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Unread 11-23-2009, 10:36 PM
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Fair! Fair! is offline
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Join Date: Jul 2004
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Default Re: Vorshlag $2010 GRM Challenge car - BMW E30 V8

Project Update #6: Sorry for the double update on the same night, but I didn't get a chance to update after the weekend cleaning thrash and we had an unexpected work night tonight, on a Monday. I broke it up because they were totally different aspects of the project... this is the Wheel and Tire and Flare update which many of you have been asking for.

I got back to the shop late Friday afternoon from dropping off and picking up parts only to find four big boxes from Aero Racing Wheels had arrived. This was the 15x10" steel "lightweight" wheels that someone on Corner-Carvers found on Aero's "overstock closeout" web page for $50/each, then Costas noticed and called me about early one morning, and I bought them minutes later. $50 each for chrome 15x10" wheels is insane, but its totally legit. First thing we did this evening was open a box and weigh a wheel...

The observant ones here will notice - "hey, those are 5 lug GM pattern wheels!" Right you are. We had planned on using custom built, steel 15x10" wheels made with the BMW 4 x 100mm pattern, but the costs on custom built steel wheels exceed our budget constraints. Hey, I'd use D-Force 18x10s if we had room in the budget, but you gotta do what you gotta do. So yea, we have to do a 5-lug swap to make them fit, but we managed to get the parts cheaply.

We rummaged around the junk yards and bought some 5-lug E36 non-M hubs E36/rotors/calipers for dirt (who wants the non-M stuff, anyway?) and even found some used E36 front struts for a song, so we're going to swap to a 5-lug and E36 brakes/front struts. Opens up a lot more options to us, really, as the E30 front suspension is kind of an albatross. The E30 front strut housing is welded to the spindle, so your strut choices are very limited. We really didn't want to go to 5-lugs, but it allows us to use inexpensive and plentiful GM pattern circle track wheels, and this was cheaper in the end.

We were excited when we saw the wheel weights at only 21.5 pounds because many steel wheels in this size can exceed 25-30 pounds (the D-Force 18x10" is 19 pounds, for comparison, so its not that much heavier). Aero makes this "85 series" steel wheel for circle track cars with a thinner gauge material, but its still rated for both dirt and asphalt (high grip) use on big 3500 pound cars, so our little 2300 pound E30 should be no problem. The 5 x 4-3/4" (120.6mm) GM bolt circle is close to the BMW 5 x 120 mm bolt circle, so with the E36 5-lug swap it should work well enough. Normally I would never recommend using these differing bolt pattern wheels & hubs together, but for auto-x speeds (and our extreme budget constraints!) its "safe enough". We don't even have bumpers, so its not like this will be a daily driver or W2W race car, you know?

Team member Chris also got his hands on a free 275/35/15 Hoosier A6, which is totally worn out but good for mock-up testing. We weighed and measured it too.

The 275 looks comically wide next to the E30's 195/60/14 tires... but remarkably is almost the exact same height.

Left: side-by-side comparison. Right: E36 rotors/hubs/calipers fit within the 15x10" wheel

So once we weighed the wheel and tire it was time for some mockups on the car, of course. McCall got the RF wheel in place with a tiny spacer and the rear went on with none, so we got the backspace almost dead nuts perfect on the first shot. Damn, we're good....

Left: Bolted the wheel on the rear with no spacer and it has a fingers width to the control arm. Perfect. Center: Rear wheel sticks out ~1.5". Right: Front wheel sticks out about 2"

The wheel is held on with one lone stud and lug nut at each corner, only good enough for mockup (we haven't done the 5-lug swap yet). While McCall and David worked on the LF fender repairs, Matt and I started mocking up flares for the right side wheels. The finished mockups looked better than any of us had imagined, but we're in for some fun turning these into steel! I'll go mount the 275mm tire on one of the wheels using the tire machine at a friend's shop this week, then we can do the 5-lug swap and mount the wheel/tire combo on each corner "for real".

Matt and I made a new rear fender mockup in corrugated

Once we get the car at ride height I can then start cutting the stock fenders for tire clearance and then start looking for sheet steel at the scrap yard to make the flares out of. Someone showed me a trick to make the edges of box flares have perfectly rounded corners, which also gives you a structure to build off of, so I'm going to try this technique on this car.

So far so good... the steel versions get started soon

As great as the wheel and flare mockups looked, David found a picture of an E30 he built previously that looked so amazing we ignored the wheels. He gave us some incredible ideas for front and rear bumper covers that cost under $30/each. I'm not allowed to share more than that for now, so I'll just end this update with the usual "more soon..."

Last edited by Fair!; 11-24-2009 at 12:49 AM.
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