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I am running Michelin pilot pilot cup on my base 2001 boxster, fronts are 225-40-18 with rears at 285-30-18, have lots of oversteer at track after 2 warm up laps, my pressures are 32 front 30 rears, any suggestions, running an airport track about 2.3 miles road course with 8 turns and chicane.

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I am running Michelin pilot pilot cup on my base 2001 boxster, fronts are 225-40-18 with rears at 285-30-18, have lots of oversteer at track after 2 warm up laps, my pressures are 32 front 30 rears, any suggestions, running an airport track about 2.3 miles road course with 8 turns and chicane.

What do your tires look like after they've warmed up and you've run some laps? Are you checking the roll marks on the top side of the tires or using white shoe polish to see if your tires are inflated properly? You should see scuff marks right at the top of the diamond if they are inflated properly. If the scuff marks go into the diamond then you are under inflated (tire roll into the sidewall) and if they don't touch the top (riding on partial tread) you are over inflated. It looks to me like you are under inflated all the way around. I generally run 5 psi higher than Porsche recommended pressures for DE. My Porsche recommended pressures are 29F and 36R so I would be running 34F and 41R for DE and that just so happens to work perfect. Some guys run even higher.

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Your pressures could be low by as much as 10psi when hot. You probably want to start with something closer to 36 all around cold. On street tires for autox, I'm running 38f/41r hot but the sidewalls are a bit softer than Pilot Cups. At the least try starting the rears at 35psi cold and see how much of a change that makes. My guess is that low you are over heating the tires and they aren't working properly due to low pressure so a smaller contact patch.

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  • 2 months later...

Oversteer (rear end steps out) with a 225/285 stagger?? That sounds very unusual. To give you meaningful input we need to know more about your car. Any suspension mods and settings, 600hp Chevy LS1 motor transplant:) etc.

On a stock car with this tire stagger the car would have significant understeer (push) unless something was disconnected or broken. Hot tire pressures taken immediately after a session are the only ones that matter.

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