This is an engineering question that relates to physics and leverage. When any vehicle slows, the load moves to the front. Since the rear is unloaded during braking, less braking force will result in the tire locking (reducing braking performance significantly). A larger rotor has more leverage (more braking torque given then same force at the caliper). A larger rotor will make it very easy to lock your rear wheel when braking. Also more weight, also rotational mass. The small rotor has plenty of cooling capacity for the braking energy it is dealing with.

I'm on 180 front and back on my trail bike. Also, I could listen to this all day. :)

Absolutelly right. Back brake shouldn’t be smaller than front. Both equal, the best. If I need to choose which one needs to be bigger I would choose bigger rotor on the back

203 front and rear for my bike. Love it.

Been riding downhill for 13years and initially I was riding 203 front and rear. As time went on I made a decision to swap 203 rear with 180. Why? Becausd it offers more ground clearance, bends not so often, sufficient for making rear wheel lock on when braking...Marshys dilema of different usage of front amd rear brake is weird to me. When I use my brakes I use them simultaneously. Thats the only was of slowing down in a controlled manmer -rear not locking, front not skidding.

He made a great point about the engine brake on a motorbike. I am using both of my brakes all the time, but there are situations where I only use rear break (corners, steeps, slippery) but rarely use front brake only (unless doing stoppie)

I agreee!!!! Wondered the same damn thing before

WOW! What an interesting topic. I've never heard anyone talk about this. I know I should use the front stopping power more than I do. But, I think for most amateur riders we should have a larger rotor in the back. Because everyone I know and ride with using the back break more than the front.

I use the front brake to stop or to slow down, and the back brake is usually used to skid because it's harder to make a bike slowing down with that brake without locking the wheel (so you use it to repositioning the bike on the trail). So in my opinion, a bigger rotor is required at the front because that's where you convert the most of your kinetic energy into heat, in the back your tyre will do the job, cause the rotor will be locked in place by the brake (not much heat to be dissipated). Probably the brands are building their bikes like that for weight reduction purposes idk. If anyone has telemetry data that shows equal heat dissipation between the two rotors please comment below, I would love to know if I'm right or wrong!

I am so with you in Tunis issue .No one uses Front Break more offroad on a mtb

When you brake your weight naturally moves fowards so need more force on the front brake to slow down the wheel.

I just put a 180 on my front today!!...I've now ordered another 180 disc rotor for the back, up from from 160s....this guy makes sense about the back brake and has me convinced bigger at the back is better.

TL;DR - run the biggest rotors you can, and just pay attention to what you and the bike are doing. I'm a bike mechanic. Most of the bikes I work on have the rear brakes more worn down than the front, regardless of rotor size. On my (previous) personal bike, I put 203 rotors front and rear. I shift my weight around when I ride, I don't drag my brakes unless I'm on really slippery, steep stuff (and even then I use both brakes), I don't brake in corners, and after 200,000' of descending, my pads and rotors were ready to be replaced. The rear were worn a hair more than the front. I never had any issues feeling like the rear was easier to lock up than the front. On my current bike, same brakes, same size rotors, but it's a mullet bike. So far, I'm not noticing any issues with differences in braking power, but then I can get my weight further back on this bike. We'll see how I feel when Hayes comes out with 223mm D-series rotors.

I think is cuz: 1. U want the same brake power feel in the front and in the rear and more % of your body weight is on the rear wheel 2. U want to have some modulation and didn't like 0-1 block feeling on your rear wheel 3. U use rear brake more than a front brake so 180mm is less expose to bent than 203mm 4. Smaller rotors are cheaper so companies dont care, throw some "better" brake and save on rotors and pads 5. Most of people use cheaper rotors, they bent quite easily so smaller is better choice

in a straight line your front brake sees a bigger load and stops your bike more, but yeah , when things get steeper and you start turning your front brake becomes more of something to just slow down a bit if you have the modulation( and do endos if needed ) and you get the most braking with the back one because your weigh is furder back

smaller rear rotor for more clearance to obstacles like rocks etc, less flex/bending issues, less weight, less costs and less need to modulate as at the front. I certainly use the front brake more than the back brake. Maybe 70% at the front to 30% at the rear. Thanks for sharing your thoughts, guyz! ^^

Because front brakes are harder to lock up, due to that being where most of the weight is. The rear brake rotor would be smaller to keep the rear brake feeling as equal as possible to the front brake in terms of how much pressure they take to lock up. Depends how much you like pulling skiddies...

I totally agree with you. I run a 203 on the back and a 180 on the front.

@The Syndicate please measure the disc- and caliper temperatures front and rear right when the rider comes through the finish (on a training run of course) i think this would give really interesting data comparing different tracks and riders.

what a great topic!!! need more views for knowledge purposes! thanks team syndicate.

I use TRP 220mm with 2.3mm thickness on both front and back, the power is unreal, I would never go below 220mm, especially with 29" wheels, they look just like 203 on a 26" wheel.

I promote 203 rear. The part I don’t like is they flex(easier to bend) more than the 180.

A smaller disc is more modular, so It doesn't lock up so easy, on the other hand the front one is bigger couse it's more aggressive but since when you brake your weight goes foreword it's very unlikely for your front wheel to lock up and slide... Therefore you can brake more aggressively without having to worry about skidding

I go through front brake pads more frequently than rear brake pads on the same make, model and size rotors.

on my enduro stock was 203f 203r but the rear just locks up too easily, since I got a 180r it feels much better balance. Look at not just size of rotor but also thickness and if that rotor is meant for intened use. For example my 130mm trail bike is 203f 180 rear but is only 1.8mm thick with organic pads and is meant for trail riding. While my 161mm enduro is 203f now 180r but is 2mm thickness with metallic pads and the rotors are meant for more gravity focus.

Weight transfer to the front wheel. This equates to more traction. Bigger rotor, more power. Less modulation. Smaller back brake equals better modulation. Smaller rotor equals smaller lever arm. This provides the better modulation.

On trails back brakes are used to slide the tail. To stop safer and faster best to use both brakes. As the body weight shifts forward and inertia, more force is on the front wheel to the ground, it needs a bigger rotor to stop.

I like my brakes to feel consistent between the front and back and want the brakes to be as effective as possible. The more power available the better!

Engineering and physics is one thing and it's true that your front rotor is more efficient to slow you down but in practice, your rear brake is more often applied in descents to slow you down in a controlled manner. My XC hardtail has 160mm rotors front and back and the rear pads are 50% more worn than the front ones and my rear rotor has more heating mark than the front one.

big front disc and small rear disc is purely for theoretical front/back brake force distribution ratio in specific braking scenario under linear forward riding condition. It does not apply to specific intent of braking, where a rider specifically wanted his rear wheel to lock up irrespective of the front.

It’s all about physics really. The front brake is always bigger because once its engaged all of the energy from mass and momentum of the rider, their bike & the speed they’re carrying is transferred to the front wheel/brake. The front tire therefore gains more traction, and can take more braking force.

203 front and rear always 👍🏼

On a motorcycle the front is used much more because of weight transfer, under hard straight line breaking all the weight transfers to the front and the back will lock up very easy, with minimal breaking force. So no need for very powerful back breaks. But in mountain biking I agree, why have a small back break? It get used more in that style of riding.

Tried it out. 200mm front and 220mm on the back. Works way better than the other way around. The front brake gets more adjustable and the backwheel comes loose easelier.

it's not just braking power, it's heat management. The larger rotors are going to run cooler given the same stopping usage. I also use way more rear brake than front most of the time. A rear wheel skid is no big deal, a front wheel skid is often carnage.

Rear time spent under pressure = 3 times more than Front, even subconsciously one is always feathering the rear. When you do want to initiate hard straight line breaking, you want the front big. 180 back and front makes sense to me or bigger. For that matter if your a single tracker / general rider / I would argue 160 back and front (not cheap stuff) is fine too. Good points, the unequal to me is silly.

@The Syndicate I personally think it depends on preference and rider parameters. It's a fact that when you slow down a bicycle (or any vehicle for that matter), the rider maintains its inertia, loading the front wheel more than the back, so it would make sense to have a bigger braking power at the front and/or less at the back to tune the needed braking power just enough to decelerate but not lock up or skid. However, it''s also true is that it only happens momentarily, and once full system deceleration (bike and rider) is achieved, the load difference between wheels returns to normal, so you never really need the difference in braking power unless if your only purpose of braking is braking to a stop. There are also other factors (besides rotor size) like: -system weight -piston number per caliper -pad material and pad backing heat management -mechanical vs hydraulic -rider skill level (weight balance management, cornering technique, braking technique, etc.) -rider preference (locking up, dragging, feathering, not braking, etc.) -optimization (braking performance, weight saving, etc.) -intent/needs (racing, casual riding) -discipline (road, touring, CX, XC, enduro, downhill) Therefore, there is no universally 'best' setup. The best setup is one where, taking all those factors into account, you should have sufficient braking power for intended purpose without compromising component function and performance. If you feel like needing more braking power, or your rotors are having discoloration, or you notice fading, upgrade braking power and heat management (4 piston, mechanical to hydraulic, bigger rotor, heatsink/finned rotors, grippier pad material, finned pads, etc.). If you feel like there's too much braking power (which sounds absurd but is possible), then simply downgrade. This applies independently to each wheel.

If you can lock your brake up without much effort, you don't need a larger brake setup. Raced motocross for years and left the rear stock but went to a 280 front rotor for single finger stopping ability. Weight transfers to the front under hard stopping. These questions have already been answered by motorcycles and physics.

I think they have a bigger rotor on the front because you put more force through the front brake and that dragging with the rear brake doesn't produce so much heat as the front. I'd still have a bigger rotor on the rear though, just because you use it more so the larger one is more durable.

Bigger is better, more power = less effort which= less arm pump. anyone who says it's easier to modulate a smaller disc just needs a better set of breaks.

Because when you are heading downhill you use the brakes the most and the centre of gravity is nearer the front wheel contact patch than the rear. It's far easier to lock up the rear than the front in any braking situation, even on the flat your centre of gravity moves forward under braking. Having said all that I personally run 230mm FR and 203mm RE as I ride a mix of steep technical and long fast downhill. I find the larger rotor deals with drag brake heat more and gives better modulation, I do not skid, ever. Skidding means you are out of control. I also use my front brake mid corner to move my ride line wider if i need to or scrub speed with it at the same time as using the rear. To do this you need proper cornering and braking technique, with that you won't wash the front wheel out.

The rear tire is always (for me) with lower rolling resistance. I like 180/160 because I feel more the rear before locking. If I have let's say xt on the front and deore on the back maybe 180/180 will be fine

I do like this format a lot.

Rear brake controls acceleration (descending) and the front does the real braking. Having a big rotor in the back sends obvious to me for heat dissipation.

People think the front gets more use and gives more power, which on a road bike is true. But do that off road you’ll be on your face quicker than a fart especially down hill. Sandy condition in the wet in an event in Surrey hills the back brake used all 50% of the remaining rear pads by half way round. The front was untouched. Note to self always start an event with new pads. Upgraded rear to 4 pot caliper and 203 discs. I think 220 will warp and rub more though? Please advise

Small brake on the rear, like mark Clark said, on any bike/vehicle when breaking the weight moves to the front un-loading the back wheels so it's easy to lock up, my back brakes locked up for 5 minutes straight don't even get warm because there is little movement, my front brake gets glowing how down steep stuff

Plus I think it all depends on rider style weight and discipline. I am a "bigger" rider, 6'4" and my riding weigh is 205 pounds, very lean. For example, I raced XC for 8 years on Shimano ICE techs 180mm and felt confident. However, I am transitioning to ENDURO and my SC HIGHTOWER C cam=e with 180mm front/back. First I swapped the POS SRAM guides for my trusted SHIMANO DEORE XT's and the was that. Now I am considering going to 203 due my size and aggressive riding style into corners etc. I feel that the 180mm may be just not letting me push it that much harder due to hard braking when needed. I will be converting to 203mm f/b.

Regarding MX bikes 2 strokes have the big front small rear with very little engine braking yet it's still large front small rear on 4strokes so wasnt for that reason

Im at 160 both wheels now. Think I'll just bump to 180 both and call it good :)

180mm front 160mm rear for me works just fine. Just trail riding though. The rear wheel breaks loose easier with a bigger rotor which is not desirable unless you really want to break the rear tire loose like this guy is talking about.

I've been asking this question myself. But since I have very little knowledge in braking technique for different riding condition (not to mention I only ride once a week on mostly tarmac), I keep my brakes on manufacturer standard (160/160).

On front wheel the braking force needs to be much bigger than on the rear. Efficient braking ratio might be something around 70% on the front against 30% on the rear. Try to stop a bike using only rear brake - you will easily lock the wheel and the breaking distance will be relatively long. On the other side when you stop using front brake only, you will hardly lock the front whell (in case you're not cornering of course - not recommended) and you will stop almost immediately. I like to use 203mm rotor on the front and 180mm on the rear because of the mentioned reason. You want stopping force on the rear to be lower. When pressing both brake levers identically (same force), you really want to have bigger stopping power on the front, not the rear. While using rear brake when cornering, the force is really minor and the rear wheel locks quite easily so it's still not a big problem to use controlled skids during cornering.

As what I guess is a bigger rider (around 110 kg / 240 lb) I definitely prefer same size front and rear. Yes your weight shifts to the front wheel / brake under heavy braking, but I definitely have more braking inputs on the rear than the front. I reckon having a powerful rear brake that will lock up at your hardest pressure at the lever means you can reduce the strength of the inputs at the lever to modulate power for the majority of your braking, and reduce soreness and arm pump in the process on longer/steeper descents.

Even though you use the rear brakes more. The rear brakes are not holding back the entire weight if the rider and the bike like the front brake. The rear tire will skid way before the front brake with the same brake effort.

203 front and rear for me. The reason for a smaller rear rotor is due to weight transfer under braking. You use your rear brake more which means you need better heat management in the rear. I believe these balance out pretty close.

Depends on riding style and terrain. I use my front brakes more than my rear, but I don't ride long steep sections.

I run 180/180 on my trail bike. However, on my road bike with hydraulic discs I have 160/140. Not only does it save weight, on the road bike my riding position puts my mass much farther up over the front wheel the second I start to decelerate, I’m quickly needing less and less braking over the rear tire(skidding is slow and unstable) and more and more power stopping the front. I learned, after only having 160/160 on cross bikes, to utilize and modulate the 160/140 setup on the road bike with better stability and confidence much faster. On the trail, I notice while I enjoy the 180/180 of my trail bike the braking force is way more than necessary to slow down and while rotation through the turns is helpful, it’s almost never a question of how much brakes I’m applying, it’s always a question of where my weight is and how stable the bike is given the modulation needed to control the braking front or rear. I think 203/180 is likely too much for my trail bike, but I can see downhill being really good running 203/180 because if you need the extra power in the rear you’re probably too close to breaking traction anyway and should have used the front to slow down more when you had traction. Brakes don’t make you a good rider, but they help a good rider ride better. I constantly find myself trail braking harder later with my front than with my rear on the trail bike, where my road bike (160/140) is far closer to even input at the lever. CN: its rider preference and since most of your weight is going to the front you can use more rotor diameter and braking power in the front than on the back before breaking traction.

Interesting. Yet when I gravity brake I'm punching my weight down while shifting back. Super modulation. Galfer wave 223x2.0 front, magura storm hc 203x2.0 rear. Zero fade. MTX RED 4 piece MT5 pads and MT5 calipers.

Thank you sir I’ve been wondering that same thing.👍🏼

I agree, I use the back brake way more than the front.

Rear wheel braking does very little to resist acceleration when compared to the front. Real stopping power comes from the front, it’s physics. Locking up your rear wheel may help in direction control, but relatively little in resisting acceleration. That being said WC riders may be happy with their speed/acceleration and increased wear on their rear rotor is representative of how much they use it for direction control, but minimal speed control (when it’s locked up, ie: coefficient of friction, static vs dynamic). Smaller rotors in the back would reduce biting power of the callipers, but in effect adding modulation (reducing how easily the rear wheel locks up). If a rider uses rear wheel braking for direction control (ie: locking it up), increased modulation could be undesirable.

Is it just me, or are the Fox Crew tryin to look Amish this week?? I'm waiting to see a horse and carraige with some kind suspension on the back...

Because when you Break all of your energy shifts forward. With a bigger Rotor upfront you can compensate for the braking power you need Btw sorry for the bad English

The whole braking is different. The rear wheel brakes quite harsh and is blocked often in order to skid, slide etc. that doesn’t produce much heat, since the wheel experiences all the friction. The front has the most weight and grip in steep sections and you use it for decelerating, what means friction over a time period and produces heat at the brake.

As long as the brakes used are not "light switch" modulation, 203mm front and rear. My 130lb wife with 180mm rotors goes through rear brakes faster than I do, at 200lbs with 203mm. Large rotors front for the straight line leverage for stopping power, and big rotors in the rear for fade resistance and to try to make the pads wear longer!

Good thoughts. I feather the front and pump the rear (brakes!)😏. I would think larger gives you greater surface area, and leverage and thus more control.

Maybe its because the stays in the back are not that sophisticated (mount) like the casting of a beefy fork?!there is a lot leverage going on over 180mm rotors… Its just a guess.

anyone who rides steep slippy terrain will know. brake bias if your back brake is more powerful than the front it will loose traction first making the back of the bike faster than the front.

I have 203 / 180 mm Shimano brakes and it's super easy to lock the rear end. Definitely don't see the need for more rear brake performance. So I'd say having a smaller rotor there makes sense - less rotating mass and better bend-resistance. Good debate though :-)

I run 200mm front 140mm rear to save weight on the back. Saw it first at world champs in Canberra. My right hand, rear brake lever, is way stronger than my left. Wouldn't recommend it for big DH tracks though.

Depends on you're weight, I'm 240lbs and ran 203 front and rear and brakes are amazing. If you are heavy you definitely want more stopping power.

My current Build 180mm Rear and 160mm Front

You have the complete mass of the rider and the bike behind the front brake. You need more power to handle the inertial forces as well as the friction between the ground and tire. If you run a FBD you'll be able to see that the normal force for the front wheel is greater than that in the rear. It's why motos have the bigger brake up front - it has to stop the motor and the rider as opposed to the fraction of that distributed over the rear. Additionally, a larger disc would offer more modulation, because the distance between the center of the rotor and the bite point of the calipers is greater than that of a smaller rotor, which gives a longer moment arm. The longer moment arm means you can apply less force to achieve the same amount torque as a shorter moment arm using greater force (ie the smaller rear disc). The rear brake doesn't need as much modulation and is still able to be effectively locked up with a smaller rotor where the front needs better modulation, considering the additional forces from the mass of the rider and the bike itself as mentioned above. Smaller disc up front, less modulation = more likely to lock the wheel = involuntary dirt sample collections. All that said, proper technique is the most important factor to consider.

To those saying is for weight saving, a fart weights more than 15 203mm rotors, the difference between 140/160mm and 203mm is in grams, not even ounces,

I feel that I would not need a bigger back brake because there is a limit to my tires grip and It is already achieved by a 180 rotor. But the front tire has a way higher level of grip which a bigger rotor fits with. Plus a bigger rotor has less modulation

Now running 220mm rear rotor 😎 203/220mm front/rear. On most bikes, 203/203mm.

Rear brake is speed control. Front brake is stopping power. Designed for different use. With that being said... 200 rear minimum! Agree with ol' Marshy! 🤘

Personally I dont like locking up the rear all the time, 140/180s dont lock up as easily. Modulation is also a reason, more leaver squeeze to play with

There are more forces being applied on the front brake, it takes less forces to lock up the rear... So no need for a bigger rear.. I tend to lock up easier with a bigger rear too, so less modulation.

Maybe helps with brake jack? Cus it’s got less leverage

Swapped a rear 180 for 203 and am never going back!

This video has inspired me to ride with a 160mm front and 220mm rear

It’s simple- it’s less sensitive to lock up! If you have a bad ass four piston caliper front and rear, you’re gonna need to concentrate harder to actually use the back brake to slow the bike without locking. I made the mistake of a four piston caliper on the back of my all Mtn bike, now I have to run different pads to use it. I am an moto guy, so I get my braking done late and hard before the turn with the front. I pride myself on outbraking everyone while staying off the rear brake, but if I could do it over, I’d put a Code up front and some single piston out back. Within 3 grams of my Guides, and then I could justify the big rear rotor I run.. Just like my last MX bike!

I actually wax my rear rotor on my road bike and run a bigger rotor on the front, I once locked up the rear brake only on the road bike and almost fell off a cliff so now I put wax on the rotor so I can still brake hard but not lock up

I prefer big rotor on the rear because i want the same brake power

180 front and rear..Half and Half....See what I did there? ;)

203's front and rear on all my bikes except my bmx obviously

I've always thought it's because you can brake harder with the front brake because of the weight transfer and therefore grip on the front tyre was better whereas the weight comes off the rear wheel and its more liable to lock up under heavy braking. Its the same with cars, front brakes are always bigger whether front or rear wheel drive so don't think it's to do with engine braking so much. Front brakes just have to work harder. On a mtb you can use just one brake and maybe if you favour the rear you will overheat the rotor, I always drag the rear into corners but never the front so that figures.

I didn't finish the video... The reason why there is a smaller disc on the back is because a bigger disc will make it very easy to stop the wheel completely and u will skid the wheel after, which means less stopping power so smaller disc will have better stoping power in this case because it doesn't skid as much. However it's a different case on the front wheel because front wheels rarely skid because there is alot of weight on that wheel during breaking. It's really not that hard to understand, I thought it's obvious 😅

It's good to know I'm not the only one that wonders the same thing. I have a160mm on the front and a 203mm on the back and let me tell you, even with that tiny 160, I get more braking power from it than I do from the back. I also ride a bike with rim brakes and I seldom touch the front brakes. Unless you want to become a human trebuchet, an over powered front brake doesn't make sense. The front brake is stronger by nature and it's the back that needs more force to compensate for the fact that the weight is being shifted onto the front

Bigger rotor, more leverage, less rider input needed. Bigger rotors ramp up quicker than smaller ones, meaning less finger travel. You can setup the levers closer to the bar. So, if you like long brake levers and fatigued fingers, go for small rotors. If you like short comfy brake levers go for big rotors. Edit: It's more about feel and confidence than theoretical performance. That being said. if you blue your rotors, they're obviously too small.

your tire grips depends on how much load(weight) your tire have, that's why F1 has a lot of traction because of downforce. when you brake, your body or weight turn to the front which makes front tire have more traction and rear tire less which make it lock up. its impossible the front tire to lock up unless the terrain is slippery or loose or you go over the bar, so overall front tire can handle big rotors before it lose traction and the rear tire has smaller rotor so it wont lock up. im 18 and I know this stuff for a professional mechanic this should be basic.

It's not just about rotor diameter. Rotor thickness (2 mm Magura vs 1.8 mm SRAM-Shimano) and rotor-vs-pad chemistry matters. Bedding-in matters. How many people actually do it right? I wonder about using sintered steel pads up front and organic pads out back, or vice-versa, or just stay with the same front & rear pads? There's one way to find out... I'm going to experiment with sintered steel pads / 203mm rotor in front and organic pads / 180mm rotor on my SRAM G2. Actually there are an infinite number of variables (tire characteristics, wheel diameter, trail surface adhesion, etc.) Even within one brand and model of rotor people seem to have dramatically different experiences. Some people scorch their rotors after a couple hours riding while other riders never scorch rotors. Maybe there's variability between rotor production runs? Maybe people bed-in rotors differently between front and rear? All of this makes generalizing about rotor diameter near impossible. So far I've only been riding stock organic pads / 180mm SRAM rotors on my Tallboy 29'er - so I don't have much personal experience to add. I tried to bed them in correctly, but who even knows if I did it right? Great video and discussion.

☠BLACK BARON☠ Good Title ... good question 👍

1:10 Yes, rear wheel steering! I utilize this technique as well. My setup is a Galfer 203mm front with Galfer Pro pads and a stock M6000 Shimano 180 rear, with ceramic-metallic pads. I think using a smaller rear rotor lessens weight transfer (the shift in mass), even if you predominantly brake with the rear (as I do) Plus, think of where the fulcrum of traction is. Slightly biased to the front. Bigger rotors mean better heat dissipation, but the trade off for weight shift/balance is probably not worth it. This is aimed at mostly DH and Enduro.

Cars and motos(road and offroad) mostly brakes in flat, not in steep sections...so, they can use harder the front brake than the downhill bikes, is my opinion.

i run 180 front and rear but a 4 piston zee on the rear and 2 piston xt up front

It's so you have more modulation at the rear so you aren't constantly locking up

Yeah larger rotor! Skid like a squid!🤣

Because it's much easier to lock up your rear brakes. I want more power up front.