Narrowing Rear end for a "Fat Lip"

[LUACE]

I am looking into narrowing my rear end for my 68 Camaro (Mini Tubs and BMR torque arm), hoping to get that “fat lip” look. I believe the standard length for a first gen is 60” and considering narrowing 2-4 inches on each side. Since many of you on the site have already gone through this I am hoping for some feedback to avoid irreversible mistakes. I’ve heard that narrowing can cause wheel flex and braking issues and other complications, so I want to make sure I don’t cut too much. In addition, I am looking for what size wheels and backspacing you guys are running. Thanks.

[LUACE]

What would be the ideal wheel size and BS if i am planning on running 335x30x18 in the rear.

[DriverzInc]

"ideal" is a relative term, but from a structural stand point, it would be best to run as close to a "zero" offset as possible, which means putting the center of the wheel as close to center in the hoop. This will not put added stress on either side of the wheel, thus maximizing weight distribution, and less wear on your axle bearings.

That being said, the most popular fit is a 12" wheel with a 5.5" BS. This puts the center of the wheel close to the middle of the hoop, taking into account cross section of the forging, and pad length. A 12" wheel measures 13" overall in width. Take into account that the thickness of the spokes (depending on manufacturer) is usually .875-1.5" thick, and at a 5.5" BS, the flange of the wheel, either welded or bolted, is close to the center of the said 13".

If you need more help, give us a call... we've been doing this for a long time, and can offer some good advice: 1-866-694-5940

[JayR]

You would also be way ahead of the game by building the wheels first, then mocking them up under the car and measuring between them because it is far easier to measure for the rearend than it is for the wheels and tires.

[LUACE]

Thanks Jon. Looking forward to doing business with you.

[aronhk_md]

Not to argue with Jon, but in Herb Adam's Chassis Engineering book he covers performance and race car chassis setup. He specifically mentions that the ideal offset is a negative one placing the hub deep inside the wheel....toward its outer edge. Since he was involved in GM design for many years, my thinking is thats why all the modern cars including BMW, GM, and all the rest have gone with very negative offsets. He didnt explain wheel design per se, but he made a point to mention it. Perhaps it has to do with the stressors on the outside wheel during cornering. From what I know of physics I believe the stressors on the hub will be less if placed so.

So what I've read is a zero offset isnt ideal, and technically doing a minitub, keeping a wide axle, and having very little outside wheel "lip" is the performance ticket........even if we may not like the look as much.

[jgaches]

You're right but you'll quickly find not only the wheel tub interference you talked about, but you'll also have no room for your lower control arm. You also want the shock and spring placed as far out on the corner as you can but on a stick rearend your packaing option are limited unless you run the shock at a steep angle to reach into the wheel hoop. Another performance no, no. Everything is a trade off :)

[daredvl22]

You would also be way ahead of the game by building the wheels first, then mocking them up under the car and measuring between them because it is far easier to measure for the rearend than it is for the wheels and tires.

Exactly what I'm doing. Only need to install 1 more 1/4 panel, roll the wheel lip, and break out the measuring tape. How does the saying go, "measure twice, cut once". Or in my case measure 15 times, sleep on it, got back the next day re-measure again....:)