Aluminum Brake Rotors

[Will98Cobra]

For those who have been running Al. Rotors, what are some of the do's and dont's that you have come across and is it worth using them

William Austin
ODU Motorsports
Chassis/Suspension/Controls

[Richard Lewis]

Well we've used 2024, Hard anodized on our last 2 cars now, with no problems. (while using the proper aluminum pads that is)

Even with our success, I believe we might be switching to ferrous rotors next year.

-------------------------
UVIC Formula SAE Team
http://members.shaw.ca/drax77/Formula%20UVic%20Sig.jpg
http://uvic.fsae.ca

[Bob Wright]

We ran aluminium oxide (ceramic) coated 2000 series aluminium rotors last year and they were pretty good. The thermal expansion is very differnent between the rotor and the coating so after you use them once or twice you get lots of hairline radial cracks in them. Its nothing to worry about though, and apparently they run the same setup on a lot of military aircraft and the same thing happens. i wouldnt try cross drilling or slotting them though- i could imagine that if the coating got a reason to start chiping off, it would all be over pretty quickly.

The year before that we had a copper/stainless steel 'mock alloy' plasma sprayed onto aluminium rotors which were also good (they had serious bite- i dont know if the pads would last long and our car shit itself so we couldnt tell).

This year we're back to good old steel- we had to wait months for stuff to get coated for free. http://fsae.com/groupee_common/emoticons/icon_cool.gif

Bob Wright
Monash University
Australia

[Hutch5375]

Is anyone using the Wilwood Aluminum rotors? I've done a little research but not a great deal and was wonder if anyone else had been looking into them?

Seems interesting that team that have been using Aluminum rotors are going back to ferrous.

Grant Hutchens
Kettering UNiveristy FSAE
Brakes/Suspension/MUNKEE

[Bob Wright]

Only going back to steel because of the time it took waiting on the things to get plasma/ ceramic coated, and because we're floating the things this year and aluminium doesnt make a good dog engaugment surface. Ali is good for rotors, so long as you have a good friction surface and its 2000 series (2024 seems best).

Bob Wright
Monash University
Australia
http://www-personal.monash.edu.au/~fsae

[clausen]

Hi there,

Interested in these things for sae cars, and also mountain bikes.

What are the proper aluminium pads that soemone was referring to?

Why do the discs need to be 2000 series alloy in particular?

Whats wrong with aluminium as a dog engagement surface? The touring cars use aluminium disc bells which have the dog engagment on them.

Regards,

Paul Clausen
Adelaide Uni

[clausen]

I have just been listening to that MP3 of the design finals that Carroll Smith did at some stage and he said that all the judges think 2000 series and 6061 brake discs are terrible. He didnt say why, just said that their experience was that it's a bad thing.

I'd love more info

Regards

Paul Clausen
Uni of Adelaide

[Bob Wright]

2000 series copes the best with heat, the dog thing is just an issue of not wanting highly loaded sliding friction on aluminium which will gall pretty badly and not last long ( you can get around this with steel on steel but then you need to bolt that to the ali as well....).

The proper pads for aluminium are the proper pads for whatever you coat them with- a bare aluminium surface is not good for braking (i think its like how you cant grind ali because it gets into the gaps in the grinding stone ,heats up and blows the thing apart), although some sprint cars do it so you must be able to get them- but you'll be replacing rotors and pads very regularly if your intending to keep the thickness down to get the weight saving over steel. with the ceramic/ aluminium oxide coated set we made we used a kevlar pad.

expansion is also an issue- ive read somewhere that some people put radial slots in ali rotors because when they expand they also want to develop a runout due to tangential expansion being greater than radial expansion- but that will be down to the individual dimensions of your rotor and the heat it gets to.( we never had a problem)

Bob Wright
Monash University
Australia
http://www-personal.monash.edu.au/~fsae

[Bob Wright]

just noticed another thing. our website has picuter of our old 2001 and 2002 rotors bur the picure of the 2002 ones on the car has a bit of a mistake. the spokes in the rotor are pointing the wrong way- under a braking load you want the spokes running tangentially from the centre to go into compression, not tension. when they're in compression the swept area is put into tension (tangentially) which helps it run straighter. if its in compression around the circle its more likely to push out into a runout during use.

Bob Wright
Monash University
Australia
http://www-personal.monash.edu.au/~fsae

[Pavan Dendi]

UT Austin has run Wilwood aluminum rotors for 3 or 4 years now. They stop in a hurry and we have never had a single problem with them. As far as brake pads go, if you go with Wilwood, go with their recommended pads and you'll be fine.

_____________________
UT Austin FSAE
http://www.me.utexas.edu/~fsae

[Charlie]

Auburn ran the Wilwood Aluminum rotors from 1997-2002. We actually ran the same set from 1998-2001, which is pretty impressive. They were black anodixed, and the anodizing never really wore off, so it's not a bare aluminum rotor exactly.

Even though we said 'They work great!' The judges always hated them, and Carroll Smith especially. He told us if we weren't overheating them then we weren't going fast enough.

He was right.

-Charlie Ping
Auburn University FSAE (http://eng.auburn.edu/organizations/SAE/AUFSAE)
5th Overall Detroit 2003
? Overall Aussie 2003. http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Jeff Gensler]

I have put Wilwood rotors on 4 FCARs and they all stopped it just fine. In fact all of them were over-braked.

All comments I have heard referring to our rotors are preconceived notions spread by those who don't have experience with them.
They never glaze over, they do not overheat, and the anodized coating does not wear off quickly. They don't fade either.
Wilwood won't tell us anything about them but we have reason to believe they are 5000 series hard anodized.

They are a design solution that can work, but then again so can lots of other stuff.....

[Charlie]

How do you know that they don't overheat? What peak temperatures do you see?

-Charlie Ping
Auburn University FSAE (http://eng.auburn.edu/organizations/SAE/AUFSAE)
5th Overall Detroit 2003
? Overall Aussie 2003. http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Charlie Monash OZ]

there is another reason why monash is not using an aluminum swept area this year, that is because the swept area of the rotor is floating therefore very little heat is transfered to the hub of the rotor. That means that the swept area now has to cope with nearly all the heat generated from braking, so even if we return to a 2024 Ali swept area later this year I think we will require a backup cast 3D set just to be sure. We have also investigated a triple plasma coating for the aluminum, 1st layer is to promote adhesion, 2nd acts as a thermal barrier and the 3rd acts as an abrasive barrier. Hopefully that will lessen the radial cracking of the coating when the ali expands. One last thing 2024T6 is chosen mainly for its ability to handle thermal cycling without affecting its strength, it has 400+ Mpa strengh (wicked material, but pricey). I did some testing on an early set of aluminum rotors and achieved a maximum of 340deg C at the surface of the rotor, Al2024T6 has a melting point of 502Deg C so well within its capabilities.

[Ahmad Rezq]

Seems old subject, But how much weight you will save with Al rotors !! does this deserve looking for the suitable AL alloy , the proper coating which is expensive and last but not least a good pad. as far as I'am concerned steel or gray cast iron are acceptable materials to use with FSAE rotors. and you can save weight by selecting a proper calipers.

[MCoach]

Ahmad, some digging you've done to find this thread!

Aluminum is typically used in series where only small brake inputs are needed rather than continuous usage such as braking from a long straight or many successive events into corners that build heat. This low usage cycle is seen in several circle track cars, particularly on dirt.

We ran aluminum rotors on our 2009 - 2011 car and I ended that after we melted the rotor into the caliper after the second lap of endurance. We had just switched to a new set after almost melting the fronts during autocross. If aluminum works for FSAE...you're not going fast enough. It is a large pain to design and service everything with an aluminum base because pad materials are limited and the base material is thermally sensitive, meaning it may yield under actual hard braking or expand to the point of contacting your calipers if there is not enough clearance. That and it must be coated to work properly. No coating, no go.

Currently, my steel design weighs less than the aluminum rotors that the replaced and we've confirmed rotor temps up to ~950 Celsius on the front rotors after typical endurance use (sometimes smoking/steaming). We've seen no issues with steel and pad life seems infinite. This year we're making them smaller...

[Ahmad Rezq]

MCoach,
hhhhhh yes I'm trying to read every single topic about the brakes in the forum.
Backing to the topic what is your opinion about cast iron i read a comment from some one said that below 5 mm rotor thickness the cast iron rotors are not good, he didn't mention the reason but i saw many teams use cast iron rotors with 4 mm thickness.

[MCoach]

I originally designed my 2012 design around cast iron but came to the conclusion that heat was less of an issue that the breaking strength and fatigue of the material itself and bought sheet steel instead. My rotors were 5mm thick steel then and you could almost grab them after a few laps. They pretty much never got hot. I also thought they were pretty heavy, but supposedly light compared to some teams. Right now I'm well under 3mm thick.

Cast iron is a good for a large, lightly loaded mass such as is used on road cars. After that, strength becomes a concern. How many mountain bikes have you seen with cast iron rotors?