Mauch712

Hello Group,
I have a 1970 Olds CS Coupe and was looking to install 18" rims all the way around and I did a disk brake conversion on all 4. I am having a hard time finding any threads on similar topics to help guide me in the right direction to find a proper fit, "backspacing, offset and tire measurements". I would like to have a wider tire in the back and was looking at the Foose Legend Chrome 5. Not any good videos out there showing a guy how to find these measurements. Any info you may have would be great.
Thanks
Mauch712

oddball

There's the wheel and tire size database sticky in this sub-forum.... That's the best single location. Note that when looking at backspacing you can (to a degree) ignore the wheel height. Backspacing problems with the tires are the same whether it's a 14" rim or a 18" rim - it's the tire height and width that matters there. Sometimes you have to change the backspace for specific clearance problems with brake calipers, but 18" rims will clear everything but the very largest stuff (talking >13" rotor, 6 piston jobs).

In general 8" wheels work well with 4.5" BS, 10" wheels with 5.5" BS. You basically want the wheel just inboard from center. 70-72's can take 10" wide wheels in the back depending on exhaust clearance.
The best way to do it is buy the tires you want then get a test fit jig (or make one). One of the guys on here even loans his out since they're quite pricey.

71 OLDS

I'm running 18's on my 71 Convertible. Here are my specs:

18x8 rims (5.25” BS- {was 4.5}) w/Nitto*** 555 255/45/18s 10”sw – 26.97”d

18x10 rims (6.0” BS – {was 5.5}) w/Nitto*** 555r 305/45/18s drag radials 12.02”sw – 28.78”d

Note the "was" part - that applies to stock setup. the BS changed in the front because of spindles and thicker rotors and in the rear because of disk brakes/thicker rotors. If you plan to upgrade spindles and rotors I would suggest you wait and get those first or buy tires a few sizes down (skinnier) and leave room for the change when you make the upgrades. The 305s in the rear are the max for an 18" wheel. You will need to roll the wheel well lips and massage the inner wheel wells a little and have the wheel and tire perfectly centered. If you don't want to deal with all that just go with a 295 or smaller. Here's a few pics:

H06Abb5.jpg
CVE2Qbk.jpg
D0oGWIb.jpg
pcOPh5r.jpg

Mauch712

71 OLDS

Thanks - it's lowered 2" in the front - .8" from the spindle and 1.2" from the spring. 1" in the rear from the spring.

oddball

71 - what disc setup did you go with? I didn't think any of the front kits moved the rim face that much.

71 OLDS

Originally it was the Baer Track 13" rotors, then when I swapped from B-body spindles to AFX Spindles I had to change to Baer 13" GT Rotors. It's a combo of the spindle and rotor that pushes the rim out. My old B-body spindle pushed the wheel out .25 more than my new AFX spindle so now my perfect BS should be 5 not 5.25. At full lock the front tires hit my sway bar on the inside. My Lee 800 steering box has stops built in for a 5 BS so that has been sent back to Lee to have them add new stops so that it won't hit the sway bar anymore. I'm not sure exactly how much the rotor pushes out vs the spindle but they both contribute. I agree with the comment above that a 4.5 BS is perfect on an 8" front rim if you are 100% stock. I had that on my old setup (before the spindles and rotors) but once you start making upgrades things change. And that's where the "might as wells" start. Why get 18" rims and not add bigger rotors? If you have the rims, tires, and rotors, why not correct the suspension geometry? What about the steering geometry? etc etc.