What size for brake rotors?

richulr · Jul 3, 2021

I'm doing my first bike build and was thinking about brake rotors. Since I'm heavy, 260 kitted at least, I thought big rotors would make sense. I bought two 203mm rotors, but now I'm wondering if I went too big? Especially in the rear.

What size rotors are everyone using front and rear? Is 203mm front and back too much?

Forest Rider · Jul 3, 2021

May also depend on what brakes you've paired them with.
My 2019 Chameleon came with 180/180. My 2016 Stumpjumper came with 180/160.
I replaced the brakes and rotors on the stumpjumper with 203/160.

Noe sue why you wonder if you went too big. What is the concern?

acer66 · Jul 3, 2021

Forest Rider said:
What is the concern?

Maybe weight and locking up the rear?

OP, I would not sweat it and just use them and if the rear turns out too big you can always get a smaller one and save the 203 for the front.

acer66 · Jul 3, 2021

Depends on your riding style, what terrain you ride and what type of brakes you are using.
I am the type who rides, working on that, quite a bit so I like the 203mm in the front.
Had Shimano Deore for the longest time and no problems.

In the rear I, heaviest was 230 plus gear, was running 180mm and next time I would do 160mm because I do not need that power in the back.

Zlorfik · Jul 3, 2021

I switched to 203/203 front and rear. It’s increasingly common. But of course depends on what you do. In my case 200+180 setup was sometimes insufficient. You can see my setup post in the brakes forum.

Forest Rider · Jul 3, 2021

I replaced M615 with XT 4-piston. Even at 160 rear rotor I'm locking up a lot more. I think the design of brake is different and I can't control the power as easily.
If a rider is slower and on steeps, the 203 could be a problem but I think with the additional rider weight, the rotor size will be offset.

I have not had too much braking performance from the front end of my stumpjumper.

ttengineer · Jul 3, 2021

I’m running dual 203s on my Ripmo and I’m 260. Sometimes I wish I had larger brakes.

Sent from my iPhone using Tapatalk

JackOfDiamonds · Jul 3, 2021

Rotor size has a pretty small effect on braking power itself. The real reason to run bigger rotors is to handle more heat and not wear out as fast. If you aren't having heat issues or excessive wear it's better to stick with moderate size rotors that will be lighter, have more clearance, much less likely to bend even if they do get hit, and less likely to squawk or shudder. There's a big jump up to 203 which all seem to be 200g unless they are super flimsy. At 180mm or 160mm you save a lot of weight and doubly so because you can still use a flimsy lightweight rotor and still be reasonably durable.

Mudguard · Jul 3, 2021

I don't know about that. I'd rather have mediocre two piston brakes on big rotors than six piston monsters on small rotors.
There's a big increase in torque. As for weight it's a minimal sacrifice. Unless you're racing there's very little reason not to run as big as you can fit. The only reason I have a smaller rotor on the rear of my main bike (203/180mm) is that when I had a 203mm on the rear it was too easy to lock the rear wheel and I was too lazy to change my technique. But if I lived somewhere with big hills and descents I'd put the big back on. As for the front, big as you can go, all the time.

Forest Rider · Jul 3, 2021

I am pretty sure my oversized rotors have zero effect on my weak legs and climbing speed. LOL

Also when reporting in the clydes forum, a few grams of rotor weight matter one. The difference between a pair of shorts in size medium vs size large is probably greater than the rotor difference.

233946 · Jul 3, 2021

203 front and rear on my DH and all mountain bike, 203/180 on my hardtail. All clamped by Magura MT5s. Plenty of power. 200mm front and rear Sram G2 RS 4 pistons on my son's hardtail. They lack power and I can overheat them on long descents. The bottom line is picking rotor sizes without accounting for the brake they are paired with tells you little. At your size, I would be on 203 or larger at both ends, the extra heat dissipation is well worth it.

I also suggest considering this article.

Ending the rotor size myth – Why you should have a bigger brake rotor at the back than the front

Small up front, big at the rear? Contrary to popular belief, many of us should ride with bigger rotors at the rear than at the front. Read on to find out why:

enduro-mtb.com

Jayem · Jul 3, 2021

There are several issues with that line of thinking. Most cars/bikes and other stuff that actually do have bigger rear rotors have weaker rear brakes at the same time, to maintain the braking balance.

It's not an invalid way of thinking, but the front still does most of the braking and when you need a good deal of braking power, you want to maximize the front. For my DH stuff, 220mm is just adequate. 200/203 in the rear is that way for the reason above, to not skimp on rear rotor size. I also run a slightly weaker rear brake on purpose, but at 203mm, it's the fade resistance that I'm going for. I think equal F/R makes a lot of sense when most brakes are sold with the same calipers F and R. If they were actually adjusting the calipers and braking power F/R, then maybe this would make a little more sense. I believe there is a magura brakeset that does this, but it's not a very popular way to sell brakes.

Anyways, again, it's not invalid, it just requires a little more critical thinking IMO.

203 is not overkill by any means. It's pretty damn hard to find "overkill" in brakes IME. I wouldn't do it for my XC race rig, but I do step up to 180 on that bike when I'm doing XC races with bigger descents, but at 260lbs, this is pretty much a no brainer, go 8" front and rear.

I am real glad that we've moved up to 220 and 225 rotors. It solves a lot of issues that I've had. In many cases the 203 and 200 was not sufficient and some of the manufacturers started making thicker rotors, which was a step in the right direction, but that only gives you the fade resistance part of it. Going to a bigger rotor gives you the fade resistance AND more power, which is needed in some situations, especially real steep sustained stuff like 30-50% grades.

almazing · Jul 3, 2021

I am firmly in the camp of running the largest rotors my frame and fork can run. No rotor is too big if it fits. The upside of larger rotors simply just overwhelmingly overshadows what little downsides there are.

jeremy3220 · Jul 3, 2021

I'm 205 lbs and run 200mm rotors front and rear on my enduro bike. I normally run a semi-slick out back and I have no problem modulating the rear brake. If your 203mm rear rotor is too big then your front rotor is also too big.

Also, rotor size is directly proportional to the amount of torque generated by the brakes. t=r*F*sin(theta)

Old Marine · Jul 3, 2021

richulr said:
I'm doing my first bike build and was thinking about brake rotors. Since I'm heavy, 260 kitted at least, I thought big rotors would make sense. I bought two 203mm rotors, but now I'm wondering if I went too big? Especially in the rear.

What size rotors are everyone using front and rear? Is 203mm front and back too much?

Do you want large or small rotors on your car? Get with the program, learn how to comodulate.

acer66 · Jul 4, 2021

Yeah, I hope the OP comes back and says what brakes and pads he/she runs since like pointed out before that is another big factor.
I am in the Shimano camp and happy with them but I hear a lot of complains how on and off they are.
But I am also pretty good, imho only of course in not stabbing the brakes.

richulr · Jul 4, 2021

I haven't bought the brakes yet. Im building a Hightower clone with budget minded parts. Everything I do in mountain biking is done looking for good deals. I think I'm going to go with basic Shimano Deore brakes. Would like four piston, but the two piston are easier to find and cheaper.

I ride in the Midwest so the trails are fairly tame, but we did just get a new downhilly type trail nearby in Ironton, and I'd like to try Bentonville someday.

Forest Rider · Jul 4, 2021

richulr said:
I haven't bought the brakes yet. Im building a Hightower clone with budget minded parts. Everything I do in mountain biking is done looking for good deals. I think I'm going to go with basic Shimano Deore brakes. Would like four piston, but the two piston are easier to find and cheaper.

I ride in the Midwest so the trails are fairly tame, but we did just get a new downhilly type trail nearby in Ironton, and I'd like to try Bentonville someday.

Check out the YouTube Channel - LOVEMTB

He's got several videos on budget builds and use of Shimano stuff. He had good things to say about the 4-piston Deore. I don't think you can go wrong. I installed the XT only because I could. I had to wait for them to come in stock -the Deore were on the shelf waiting for me. ha
Watch the YouTube channel I talked about -he goes into detail in most of his brake videos about caliper design, where is a good place to have a brake hose come in, etc. He will suggest not using one particular series just because of the port location.

mtnbkrmike · Jul 4, 2021

After fiddling around with rotor sizing, I landed on 203/180 on all my bikes (Shimano and SRAM 4 pot brakes; metallic/sintered pads).

As usual, there are no absolutes. Just ask Troy Brosnan who runs a 203 F and 220 R - see 3:56 below...

https://www.pinkbike.com/news/video-ben-cathro-takes-a-deeper-look-at-troy-brosnans-world-cup-winning-canyon-sender.html

"...[T]here are a few things on this bike that are going to fry some viewers' brains...".

jeremy3220 · Jul 4, 2021

That's only weird on the forums, practically no DH racers run smaller rear rotors. Myriam Nicole is also running a larger rear rotor.

ocnLogan · Jul 4, 2021

Braking force increases approximately linearly with the increase in rotor size.

Total heat capacity, and ability to shed heat also increases as rotor size increases.

I run 200mm front and 203mm rear rotors on my bike, and have absolutely zero problems keeping traction on the rear tire when braking.

That said,The very first day after the swap from my old 180mm rear rotor to the new 203mm rear, I did have to mentally adjust a bit to prevent lockup. But since then as I said, no problems.

The reality of the situation is that when you are actually hard braking, the front brake is definitely doing more of the actual stopping power. But mountain bikes, unlike most motorsports, can’t simply just let off the throttle and coast (most competitive Motorsport that we often compare mountain bikes to are raced on a flat average grade/don’t have sustained downhills, rather periods of hard braking). Which means we have to control our speed entirely by braking.

And the while the front brake is used for hard braking (actual slowing down), the rear tends to be dragged a lot more/ used to “not speed up”. This is just because rear only braking is much safer (ie, you can often safely use it in situations where grabbing a bunch of front brake would easily cause an OTB/washout/etc).

So IMO, if you live anywhere with long downhills and have problems with rotor overheating, you should probably have at least evenly sized rotors. Maybe even larger in the rear.

If you do more punchy up/down/traverse styles of riding it’s probably not as important. So you could probably save a bit of weight if needed.

Jayem · Jul 5, 2021

ocnLogan said:
Braking force increases approximately linearly with the increase in rotor size.

Total heat capacity, and ability to shed heat also increases as rotor size increases.

I run 200mm front and 203mm rear rotors on my bike, and have absolutely zero problems keeping traction on the rear tire when braking.

That said,The very first day after the swap from my old 180mm rear rotor to the new 203mm rear, I did have to mentally adjust a bit to prevent lockup. But since then as I said, no problems.

The reality of the situation is that when you are actually hard braking, the front brake is definitely doing more of the actual stopping power. But mountain bikes, unlike most motorsports, can't simply just let off the throttle and coast (most competitive Motorsport that we often compare mountain bikes to are raced on a flat average grade/don't have sustained downhills, rather periods of hard braking). Which means we have to control our speed entirely by braking.

And the while the front brake is used for hard braking (actual slowing down), the rear tends to be dragged a lot more/ used to "not speed up". This is just because rear only braking is much safer (ie, you can often safely use it in situations where grabbing a bunch of front brake would easily cause an OTB/washout/etc).

So IMO, if you live anywhere with long downhills and have problems with rotor overheating, you should probably have at least evenly sized rotors. Maybe even larger in the rear.

If you do more punchy up/down/traverse styles of riding it's probably not as important. So you could probably save a bit of weight if needed.

Does the heat capacity increase linearly? I don't think so, a relatively small increase in diameter (like 20mm) results in a significant increase in brake-track area (for heat absorption and dissipation)

I agree with all you are saying though.

CrozCountry · Jul 4, 2021

Definitely run them. At your weight you need a lot of thermal energy dissipation. Once you adjust to the feel of them, there is no downside. Mentioning weight difference in rotors which accounts to a few grams is irrelevant for a 260 pound rider.

richulr · Jul 4, 2021

I'm definitely not a weight weenie

uzurpator · Jul 5, 2021

Ending the rotor size myth – Why you should have a bigger brake rotor at the back than the front

Small up front, big at the rear? Contrary to popular belief, many of us should ride with bigger rotors at the rear than at the front. Read on to find out why:

enduro-mtb.com

I have discussed this article on my vlog here:

The TL

W: is that due to vehicle dynamics you always want more forciful brake on the front, because there is more braking to be gotten there. The rear brake does however see more heat because people ( myself included ) tend to drag it.

The argument for upping the rear rotor size is getting more heat dissapation capacity, but it always goes at a cost of less control of the brake as regardless of everything, modulation is inversely proportional to brake force. On the front this is not that much of an issue, but on the rear at some point it becomes hard to keep the wheel from locking and wheel being locked slashes brake force by about 50%.

So to answer question of the OP. If you can control the 203 on the rear, go for it. For a clyde it really isn't a problem. A svelte 120lb woman might get a problem, but someone twice as heavy, not an issue.

On my FR bike I ride 226/180 rotors with Hope Mono 6 Ti brake front and X2 rear ( 6 piston front, dual piston rear )
On my Enduro bike I ride 203/203 rotors with Hope 6 brake and formula RX rear ( 6 piston front, dual piston rear )
On my road bike I run 180/160 with mono 6 Front and x2 rear ( 6/2piston )
On my gravel bike I run 180/140 mechanicals.

So - on just about any bike I've got brakes biased towards the front. But I also did run 203/203 Saint and Hope 6 setup for quite some time without issues. I'm 230lbs.

ocnLogan · Jul 5, 2021

That brings up an interesting point.

There is no argument that the front tire does most of the work actually slowing us down when we ride. But, does it need to be the most forceful brake? I guess technically if you could have a rear brake that was lower power, and was much more resistant to overheating then I'd agree that you technically need more power on the front. But since most people (not you though as I notice

) run the same brake caliper front and back, so the only way to adjust heat capacity in the rear is by adjusting pads, or rotor size, both of which affect power as well.

And if you're making sure the front brake is more powerful with a larger rotor in the front while keeping the rear beefy enough to not overheat, then it seems like the same issues with jumping up rotor size in the rear, would also apply to the front. Although, instead of skidding for a moment, you're probably more likely to eject yourself out the front door, or wash out the front tire. I get that the front tire should theoretically have more traction due to weight transfer, but locking it up easier doesn't necessarily seem super desireable either (especially with less than perfect traction).

That said, I'd totally agree that you need to have enough braking force on the front to get the maximum stopping power available in any given situation (basically enough to break traction on whatever surface you're on). Thats why even people that advocate larger rear rotors, aren't saying to severly undersize the front rotor (like 140mm front, 220mm rear or something wacky like that). I'd assume that most people discussing what braking is "best" are running at least a 180mm or larger on the front either way. And, honestly, most 4 piston brakes these days have enough power on those size rotors to throw most anyone over the bars with just an enthusiastic squeeze of a single finger.

For what its worth, I also agree that the larger rotors do have more braking force, and thus is technically/theoretically harder to modulate. So I'd say the larger rear rotor setup works better with brakes with more modulation, rather than less. I personally run a set of TRP Quadiems (definitely on the "modulation" side of the braking spectrum). Luckily though, I feel that "most" people seem to be able to adjust to changes in their braking setups pretty well.

Finally, like you/others have said, a lot of that is kind of academic at this point. Because I'd say that while there are differences in opinion on what is the absolute best... I really doubt that anyone would ever say that 203mm rotors front and rear for someone who is 260lbs +, isn't overkill by almost any definition. As long as everything is working fine for someones personal riding area/riding style, then honestly who cares

.

Ironchefjon · Jul 5, 2021

8 inch rotors on everything from my 120mm tallboy to full blown DH rig. I don't compromise on braking power at 250 lbs.

Jayem · Jul 5, 2021

While my rear rotor is still not bigger than my front, I did go with a 203 for the fade resistance and used a weaker caliper, E4 instead of V4 like the front. Still really easy to lock the rear. Wouldn’t try an x2 in the rear, they just don’t have enough pad material.

TNC · Jul 5, 2021

Jayem said:
While my rear rotor is still not bigger than my front, I did go with a 203 for the fade resistance and used a weaker caliper, E4 instead of V4 like the front. Still really easy to lock the rear. Wouldn't try an x2 in the rear, they just don't have enough pad material.

Funny you mention this. I'm preparing to install a 4-piston front brake setup on my '08 Nomad...which brake yet to be determined. I've been running old 2-piston Avid Elixir R's on 203 rotors with good results. Only a few places in Moab was the front brake on the verge of being insufficient...bike was decently light with air suspension and such.

Now, after installing a rather powerful mid-drive Bafang motor on that old ride, the bike, battery, dual crown coil fork, coil DH rear shock, and the biggest tires I can stuff in the bike...I'm finding I actually need a little more front brake. The back is perfect, but I think the 4-piston front of some stripe will work well. I think this idea of not requiring the front and rear brake master cylinder/caliper models to be in lock step is perfectly logical in some cases. My motorcycles have been doing this for many years.

This discussion of brake/rotor style and size brings up a bad memory of insufficient sizing. For some stupid reason a friend and I decided to hike-a-bike up Moab Rim one year and ride it downhill...before the chairlift which is long gone now. Back in the day they actually used to have a DH race down this insanely steep trail. I was on a '99 Bullit with 6" rotors and Hayes brakes. Going down, the brake fade, squealing, and smell was horrible. It was a little terrifying in a couple of corners where the brakes all but went away. At the bottom, the rotors were absolutely blue and the pads glazed beyond use. On another year when the lift was there, a later Bullit with 8" rotors, dual crown, and coil shock proved to be less death defying...LOL!

Tjaard · Jul 6, 2021

If you are over 220lbs, I would never run less than 200, front or rear.
Every time the Germans test brakes with a 220lbs guy, they can get the majority of them to fail with 180mm rotors on a steep, long descent.

gramr · Jul 7, 2021

For sure.

I say you can never go too big when it comes to rotors. I run 220/203 with quad-piston Magura calipers whenever possible. In my experience, that combination can reliably and powerfully slow down even a loaded cargo bike with a total rolling weight of well over 500 lbs (220 rider, 220 cargo, 80 bike) on long steep winding mountain descents without fading or losing any modulation. I love the feel and control of you get from a really great set of brakes.

bigjp · Jul 16, 2021

I weigh 275 and live in Utah which has lots of long steep downhill runs. I run 203s front and rear and I am getting ready to move up to 220s front and rear as I have had times where I wanted more stopping power or more heat management.

TNC · Jul 16, 2021

jp, just curious, what brand/type of brakes are you running? Were your conditions in southern Utah or places like Park City?...or both?

CaveGiant · Jul 16, 2021

I can't believe we have weight weenies on a Clyde group!

Fit the biggest rotors you can.
I ran 225mm front and back on my last bike.

I've had to downgrade to 203mm on this frame due to clearance issues.

If my 100lb wife can control 203mm rotors with DH brakes and XC tyres you should feel a tad silly for thinking you can't.

Get the biggest best brakes you can, you never know when you may need them.

Deore are amazing for the cash, but like all shimano brakes they will overheat on a long descent.

TNC · Jul 16, 2021

Thanks jp...good info.

v33sonata · Jul 19, 2021

I maxed out my front fork rotor. each for has a limit. see the video here

mtnbkrmike · Jul 20, 2021

Quick question - I run 203/203 on all my bikes, which seems to work great for me. Have any of you running 225s experienced any annoying rotor warping? I assume 225s are more susceptible to this than 203's, which are in turn more susceptible than 180s. Or maybe not...

What size for brake rotors?

Ending the rotor size myth – Why you should have a bigger brake rotor at the back than the front

Ending the rotor size myth – Why you should have a bigger brake rotor at the back than the front

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