I know 180mm rotors have more leverage than 160mm, but how can that make a difference on a bike?

It’s to do with the fact they have more leverage!

For a given brake, force at calliper is constant, therefore the further from the hub you apply that force, the more effective the brake. They also disipate heat better as there’s a larger mass/surface area. The trade off is less modulation and more weight.

I think you have answered your own question

Someone failed their Physics exam 😆

Dumbass

For the same reason that it is easier to undo a nut with a 200mm long spanner than a 50mm long spanner.

I’m sure the extra surface area for heat dissipation plays a small role.

The rotors are not ‘more powerful’
Power comes from the caliper.
Larger rotors have more ‘leverage’ if you like, and turn the same pressure at the caliper into more braking force at the rim*

* I think! 🙂

Or to explain the same thing in a different way, force x distance = work done. You apply a fixed force to the brake. If the rotor is bigger then it’s travelling further in a fixed time so you’re converting more energy to heat so you slow faster for the same brake pressure.

“I know 180mm rotors have more leverage than 160mm, but how can that make a difference on a bike?”

Um… Why would it not make a difference on a bike? Do bikes occupy some parallel universe where normal physics doesn’t apply?

Anyway, words 3-9 of your question constitute the answer.

Dumbass

Talk about saying how it is! lol

it does have more leverage, but there is less friction on the disk, as 2 surfaces travelling over each other have more friction when the speed differential is less.

larger rotors heat up less though

Why are 180mm rotors more powerful than 160mm?

Well…. the rotors are not more powerful.

Neither is the calliper.

So to answer your question they arn’t.

So if you were clever enough to invent a system that used the rim as the braking surface then you’d have a brilliant brake.

Yeah, until it either wore out, got covered in crap, etc 😉

but there is less friction on the disk, as 2 surfaces travelling over each other have more friction when the speed differential is less

Not true – friction interface is an incredibly complicated subject and simple statements like this are mis-leading 😆

invent a system that used the rim as the braking surface

Now dont quote me on this but wasn’t this ‘invention’ used before discs on bikes. I’m sure i used these things called ‘v-brakes’ and also some ‘magura’s’ and before all of that i used ‘cantilevers’ but i’m quite positive that my disc brakes worked better than all of them 🙂

There is no extra leverage from the disc size nor is there any extra leverage from the calliper. These will always remain the same whatever size disc you run.

Picture this two bikes side by side. One with a 180mm disc, the other with 165mm. If both bikes started braking at the same time the reality is the larger disc would offer more surface area to the pad over the same distance covered under braking. Simple!

I’m sure i used these things called ‘v-brakes’ and also some ‘magura’s’ and before all of that i used ‘cantilevers’

No you couldn’t have done – you wouldn’t have stopped by now.

Birch1983 you are a dumbass too

Birch – FAIL!

Picture this two bikes side by side. One with a 180mm disc, the other with 165mm. If both bikes started braking at the same time the reality is the larger disc would offer more surface area to the pad over the same distance covered under braking. Simple!

Wrong 🙂 Have a think about it.

it’s called mechanical advantage

Birch, harry tonight’s reading:

http://en.wikipedia.org/wiki/Mechanical_advantage

So if you were clever enough to invent a system that used the rim as the braking surface then you’d have a brilliant brake.

Yeah, until it either wore out, got covered in crap, etc

The best solution to this issue is to combine the two. You have a secondary rim near the actual rim, which you use as a braking surface. Erik Buell does this and calls it perimeter braking.

You have a think about your comment. Same speed initially and same total stopping distance. The larger disc will expose more surface area! Study physics.

can’t believe some of the nonsense in here!! worse than the logo thread!

Or simply read this..

http://www.bikeradar.com/gear/article/buyers-guide-to-disc-brakes-45/

And pay particular attention to this….

Power varies with each calliper and its pad surface/leverage, but the biggest difference is in disc (or rotor in the US) size. The bigger the disc, the more leverage your brake has on the wheel and the faster it can stop it. Each 20mm increase in size roughly equates to a 20 percent increase in power.

NOW GO STUDY PHYSICS DUMBASS!

What we really need is a disk rotor the same size as the wheel.

You have a think about your comment. Same speed initially and same total stopping distance. The larger disc will expose more surface area! Study physics.

hi dylan

flow – Member
Dumbass

lol.
+1

So all you guys are saying that you use brakes?

😉

Yep, and Harry333, Birch1983, Peterpoddy and Clubber are thick as shite

Birch – do the pads grow in size? Does their surface area increase? LOL

Okee day, basic stuff, between a 180 and 160 braking system look at what stays constant and what changes.

Constants
Force (the calliper applies the same amount of force regardless of rotor size)
Friction Surface (brake pads and the area the contact area doesn’t change)

Variables
Distance of the contact points (pads to disc) to the axle (moment of force)
(We are going to ignore thermal properties)

And then if you get some cheese and add that to the rotor you can fill your head with it.

So if you were clever enough to invent a system that used the rim as the braking surface then you’d have a brilliant brake

and if it were hydraulic it would be even better!

oh, they did that already – Magura HS33s 🙁

So if you were clever enough to invent a system that used the rim as the braking surface then you’d have a brilliant brake.

Now I’ve often wondered about this, and even though about asking, but you generally get called something like Dumbass for asking silly questions on here.

Why is a rim brake, which effectively uses a maximum sized rotor, less powerful than a tiny disc at the hub? Fair enough the rubber brake block is going to be less efficient that disc pads as you don’t won’t to wear your rims away too quickly, and cables may be less effective than an hydraulic system, but surely that can’t account for all the difference.

All brakes are the same. That’s why I have 203s on my rigid singlespeed and 160s on my Alpine 160 (the 160 is Orange telling you what brake to use).

I may be lying.

PJay- the coefficient of friction between pad material and disc material is different to those between brake block material and Al rims. The additional weight of a steel wheel needs to be taken into account as well, although it’s relative longevity compared to an Al braking surface also needs to be taken into account.

Are ceramic rims still available?

Can one not have a grown-up discussion without some kiddy calling someone else a dumbass? 🙄

Yep, and Harry333, Birch1983, Peterpoddy, Clubber, IGM and PJay are thick as shite

Had to re write the thick as shite list

Buzz-lightyear

This is primary school stuff, hardly a grown up question.

If you don’t like it you know what to do.