[Closed] can rotors be too big?

No, never!

Bigger is best, if the car park at CdB is anything to go by 😉

I'm tempted by some V2 brakes but deliberating over rotor size.

Bigger rotors give more power but less modulation.

They also dont get as hot which some have suggested makes the pads more difficult to bed in.

Bigger rotors also weigh more, as not only do they have mroe area, they also need more suppourt for that area as the leverage is greater, and then they have to be made thicker as well, which is why racers run 140mm rotors.

Its probably my theory and it is only that - a theory. It runs like this:
Big brakes [b]used gently[/b] will rarely if ever get up to temperature so the pads will not condition properly nor will the disc get and replenish the layer of smeared on brake pad material. it might lead to excessive pad wear.

Whilst this is a theoretical explanation for increased pad wear some folk suffer it is by no means proven.

thisisnotaspoon - Member
Bigger rotors give more power but less modulation.

How so?

I got some 203mm on my Five - on most things they are overkill - but occasonally they come in handy 😉 I get the pi$$ ripped out of me though for having them 8) And on steep long descents I don't get dead arms coz I have weedy little arms and limp wrists 😉

180 < THE ALPS < 203

You have a greater lever acting on the hub with bigger rotors, therefore applying the same amount of frictional force through the brake lever and pads you are applying a greater stopping torque (Force x distance from fulcrum) therefore you need to make smaller/finer movements at the brake lever.

It's not less modulation, it;s harder modulation. You can correctly modulate any brake with the right finesse.

i think rotors should become as big as... oh.. rims. then we could use the edge of the rim as the braking surface!

dunno, read it on a motorsport site (its on the internet so must be true!), and was backed up by the 8" dinner plates i was running at the time, the 6" hayes was fine, the 8" was just on/off.

I've got old E4 brakes right now with 205/185. Just wondering with the V2 claiming to be more powerful, could I go smaller or should I just max out and get the 203/183. Whenj I upgraded to the bigger rotors, I didn't notice any change in pad life but I didn't really notice the claimed 20% increase in power that people predict. Either that, or other the years my hands got 20% weaker.

Almost my thinking DrDomRob, I don't see how modulation can be easier with smaller rotors as you won't have the same confidence in them and are more likely to grab as much brake as you can. More power from bigger rotors Shirley gives you the confidence to relax and brake with finnesse

I don't have a problem with pad wear or modulation, and when in the Alps they definately coped MUCH better with the heat build up. In the UK I don't really notice much difference until I get into trouble then I know I can stop much quicker than I would if I had smaller rotors. I possibly went a bit overkill with the brake choice (09 saint 4-pots) so seemed rude not to get the big rotors 8)

So, if there was anything in TJs theory (not sure if there is or not), the advice would be: - get big rotors and then just to be safe, brake late and hard to get them hot?

Works for me.

Does it not depend on weight of rider as well ? I remember when I was learning and all the boys were buying bigger, (as in Boy-World bigger is always better), most people laughed at me and said at my weight (less then) I would never need them and I would be better off learning to ride with more skill, smoothly, and brake less. Good advice I feel !

I'm happy with 185s.. Can't imagine needing bigger, I can practically shear off my forks with these already.

There is a difference between confidence and finesse. One does lead to the other, before you can really learn how to use the brakes effectively you need the confidence they are going to stop you if you leave things a bit late.

It's easier to modulate smaller brakes because you have to apply larger forces at the lever to them to create the same stopping power. It's easier to explain if you consider it is a digital system.... but it might just get boring so I'll merely say more lever forces = more lever movement = more feel.

so, on what Hels said, big rotors for me then!

+1 DrDomRob - I have 160 for HT and 203 for my "all mountain" Five - I have to feather the brakes more on my 203 setup (Hope M4's) compared witht the HT (Avid Juicy Carbons).

Onzadog - that would work then,

neil853 - thats why I said gentle braking with big discs - not alpine stuff but mincing around in UK winter mud. Brakes have a temp range at which they work best - there is a minimum and maximum and you want to remain within this range as much as possible

180 < THE ALPS < 203

I don't have a problem with pad wear or modulation, and when in the Alps they definately coped MUCH better with the heat build up

When they are bigger than the wheels and tyres, they tend to lessen the overall grip a bit.

Only a visual thing but big rotors are ugly especially on a fairly simple HT. 160mm back and front for me - more than enough with Elixir CRs.

Here here Surf-Mat. I had huge problems when I tried to fit truck brakes to my bmx. had to mount the calipers ont the frame which reduced steering efficiency significantly also.

The next time I fall off I am putting it down to sub-optimal brake temperatures.

juan i am not a pro rider and do make mistakes 😉

The brakes i have allow me to get away more easily with the mistakes i make. Its fine saying braking better and less but by the time you get to a given situation its too late. I can only give a before and after comparison of the brakes i've had and the response is based on that.

You don't NEED big brakes, but for me they work well.

you better not brake too much over the weekend otherwise I'll be passing you!! 😆

i think rotors should become as big as... oh.. rims

Like this contraption?

[img] [/img]

If your a big hefty fella go for a minimum of 180mm but if your a industry average kind of guy stick to 160mm cept on a dh/fr rig.

I run 185/160mm on my AM/FR/DH bikes. 160/140mm on my Commuter/XC/Trail bikes. Never been underbraked either in the UK or the Alps. Maybe I [i]need[/i] to go to Whistler to test the brakes properly.

ETA: That rim brake looks beaut. And I'm nudging 17-stone in the romper kit.

I'm 10.5 stone and run 203 rotors on both ends of all my bikes, dh race, xc fs, xc ht etc. I like the extra power, i can see no reason why more power is a bad thing.

no

Anyone have any comments on TJs theory? I can see some sense in it and TJ admits that it's just speculative. Any thoughts?

I think I remember Peaty's v10 having something like 160f 140r last season.

He's a big guy...

This seems similar to the 'floating' rotors thread - the conclusion was that they look nice but aren't really necessary.

There's plenty of evidence of TJ's theory in motor based sports. He's just extrapolated it across to MTB systems. No reason to think it wouldn't apply there IMO.

My experience?

Normally run 180/160 - no problems and I'm 16st.

For my trip to the Alps I thought I'll stick 200/180 on and I'll have a test ride round local trails (Dalby) to make sure it's OK.

It glazed.

When I took it to the Alps a week later (having sanded the pads to remove the glaze) the setup worked extremely well.

Longer steeper descents seemed to make it work - hotter pads and higher pad pressures? I think so but one man's experience is not proof.

supinerider - Member
I think I remember Peaty's v10 having something like 160f 140r last season.

He's a big guy...

pad compounds anyone?

yes pad compound. No one else seems to spot this though. For example, Hope brakes didn't do well in terms of power in the recent test but they do seem to have the best pad life. Surely not just a coincidence.

Formula did well in terms of power, don't they have a short pad life?

surely any brake is just a question of leverage and hydraulic advantage. If the lever moves Y distance and the pads move X there's not much else it can be (assuming pad areas are similar).

Wish they'd done that test with a control pad.

I had a 220mm rotor on the front of my dh bike for a while. It was a bit silly looking. No lack of modulation though.

Another thing for TJs theory.. Smaller rotors will dry off quicker in rain as there's less water to wipe/evaporate off.
Plus they will hold less grit (if you're riding in sandy conditions) and kill your pads slower.

Also.. Agree with the hope pad compound thing.. You've got to work damn hard to wear a sintered pair out... Shimano's though: nom nom nom...

anyone else have any thoughts on the effects of pad compound?

Pad compound will have a huge effect - it will alter the heat transfer and the heat range as well as the obvious effects on friction coefficient and lever feel.

Then you have all the variables of different types of pad - sintered, resin, kevlar etc etc.

I agree. I think that's probably got more to do with how brakes are reviewed/perceived than the design of the brake.