Bigger disc - does it matter?

plugp7

I've starting to fit larger discs rotors to my P7 and was wondering about maximum sizes.
In my mind, it should be largely irrelevant what size disc you fit as even with 160mm discs you can easily lock up wheels and at this stage you have put into the frame and fork the maximum forces you can exert. Surely at the point of breakaway of the tyre to to ground, this is the maximum force that can be applied irrespective of disc size?
BTW, I failed "O" level physics!

Greer_

Many forks have max disc sizes - any bigger will void the warranty. I'm not sure of the reasoning behind it but it is something to do with the braking force, or perhaps the twisting force as the force is only applied on one leg. I would've thought bigger rotors would produce more force, but they also help dissipating heat

nicklouse

Bigger discs have a greater ability to store/dissipate heat as well as the greater braking forces.

estampida

yeah they are more constant in braking, and you only need to juice up the front brake really

the other way is to fit better brake hoses, bigger hose volume and less stretch in the hose, but it can work out expensive - and have never used the cheapo hose (only goodridge) so not sure on the discount versions

cooldad

Hoses will make no noticeable difference.

plugp7

I get the size more power and better heat dissipation and hose volume will make little if any difference, just feel better (more direct) cos of less ballooning.
My point was that the same amount of force is applied at the calliper and thus transmitted to the fork/frame irrespective of disc size, to cause the tyre to break away from the track.

supersonic

You are right - ultimate braking is determined by tyre grip. Larger rotors mean less lever force is required for a given force at the caliper.

tofu21

From my experience I would either match the front and rear sizes or drop one rotor size. 203/185 or 185/160 etc...

I have run 203/160 and it made the bike very front heavy on braking and unstabalised the bike.

plugp7

supersonic wrote:

You are right - ultimate braking is determined by tyre grip. Larger rotors mean less lever force is required for a given force at the caliper.

My point exactly. I'm in the process of fitting a 205/185 setup (from 185/160) cos I have problems with being able to apply enough grip in cold weather (medical condition). Just set me thinking about warranty issues an effect on components.

felix.london

Get more powerful brakes

plugp7

felix.london wrote:

Get more powerful brakes

+20% more power over what I have now at a cost of £25 seems a good deal to me.

mrmonkfinger

felix.london wrote:

Get more powerful brakes

a bigger disc is most likely the cheapest route to more powerful brakes

tofu21

mrmonkfinger wrote:

felix.london wrote:

Get more powerful brakes

a bigger disc is most likely the cheapest route to more powerful brakes

Apart from making sure the rotor and pads are clean and that the brakes are setup and recently bled.

Chunkers1980

Not bled my brakes in a while, they work fine.

tofu21

I find that my brake fluid looks cloudy after 12-18 months depending on how often and where I ride.

mrmonkfinger

tofu21 wrote:

mrmonkfinger wrote:

felix.london wrote:

Get more powerful brakes

a bigger disc is most likely the cheapest route to more powerful brakes

Apart from making sure the rotor and pads are clean and that the brakes are setup and recently bled.

Goes without saying.