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      11-05-2010, 05:29 PM   #1
TurboHank
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What tire pressure to set for track session

Howdy folks,

I am taking my Z4 35i back on the track tomorrow at the Infineon Raceway near Napa Valley. I was wondering what tire pressure I should set relative to the suggested PSI pasted on the door frame? I have heard two theories:

1. over inflate: this way, the tire will be more rigid, thus better performance. But it might just blow up on my ass.
2. under inflate: so that when heated up, the pressure would equal that of the recommended setting, and not blow up on my ass.

What do you guys think?

Hank

PS. the first time, I didn't even think about it, just took the car on the same track and horsed around.
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      11-06-2010, 12:13 PM   #2
richard in NC
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My theory is to slightly over inflate by 2-4 psi. I've never had them too high at the end of a session.

The best thing to do is have a tire pump and gauge handy. Check and inflate before the sessions and check as soon as you can after the sessions.

Ideally, use some chalk on the sidewalls to see how far they roll over. Inflate a bit the next time if they do go beyond the edge of the tread (should see triangles at the edge). Note RFTs are unlikely to roll over much at all so under-inflation will be masked by the extra stiff sidewalls.

Note if you under inflate, it will take several laps for them to get to temp. They'll likely increase significantly due to the extra heat of rolling over more.

If you over inflate, they'll be good quickly but may get "greasy" after several hard laps. Simply back off a bit and you'll be good throughout the session.
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      11-07-2010, 09:06 PM   #3
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What kind of tires are you running?
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      11-07-2010, 10:29 PM   #4
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Quote:
Originally Posted by richard in NC View Post
My theory is to slightly over inflate by 2-4 psi. I've never had them too high at the end of a session.

The best thing to do is have a tire pump and gauge handy. Check and inflate before the sessions and check as soon as you can after the sessions.

Ideally, use some chalk on the sidewalls to see how far they roll over. Inflate a bit the next time if they do go beyond the edge of the tread (should see triangles at the edge). Note RFTs are unlikely to roll over much at all so under-inflation will be masked by the extra stiff sidewalls.

Note if you under inflate, it will take several laps for them to get to temp. They'll likely increase significantly due to the extra heat of rolling over more.

If you over inflate, they'll be good quickly but may get "greasy" after several hard laps. Simply back off a bit and you'll be good throughout the session.
Hey Richard, does your z gets over heating issues on the track after a couple of hot laps? Also do you engage the gears manually or leave it in sports auto? Thanks !
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      11-07-2010, 10:40 PM   #5
richard in NC
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I've never had my Z4 on track. Most places around here don't allow roadsters without rollbars. I would be in manual mode on track using the paddles.
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      11-07-2010, 10:41 PM   #6
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Quote:
Originally Posted by TurboHank View Post
PS. the first time, I didn't even think about it, just took the car on the same track and horsed around.
there's your answer...
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      11-08-2010, 12:29 AM   #7
TurboHank
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Hey thanks for the reply. It turns out that my tires were over inflated from the recommended settings by a few PSI, so I took it right to the track.
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      11-08-2010, 05:54 PM   #8
TurboHank
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some pics from the track event, we had 6 N54 engines in our group that day. My #19 Z can be seen.







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      11-09-2010, 04:56 PM   #9
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Regarding tire pressure and the stock run flats that ship on the z4, the question is sort of moot with run flat tires because they maintain a rigid side wall even with reduced tire pressure. Thus, you can reduce to a certain psi, but the tire will maintain rigidity and the reduced pressure will not change the performance characteristics. It is also a bad idea to use run flats below the suggested psi for the same reason--inducing forced rigidity in the side wall of the tire. My two cents is use the recommended pressure from bmw, or use another, non run flat tire for racing.
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      11-11-2010, 05:41 PM   #10
TurboHank
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Yea my tires were slightly over inflated when shipped from the dealer. So I will continue using the stock run flats until I swap regular tires with them down the road.
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