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      07-06-2008, 04:14 PM   #17
sg335
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Drives: 335i
Join Date: Apr 2007
Location: Los Angeles

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OK. So...
There is a concern that decreasing the width of the rear wheel can cause more oversteer in certain offsets. Given the stock 9.5" wheel with an ET23, moving to a 9.0" wheel with an ET30 (TRM with ET35 plus 5mm spacer) will put the rear wheel 1mm closer to the inside and 13mm farther away from the fender lip. This does not widen the track and should produce a looser feel. In order to have the same width in track, you would need to run an offset of ET17 on a 9.0" wheel to match the stock wheel/offset. This would put the wheel at the same place in relation to the fender lip, but would put it 12mm farther away from the inside. Given a constant center line, this would widen the track and should take away some oversteer. Running 265's on a 9.0 vs 265's on a 9.5 will also provide some additional squirm and feel of increased oversteer. A 20mm spacer could be used in the rear on a 9.0 ET35 wheel which would make it a ET15. A 10mm spacer on the ET35 wheel will give it an offset of ET25 and this would put the 9.0 wheel at 4mm farther away from the inside, and 8mm farther away from the fender lip. Maybe the best starting place in the rear that will provide less oversteer than the 5mm spacer does.

As for the front, the stock wheel is 8.5" ET29. Using the TRM wheel at 9.0" ET35 with a 5mm spacer, you end up at ET30, which will put the wheel 7mm closer to the strut and 5mm closer to the fender lip. A 10mm spacer will provide an effective ET25 offset, so the wheel will be 2mm closer to the strut and 10mm closer to the fender lip. Compared to running the rear stock wheel at 9.5" ET23 in the front, the 10mm spacer on a 9.0 provides 8mm more clearance to the fender lip, as the 9.5" ET23 wheel is 6mm closer to the strut and 18mm closer to the fender lip.

I would therefore suggest that when running a 9.0" ET35 wheel at all four corners, we should run a 5mm spacer in front and a 10mm spacer in the rear as a starting point to neutralize as best a possible the oversteer effect. 10mm spacer in front and a 5mm spacer will surely produce more oversteer, and no spacer in front and the 20mm spacer in the rear will produce the least amout of oversteer and probably more understeer than wanted.

Interesting details to discuss. This all changes of course when talking about a different wheel offset! Although the calculation difference from stock will still be easily computed. I have concern with a 9.5" wheel on the front especially when lowering the car, but DINAN seems to be able to do it in front with a larger tire. I don't think they would recommend it without their camber plates though. And I would have no concern with this type of agressive fitment if you run anything over -2.0 negative camber in the front.
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