Is Bigger Better? The Science Of Superior Braking Performance

[@gmbntech]

What size brake discs do you have on your MTB? Do you have the same size for both or mix it up?

[@WorkLessRideMore]

200 front 180 rear seems fine with 4 pot xt

[@rider65]

Don't know if you read my commentary on the last brake gmbn video, but I explained how brake rotor size has nothing to do with braking power- as far as bigger = more power. A brake rotor in essence is like a heat sink. Surface Friction creates heat which is then absorbed and dissipates heat, converting kinetic energy to thermal energy. What a bigger rotor will do is stave off brake fade more efficiently than a smaller rotor. Thermal conductivity is the goal. You want pads that can absorb and dissipate the proper amount of heat from the friction to the rotor and still be within an operating range that will optimize braking power. Once the pads have surpassed their efficiency operating temperature they will begin to glaze from overheating and no longer be able to transfer the heat energy to the rotor and vice versa. If the rotor becomes overheated the pads will absorb excess heat from the rotor as well as heat from the applied forces of friction. And the result is that the friction coefficient will diminish- I.E.- brake fade

[@floydblandston108]

@@rider65 - you forgot about leverage. Remember; physics believes in you even if you don't understand it.

[@rider65]

@@floydblandston108 😂 nice try their Fredo... leverage can only change from the master cylinder pressure itself. Go back to school Sonny Boy

[@floydblandston108]

@@rider65 - it's called 'angular momentum', look it up.

[@floydblandston108]

Important point; once your wheel is sliding, you're not testing brakes, but tires.

[@michaelgunawan2319]

Exactly. A lot of people think they need more power. You need better heat dissipation, better tires, etc.

[@darrinkulyk9560]

Its A Combo Deal ALL depends where you Ride And Skill Level

[@JamieTec]

Ya, once your tires lock up, the entire braking system becomes irrelevant to the conversation of braking distance and control

[@MyBetsie]

Once the tyres lock up you are still testing the brakes in real conditions. The back wheel can still jack on trail, especially on a full sus, if the brakes are poor they may not remain locked, also you will modulate to just before the lock up, better modulation and power means your hands won't get as fatigued on longer descents.

[@floydblandston108]

@@MyBetsie - she was measuring stopping distance....on pavement.

[@scoto1976]

Locking up the brakes and skidding isn't the most effective way to stop a mountain bike.

[@BrianAlfordDrummer72]

I have the same Shimano MT6100 breaks on my Trek Roscoe with 200mm front and 180mm rear rotors. I also noticed an improvement in breaking and feel from the stock MT200’s and 180mm front rotor it came with. I dont do any downhill trails so this setup works very well for me and didn’t break the bank upgrading. Thanks for the video! 🙏

[@tehalexy]

ppl call me crazy to run my bike with 246mm Rotors. I'm 120kg ... when 60kg riders think 220mm are fine ... I'm def allowed to run my 246mm :D

[@dukemasterpro]

I’m more impressed by Little Champery on a hard tail than the brake tests themselves 😮

[@gmbntech]

We had to do a proper stress test 🤷‍♂

[@dantuttle2050]

A couple of other things to consider here are brake pad composition and how that relates to the rotor temperature ramp up. Disc brakes need some temperature to function and that temperature is dependent on pad material; resin vs. sintered. The stopping distance test showed that the rear just locks at the pad "bite point", where the pad makes initial grip, and the 220mm rotor took longer to heat and provide the needed stopping power to slow down then the 200mm. The bite point is different between pad materials as is how quickly they heat the rotor up. If you watch most types of car racing you will notice that the teams change the brake duct sizes to keep their rotor temps in the optimum range. Formula 1 is a good example. If the driver lets the brakes get too cool, they are useless. What it all comes down to is experimenting to find the best combination of pad material and rotor size that works for the rider and their terrain. On my hardtail with 2 piston calipers and sintered pads I never felt I needed bigger then a 180/160 front & rear.

[@matt_acton-varian]

Formula 1 brakes are carbon rotors and are designed to operate at high temperatures. Bike brakes are designed with normal riding conditions in mind and will be operational at cooler temperatures. They may not be optimal. The same reason normal car's brakes are metal rotors; they need to work straight away.

[@DB-sd3cw]

Good lord man nobody is reading that novel

[@didiermeister98]

I just did

[@lenolenoleno]

@@DB-sd3cw You should, you'd learn something. Exactly what @dantuttle2050 said is correct.

[@DB-sd3cw]

@@lenolenoleno can't imagine being so lame you have time to comment on a 5 month old reply. No wonder you have time to read that novel, you have nothing else to do it seems

[@elih9588]

Thanks for the cool test! Even without a performance benefit, I like the bigger rotors for the lower force needed on lever pull. This equates to less arm pump on a long descent.

[@aspiringastronaut9992]

Agreed this is my reason as well.

[@MBj1703]

same here, went to 223 for less force needed and less arm pump. PS: blocking rear wheel makes no sense for a breaking test ;-)

[@gmbntech]

@@MBj1703 Totally agree, locking the rear wheel isn't the most efficient way of stopping. I think the combination of Anna being a light rider and the extra stopping power up front (which would load the front wheel more) meant there wasn't much weight on the rear tyre so it is difficult to stop it from locking up. Next time we will try it with a heavier rider and see how that affects it!🤘

[@rider65]

No such thing that is a fallacy. It takes the same amount of lever Force no matter what size the rotor is what you're referring to is torque. Not lever pressure. This is simply your perception but not reality in terms of the laws of mechanical physics

[@MBj1703]

@@rider65 Whatever "you" say. Fact, you need less lever pressure on bigger rotors to generate the same braking power which leads to less fatigue of the fingers and arm pump. It's simple physics 🙂

[@prfgrn2382]

This is a cool test. Would consider the 220s now for less arm pump. Currently running a 200 and the difference from the 180 is huge even a casual rider like myself was able to notice.

[@dylan-5287]

Interesting video. Definitely do a part two with a longer test track. Also add in a heat dissipation time. Like heat of rotor right after then another minute after to see how much heat it lost.

[@kaneda4102]

Reducing the fatigue in your forearms and losing brake fade were the two things on my mind with this.

[@Alanvictoryoung]

Great test! I went to 220 front and rear for a long time now and I’m a light weight rider. Less finger and arm fatigue and fade resistance on long (10min+) steep runs are the main reasons. Also when I ride a ridiculous amount per week it keeps my body get beat up as much. It takes a while to get used to how powerful it is but once your brain adapts the grabbiness is manageable.

[@letsgoletsgoletsgoletsgoletsgo]

Very few forks and frames are rated past 203 mm you're not worried about things breaking?

[@darrinkulyk9560]

Ya Get To Use The ADVANCED Braking Techniques Like Feathering And Trail Braking . I ride Whistler ALL Day Without Arm Pump .... of course im fit and Ride Alot So I dont Brake as much as most riders . Makes For Very Fast Flow

[@TheButlerNZ]

@@letsgoletsgoletsgoletsgoletsgo Funny thing... you can get a 180 rotor to lock up on tarmac down a hill... any thing beyond lock up is ... well still locked up... So riding a 180 near locked up down a tarmac hill until you come to a stop is EXACTLY the same load as a 220mm near locked up... so the rating is really a bit of a joke unless they expect you to use brakes on that fork that cannot force the wheel to near stall. I can load my forks on my old Vee Brakes as well as the 200's I run... the Vees just don't have the feel and fade/burn away quicker. The big difference is the Vees required an entire vice grip of fingers vs the 1 finger braking I get with the XT's. (And I ran a Schwalbe Nobby Nic with the vee's so there was a good amount of force back from the tyre grip.

[@letsgoletsgoletsgoletsgoletsgo]

@@TheButlerNZ wow I've never thought of it like that , you've got a good point , but why do bike manufacturers put a max rotor size though ?

[@TheButlerNZ]

@@letsgoletsgoletsgoletsgoletsgo Because you want to go bigger on the rotor, so they want you to go bigger on the forks... and guess who just happens to be selling the next model up... the same people that rated their cheaper ones... There is a point... Bigger rotors, more ease to overload the forks... Like a lot of base $ forks that you could destroy with a good tyre and Vee brakes... I think the big thing is a hard landing with a handfull of big rotor brake will give huge torque to a set of forks where a smaller rotor will be forced into rotating... THEN you will see meaning to the fork rating... If you just ride DH without big air to flat under hard braking... I'll go with my 1st 'theory'. (I used to load the front of the trailbike when I needed to get a bit more 'Stop' without reaching a lockup but generally I was too mediocre to really push a YZ250 to any real limit.. Plenty of big air to flat but always with plenty of runoff.

[@robertsilva5041]

Lean back when braking. Also. I've seen tests that were done multiple times in each of your categories and the ones that responded better, was after the first initial braking. As if heating them up at a certain point seems more effective. Excellent job yes

[@HeretiCflow]

I think for lighter riders like her 220mm doesn't make any sense. As she noticed, they lock up on her too quickly especially in the rear and thus reduce braking efficiency. For me personally a 220mm in the front is the way to go on my Enduro bike, but I'm also quite a bit bigger and heavier than she is. So essentially 220s do for me what 200s do for her her.

[@rickywoods3101]

Yup , plus I like to be able to lock the rear wheel really easy

[@darrinkulyk9560]

PAD Compound IS Key

[@MehmetSevil]

As heat builds up in the rotors and pads the "capacity" of the brake system gets filled up and tires get more and more prone to locking up as the energy finds it easier to skid the tires than to turn kinetic energy into heat where there's already a lot of heat built up. I like to think of the rotors as pools in which I can dump my kinetic energy as heat. The rotor size is the volume of the pool, the heat dissipation is the sink of the pool. The bigger the sink the faster it drains (duh.) and the larger the volume the more speed I can dump into it at once. It is surprising how many riders are willing to let go of that braking performance for the measly gain of a few grams. Better braking means higher overall speed through confidence, control and safety. Tire grippiness is what determines how full the pool can get before I start skidding which is to be avoided if we want efficient braking. Just my 2c.

[@fcbotieno]

7:12 "perhaps the 220's where too powerful, we skidded" that is what happened. Once the wheels lockup the tires are no longer able to extract its maximum grip/braking capabilities. 180mm had no skid. 200mm skidded just a bit. 220mm skidded too much to stop maximally. The larger rotors also have a higher thermal capacity and thus requires higher temps to be optimal. Just as the video concluded, the bigger the rotor the higher loads are required to get the most benefit(heavier rider and/or DH applications)

[@fcbotieno]

@@lukedangles-mckenzie2024 what is your point?

[@punisher40revenge73]

Try using a bicycle computer for speed start to finish in each run or stopwatch for a more accurate reading. Thanks great video!🇨🇦

[@topcat304]

On my 2015 trek Remedy 7, the stock parts were Shimano deore 2 piston; 180/160 rotors. When I raced and the descent was greater than 5 minutes, I had brake Fad ( big loss of power). I switched to 203/180 seven years ago and have not had one moment of power loss or fad inside and outside of racing!

[@gmbntech]

Sounds like you've got the perfect setup! 👍

[@rustychain9518]

My Trek Fuel EX has 203/180 with TRP 4 piston calipers and they’re perfect for me but when my wife who’s 100 lbs lighter than me rode my bike she hated the brakes because it was so difficult for her to modulate them. She much prefers the Shimano MT200 180/160 on her Polygon Siskiu D7 that feel like mush to me…it’s all very personal.

[@nathanielbrice8725]

Don’t care about the accuracy of the tests, just loved watching the video! Great stuff! 👍🏽

[@alanmartinezrodriguez884]

I'm pretty sure they did but, just in case, were the rotors bedded in properly? That can dramatically affect the performance of the brakes. Also, it would be nice if you could mark the braking point and not only the stopping point. Maybe you did Mark it but it wasn't told in the video. Finally, don't take your foot out of the pedal before the stop has been completed, Anna! That can affect the result as well. Maybe go flat next time, so that you can focus on the braking only. Just a few suggestions. Love it, guys. Keep'em coming and go Anna!

[@banana122049]

My trails are very short descents and punchy climbs. I could be entirely wrong but I've found that a 160 on the rear spins up heat faster and grabs a lil harder for me in the short braking spurts i deal with at my local trails. I think on a long decent I'd melt it and fly into the trees though. (I'm a wheel bending 285lbs) Something to think about if your descents aren't long at your local trails!

[@rider65]

You are correct a smaller rotor will heat up quicker thereby transferring the kinetic heat energy into thermal energy into the pads. For a short period of time a smaller rotor will be more efficient but on any sort of prolonged usage the smaller rotor will no longer be thermally efficient

[@simonm1447]

You should try to descend Khardungla in Ladakh. It's a 5300 m mountain pass which descends to 3500 m on a distance of 40 km. A full hour of descending. Riding it up is a good training

[@beno9966]

Go bigger and move to resin if you want modulation, usually good on the front where you are less likely to be dragging the brake as resin will wear much faster.

[@KDog2264]

Drag test would be a good test. Your trail test, yes make it longer, but also do different trails one being a fast flow trail and the other being a slower tech trail.

[@philipcaldwell3187]

It would be great to acquire data for each rotors thermal time constant. You were sneaking up on this important metric with the IR measurement in the last measurement of the 220 mm rear tire rotor. The faster the rotor can shed heat the lower the operating brake temperatures would be for extended down hill runs which demand more frequent braking. Brake temperature beyond a point is the nemesis of consistent braking authority. Nice color match with the dead cat, kudos to your production crew!

[@KaizersPOV]

"For me, bigger is better. I'm using 203 on the front and 180 at the back. It took me some time to get used to the stronger brakes, but the upside is I can brake for much longer. Going down, more material takes longer to heat up, delaying the onset of brake fade." this is a much cheaper way than to invest on Ice tech rotors and finned Pads.

[@RedWingsninetyone]

For me, the only real difference I've noticed in going from 180 front to 203 is that my 203s are noisier and I can't figure out why. The only thing I haven't tried at this point is swapping out the pads or rotor entirely. I don't notice any difference in stopping power for my needs, but then again my 180 was on a 27.5 and my 203 is on a 29, so that could be the difference.

[@50whatnomadtravelnursemtb5]

I run 203 front and rear on all my mountain bikes! Absolutely the size matters with bigger heavier riders and ebikes. But I think it’s not about worrying about locking the wheel up it’s more about using less break lever pressure for same power, less hand fatigue, less rotor wear. If you’re just cruising down a green trail then yes 160 or 180 is just fine.

[@Naper1881]

I'd love to see a part 2 with a dragging brake test! I don't have a MTB these days, but I've got a heavy cargo bike and big hills around me. I do a lot of brake dragging to keep the speeds low and my baby girl on the back safe. Currently my bike only has 180s and I'm thinking of upgrading to 200s or maybe 220s.

[@nathantoney.1501]

We’re all rotors bedded exactly the same?

[@vlbz]

Same experience here. Running 203s. 220 is too strong, I find myself locking the wheels too often.

[@AdamosFF]

220mm in front, 203mm in back and, 4 pistons brakes on my enduro. I like how they feel

[@rafagm7457]

I really liked your video, thank you . I would really like to see this test using perhaps a heavier bike with a bigger tire like a full power ebike, I think the benefits of a 220 brake should be very noticeable there.

[@FirestormAA]

I think drag brake test on a down hill will be more realistic for the bigger rotor. Great test anyway to show but replacing the rotor itself can really change the entire dynamic of the stopping power & feel.

[@beno9966]

Exactly. People tend to drag the rear and that's why it wears and heats up so much.

[@Clint_the_Audio-Photo_Guy]

I've got 3 different bikes with 3 different brake discs, and I never felt like I didn't have enough brakes. I haven't ridden my new Pivot Switchblade yet, but it's got the biggest brakes of the three with 203mm in front and a 180mm rear, but with 4 piston STX calipers front and back. I'm sure the braking will be ruthless. I have no desire to change rotors on any of them. The front brake is supposed to be doing like 70% of the power, you definitely seem to favor your back brake. I've had quite a few motorcycles, and the last one I owned had dual 320mm rotors up front with 4 piston Brembo calipers on it, and just a single 220mm rotor in back with a two-piston caliper because the front is where the power comes from. During the panic stop testing, you could have used the front brake harder instead of locking up the rear and dragging the tire. I know in the loose stuff you're worried about losing the front end, but there's more front squeeze to be had IMO. ;)

[@LKSSRLBG]

I did this test myself with 160, 180 and 203 mm discs and 2 types of Shimano organic pads too: G02S and J03A Ice Tech. Elevation gain: -400m, -10% of inclination all the time. I came up with the test because every time I went there, my Deore rear brake with 160mm and the basic shimano organic pads faded completely away. It wouldn't even lock the rear wheel down there. And I found out that 1 Ice Tech on brake pads don't show any difference, 2 the same set of brakepad and rotor on front show a better fading behavior than on rear, and I think that's because a cleaner and more direct wind can blow at the front end more than at the rear. Also, I found that if my 180-160 set of discs were not enough to the local terrain, I should upgrade them to 203-180, and that's what I did. The test was conducted where I live, south Brazil, very accidented terrain.

[@nevillepretorius8948]

Loving Anna's custom built Nukeproof ❤

[@andrewsonleitner9882]

Great info Anna I upgraded my rotorsq to 200 but have not installed them yet but watching your test runs looks like I made the right move can't wait to install them thanks so much

[@gmbntech]

Please let us know how it goes! 🤙

[@TheButlerNZ]

Have you considered braking with your middle finger.. (Possibly the less strength may help.. Personally I tried but my other fingers got in the way with my brake position)

[@GreatCreative]

I think this video just saved me a lot of upgrade money. I run XT M8120 4-piston with 180mm rotors and they fade quickly on descents. I was considering a new set of brakes. After seeing this, I'm just going to buy 203mm rotors and call it a lesson learned.

[@benjy288]

I would take this test with a very large grain of salt, braking performance on dirt is almost always limited by grip, not by how big your rotors are, I've gone from 200mm down to 180mm and my braking performance hasn't changed, the only thing that has changed is the smaller disc requires slightly more squeeze from the lever on very steep descents, maybe the issue is the weak 2 piston calipers? they probably can't get away with running a 180mm rotor.

[@PlaySafeProductions]

Upgraded my Slash 8 180/200 to 200/220 after my brakes were overheating on longer runs. 10 minutes plus. Made a huge difference, with no overheating. I also like the sensitive braking, which some people may not like.

[@gmbntech]

Sounds spot on! You can always switch to a braking system like Srams where the modulation is far greater giving a less sensitive lever feel, but easier to modulate power.

[@Neilz911]

I Had a similar Problem with my Cube one 77, solved IT with a 200mm Rotor at the rear.

[@rider65]

There's so much science with regard to the laws of mechanical physics behind braking systems that trying to put it into layman's terms is just going to confuse a lot of people who don't want to bother to learn basic physics. It's about frictional forces, torque, thermal conductivity, thermal efficiency, heat-energy conversion, heat-energy dissipation. Kinetic energy converted to thermal energy. Bigger rotors do not provide more braking power. Bigger rotors offer more braking efficiency. But this is just one part of the equation. Caliper size I.E.- 2 Pistons or 4 Pistons, pad size, pad material, master cylinder ratio and fluid all contribute to the efficiency the effectiveness and the power of a braking system.

[@j.albertogratacos2076]

I have two similarly equiped bikes, but one is a hardtail, the other a fullsus. Both have 203 up front. The fullsus also has a 203 rear I kept the rear down to 180. One of the hardtails biggest drawbacks is braking on lose, chattery terrain because the rear starts to bounce and skid. I feel a larger rear rotor would make it skid more.

[@TheButlerNZ]

I agree... You could try harder pads to decrease grip to the rear... I still think that rear brakes are overrated and you can be a better rider the less you can force yourself to use them.. but that comes from years of motorbike riding where onroad rear brakes are actually dangerous (a lot of racers make them near useless so they don't accidently use them in a race) and on the trailbikes I became faster on my old bike when the drum rear failed and I learnt how to brake hard upto a corner and no brakes through it (to the point where I was entering corners with the rear in the air (which is why I say rear brakes are useless (Except for stopping at slow speeds like lights.

[@TheDizzyCyclist]

Nice to see a 200mm rotor being tested. Not all of us can run the “standard” 203mm rotor.

[@petererbse6253]

I would love to see a drag brake test, especiallyon the rear. Get it up tp speed in a controlled Environment and drag the same distance. Maybe also how quick the rotor is cooling down in 15, 30 seconds.

[@scottersandman6408]

no 160s? entry level starts there in my eyes. I did go from 160 to 180 in the front and found better power on tarmac

[@reinholdachleitner2069]

Awesome video love your Nuke Proof hardtail.I use 180mm front 160mm rear.Super strong combo.💯💪🏻🚴‍♀️

[@mtbboy1993]

No matter the size I keep warping rotors. But some reasons for that can be sticky pistons, so lube the pistons. Rebuild caliper with new seals if needed. Only do that hwen they leak and get stuck even with lubing. I gone side is sticking there will be a bad brake feel and pad will have a gap between the rotor. And other sid eiwll bend the rotor. But even with perfectly working brakes I keep bending rotors. I run 223mm rotors front and rear. In warp rotors less with bigger rotors but still do it. I ran 180mm rear, 203mm front Hope Tech floating rotors. Now I run 223mm Trickstuff rotors. I opted for rotor with no rivets for no creaking, got them second hand offered to me for half of retail so had to try it. Hope floating rotors defenitly perform much better than resin only rotors in same size, I've had 160 rear 180 front on my previous bike. So massive upgrade. But after years of use it creaked in the rivets.

[@LaurentiusTriarius]

I used to think always bigger the better but I came back to 203 up front and 180 rear for optimal balance of raw power. That would be a fun test, playing with size combinations like 160 up front 220 rear! Drift machine?

[@dannyhouston5546]

The brakes should be hotter but cool quicker with increasing radius. The velocity of the disc that contacts the brake is greater as the radius of the brake gets larger, making for greater temps. But the increase in surface area enables them to cool quicker. The ideal larger brake would be if the surface area of the friction pad was increased, not the rotor. Or have dual parallel discs and pads. They are probably on the way

[@gmbntech]

Dual parallel disc would be cool to see! 👀But a bit heavy for MTB I think we could see them appear first on an E-bike but is there really a need for them? 🤷‍♂

[@floydblandston108]

@@gmbntech - We'd be better off first going back to Magura's 'Gustav' sliding caliper system.

[@TheButlerNZ]

@@floydblandston108 I love my Gustav's on my old Foes Weasel (made it to GMBN mention a couple of times now, see my walkaround vid for a view of the Gustav up front.)...

[@TheButlerNZ]

Not sure your right with the hotter bit... Take it to an extreme (caliper the size of the rim... The disk will have cooled by the time the wheel has done full rotation, but the pads will be hot... but not necessarily as hot as a small rotor as the force will be so much less required.... so less force, more heat dissipation... the rotors should be cooler... The problem I see is that with less modulation, I think Anna may have been riding the brakes a little more to keep 'feel' for them. ( found myself doing that for the few days after getting my 200mm brakes clean and running (when I 1st got them) before switching to 1 finger.. and literally overnight never went back after the 1st 1 finger ride. (which I got on film on about my 3rd U-toob video)

[@mikelong5207]

The distance test is subject to far too many variables such as initial speed, surface temp and modulation of the brake and as such can be misleading, to understand which brake produces the most braking you need to do a G force test with a G meter and do multiple runs to produce a bell curve, this way you get a clearer picture of the brakes performance. the braking limit of the bike is not the brake disc and caliper but the coefficient of friction of the tyre to surface, a small brake can lock up on mud for instance. you also have to factor in the weight of the rider bike combination, a 60kg rider on the same weight bike as a 100kg rider produces vastly less kinetic energy at the same speed, so to produce the same G rating under braking a heavier rider will require a larger brake. Some riders will prefer a more sensitive brake lever that is lighter to modulate and control, that lends itself to a bigger brake whereas other prefer a brake they can grab without lock up, opposite requirements. Then we get into the kinetic issues such as weight transfer, a taller rider will have a higher center of gravity than a shorter rider and therfore transfer more weight to the front wheel under braking requiring a larger brake, all of which is subject to our initial starting point of the coefficient of the tyre, which as mentioned earlier is the limiting factor. suffice to say you have to tailor your brake sizing to your own requirements, the only given factor is, due to weight transfer to the front you can reliably use a smaller disc at the rear to control lock up as weight and therefore friction is reduced by weight transfer under heavy braking. On my own bike I use a 203mm disc and 4pot caliper on the front and a 160mm with 2pot on the rear, this is because I am 6ft 2" tall and weigh 105kg,

[@BinManSays87]

Size makes such a difference I remember way back when I saw one of the bigger boys light a fag/cig off his160mm hope mini after his lighter died then years later a rider who was also there found 180mm just didn't get hot enough to pull off the tame trick

[@jacksondaniels8169]

Nothing was noted about tire grip. Your tires have a lot to do with how effective your braking is. GALFER makes a 243mm rotor. Overkill unless you're doing a bomb run down Pikes Peak. IMO, 220/203 is a good combo for aggressive enduro/DH riding for riders over 180lbs. Why would anyone gage their bike performance on EWS or XC racers. It's all about feel and performance on the trail.

[@vincentprost5623]

What about the brakes ? Were they 4 pistons ? What about the compound of the pads ? What about the bedding-in of the discs ? What about he optimum working temperature of the pads and of the discs ? Maybe the fact that braking at a low temperature gives a quite random result between the different rotor size.

[@marcusslater149]

the other thing is.....were the speeds at the point of applying the brakes the same?

[@benjy288]

Weak shimano deore 2 piston brakes, they really should have used 4 piston brakes, no body uses 2 piston brakes on a proper mountain bike.

[@blurglide]

I don't think brake size would help in this test other than lever effort. The main advantage of big rotors is their ability to absorb and dissipate heat in multiple stops

[@rider65]

There is no change in lever effort at all because that would mean you'd have to change the ratio in the master cylinder as it pushes the hydraulic fluid through the caliper into the Pistons. It's a fallacy. It's simply psychological perception

[@blurglide]

@@rider65 A bigger diameter rotor is moving faster through the caliper (or has more leverage on the hub). Therefore, you need to squeeze the lever less for the same level of braking force.

[@blurglide]

@@rider65 Another way of saying this is that a given level of lever effort will result in more braking force if you have larger rotors.

[@renzoeltigre]

Next time avoid locking the rear tire specially on asphalt, that situation show that brake balance is not well performed and modulation is not executed properly. Removing those mistakes will provide more accurate results

[@kodithebear]

I find with big rotors I set my levers to bite close to the bars. This stops lockups unless you really grab a handful. Way better modulation.

[@trialsta1]

I've put a bigger rotor on the front and a smaller one on the rear than the stock setup. There was too much power on the rear for the amount of grip that wheel has, making it hard to modulate to the point of lock up. I suspect bikes coming with too much rear braking power is why we have so many braking bumps at trail centres!

[@gmbntech]

That's something to think about! 🤔

[@Numberofbillion]

Thanks for the video, Stop distance, heat & times are always going to be 'rubbery', you'd have to go a brake dyno & thermal camera, FEEL - or modulation - i think is key, the harder you have to squeeze - the less FEEL, so go bigger Also you taught us we need to bed-in the rotors with pad material??

[@julianw5692]

It could be worth doing the stopping distance tests with maguras abs system to reduce the importance of tyre grip.

[@bionic909]

Ive had my discs glowing red in the alps

[@jeffjohnson8963]

I started smelling my brakes descending down a fire road at the end of the day just trying to keep it under 25mph. In the trail I haven’t noticed brake issues. Next time maybe try a smooth fire road and some fairly fast sustained speed. Bravo on this segment!!!

[@mustclime5311]

Old car guy here....if you are going to track day your car, the first thing you did was mount the biggest brakes you could fit on the car. my e bike and my mountain bike both have 220 rotors.

[@PghMtbRides]

Ive been toying with the idea of running a larger rear then front since I'm pretty even when braking front/rear and rear disc discolors

[@fra93ilgrande]

For XC, I use 180 front and 160 rear on my 29er but 160 front and 140 rear on my 26er

[@MyBetsie]

You need to do this on a full suspension bike for real reaults to compare to why enduro racers use 220mm rotors. Hand farigue, especially with basic brakes makes a big difference on longer runs too.

[@cegalleta]

What about rotor thickness and two piece vs one piece rotors? A huge deal with going bigger is that it's easier to warp rotors under hard braking

[@thevapingpolisher9717]

I run 180 front and rear on both bikes

[@rhettcorbett3346]

Hope floating/ventilated 203 front & rear on both of my V10s. Tech 3 brakes on 1 bike & Tech 4 on other.

[@LordVineet]

My observations: 1: TEMPERATURE CHECK - The temp check should have been done right after stopping by 2 diff individuals (one for rear and one for front). Why? Because the front rotor is cooling down whilst you are checking the rear rotor temp. Also note the weather /temperature outside because I believe that also makes a lot of difference. 2: STOPPING DISTANCE - Although it gives a fair idea about the results. But to be on the fair side, the riding speed should have been checked and maintained for all the 3 rotors. In other words, the speed should have been similar for all the rotors before applying the brakes. Overall, the test is interesting. I would suggest a combination test next time. Like, 200 in the front and 180 in rear vs 220 in front and 200 in the rear and how braking power performance differs vs same rotor size in front n back.

[@TheButlerNZ]

I think stopping distance using a bike with ABS (I know, near impossible but the brakes need to be allowed to impart max load without locking... unfortunately ther is a point where the tyre will brake loos regardless of what brake you use... so at some point, no matter how big the rotor, you would reach a limit where bigger would only supply a unusable amount of extra force (but of course if you could modulate it, the lighter weight on fingers would be a plus.. but again the feel would get to a point where you couldn't modulate as the forces would be too close/small for finger 'feel'. I think with proper setup (pad change etc to get the best force needed for finger modulation, a 220 would be better.. A harder compound rotor (higher carbon?) would reduce the overpower and increase life... but do bike manufacturers want to produce a brake that can be made cheap (2 pot) and have both pad and disk last longer (so they can't sell you more parts per month). (This is why they love selling the crap low end gear that actually costs the same as the high end to produce... tell me why the XT gear they made 20 years ago isn't the base cheap gear.. instead of actually just as expensive if not more expensive cable systems (just look at all the parts needed in a cable caliper compared to 8 main bits in a hydraulic base model caliper (2 halves, 2 pots, 2 seals, 2 pads)... As for temp check... 3 people (4 incl Anna... tho Anna could play the 3rd role.... Anna pulls up. 1st person starts a clock... person at front and rear take reading & note it down, 1st person calls 5 sec intervals and front and rear record temps... result is a graph of, not only heat at stopping, but heat loss over time after stopping... Thing is... GMBN want a nice simple result and not a lot of people involved... so we get an Idea of a real result but not a truly scientific one... but if the Idea comes up with anything odd/interesting, it may spark someone to do the extra mile.

[@M2rider3lisium]

I have 180 mm disc brakes on both wheels,with a pair to 2 pot brakes on the Hardtail,is a lot of stopping power

[@genecatcher1]

It is not up for debate or doubt. Always the front disc has a larger diameter. Even with cars. A matter of angular velocity

[@janeblogs324]

Except on downhill MTB where you use more rear brake

[@genecatcher1]

@@janeblogs324 Correct.

[@rickywoods3101]

I know people that run larger rear brake rotors for downhill or so they can easily lock up the rear fast and easy

[@genecatcher1]

Regardless of front or rear disc, the larger diameter disc has better braking capabilities.

[@fud1376]

Scintered pads should be anyone's 1st upgrade...Check ya rotors are compatible though, most basic ones are for Resin pads only..!

[@simonrook5743]

You can use metal pads on resin ‘only’ discs just fine, they just wear out a bit faster. But most discs get binned for distortion long before that.

[@nwimpney]

it's all about getting used to the feel, and how you're using them. If the big rotors are hotter, it's probably because you were dragging them more, Likewise, on the emergency stops, you might have been going a little too light on them overcompensating, since they feel too grabby. Any of those probably has more than you need for the max braking your tires will hold, so unless you're concerned about fade on sustained braking, it's mostly about matching it for the feel you want on the lever.

[@noxed11]

Horses for courses. On my enduro bike I'm happy with 203mm front and 180mm rear. Tried 203mm rear with a four piston Zee and it was actually too much brake for me on pretty steep trails. Finger rest on the lever in the air would start locking up the rear and then dip your nose on jumps. Combination of quality caliper and adequate rotor size makes more sense than just upspeccing rotors. On DH bikes, or enduro racing, then by all means, 203 or 220 makes sense, but I think there is a thing like too much brake for purpose.

[@chrisl2656]

Nice premise for a video, but... A rotor with only an extra 30 degrees in it is a rotor that hasn’t been working hard, although IR thermometers aren’t an accurate way of measuring the temperature of shiny metallic things, so maybe they were actually hotter than the reading suggests?

[@rider65]

"Although friction force is, according to Amontons’ law (Chapter 2), independent of the apparent friction area defined by the surface area of the brake pad or lining, the friction material may suffer mechanical or thermal failure if it is too small. The minimum surface area of friction material required to ensure satisfactory service is normally determined by consideration of two criteria, which may be specified by the friction material manufacturer or developed from experience by the vehicle manufacturer. Shear loading relates to the shear strength of the friction material or the pad/backplate bond, and power density (also called ‘work rate’) is a measure of the rate of heat transfer into the friction material that it can withstand before its structure breaks down. It is usually necessary to consider both criteria and design the friction material size to meet the higher value. Wear, which is also related to the size of the friction material surface area in frictional contact with the rotor, is evaluated later in the brake system design process (Step 5) but experience has shown that if the limits for shear loading and power density are not exceeded, the friction material wear is unlikely to be unsatisfactory. Shear loading refers to the friction force per unit area of the brake pad or lining, as illustrated in Figure 6.3. Assuming that the wheels do not lock, this can be calculated from the braking force at the tyre/road interface (Ti; see Chapters 3 and 4Chapter 3Chapter 4). For an axle with two disc brakes each with two pads of friction surface area Ap"

[@warrenyoung173]

If you really want to get an idea of heating and cooling, The Bike Sauce channel put a data logger on his disc and did testing on a road for consistent, hard braking. I've been meaning to repeat this to compare Ice Tech to cheap rotors... Heat dissipation rate. 50C is nothing to be excited about. Heck, sometimes the ambient temperature is 38C. I've measured 100C without fade. Pretty sure pads and oil are rated well above that.

[@simonm1447]

If you temper stainless steel it gets different colours. It gets the same colours if it heats up at braking. If parts of the disc reach 200° they get yellow, if they get blue they are more near 300 °. My disc rotors are yellow beside the braking surface.

[@stefanvasilev2013]

Realistically, you can lock your wheels with either size, so the braking power is there in all cases and it's limited by traction, i.e. tyre/terrain combo. The size difference matters technically only as far as heat management is concerned. Dissipation is a function of surface area and one can easily have a minimalistic 203mm rotor with less surface than a bulky 180mm rotor. Regarding heat accumulation, a bigger rotor will always have more braking surface (larger circumference that comes in contact with the braking pads), so it should heat up slower than a smaller rotor. Larger rotors provide different feel due to modulation, which isn't really bike (or rotor) performance, but rather rider performance. Note that in all cases the contact surface is the same since it's determined by the pads' size, so the difference in modulation is only due to the radius, i.e. you are playing with leverage - that's literally like changing the length of your brake levers.

[@martinangelomooney1010]

I actually did the same. I have a 4 piston deore but I was using 160's so it was really not as snappy but when I changed to a shimano 180mm it made a big difference. I only do light but fast trails and with the 180's front and rear I can descend with ease and yes less fatigue doing 1 finger braking.

[@borismue]

I am a heavy guy with 220 pounds naked. Brakes are a big thing for me. It is not only the size it is the thickness. I am riding discs with 2,3 mm since many years. 180/160 on my gravel bike stop me from 100 km/h to 0 without fading and loss of brakepower. It is the thickness, believe me.

[@fullsendmarinedarwin7244]

That’s what she said 🤣

[@ravennexusmh]

180 is the smallest rotor i'll use, anything lower feels a bit naff to me. thats the size front and rear i use on my gravel bike. 203mm front and rear on my 170mm travel trail bike. best thing about bigger rotors is the less lever pressure needed for the same braking force. great for when you hands are tired and you've no energy left. it can often take a few weeks to full bed in a brand new rotor. its highly likely that those 220mm were bought for the test and never used and will take time to clean off the machining on the surface and transfer pad material. the new 180mm sram centerline have taken weeks of day to day riding to stop that still wearing in sound

[@nitrous50]

@gmbntech could we hear a little more about the hardtail you were using for the test, I noticed you didn’t have a fox or rockshox fork. Great job Anna as always!

[@bitswede]

Bedding in large rotors can be difficult for lighter riders. Magura warns about this in their instructions.

[@enriquehernandez155]

This is great info ., am go going with 180,frontc 200 rear 😮 am my build😮

[@TitoJoebs]

@GMBNtech..... Hi guys. at 12.09 caption said "REAR DIC BRAKE" (220mm rotors) ???? Wasn't this proofread before posting? Was this overlooked? It's the first time that this happened!

[@philiphales9993]

Interesting ...what about cheap cable brakes with bigger discs ? ( more likely what I'd do 😊 lol )

[@jagfrediani]

Thanks for the vid 👍🏼👍🏼... Any drawback when moving to larger rotors? I guess they are a bit more expensive? Are they more prone to bending? Are you more likely to hit a rock on technical trails?

[@dunatic1313]

If your not getting the pads up in temp due to excessive power for the riders weight, style, tire grip and speed then they wont perform as well as say a 180mm.

[@evanloudenback3700]

Interesting video, definitely do a part 2! My friend and I have argued about this before lol I'll have to send him this video :P

[@davenawahine4428]

I'm experimenting with a 245 front on my levo. With TRP EVO brakes.

[@semtex1]

Locking wheels isn't breaking. We need to use breaks modulation to perform effective breaking. :)

[@aleksanderaleksandrov168]

If you are a heavier rider, like 85/90 kilos and more and you ride steep and long tracks bigger is better, I changed from 200mm center line in the front to 220 hs2 rotor, I don't feel much more braking power, but there is a difference, and a thicker rotor is a good thing too 🙂

[@Wi3Mmtb]

It would be great to see 2nd part with test on longer trail, dragging brakes and maybe test with strapping more weight to the bike to see how disc react with your weight vs heavier rider on the same bike with same setup (important to have the same rider + weight to have same riding style)

[@sp00n]

Is rather suggest a second, heavier rider doing the same tests simultaneously. Adding 20 kilos or more to the bike/rider doesn't seem feasible

[@dexterlines1735]

I went 220 and never looked back far less fatigue in the fingers and arm pump

[@sbonel3224]

did you find it hard to get used to using less power to get the same braking as with smaller rotors sizes? Cause I hear a lot of people saying that they lock the wheels with 220

[@RicardoPetrazzi]

So, here's a quick tip - not always need to Size Up in rotor diameter - try just getting one of the ticker ones, same size. I changed from 200mm diametr SRAM Centreline - 1.85mm thick to SRAM HS2 2mm thickness - same pistons and callipers - massive stopping power differnce. You don't always need to go larger diameter - so no extra adapter needed either. simples. 🙂

[@SergejGrabun]

as @floydblandston108 said - while braking you didn't really change the way you modulate (or did not modulate at all) nor your body position. There was very little gain in braking if you don't actually use the grip of tires. I was surprised that you didn't pay attention to that more, you know better! :) Braking distance should be measured ONLY if you did not skid. also forth mentioning that not all discs have same surface and is not acting same with all types of pads + include the 'bed in' period required and etc... there are quite a few variables, but for the purpose of this video - the point was made! :) Very interesting video anyway! I am happy with my Magura MT5 with 203 up front

[@kobanagy]

Would be smart to mention, that the 220mm rotors for YOU were inconclusive compared to the 203mm ones. I say for YOU, because you weigh (let's say) 50kgs, but for a 100kg rider, a 220mm rotor may be even less "powerful" as the 203mm for you. Also you (pretty nicely nailed) mentioned the grip of the wheels (tires) that you need for those bigger rotors to "shine". On tarmac, with that knobby tires you have everything, but grip. And the last one: you compared some "bedded in" discs to some brand new ones. The brake pads needs to "wear together" with the discs, which needs a bit more time (miles) to offer the maximum of their potential. Ultimately: the "heat check" was also inconsistent. If you're curious about that, you should not ride them on a trail, then you measure 'em yourself, hopping down from the bike. For this test should be more accurate a longer and steep descent (for even more consistency a paved road), where you brake your bike to a certain speed, and maintain that speed (for example 25 km/h) from top to bottom. Then someone should wait for you with a switched on heat measurement tool at the "finish line", for immediate "reading". As you've noticed, these rotors cools down pretty quickly, so every second counts. Recommendation for a future, even more accurate test: be more constant in measurements, speeds, disc/brake pad conditions, and you could involve (at least) 2 more riders (a 75kg, and a 100kg one) for demonstrate which rotor is the best for your audience. Cheers! PS: switching from a 203mm rotor to a 220mm one is a 8.78% increase of braking surface area (you have to calculate the contact surface with a brae pad, not just a line -> circumference of a circle). And yes, I said 203mm, because Shimano SLX rotors are available in 160, 180, 203, and 220mm variants. There's no 200mm option.

[@ms.karihart2983]

Love the content, real world testing very good

[@denfath5010]

I dont think your area increase calculations are quite right as you dont appear to have worked out how much metal is missing due to all the holes. Because the less metal you have ( because of the holes) the harder you have to 'work' it to obtain the stopping power and then the harder you work it the hotter it gets ! It would be interesting to see different rotas the same size with smaller or even no holes. A easy way to put more metal between the pads. In addition to all this i always use sintered bronze pads ( wet often muddy conditions in the UK) i found them to be better than the fiber originals. I have also swapped the front disc for a solid rota. This gives more feel and power under the heaviest of braking in the dry but does require a turn of the wheel to dry off in the pouring rain. So a 'few' holes are probably preferable.

[@LaurentiusTriarius]

You have to account for the hole's friction, think cheese grater 😂

[@janeblogs324]

Psi, pounds per square inch. Less metal= more force

[@denfath5010]

@@LaurentiusTriarius 🧀😂

[@denfath5010]

@@janeblogs324=Greater rate of wear.

[@fabian-barrington-hirst1974]

Love you anna.just had a s-works epic ht built for me,and these are always 160,mm rotors with xt brakes,find myseld doing a traffic copper running commentry,stop stop stop,this has made me think.maybe look to go to 180 mm front and rear,bit surely brake compounds play a part too❤