Project Update for April 1, 2011: No April Fools silliness in here, just some thread questions, my answers & the logic behind them.
First off, I don't mean to be argumentative or sound like a know-it-all, because I surely do not. Let me try to explain why I keep saying a wheel that "fits" or "doesn't fit". I strongly believe using as much tire width as you can possibly fit, and sometimes even more (flares), when the class allows it. And to use the proper wheel width for a given tire, if not more. So I go to great lengths to maximize wheel and tire width on my cars.
I have been test fitting, measuring and weighing race wheels for 20+ years, and have amassed a lot of data, so I just cannot believe almost anything I read on the interwebs about wheel and tire data. As we all here know, most of the "facts" posted on most forums are just regurgitated crap someone else read somewhere. You see it enough times and it becomes fact, even when its bunk. Even data published on websites (
especially wheel weights) or from wheel retailers is often incorrect. Its shocking to me how few of the population knows how to weigh a freagin wheel accurately. I've sent more than a couple of sets of wheels back for a refund when their published/promised weights were off by 3 or more pounds (I warned them up front and they agreed to that stipulation each time). I'm not prejudicial about my skepticism -
I simply don't believe anybody. 
I have to see it with my own eyes. I might as well be from Missouri... since you have
to show me.
So if someone says "this wheel fits" or "this wheel weighs about X", I need to see a picture. Or a dozen. And then measure the wheel for myself to verify width, backspace and weight.
Huge skeptic. Then I'll still want to see the car raced (load the suspension up and see if the tire touches) and look at the wheelwells for tire residue or watch for smoke. I've posted about certain tires not fitting a given car and than seen the inevitable "I race on that giant tire and it fits!" posts. Then later see them at an autocross or the track and watch as plumes of tire smoke pour out of their car. Or watch as they crawl around at half speed, so they never load up the suspension or tires. So my definition of "what fits" is probably different from someone else's.
And different racing conditions have different tire clearance requirements. A typical
autocross car sees only
spikes of G-loading (slaloms and small turns) but on a
road course everything happens SOOO SLOOOOWLY... with loooong turns... so you tend to load the suspension up laterally for much longer periods of time, and see higher g loading. If you touch the curbs at all that can load the suspension even further. If a tire rubs a bit on an autocross car, what's the worst that can happen? You're never on course for more than 60 seconds, and you can check for the the tire rubbing and residue after each run when in doubt. On track you are out there for 20+ minutes, and a lot can happen in that time if you have a tire touching a fender...
When we stuffed 18x10" wheels and 265/35/18s on my E46 330 (above) it worked fine on the street and even autocross, but when I ran it at the track in TTD the rears would rub the outboard upper section of the fenders BADLY. It took hours of massaging the rear fenders - and proper tire testing with the shock on the bumpstops without a spring installed - to clearance it fully for track use.
So, let's see some pics...
Originally Posted by blackbolt9
How much better do you want them to fit? JBS Motorsports Boss 302R with the BBS wheel, no spacers on the rear. Photo stolen from Rehagen website, I assume taken by Wes Duenkel
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Hmm... OK, from that angle that wheel looks like it fits... its a little close in the rear, but it would probably work.
So are you telling me the GA cars use the cast BBS wheel? I've
heard (there I go using second hand info!) that there's
another 18x10" mesh wheel that BBS makes (at double the cost) for the GA teams that has a different offset for the rear. Of course if you're going to GRAND AM races and working at Rehagen then you'd know this to be true or false better than me, so I will defer to you. What's the skinny - is there indeed a
street version of this 18x10" BBS wheel, and a different GA wheel?
And as for the 7.0" backspacing claim I made, I trusted the interwebs and look - its burned me again. The
early data I found on Rehagen's website about the cast 18x10" BBS showed that it had a
7" backspacing and weighed 20-21 lbs. I literally cut and pasted that data from the website right
into the caption on this picture, last year. And of course there's the $637 cost.
Since then I've tested an 18x10 with 7" backspace on the rear and it stuck out on my car a bit more than I liked. But if its now showing to be a 7.2" B.S. wheel, that would indeed fit better out back (barely), and that is also the most backspacing you can get away with on the front before losing clearance to the strut. So if its now showing as a 7.2" backspacing then that's probably pretty darn good. But did someone say you still have to use a spacer up front to clear the caliper?? That seems like an odd requirement for a $637 wheel...
But If I was going to spend
over $600 on a 18x10" wheel it damn sure wouldn't be a heavy-ish cast wheel. CCW monoblocks are
only $700 each (ha! only), and can be custom made to your specs. Very strong, might even be light (depending on who you believe - I believe calibrated, digital scales, but have yet to see these wheels pictured atop one). And if I was going to to make a custom set of wheels for this car for track use, I'd make them 10.5" front and rear, and maybe even 11" on the back. If I wasn't running NASA TTA with its imbalanced points penalties for tire width, I'd put as much tire under this fat-assed Mustang as we could fit. Probably 295 fronts and 315 rears. But tire width is heavily penalized in NASA Time Trial... anything more than a 285mm and I'm looking at a class bump up to TTS, so that's not going to work. Since I can only afford the class points for a 285 (grumble) then a 10" wheel is sufficient, therefore its easier to make a single wheel fit front and rear. And therefore not really beneficial to make a custom set of wheels. And hence why I'm
spinning around in circles trying to find an 18x10" or 10.5" 1-piece wheel that's off-the-shelf and under $400 each.
And I think my comments were misconstrued (and poorly written) about lightweight wheels - the autocross set I need (18x9) can afford to be very light, as running over cones in a parking lot doesn't take the same strength of wheel as track abuse. But even on track this car isn't raced W2W (only TT + HPDE), so it doesn't see the "fighting for the lead" type of abuse the Continental GA cars would normally, so it can probably afford to be a bit lighter than what the GRAND AM teams use.
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