Disc Grinding

[flange]

I'm not going to just 'accept' something that I don't agree with. Its a sound question that in theory has a point. Whether it works in practise or not is to be decided.

You have to try things to progress young jedi

[nmt_oli]

Ok, grinding a standard disk brake rotor, without changing anything else will not produce as good a brake as leaving it standard.

By roughing the surface of the rotor, you are just creating something that will cause a very high wear rate, while actually producing very little stopping power.

The logic behind grinding rim brakes, is very different to this case, as derf has explained:

Its to do with the pad being soft enough to "mould" into the grinds you have made. If you have a pad which can do this (like a rim brake) it will be loads better because the total braking surface is increased. But on a disc (with hard pads) they will not "mould" into the grinds so the total braking surface is decreased, therefore decreasing the overall friction, and reducing the braking power.

Its not just the fact that the surface area is increased, it’s the fact the pad locks into the grooves as well, for the pad to slip it would have to change shape to accommodate the profile of the braking surface, and while the pad is happy to deform in line with the pressure its being applied with, it will not easily deform the other way, very hard to explain this, basically the ridges would have to move across the pad, but cant since the pad material would have to be pushed back, which it wont do, any slipping provokes very high wear rate.

With a disk brake, the pad is so hard it will not conform to the contours of the braking surface, so you will not get the beneficial lock (in fact you will get a decrease in overall friction, despite the larger pressure) so the disk will just rub past the pad, and any energy that is taken from the movement, is used in the scraping of the pad material off the surface (the same as sandpapering the pads), hence very high wear rate. With a flat pad, and a flat disk despite there being little friction at low pressures, there is plenty at high pressure and it is turned into heat, rather than wear.

It is true that if you glaze a pad, you need to roughen the surface and bed it in again, but that’s another matter altogether.

The whole point about disk brakes is the modulation, everyone knows that they don’t quite have the hold of a trials set up magura, hence why few people use them for trials on the back. Disks are very consistent and predictable, and that is only achievable with a smooth surface – even if grinding did work, it would be very hard to get a consistent surface.

And before anyone mentions grooved disks on cars, they are not there to increase braking power, but to help stop pad glaze, and remove dirt and debris from the pad/disk interface. The numerous holes on bike disk brakes perform the same function.

This is my opinion based on what I know and have experienced, I’m afraid I cant explain the science any better- If I have time in between revision I will do some research and post again!

Edited January 19, 2006 by nmt_oli

[2sixstreet]

Speaking of slotting rims to remove pad glaze. I did this on the front and found it to be very effective. It keeps the pads nice and fresh which provides better braking performance without a full on grind.

[011001000110010101110010]

But if your going to do that, why not just grind?

[2sixstreet]

Quite simply I dont have a grinder and I thought this would be a good alternative.

[nmt_oli]

The rim slots allow water to escape from the contact patch, important if yourrunnign trials pads with no grooves, and it also maitains a mostly smooth braking surface maintaining modulation, which is desireable on the front. If you were to full on grind it, it would loose modulation, and be worse on pad wear.

[rupertsub2003]

if you are seriosly thinking of grinding a disc brake obviosly u aint got it set up properly as they are excellent and dont need any more power !!

[fat-jake]

nah i think that is a terrible idea,,, if grinding rotars made them better cars and motorbikes would come with em.......

fat jake

[Synergy]

i dunno i would like to see proof first like a proper experiment.

[mat hudson]

my mates broter ground the horrible black finish off the old shimano xt rotors, that brake is amazing. its a shimno xt 160 if anyone wanted to know

[011001000110010101110010]

Or buy an old Hope mini and fit and forget. It will be an amazing brake and i have never had a problem with mine.

[T_PRO]

nah i think that is a terrible idea,,, if grinding rotars made them better cars and motorbikes would come with em.......

fat jake

Good point

[adamtrials]

My mate did it, ill ask him when he comes on msn what it was like.

I can remember his brakes were quite sharp, but i never rode his bike

with none ground rotors so i dont know if it was an improvement.

[trialsinchris]

if grinding doesnt work on rotors what about just ruffing them up a bit like with a sander or somet

[Street Lee]

Sorry to raise an old topic but I'd like to know why warped disks are "Myth"? I've had several cars where I've warped the disks slightly due to spirited driving and have proven this by taking a straight edge to the disk. How can it be a myth if I've witnessed it? And what other faults would cause the same symptoms (wobble in steering wheel and juddering pedal) as warped disks when the wheels are freshly balanced?

[street trials rider]

grinding disks is only a way to destroy yoru rotor and pads...... if you want better breaking with a disk buy a good brake

i've had it explained to me many times over the years why its useless, fact is (as mentioned) both surfaces need to be smooth, if all else fails, clean yoru rotor with a baby wipe every few week, and leave it for about 5 mins for it to evaporate off (works same on rim brakes, but lasts about 15 mins)