Alluminium disc rotors, your thoughts?

[John Orchard]

Hey Guy's,

l've been thinking of making an alloy rear brake disc for either my dirtbike or roadracer. l don't use a rear brake overly hard; vertially never on my roadracer, plus l don't like a savage rear brake.

l was thinking that alloy might have a lower friction coefficient plus be much lighter (less unsprung weight and all that), yeh it would wear out quicker but eh?

Idea's on what grade alloy; less chance of shattering or warping?

[pokey]

ally disks? Id share my drugs if I thought of doing that.

You do know that once the oxide is removed you have silver butter to play with.
 Cant say Ive heard of anything other than ceramic, CF or iron disks. Probably a good reason for that.

Rear disks dont have much braking effect due to the inertia and weights being on the front. drum rears are just as good as you probably know. If you dont want weight use a smaller dia disc from a pitbike.

[David Lahey]

The strength vs temperature relationship for aluminium and its alloys is such that it would be useless for motorbike brake discs

[David Lahey]

As for weight saving compared with steel, aluminium (at room temperature) is approx 1/3 of the strength of steel and approximately 1/3 of the density of steel so there would be no weight saving

[GMC]

I think it would be a fail, the alloy would be too soft and the surface would peel and tear away. Not just wear quickly but rip itself to shreds quickly

Any heat treatable alloy would lose its temper from the braking heat
5083 has a close grain structure and might be the best bet but I think if there was anything in it the Formula One guys would have been onto it already.

I think Titanium might be a better option that alloy but again if F1 don't use it there must be a reason

[John Orchard]

Thanks, l can put that idea to bed ;-)  What planted the seed in my head, a couple of years ago l saw a GP125 roadrace bike with an alloy rear disc; it might have just been there for looks?

[djr]

I think the only aluminium rear disc's I can remember seeing is those combined rear sprocket / rear disc set up's, that a few people have tried and then abandoned .
{ seem to remember a Hagon grass track / long track bike with this set up }
 I guess you could get the surface coated with something  to improve wear - anodised / chrome / nikasil  maybe ?
 but a lot of expense for little or no gain

[skypig]

Some MTB discs are (aledgedly) alloy sandwiched with Stainless steel. Including “Shimano Ice Tech”.
I wonder if a whole MTB setup would suit for your rear? Floating discs up to 203mm are common. Tiny calipers to suit.

[mboddy]

Zanzani disk for your road racer: http://www.motobi.com/zanzani_2015/dischi.html

[sleepy]

Alloy discs are quite common in open wheel speedway cars. Very critical to use the correct compound pads with them. Also using Titanium rotors now as well.
https://www.speedwaymotors.com/Wilwood-160-14185-Super-Alloy-Slotted-Rotor-10-Inch-6-x-5-25,268419.html
Not cheap but very light.

[Momus]

Against my better judgement I made an aluminium disc for a 100cc sprint kart about 20 years ago. Was made from the garden variety 5083 H321  plate and electroless nickel plated.  It held up for at least a couple of meetings despite my dire predictions and I had no report of it's failure.

Aluminium has about twice the heat capacity of iron, or stainless steel, so for a given energy input an Al. disc half the weight would absorb the same amount. They must have been running pretty cool though.

[Gippslander]

Check the rulebook b4 using titanium
(happy to be corrected but as I recall it's ok to make components out of any old aluminum but titanium of which even the crappiest grade is stronger than ally is a not on - go figure)

[sleepy]

Aluminum rotors for use on front of speedway cars. Could be a little to thick for some bike calipers though at 8mm.

https://www.speedwaymotors.com/Speedway-Front-Aluminum-Brake-Rotor-10-875-x-312-Inch,20054.html 

[OverTheHill]

Reminds me of about 20 years ago when my son bought home his first roadrace bike--an NSR250 turned into an RS250 with go fast bits. I took it for the obligatory thrashing down our road going far too fast & trod on the rear brake. Think it had those sintered bronze type pads & instantly ripped the disc to bits & packed it all up against the pads & locked the wheel solid. Was bloody lucky to escape from going sideways down the road. Had to carry it onto the trailer for the short trip home. Of course he said what the %^&* are you doing using the rear brake lol.

[GMC]

According to the moms Titanium is illegal for axles, not sure about other items