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Old 07-21-2020, 09:22 AM
smithpr smithpr is offline
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Join Date: Dec 2004
Posts: 571

Some really good discussion. But first let's talk about what an amazing race weekend for AS. 9 Cars at two different events. Mid Ohio AS racing was the best I have seen for years. I wasn't great but had a great time with all the amazing racers. We had a Cadilac, a restricted prep mustang, the normal bunch of FP cars, and a number of RP camaros. Don't focus on the MPH with the RP cars they pull like heck but do give up a bit of top speed but they were all competitive.

As to the rotors. I have been going through a set of rotors every weekend so I started looking at rotor sizes and weight and quickly realized that the AS rotor size was the smallest given our weight. For example, TA2 uses a 12.2 rotor but they weigh 2830. I discussed this with a number of other racers and they also voiced significant concern about the longevity of rotors.

In addition, the 12.2 rotor is a bit of on oddball size. When looking at kits for some of our cars the only kit rotor size that was available was for a 13 inch rotor. Also a number of competitors are using the very low-cost corvette rotor and spending money to have them cut down. In addition, there is a massive amount of support with the round round guys for the 12.81 or 328mm rotor so there is a ton of this stuff out in the market at very low costs. Spend a little time on eBay or the various other used race car parts sites.

The larger rotor can weigh more and therefore have increased thermal capacity so the rotor will be running more in its preferred heat range.

There is no requirement to run the bigger rotors and if your rotors are lasting then keep them. Furthermore, the smaller lighter rotor takes less energy to spin up and down and therefore will be faster. As a point of interest, NASCAR at the top series does not specify a max rotor size but only a minimum size further providing proof that bigger means more weight and likely slower.

Most of our calipers are able to run a bigger rotor. Remember it is only a little more that 3/8's of an inch bigger on the radius so that is how much you would need to move the caliper up.

This change increases the availability of parts at a lower cost and will increase the life of our parts.

I hope that this helps.

These are my views and should not be interpreted as the views of SCCA, the CRB or the Adhoc.

Let's get out and race our cars. It is an amazing class.


Last edited by smithpr; 07-21-2020 at 12:02 PM.
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Old 07-21-2020, 01:18 PM
jimwheeler jimwheeler is offline
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Join Date: Oct 2004
Location: Kansas City
Posts: 5,248

I measured and I have about 1/8" clearance, so larger rotors would entail all new wheels, even if I stayed with 16". I understand your points and Andy's but have had no problem getting good quality rotors (Wilwood) at a reasonable price. They seem to last quite a while with their new version. I just don't see the need for it. P.S. I am much more likely to support Andy's better gear ratios idea, which I pushed for all of the years I was on the ASAC and the CRB. If it had been done early, the savings in damaged caused by the lousy ratios, would be in the millions.
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Old 07-21-2020, 01:35 PM
smithpr smithpr is offline
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Join Date: Dec 2004
Posts: 571


I hope you are doing well. If what you have works for you then leave it. You will be faster with less rotating mass. That is what is great about this change. If you want longer wearing stuff but are willing to give up a bit of speed go with the bigger rotor. The speed difference is pretty small so I will be going with the bigger rotor.

Stay cool and safe and hope to see you racing soon.

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Old 07-21-2020, 01:38 PM
PbFoot PbFoot is offline
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Join Date: Feb 2008
Posts: 216

Idea. Simple change to address issues with brakes, tire wear, and driveline stress. Change maximum tire width from 275 to 255.

Our 8" wide wheels are designed to work with 255 tires not 275 tires. Less contact patch means less stress on the brakes and the driveline.

AS ran on 255 tires for the first half of our history and the racing was great.

No need to upgrade the brake rules, or buy new wheels, plus the tires are a little cheaper.

Sure we will slow down a little, but maybe we can use that fact to lobby to get out of the GT1-2 race group. Maybe we could swap race groups with T2.
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Old 07-21-2020, 05:12 PM
MarkMuddiman MarkMuddiman is offline
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Join Date: Dec 2004
Location: Belleville, MI
Posts: 156

You may go faster on 245s than 275s.
The whole car sits lower so the cg and roll centers go down.
The smaller tire is lighter, and rotating inertia is lower on two counts: weight and diameter.
Probably won't give up much lateral grip on the front, because the 275s are utilizing the tread width well.
Rear lateral grip may be reduced.
May be able to back off the camber some, and get better braking, or at least more stable braking.

I do like the idea of swapping groups with T2. Only issue is AS mid-pack will be mixed in the fast STU and STL cars. Who wants to get beat by a CRX?
Mark Muddiman
AS #71
Detroit Region
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