Rear End Instability?

[Timbo2]

Thanks for the feedback so far. BTW I meant to say that it felt like it was going into oversteer, NOT understeer

[Flavor 987S]

Could be a bunch of things:

What are your tire pressures?
What is the production date of the tires?
Are all 4 tires a matched set?
Are the rears mounted in the right direction of travel?
Are you using too much tire dressing?

[landrovered]

I have felt a tendency to snap oversteer since I put Hankook EVO tires on the rear of my Boxster S. They are softer than the normal Michelin Pilots and have a greater tendency to get twitchy at higher speeds. It was very disconcerting the first time it happened. Neither Michelin Pilots or Yokohama S Drives we like that but the EVOs are quite twitchy.

I have read numerous articles about GT40s and their dislike of soft tires and tendency to snap oversteer. Since the Boxster is a mid engine car as well, it would follow that it would suffer the same problem

[Timbo2]

Originally Posted by Flavor 987S

Could be a bunch of things:

What are your tire pressures?
What is the production date of the tires?
Are all 4 tires a matched set?
Are the rears mounted in the right direction of travel?
Are you using too much tire dressing?

Hi Flavor987S. Tyre (English spelling!!!) pressures are 37 rear 30 front. Not sure how I can check manufacture date, but the rears were fitted Oct 2009 (so I guess no - not a matched set). All correct rotation direction. Tyre Dressing!! - what kind of a guy do you take me for?!

[Flavor 987S]

Originally Posted by Timbo2

Hi Flavor987S. Tyre (English spelling!!!) pressures are 37 rear 30 front. Not sure how I can check manufacture date, but the rears were fitted Oct 2009 (so I guess no - not a matched set). All correct rotation direction. Tyre Dressing!! - what kind of a guy do you take me for?!

Your front tire pressures are too low. All 4 tires need to match. Go to Tire Rack's web site, and read about how to determine your tire's manufacturer date. Don't use tires more than 5 years old.

[TWODAN]

wow. i looked on my door jamb at the beginning of the season for the correct tire pressures. mine read 29 front, 36 rears. they were all at 36psi, so i dropped the front two. i believe i have the original conti's on the car with 9K on the odo. who's correct?

[Timbo2]

Originally Posted by Flavor 987S

Your front tire pressures are too low. All 4 tires need to match. Go to Tire Rack's web site, and read about how to determine your tire's manufacturer date. Don't use tires more than 5 years old.

Manufacture's spec is F29/R36. Where are you getting your info, or is this based on experience?

[Beelzy]

I think it could be the tires. I have Michelin rears that I recently had installed, and
they tend to "break loose" more readily than the BF Goodrich tires I previously ran.

[thstone]

Tires should start at factory pressure, 29F/36R. If you're driving hard, then the pressures will go up and the tires will start to slide around rather than grip like they usually do so you might need to bleed off a little air as you go harder. My PS2's feel like they are riding on grease when the pressures get too high and I am pushing the car hard.

Make sure the alignment is spot on.

Have all of the suspension re-checked and tell the tech what happened. A health check is a nothing compared to a performance handling check. Anything worn will expose itself at 115mph in a corner.

Shifting in a corner at 115mph will definitely upset the balance. Get your shifting done before the corner.

[Flavor 987S]

Originally Posted by Timbo2

Manufacture's spec is F29/R36. Where are you getting your info, or is this based on experience?

I guess I am wrong about OEM tire pressures for an 986. On my 987S with 19" inch wheels, OEM spec's are 34F/37R. I tend to run about 1 PSI lower than spec. Michellin PS2's.

Did not realize front tires pressures are so low (30 PSI) on a 986.

[Gilles]

Originally Posted by Flavor 987S

I guess I am wrong about OEM tire pressures for an 986. On my 987S with 19" inch wheels, OEM spec's are 34F/37R. I tend to run about 1 PSI lower than spec. Michellin PS2's.
Did not realize front tires pressures are so low (30 PSI) on a 986.

Flavor, also on the 987S w/19's
I found out that running about -1 on the rears (34/36) the tires wear more evenly, otherwise the rears will wear too quickly on the inside.

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