprung mass).

[@everywherelocal]

yeah! 👍

[@buteneersmarc7610]

We miss you

[@andrextr]

I am here =)

[@tkdbboy]

That ratio differential of rear mech + cassette vs gearbox is interesting! Do you think the unsprung mass benefits of a bike using gearbox is exaggerated nowadays? I haven't ridden one myself so with such a small ratio difference, my real world expectation would be I'd notice barely any difference.

[@paologobbo]

Really interesting. The lasr question means a lot: is a 500gr weight saving (on rim, hub, tire, groupset, maybe frame parts) enough for an improvement?

[@sdqsdq6274]

lol its not good news , less weight = more money spent , lol

[@phenax1144]

@@sdqsdq6274not necessarily because now you dont need to save weight on the frame and elsewhere so no money spent on expensive carbon frames

[@dank6761]

I am glad you made this video after my question I proposed about the Zerode and sprung mass in your other video. However you did not reply to me about what I told you about the rider not 'always' being part of the sprung mass of the bike. There is times during riding for example where the large inertia as proven here in your tests but rather of the rider thsn the bike means that the riders bodyweight is also not always in sync with the frame of the bicycle. This is why gearbox bikes have a noticeable difference in performance. The same goes for the front fork, sometimes you press lightly with your hands through the handlebars and sometimes you press more. Your videos and physics models are very good but you must know that they do not tell the whole story. The reason you are unable to determine in this video if the 500g unsprung masa makes a difference is because of the overly simplified physics model. You need to find away to seperate the riders mass from the frames mass and run a physics simulation.

[@andrextr]

Hi Dan. I do found a difference in the model with small weight differences, but that was only visible on higher frequency bumps. This video does not intend to answer all complex questions. It was an educational/ proof of concept approach only. To test the gearbox question my suggestion is to use some kind of vibration test rig (similar to those used on cars) and see how wheel tracks the vibrations (slow motion camera?). But I do think you will get a diference, the only question is whether thats a relevant or significant difference or not, but this is highly subjective (for some it might be relevant for others might not be). Anyway I do like the gearbox concept over the classical transmissions for other reasons besides unsprung mass. Cheers 🍻

[@rjdkcfj]

Hi, I think you should have factored in the gyroscopic effect of the rotating mass, where small increase of weight of eg a tire might significantly increase its inertia.

[@andrextr]

Hi, it's a good point, but in this case the gyroscopic effect has no relevance because the wheel moves up and down without changing the axle of rotation. A spinning wheel only resists to the efforts of tilting the wheel (horizontal / vertical) or turning the wheel (right and left). Moving the wheel up and down without twisting does not cause gyroscopic resistance. This is a experiment that can be done by holding a spinning bike wheel... Your point applies more to when you are accelerating the bike forward (heavier wheels makes it harder to spin faster, and to slow down also). Cheers.

[@franzmauermann4386]

Nice Video, but i think y miss one think. The Rider and the mainframe aren't one solid piece. That's why heavy E-Bikes Feel smooth over bumbs. The Main frame is around 10kg Heavier than a normal.The relation between unsprung top sprung weight is 50% (5/10) to 25% (5/20) in the E-Bike. So you get Less severe blows to feet and hands

[@joubercorlaitic.nascimento9706]

Heu man, any chance you can do the analysis of the canyon spectral mullet?

[@APEX.86]

Thanks for the video! What software are you using for these dynamics simulations?

[@andrextr]

Algodoo...its not very professional but its free and it's okay for simple simulations / science education... Cheers

[@APEX.86]

@@andrextr Sweet, thanks man. Sometimes fast and simple is more fun.

[@AdrianSchwizgebel]

Very well visualized! Thought of a simulation like this for a long time but didn't know what tools to use. Can you tell me what software you've used? Also another question: Is the weight of the rear triangle really to be taken in consideration with its full weight? Because the rear triangle doesn't move the same distance as the wheel (at least not in every point) shouldn't it's weight be divided by some amount before adding it to unsprung mass? Non the less, it was interesting to see that a gearbox setup doesn't improve traction as much as some may believe. Thank you!

[@andrextr]

Thank you. Yes, that was a good point and I also think the same as you. This is why I measured the unsprung mass of my bike by removing the shock, put the rear wheel on the weight scale and holding the main frame and allowing the suspension to compress half travel (without shock). So, in this way, I think you are getting the correct picture instead of the full weight of the parts separately (because part of the rear triangle weight is supported on the main frame).

[@AdrianSchwizgebel]

@@andrextr Wow right, when you measure it that way you should get the right weight to use in the calculation. Thanks for your reply!

[@andrextr]

By the way the software is Algoodoo, it’s not great but it’s free and for simple stuff might be okay

[@pimansuki]

Hi Andre. Love your objective explanations of how suspension actually works thanks. I found it interesting because I ride a Zerode which has a gearbox is and this very low unsprung mass on rear wheel. I have a related question around tyre volumes: Effectively tyres are undamped suspension I guess. Have you tried measuring or analysing the effect on suspension of different tyre volumes? Say difference between a 2.5 and 2.8 tyre. I’ve been switching between sizes of Maxxis minions trying to gauge the real differences in overall performance (speed, grip, traction etc). Perhaps surprisingly the 2.8s (on 38mm rims) are definitely the fastest rolling, most braking grip, and seem to have best traction in most circumstances. But logic tells me the bigger undamped volume should in fact be compromising suspension performance. Your thoughts? Cheers, brendon.

[@andrextr]

Never measured the effect of tyre. Its a dynamic process hard to simulate. Also a larger tyre on larger wheels also has larger contact surface with the ground, which influences traction. And thus you can theoretically run lower pressures because the contact surface of the tyre is higher (F=P*A).

[@pimansuki]

@@andrextr yes, I guess you can get the same “tension” in a bigger volume tyre with less pressure, so therefore better roll-over and more grip via contact area at the same time.

[@laurynasjagelo5075]

@@andrextr isnt the problem in MTB that grip is not consistent - unlike in roadbiking world. So thinner tyres actually have the ability to cut through dirt, theoretically, more often resulting in more grip?

[@testtesttesttesttest884]

So should I carry water on my back or frame?

[@FightFilms]

Would a heavier coil shock somewhat mitigate the negative effects of more unsprung mass?

[@phenax1144]

Yes but not by alot since in comparison to the weight of you plus the frame it will be a small change in sprung mass

[@jcreedy20]

Nice! I would like to see a video of how to deal with a large un-sprung mass. I have a large hub motor on my ebike, that and the wheel/tyre and swing arm probably weighs 17 kilograms. So In an ideal world you would have a mid drive and a lite weight rim, but the benefit of my hub motor being super reliable outweighs the loss in handling for me, but if i can negate some of that bad handling??. So if you know any tricks on how to deal with a large un-sprung mass, then please pass on your wisdom.

[@TheDoctor46vr]

Don't you mean the weight disribution is bias to the front? How can the rear be heavier when some forks weigh 2kg.... It would have been nice if you spoke about the ratio of weight compared to sprung mass. My understanding is unsprung mass weighs roughly 4x of sprung mass. Lastly, it would have been nice if you spoke about the difference in acceleration and deceleration when reducing weight of unsprung mass.

[@Leviathandk]

Are you going to analyse the canyon neuron? :)

[@andrextr]

On video no because it takes a lot of hours to do, but I can do a PDF analysis report. Drop me a request on my website (andrextr.com). Cheers

[@ridesafealways4929]

Does the GT Fury 2015-2018 IDrive suspension design cause it to add unsprung mass from rider's weight to the rear triangle? How does this affect suspension?

[@ridesafealways4929]

Followup. I don't know if it's scientific or not but me losing 10kg of body weight made my gt fury transmit less high speed chatter than when i was heavier.

[@goaserchomp664]

andrextr If you stand up on your bike does your mass become Unsprug weight because your arms and legs act like suspencion? I ask because is it better to carry water and tools on the frame or on your person?

[@andrextr]

Nice tricky question but I guess that I prefer to carry them on the frame because lower center of mass and mostly because its more convenient and comfortable. By the way, 60% of our body mass is water, so I will let you think about that 😆

[@sdqsdq6274]

notice you got no video on why suspension is place parallel to the weight , isnt horizontal better ?

[@juanpviera]

I think in the video you are only talking about "tracking" performance, which isn't directly necessarily linked to faster times down the track. In fact, there are MANY situations where you want to float over the ground and not track it, which makes it easier for the rider = faster. Whoops in supercross are the perfect example. Then when you talk about rebound making it unstable, you are showing a video of a 1DoF model, but in the moving ground simulation where you actually show the faster rebound in this video, the suspended mass is even more stable in that particular example. Then, what about the added stability of a heavier wheel for the suspended mass AND the gyroscopic effect? Overall performance (lower elapsed time from start to finish) is a very complex variable, which greatly includes rider which these simulations completely exclude. I think you should clarify in your video that you are only talking about performance meaning how good the wheel tracks the ground. And in this regard, I think you miss one of the biggest + of having low unsprung weight which is, if you do want to track the ground, it makes it easier to achieve that without going crazy with the setup, it just happends more "on it self".

[@kermanliu6909]

Hi, André. Can I reprint your videos to Chinese Website？ For better understanding, I would like to translate your videos and add subtitles. I will not use your videos for commercial purposes, just for better spread the knowledge of mountain bikes suspension. I will indicate the author and your KZbin homepage below the video. I really like your videos, you put suspension in an easy way to understand how they work and how to better tune it. For many reasons，Chinese people are unable or hard to watch videos on KZbin. I hope I can get your permission.

[@andrextr]

Yes ok 👍

[@kermanliu6909]

Thanks :）

[@p199a]

Does rear suspension leverage ratio multiply the unsprung weight ?

[@andrextr]

Not necessarily. What matters the most is the weight/mass of the moving part of the suspension. Now, with higher leverage ratios you also need higher springrates and firmer compression damping to compensate (but this is not directly related with the topic of this video).

[@premiumboard21]

Hey can you analysing any trail bike from polygon?

[@andrextr]

Yes, no problem for Naild R3act

[@yangyeshuai3686]

Meanwhile I use a 15kg rear hub motor with a 130/90-10 tire on a hard tail fat bike frame with 22 inch front wheel

[@dansteadman2528]

what is the effect of crazy chainguides (like the one on the commencal supreme dh or norco aurumn) on antisquat values?

[@andrextr]

It depends a lot on the position of pivots and chain idler, but usually these type of systems (so called High pivot suspension) can achieve good antisquats (near 100%) without any chainextension and pedal kickback. So, the antisquat results mostly because of the swingarm angle (which in turn results into a more rearward axle path) and the chain pulling effect is minimal. Overall these designs are better in my opinion. Only problem is the transmission/ extra drag etc.

[@dansteadman2528]

@@andrextr Thanks a lot. I have been intrigued by these systems for some time now. Your videos are very informative! Thank you!

[@allseasons765]

But the unsprung mass on a bicycle I would say is lower than 4 to 5kg. Because it's distributed across the front and back wheel, and the wheels are independent. The suspension pushes them both down separately, so in fact the unsprung weight doesn't act like a 4kg one, or am I wrong?

[@andrextr]

4kg is an aproximation of the weight of rear suspension unsprung mass and includes wheel tire cassete brake and part of rear triangle mass… in lighter bikes it may be lower number

[@phenax1144]

For the front wheel it will be lower but you will probably also have lower spring rate in the front

[@thebikelab2212]

How would longer chainstays and leverage ratio affect this?

[@andrextr]

I don't think that there is a direct correlation between these factors. What matters in this case is the total weight of the unsprung mass (the moving part of the suspension)... The average leverage ratio affects more the amount of damping and springrate needed...usually higher leverage ratios need stiffer springs and stronger damping (this happens when you have a small-sized shock for so much travel). But I guess that's not directly related with this video. Cheers.

[@thebikelab2212]

@@andrextr abrigado!

[@capeljov2666]

okay... all back to 26inch wheels! :D

[@andrextr]

Im still on 26 😅

[@capeljov2666]

@@andrextr Hehe nice, it's always good to keep one in the shed... And it's true about the rebound, I made it to low and the bike threw me around like crazi, and when I came to two bigger bumps the second lunched my rear wheel so hard that I faceplanted instantly. It felt same as fully hitting front brake in a turn. LoL

[@chrisfit]

But to say it “performs better” might be incorrect right? The lighter weight tracks better, but that doesn’t make it faster right? Wouldn’t the ground being in contact with the wheel make it slower due to rolling resistance? Maybe that was the counter intuitive part you mentioned.

[@andrextr]

I was thinking more in the perspective of going over a downhill bumpy track. A lighter unsprung mass allows you to go faster near the limits without losing the control since the wheels stays more time on the ground, and not in the air. Losing contact with the ground in sucessive fast bumps can make you loose control. In car racing and F1 the unsprung mass is also important to improve handling and steering and keep the traction with the track. However, I've read that, as you point out, a very light unsprung mass can have some drawbacks (in passenger cars) since the wheels track better the ground they can pass more vibration from the road imperfections to the car cabin and cause more rolling noise and vibrations inside the car. Cheers

[@benoc9966]

Being in control is always going to be faster regardless of the rolling resistance when downhill is concerned.

[@Tony_Sab]

9:02 I really can't understand how this makes sense wtf

[@andrextr]

Lighter objects accelerate faster.

[@Tony_Sab]

@@andrextr but if F=ma then a=F/m which means a=mg/m so a=g which means that they should have the same acceleration doesn't it?

[@andrextr]

@@Tony_Sab if "a=F/m" then for a given force (spring force from the suspension pushing the wheel down) the higher the Mass, the lower the acceleration... heavier objects accelerate slower than lighter ones, under the same force. Inertia... Cheers

[@AlexA-vd7li]

How are you? You look tired.

[@andrextr]

Eheheh thats what happens when you don’t ride your bike for 4 weeks. But now I’m good again :)

[@AlexA-vd7li]

@@andrextrOh, then everything is ok. :)

[@joviallmountain2676]

I was wondering the same. You look even sad, i was worried.