Why are 180mm rotors more powerful than 160mm?

But if you have stopped in a shorter distance with the bigger rotor then does that not negate the difference in distance travelled by the rotor?

edit. I did agree but I’ve gone fuzzy headed. Bollocks, I need to think about this more..

pdw whats your answer to this?

its angular delta will remain the same as the wheel

composite pro, I had hoped that was implicit in what I said before..

Bigger distance with a smaller rotor, or shorter distance with a bigger rotor, I think for a given force at the calipers, the pads will have covered the same distance over the disc, as you’ve lost the same amount of kinetic energy either way.

this is the same conclusion that I came to above and the way you have written it makes it seem sensible. If its shorter distance (or less revolutions) to come to a stop this means you come to a stop faster, this is exercising me slightly..

If it takes one rev to stop and its doing 1 rev a second then the equation I listed above works fine, the time t which divides through the 2 pi radians is equal to the time t for the work done.

Wt = Ff x r x (2 x pi)/t x t

So for a 180 disc the term r goes up and hence I had assumed the 2 pi is multiplied the ratio of the radii (80/90) = 0.88, but actually I think both the number of radians goes down and the time goes down so its probably not the same distance travelled..

Am I making sense?
I think this is possibly only solved by integration.

the revolution (or rotation) is the same on either sized rotor (160 or 180), unless I am missing something drastic, which is quite possible.

it’s summink to do with physics innit..?

Heechee. If a larger disc has more torque then it will stop your bike faster. Agreed? So if it stops faster the total number of revolutions from when you apply the lever till when it stops is less. Agreed?

I agree with the larger diameter increases torque. Not so sure the revolution or rotation is any different. I am no expert though, and would take no offense at being proven wrong.

YAWN!!!

Easy explanation is leverage applied to the disc verses the wheel size

Put massive 19″ wheels on your chav corsa the brakes feel rubbish because the big wheel has more leverage against the disc go back to a smaller wheel 15″ and the leverage on the disc is less so the brakes feel more powerful

Swap this around to fitting a bigger disc for the same size wheel the leverage is the same at the wheel but the bigger disc doesn’t work as hard for the same braking effort at the caliper

Effectivly giving you more available power only to the point of how much grip you have before you lock up

Also bigger discs get rid of the heat better giving better braking as everthing heats up the disc can keep cooler as thereis more material to disapaite the heat

Didn’t read all four pages so I may have missed the point

Toys – your equation shows that work done in a revolution is proportional to disc radius. Or to look at it another way, it’s proportional to the swept distance i.e. The distance that the pad covers around the circumference of the disc. To stop a bike, you need to do the same amount of work however you do it, so whatever the disc size, the pads need to sweep the same distance. Which means more revolutions of a smaller disc i.e. A longer stopping distance.

pdw yeah I understand that, but look at the time taken to stop. In the work done equation there is a time term t, if you reduce the number of rotations by using a bigger disc, then it takes less time (or increase by using a smaller disc.)

All I am saying is that at first I thought I could equate the work done equations for a 160 and a 180 disc to find the reduced number of revolutions, (which is obviously the ratio between the disc radii) but actually you have two unknowns, the change in revolutions and the change in time, so my crap maths doesnt work. Needs integration, or possibly an approximation method. Its obviously too dull for anyone else but it has just interested me a bit..

Jebus! That’s 5 min of my life I won’t get back, and I was only skimming too!
They stop you quicker, cos they’re bigger.
Night night.

HOW DID THIS GET TO FOUR PAGES?

Only skimmed the junk but there’s more made-up ‘science’ here than in a creationist’s textbook.

LOCK THIS THREAD PLEASE, IT IS DOING MY HEAD IN!!

pdw yeah I understand that, but look at the time taken to stop. In the work done equation there is a time term t, if you reduce the number of rotations by using a bigger disc, then it takes less time (or increase by using a smaller disc.)

I’m sure no one will thank me for resurrecting this thread but…

There shouldn’t be a time term in the work done equation. In the equation you wrote, the time terms cancel out. It really is just force * distance, which in the case of a disc is force * radius * 2 * pi * number of revolutions.