2004-2007 Cadillac CTS-V Performance Mods Discussion, How to: Widen your rear wheels in Cadillac CTS-V Series Forum - 2004 - 2007; Haven't done it yet - still trying to get a hold of some wheels - but I found a reputiable ...
Talked to Eric a few times... seems like a very knowledgeable guy. His shop widens ~100 wheels a week - lots of drag and road-racers looking for wider wheels. He says he has never had a failure.
He does not cut the wheel in the middle and add an additional 'band' (2 weld seams) like most places do. Instead, he cuts the inside of the wheel off and welds on a brand new "wheel blank" from an aftermarket 3-piece wheel vendor (Budnik wheels) - thus 1 weld seam, and he says he can widen *any* wheel. He can widen to any size to the 1/1000 of an inch.
Two week turn around time... and costs $300 a wheel for 18" wheels. (Didn't ask about a GP).
After doing some fairly precise measuring, i came up with:
Wheels only: +13/16" wider -> 9.31" wheel
Wheels + spacer: +15/16" wider -> 9.44" wheel
Wheels + spacer + wheel lugs: +1 5/16" wider -> 9.81" wheel
All with 275/40/18 tires... tire clearance is not an issue.
The maximum the wheels can be widened without using a spacer is 13/16". I dont believe you can go wider... the problem is the inside lip of the wheel hitting the trailing arm, all the other suspension pieces are over 1" from the wheel. I did talk to BMR, they said their trailing arms would not give any more clearance.
Wheels + spacer
The maximum the wheels can be widened with a spacer is 15/16". The maximum spacer size I believe can be safely used is 1/8" (13/16" + 1/8" spacer = 15/16"). I tried a 1/4" spacer, and the wheel lugs are not long enough. A good rule of thumb is 7 full turns of the lug nuts, with a 1/4" spacer you get 4-5 turns.
Exposed threads on lug nuts:
But the wheels look good pushed out 1/4"... they fill up the wheel well nicely:
Wheels + spacer + wheel lugs
The ultimate widened wheel is +1 5/16". You'll need a 1/2" spacer and longer wheel lugs. (13/16" + 1/2" spacer = 1 5/16"). I believe pushing the wheels out 1/2" will get them flush with the fenders. But I have no idea where to get longer wheel lugs from.
The longer wheel lug route is too much work and hassle for me. If I do this, i'll get 9.44" wheels made and use an 1/8" spacer... perfect for 275/40/18 tires!
Dreamin, Lasstss, other wheel/tire & ruler whizzes:
Do you have any feel for whether a stock wheel widened to 9" would fit in front? Seems like it would. And what size tire? Just doing some quick mm/in noodling, seems like the widest tire that would fit that rim is a 265/40.
Call me tame, but I'd like to run the same rims & tires all around. Mmmm, rotation GOOD!
This might be a stupid question, but, is it possible when the wheels are widened to have whatever spacer that is going to be used welded to the wheels? If so, then what about using the thicker spacer, welded in place and then counterboring the lug nut holes so that you still get enough turns of the lug nut with the stock lugs?
Law: a 9" will fit in front but you'll need a spacer... probably 1/4" spacer... Not sure if 265/40 will fit... it *should*.
If you're close to Eric Vaughn Machine, you should go there and maybe they'll measure and tell you exactly how much you can widen FR & RR
Wild: I would just install longer lug bolts... drilling the lug nut holes deeper on the stock wheels isn't a good idea... and good luck balancing the wheels! Installing longer bolts isn't that big of a deal.