[Closed] Do bigger rotors wear out bushes quicker?

[url= http://singletrackworld.com/forum/topic/200-rotor-goodbye-bushes ]REPEAT AD INFINITUM?[/url]
Yes / No / Depends on rider.

I'm going to go no - as it's the same torque to slow you down the same amount.

Force is going to be greater for the same torque (as it's being applied closer to the axle) - but not convinced you're going to have any appreciable effect on the bushes.

thanks bigyinn.
are you pulling me up for asking again in a different way cos i got no response the first time?
not ad infinitum no, just a second time, phrased differently.
perhaps this has been asked a lot? i do usually search before asking something. maybe i didn't this once.
it interests me so i thought i'd try again.

euain, isn't it the other way round: same [i]force[/i] to slow you down the same amount, but greater [i]torque[/i]?
not saying i understand torque properly...

could easily be down to new non-avid brakes, bigger rotor and regular bush wear anyways all happening at once

If merely braking harder wears out bushes faster, and you have the skill/grip to brake harder than your little rotors allow, then yes. But considering that your bushes absorb smashing into rocks and landing jumps, then it will be by an un-measurably small amount that doesn't matter at all.

Or:
Isn't the whole point of better brakes to help you stay out of the bushes, avoiding any wear on the local shrubs at all! 😀

No.

The Brake rotor size won't be the only variable.

What is you maintenance regime like for the forks, kept them clean? changed the oil regularly, etc?
And then how much of a mincey braker are you, especially now, with the bigger rotors?

I suppose "over-braking" and plowing into stuff with the fork packed down, puts a bit more stress on the fork/bushes but that's not the fault of more effective brakes, more the way the bike is being operated.

Not to suggest its your fault OP but... Actually I am suggesting its all your own fault... Sorry.

Looking at it mathematically:
- Big rotors = increased torque. Torque is defined as a force x a distance (lever arm). If the force you apply to a disc rotor remains the same but the lever arm increases due to bigger rotors the outcome is greater torque.
- Work done / horsepower = force x distance. This can be further reduced to the amount of work done / time. Therefore, if applying a 2x the amount of torque to do the same amount of work (ie. stop you from 20 mph)the time taken will be halved. That is why you tend to stop faster with bigger rotors (ignoring cooling, pad contact area advantages etc).

Now whether an increase in torque wears out bushes quicker is very difficult to say. IMHO anything that introduces a bending moment whilst sliding through bushes is likely to wear them out a bit quicker. So, probably yes - but probably not so much that it's a problem.

forks are well maintained (except bushes obviously!)
not too mincy a breaker, but yes there's been some plowing into stuff with the fork packed down.
reckon i'd be better going back to 180s regardless so i've got more range and can still horse them on sometimes. now they are pretty much horse-on or off.
guess that's really what's making the difference.
can anyone resolve my (mis)understanding of torque for me tho?
edit, thanks oliwb!

My Drop off 2 has had a 203mm rotor on it since 2007. It's never been serviced and has only had its oil changed this winter. Bushings aren't knocking; the seals are stictiony.[/anecdote]

In theory yes they could, but the amount of force you can exert is limited by the grip of the tyre.

- Big rotors = increased torque. Torque is defined as a force x a distance (lever arm). If the force you apply to a disc rotor remains the same but the lever arm increases due to bigger rotors the outcome is greater torque.

For a given rate of deceleration, you're keeping the wrong thing constant though. Assuming on either rotor you can brake as hard as you want - until the wheel skids - the force at the rim is constant for a given rate of braking. So the torque is the same - force x distance it's just whether you make the distance larger (larger rotor) and the force smaller of vice-versa.

You're correct assuming that the tyre break away point is likely to be the limiting factor on how much torque you can spply. However, the physics is pretty simple if you imagine a fast road descent with two bikes fitted with different rotor sizes and hauling on the lever with the same force. The larger rotor has a longer lever arm and so torque is increased. You subsequently stop quicker than you would with the small rotor due to the amount of work being done.

There are a lot of variables to consider, even aside from tyre grip. The OP asked a pretty simple question and the answer is yes - a big rotor has the ability to put more torque through suspension bushings. Whether or not you can ever actually achieve that depends on the rider, the equipment and the environment.

You're also assuming that you can lock the front wheel in both scenarios. Having owned some avid's in the past it's entirely likely that he can't even lock up on demand with a little rotor.

i was overcomplicating it. somehow thought torque was something more extrapolated than it is.

so keeping force on disc from pads constant, you will simply stop in a shorter distance with bigger roter (kinda obv)

keeping deceleration constant, you would need less force from the pads with a bigger rotor.

so i guess the main factor which comes into play with a bigger rotor, is that i often brake harder than i would/could with a smaller rotor, just because i can. and this will presumably put more strain on bushes, though whether difference in wear is noticeable is debatable.

guess it's time to change the bushes then.
worth getting the tool to do myself? everything else has just been done.

Might have been mentioned - what forks have you got? I've changed bushes on some fox 36's and some old skool Marzzocchi's without the aid of a special tool in the past.

Your explanation ^^^ is correct though.

got sektors. solo air