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(E36 M3) Lower CG/big ri

Bob Tunnell said, regarding offsets and clearance...

> I just wanted to comment on one statement that Carl made that may be
> slightly misleading regarding wide wheels with a lowered suspension.

>  Carl said:
> 
> >Now, the problem of clearance and wide rims.  I do not think that
> >the 8.5" rims will be a problem, especially with 235/40/17 BFG
> >R1's....IF they existed. They don't.  <<snip>>  The size you REALLY
> >want is 245/40/17, which DOES exist in a Hoosier.  Problem is, it
> >probably WON'T fit without flaring your rear fenders, and adding
> >spacers to both front and rear.  It will fit with the stock ride
> >height, but NOT if you are lowered.
 
to which Bob replied, quite accurately...
> I agree with all of that except that you will not need spacers on
> the rear, only the front.  In fact, you will need to *increase* the
> offset (bigger number, tire closer to the chassis) in the rear to
> give more clearance for the fenders, unless you're doing *major*
> flaring.  There's plenty of clearance between the tire and the rear
> shock/spring, although a stock muffler will get a mild rub now and
> then.

Carl now sheepishly corrects himself...
I recently responded to this before really thinking.  Bob is right:  
The *rear* wheels do not need spacers, which would take the outer edge of 
the tire even *closer* to the fender, increasing the rub.  The rear 
wheel needs more *offset*, as Bob said, which will move it in closer 
to the center of the car, and away from the fender well .  I stand by 
my comment on "trial and error," however, in that the inner edge of 
the tire might now rub on your muffler, if it is of a different size 
than the stock muffler.  I rub on my Supersprint, even with the 
"little" 235/45/17's.

Bob goes on to suggest...
> I experimented with 8.5" rear wheels with 43mm offset (stock is
> 41mm) on my stock-height M3.  The 235/45/17 BFG R1's fit without any
> problem and would also fit on a lower car with that tire.  However,
> when I went to the 255/40/17 (same height as the 234/45, but .8"
> wider at the contact patch) they fit at stock ride height, but would
> rub slightly as the car was compressed on the suspension.  I'd
> estimate another 2-3mm shaved off the hub face would eliminate the
> problem, but that makes me nervous from a strength standpoint. If I
> had wheels custom made, I'd order them with 46mm offset, but that's
> still just an estimate.  YMMV.

The 235/45 will fit with a *stock, 41mm offset*, even on a lowered 
car (this is the setup that I now have) .  With the caveat that the 
muffler "might" rub, I would now agree with Bob.  The 46mm offset on 
the rear wheels would very likely accomodate a 245/40/17, even 
without flairing.

The front wheels would require wheel *spacers* to keep the larger 
wheels from rubbing on the lower spring perches, especially of your 
car is lowered.

CONCLUSION:  at least for now, it sounds like the setup is the 
following, assuming that you want to run the same size wheels and 
tires front and back:  you will want to have the same offset on all 
four wheels, so that you can rotate;  46mm, 5mm over stock, sounds 
about right.  You will then add spacers to the front hubs.  I think 
that the spacers would have to be quite thick, to accomodate the new 
increased offset, and then to take the wheel out to avoid rubbing on 
the spring perches.  If the spacers are more than 20mm, which I think 
that they might be, you will need to use the spacers that have built 
in lugs.  

This is all very difficult.  Nobody said having this much fun was 
going to be easy!

Carl

please, correct me if you think that I am getting off base.  This is 
definately not intended to be taken as anything other than theory.


> In the front, I think Carl's right about needing the spacer. The
> most obvious clearance problems are between the tire and the strut,
> not the fender.
> 
> One more thing...a company somewhere in the southeast called MRT
> (Marsh Race Tires) makes carbon fibre wheels for sprint and other
> circle track cars.  They're ugly as sin, but light as a feather.  I
> checked on them a couple years ago when I was desperately looking
> for ways to make my 318is faster and they weren't as expensive as
> you might imagine -- something like $300-400 each for 15".  I never
> ordered any because they didn't make them in 14", but I'm going to
> look into them again now that I'm in the 17" market.  I don't have
> their number handy, but I'll pass it along when I find it again. 
> (Be prepared for perhaps the most entertaining phone call you've had
> in a while... "You wunt'em fer a whut?!")
> 
> Anyway... good luck and happy lightening and lowering!
> 
> Bob Tunnell
> bobt@domain.elided
Carl R. Buckland
1000 Boston Bldg
Nine Exchange Place
Salt Lake City, Utah  84111
801-531-6686
Fax 531-6690
E Mail buckland@domain.elided