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Old 10-29-2018, 06:16 AM   #1
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Lightweight wheel setup for AutoX

I'm considering a new set of wheels for next year's autocross season. This season I used a set of OEM 7.5/9 18" turbo twists with 225/265 re71Rs. And I generally could pax in the top 5 or so out of 70-90 racers. The GGR PCA group does a points based classification so I can go to 8" fronts with 9" rears without changing classes. OZ Alleggeritas are probable about 5-8# lighter per wheel. I'd probably use the same tire setup because I prefer a bit of understeer (I know it may seem blasphemous, but I don't do well with a loose backend).

I know on paper the lighter wheels should help, can anyone weigh-in on their personal experience? And did you think it was worth it?

Thanks
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Old 10-29-2018, 09:50 AM   #2
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Since the tire widths would stay the same, the only benefit is weight and the 16lbs that you might save is the same as two gallons of gas. In theory, there will be an improvement from the lower unsprung weight but I worry that it will be imperceptible in comparison to other variables.

If you are consistently within a tenth of a second of the being on the podium, then this might be worth it. It certainly won't hurt so you have nothing to lose but some money in the short run and chasing the podium is often a matter of optimizing several variables to get the needed aggregate result (meaning that picking up a tenth here and a tenth there all adds up eventually).
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Old 10-29-2018, 10:27 AM   #3
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Also don't forget to weigh your tires. I've seen guys save 4lbs each on wheels then throw heavier tires on and negate all the savings.
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Old 10-29-2018, 05:11 PM   #4
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A reduction in wheel weight is a much bigger deal than a reduction in weight from the chassis. That’s because you are accelerating or decelerating the rotation of the wheels which are moving much quicker than the chassis.

Besides that, any reduction in unsprung weight is always a good thing.
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Old 10-29-2018, 06:46 PM   #5
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I don’t think the cost is worth it. Go out with less fuel and it costs nothing. Stay away from pizza the night before too!
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Old 10-30-2018, 04:19 AM   #6
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If you loose say 7 Ibs x 4 wheels= 28 Ibs rotating mass.. That is a great improvement and you will definitely notice the difference. I made a similar switch, would never go back! Go for it!
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Old 10-31-2018, 02:31 PM   #7
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from what I recall, every pound of rotational mass equals 10lbs of vehicle weight so, -28lbs on wheels is 280lbs of vehicle weight you just dropped.

I'm not a track guy and I have no personal experience, however, I did stay at a holyday inn.......

Have a good one!....
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Old 11-01-2018, 08:22 PM   #8
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Everything matters. Lighter wheels help, lighter seats, lighter battery, lighter fuel, lighter driver. How much will they help? Not a lot but...

My brother has a set of those for his Cayman. He likes them and they seem pretty strong.
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Old 11-10-2018, 07:32 AM   #9
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Quote:
Originally Posted by gonzzo View Post
from what I recall, every pound of rotational mass equals 10lbs of vehicle weight so, -28lbs on wheels is 280lbs of vehicle weight you just dropped.

I'm not a track guy and I have no personal experience, however, I did stay at a holyday inn.......

Have a good one!....
Depends on where the mass is... if weight is reduced closer to the wheel center, then the effect is not as much as reduction far from the center.
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