Fitting BMW wheels to the CTS



In some ways the CTSC is a very confused car. It has some elements of a track day or drag car (staggered wheels and tires, very low profile fast wearing best in the dry tires, LSD.) But not "enough" to be sucessful. The Crossfire coupe is much better for that.

I do not care for wheels with many spokes or eraser tires, have fitted more compliant 235x60R17s on five spokeish BMW wheels that took a bit of fettling but IMNSHO look much better - a lot like the American Racing Estrellia that I have always liked.



The difference was that I had bought the BMW wheels for a pittance and wheels that are 5x120 and have 14mm studs are not common (except in modern German cars like Mercedes, Audi, and Opel).

Like many things that happen the wheels were on one sde of the garage and the CTS was on the other and it was raining...

However a mentioned before there was an interferance between the spokes and the brake caliper - bad in front and minor in rear.



To solve this a set of 8mm wheel spacers were puchased. 10mm are common and cheaper but I wanted the minimum offset change to minimise potential bump-steer. On another car I had gone from 46mm factory wheel offset to 38mm wheels with no issues.

However the 8mm spacers created another issue, insufficient threads on wheelstuds for full engagement. This had two solutions: longer wheel studs (hard to return to stock, difficut, expensive) or different lug nuts (easy, cheap).

So set of 14mmx1.5 "tuner" lug nuts with a .300" extended shank were procured.



These have a full eight turns of engagement.

Next there was a bit of controversy: BMW called for 100 lb-ft torque. Cadillac 140 lb-ft. Personaly think 100 lb-ft is "enough" and the 140 spec was to solve and issue with the J55 brakes. I have smaller JE5 brakes. And on the gripping hand 140 ft-lb is inside the elastic range of a 14 mm nut so what the hay.

The end result came out very well and while clearance on the caliper is minimal (about 1 mm) since the caliper and the wheel are fixed in relationship to each other, several tanks of gas have shown no rubbing or clearance issues on any wheel.



This end result is part of my changing the CTSC from a peudo track day car to a great GT car. It works for me.

Note: after about 1,000 miles I noted some indication of contact between the wheel and the caliper bar on the passenger side on hard braking so have applied a die grinder to bevel the edge of the bar by about .010" on both front wheels. I then painted the surface to tell easily if there is any continued contact.The clearance is now over .040". Anyone attempting this I would suggest making sure you have at least the same clearance on the caliper bar and no play in the wheel bearings.

No two cars are exacly alike. Any time you try cobbling together something like this make sure you have proper clearances. Caveat y'all.

And when retorquing the wheels I found thwo lug nuts that would not torque. At first I thought the issue was a stretched stud but on examination it turned out to be a cracked lug nut. I have never seen this happen before.



Now when buying nuts on ebay, they often do not provide full specs. In this case the OD of the extended shank measured .60" which indicated a .024" wall thickness. I have since acquired a set of Gorilla lug nuts, #68148 which have a .62" diameter and a .034" wall thickness. These should be about 40% stronger than the first set.

Right now I have changed back to the 18's but plan to try the BMW wheels again now that I have bevelled the bars and have the Gorilla nuts. I will also reduce the rear space to 5mm but need to keep the 8s in front to clear the caliper. RSN.
Copyright (C) 2019 by Padgett, notary sojac.