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Old Mon, May-10-2010, 03:24:50 AM   #5
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Downsides to running wider tires:

Okay, so having established how to run bigger tires, let's talk about why you don't wan to do it. Wider tires will:
-decrease fuel economy
-make the car slower accelerating
-make the car tramline a LOT more
-increase road noise
-make you hydroplane at slower speeds

Not great things, and the wider you go, the worse it gets. In exchange, the benefits are:
-decreased understeer
-better braking

Getting started with tire pressure on the track:
(this is just to get you started. Once you get comfortable, you can tweak the pressures to bias the car towards over or understeer.

To get started, set the tires pressures to the pressure recommended by the manufacturer. If you're running street tires, set it to the BMW recommended pressures on the inner door frame. Get a tire marker pen and draw a line from the center of the sidewall to the contact patch. Go out and do a couple laps, building up till your at your full speed. Pull into the pits.

The amount that the paint has worn off the tire shows you how much tire rollover you have going on. Some is good, too much is bad. On dedicated track tires, there's little triangle that indicate the exact spot where rollover should stop. If you're rolling over beyond the tip of the arrow, add some pressure to the tire. If you're not making it to the tip of the arrow, let some air out of the tires. If you're on street tires, it's a little trickier. Generally speaking you want to make sure you are staying in the tread blocks, not driving on the sideways. Some tires have blocks that are designed to go out more than others-- PS2s, for example, are designed to have some rollover to get you into the maximum grip blocks.

The above technique should not be used for street tires, as there's much more going on there-- tires that aren't up to temp, varying loads, pot holes, etc. Street use requires more pressure than track use to be safe.

Current Cars: 2005 IR/IR M3, 2001 LMB/blk M5,04 M3 wagon, 2017 i3
Past cars: 04 M3, 03 530i, 96 M3, S50B32 e36 M3 CM race car

Last edited by Obioban; Tue, May-11-2010 at 03:08:46 AM.
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