John Coffey wrote:Aluminum rotors are used on Midget circle track cars, racing bicycles, some motorcycles (rear disk), and some go karts. In the context of the FastTrack proposal (ST class cars) its a really stupid idea. As Marshall said above, the basic material properties of aluminum make it a poor choice for brake rotors that see temperatures above 400F. Artificial aging of aluminum (to get to various levels of heat treat) is done at temps in the 400 degree range - that's why an inattentive powder coater can take an aluminum rim at T351 or T651 temper and drop it to T0 in 15 minutes.
I agree that it's a poor choice, but that doesn't stop someone from trying it.
Why would you create a rule that gives an allowance for an expensive custom part that might be a single event item before needing replacement but have a real performance benefit. Does that sound like a good thing for ST???
Dr. Conemangler
aka The Malefic One
2015 Wildcat Honda F600
Steve Ekstrand wrote:Why would you create a rule that gives an allowance for an expensive custom part that might be a single event item before needing replacement but have a real performance benefit. Does that sound like a good thing for ST???
Not if the SEB wants to control costs. That was the alleged thinking behind the minimum 20 lb. seat + bracket rule for SP. Of course it doesn't prevent someone from buying a mega light expensive seat and adding ballast to the bracket, but that argument was offered up.
Steve Ekstrand wrote:Why would you create a rule that gives an allowance for an expensive custom part that might be a single event item before needing replacement but have a real performance benefit. Does that sound like a good thing for ST???
I'm pretty sure someone isn't going to win a national championship because they have Aluminum rotors... but it would be pretty damn easy to lose one because of it.
With an aluminum rotor and hat machined from a 2024 billet (7075 isn't a good choice because it loses strength in high temp use) you will most likely save 20 lbs. of unsprung weight over a comparable steel/aluminum hat combination. That's a significant advantage over an equally prepared and driven car. I don't know how long those rotors would last, but in a light weight ST car I'm sure they can make it through 6 runs. Even if they last only 3 runs, you have a day to swap in a new set before second course at the Nationals.
Again, its not a good idea but with lots of money and a test day, a savvy competitor can gain an advantage. FYI... a 12" x 12" x 1.250" thick billet of 2024 is around $300. Add in machining costs and you're looking at a $500 rotor as I posted earlier. Funny how I already had that roughed out...
John Coffey wrote:With an aluminum rotor and hat machined from a 2024 billet (7075 isn't a good choice because it loses strength in high temp use) you will most likely save 20 lbs. of unsprung weight over a comparable steel/aluminum hat combination. That's a significant advantage over an equally prepared and driven car. I don't know how long those rotors would last, but in a light weight ST car I'm sure they can make it through 6 runs. Even if they last only 3 runs, you have a day to swap in a new set before second course at the Nationals.
Again, its not a good idea but with lots of money and a test day, a savvy competitor can gain an advantage. FYI... a 12" x 12" x 1.250" thick billet of 2024 is around $300. Add in machining costs and you're looking at a $500 rotor as I posted earlier. Funny how I already had that roughed out...
7075 loses strength in high temp use. Good to know. I would have thought 2024 was too soft.
Bob Beamesderfer wrote:
7075 loses strength in high temp use. Good to know. I would have thought 2024 was too soft.
they all loose strength with temp. 2024 just looses less of it then 7075 does.
also I was wrong about heat capacity. Al does have a higher heat capacity then steel does. it also has better thermal conductivity then steel. the real problem is just the poor high temp properties. if you made an aluminum rotor that weighed the same (really weighed more) then a steel rotor to keep the temps under control you could make it work. But because the Al is less dense you'd likely end up with a rotor that has higher rotational inertia thus negating any performance benefit.
and all of that design work that you put into making a functional aluminum rotor is all wasted anyways because by that point you could have just put on some carbon rotors and been done with it.
Bob Beamesderfer wrote:
7075 loses strength in high temp use. Good to know. I would have thought 2024 was too soft.
they all loose strength with temp. 2024 just looses less of it then 7075 does.
also I was wrong about heat capacity. Al does have a higher heat capacity then steel does. it also has better thermal conductivity then steel. the real problem is just the poor high temp properties. if you made an aluminum rotor that weighed the same (really weighed more) then a steel rotor to keep the temps under control you could make it work. But because the Al is less dense you'd likely end up with a rotor that has higher rotational inertia thus negating any performance benefit.
and all of that design work that you put into making a functional aluminum rotor is all wasted anyways because by that point you could have just put on some carbon rotors and been done with it.
Bingo! Carbon rotors would be lighter than aluminum. Picked one up once and it was weird how light it was despite being about 12" in diameter.
I misread the brake proposal. It doesn't apply to STS. But something I find strange is that rotors and drums aren't treated equally. You can change rotors, calipers and brackets. You can go completely custom and lightweight, you can go to aluminum. But I don't see any allowances to change the drum system in ANY way other than a conversion to discs.
Dr. Conemangler
aka The Malefic One
2015 Wildcat Honda F600
