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      10-21-2010, 12:10 PM   #23
DerekSelmanRacing
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Suspension is stock sport with the exception of ft camber plates; running about -2.9. I suppose that could make a difference.
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      10-21-2010, 12:18 PM   #24
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Quote:
Originally Posted by Dubbedown View Post
but if i run 235, what's the lowest offset i can go on a 8.5" in the front, 45mm? maybe i will go staggered after all....
8.5" x et40 = outer movement of +13mm (closer to fender)
= inner movement of -1mm (farther from strut)

inner tire clearance should remain the same as stock, outer clearance should be the same as moving to your E9x staggered set (197's right?) from stock. because you're increasing the rim width to 8.5", the center line of the tire/rim will move closer to the center of the car by roughly 1/8" compaired to the E9x 197's, BUT it's still 1/8" GREATER track width than the stock 8.0" x et47.

so...

you'll gain contact area, relieve bearing stress, shouldn't rub, and narrow track vs. the 197's

or...

you'll gain contact area, slightly stress bearings, shouldn't rub, and widen track vs. stock

holy smokes... i need more coffee!
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      10-21-2010, 12:31 PM   #25
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for what it's worth and for viewing pleasure... stock sport non-///m E86 alignment specs

Front Camber = range of -0.5 deg to -1.4 deg
Front Toe = +0.05 deg to +0.18 deg (toe in)

Rear Camber = -2.6 deg to -3.1 deg
Rear Toe = +0.17 deg to +0.37 deg (toe in)

as long as these values are the same left to right, the vehicle is considered to have appropriate alignment.
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      10-21-2010, 01:13 PM   #26
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Quote:
Originally Posted by v3.0si View Post
this is good news for dubbedown! if JCz04Bimmer was able to run 265's on the front of his ///m, certainly a 245 square setup will fit on a non-///m. clearly my math earlier is missing a variable...
The variable is CAMBER and, to a lesser extent, the springs you are running. If you run more than 2.5 degrees of negative camber, you have more flexibility. You can run a more aggressive offset (lower number; wheels further out) which keeps you from getting close to the damper/spring while still clearing the outside fender wall. Also, if you run a progressive spring (OEM, KW, H&R, etc) you have a bit less room on the strut-side. If you run a linear spring (TC Kline, Ground Control), then you have a bit more room on the strut-side.

I can't remember what the offset was when I ran the 265's but I think it was around 40. Maybe high 30s.

My advise when it comes to fitting oversized tires is to go with a less aggressive offset (read: high number) and use spacers to get it just right. When spacers are installed properly, they're absolutely fine.
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      10-22-2010, 10:12 AM   #27
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Quote:
Originally Posted by DerekSelmanRacing View Post
Suspension is stock sport with the exception of ft camber plates; running about -2.9. I suppose that could make a difference.
Interesting, end of day I'd like to aviod buying camber plates just to get these fit. The wheels I'm looking at are 18x8.5 et42 on all 4 corners.. I know the 235/40 is too tall so it seems like either 225/40 or 245/35, and I'd like to go with the latter.
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      10-22-2010, 11:49 AM   #28
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i just looked at an '08 ///m coupe with this setup...

9.0" x et 40 with 265/35R18's in front, no rubbing at the fender liner and minor rubbing on the strut tower. the car was lowered on H&R's.

this is a good sign that 245/35R18's on 8.5" x et42's will fit.
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      10-22-2010, 12:06 PM   #29
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Quote:
Originally Posted by v3.0si View Post
i just looked at an '08 ///m coupe with this setup...

9.0" x et 40 with 265/35R18's in front, no rubbing at the fender liner and minor rubbing on the strut tower. the car was lowered on H&R's.

this is a good sign that 245/35R18's on 8.5" x et42's will fit.
thanks again... i just didn't want to commit on new wheels, and then let alone buy new tires just to find out i'm stuck with an expensive package that won't work.
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      10-22-2010, 12:52 PM   #30
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This is one area that I haven't really delve into, since 1) I don't run spacers for track and 2) The offsets I run is typically within a few mm of factory. There's a couple of points I'd like to contribute though.

First, the talk about scrub radius only affects the front end, but increasing/decreasing offset also affects the rear. One thing few takes into consideration, is that by decreasing the negative offset, you are in effect decreasing the wheel rate if you do not change the springs, since the "lever" effect is increased. Especially on the rear, where the springs are typically mounted further inboard than the front. This is one of the reasons why I never really was all that interested in messing with the wheel offset, and unless clearance is an issue I typically stay as close to OEM offset as possible, since the effects are somewhat unpredictable and non-linear...The same decrease in negative offset front AND rear may actually result in increased understeer.

On my E30 318is, I had to run a 5mm spacer up front to clear the brakes with my generic Civic rims (when the brake pads are below 5mm the wheel fits fine. Brand new pads would have the caliper catch the back side of the spokes). When I took it to Sears Point it actually behaved better than I expected, so even a small change in offset could have some pretty dramatic effect. But it is definitely one of those things where, to me, the goal is to fit the biggest and widest set of tires and rims possible, not use offset to fine-tune my suspension geometry.
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      10-22-2010, 01:53 PM   #31
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Quote:
Originally Posted by The HACK View Post
...definitely one of those things where, to me, the goal is to fit the biggest and widest set of tires and rims possible, not use offset to fine-tune my suspension geometry.
for comparison sake... what are the specs on your wheels and tires for your track setup?

also, your lever analogy has credence (you already knew that though). a smaller, more aggressive offset makes the effective axle length longer, therefore reducing the amount of force required to compress the suspension overall.

how much change in offest is too much? if the change is only a few mm in offset, then increasing treadwidth anymore than... say... 10mm, will most likely cause clearance issues with the inner sidewall and the strut tower.

again... i have no experience on track, so this is all new from a performance aspect for me. i'm sure others reading will find this very interesting, and may be able to apply your experience with these cars in their own ways.

HACK - thanks for contributing!
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      10-22-2010, 04:24 PM   #32
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I chatted about this with a local driving school instructor and he suggested that a change of 10-12mm should "fall into the subtle category". For street driving, it shouldn't be that perceptible. For track driving, I expect you'd see much larger differences with camber or better tires.
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      10-22-2010, 04:31 PM   #33
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I use 245F/275R Nitto NT-01 on STOCK rims for my track setup.
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      10-22-2010, 04:36 PM   #34
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