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      03-18-2013, 11:48 AM   #8
Pete_vB
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Drives: '69 GT3, GT4, 1M, 912
Join Date: Nov 2010
Location: SF Bay Area, Shenzhen, Oman

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So I did a little research and gave this some thought. I also autocrossed the car again this last weekend with the half-warn front PSS and fresh rears.

First, with this tire setup it drives like a completely different car. Rather than being easy to provoke throttle on oversteer, it actually takes some effort, much more than I've ever experienced in this car before. This tells me that even at over half tread depth the front PSSs have lost a fair bit of grip. The car actually feels very fast with this setup, letting you get on the power very early, but time is definitely being lost to mild understeer in sharp corners.

In hindsight I guess I shouldn't be too surprised that the PSS go off with age:

1. I know the PSS compound shares a lot with the MPSC, and that tire is well known for "going off" with heat cycles.
2. Thinner rubber grips less. While this seems counter-intuitive, especially to guys that shave their street tires to go racing, but really that's done to reduce heat buildup and tread-block squirm. If those are not issues, then tire with more rubber will be stickier.

See this quote from dunlop racing tires:
"Heat Cycles is not an issue with Dunlop racing tires as it would be with other brands. The more important factor is how much tread is left on the tire. Stable fact: thicker rubber has more grip and develops more heat, thinner rubber has less grip and runs cooler. After each session you have less grip. As the tire wears out, you have less and less grip. It could be slight or it could be large."

Based on this, two things occur to me:
a) Next time I need to plan on replacing the rear tires much sooner, far before the wear bars, to maintain decent performance and overall car balance, even if I'm not driving in the wet.
b) I don't think I'd ever recommend anyone change the front tires on the 1M without changing the rear, even if they are the same type of tire, unless they are simply not pushing the car. I think it would likely be a recipe for oversteer.
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1M, GT4, 1969 Porsche 911 w/ 997 GT3 Cup Motor (435hp & 2,100 lbs)
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