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Has anyone successfully mounting anything larger than 315's on the rear of their 70-72 Cutlass S? I would love to run 345-25-20 or 345-30-19 on the rear. I'm curious if many have done so.
Nope. Just the exact amount of back spacing on the wheel ….which for these tires is 5.5”
I imagine if the tire didn’t have such a big sidewall, you MIGHT be able to go with 6” BS?
We tried with a 345 on my 71 442 and it literally goes from the frame rail to the lip. With a 12" wheel a 345 is 13.8" to 14.1" wide. The measurement from frame rail to the lip on my 442 was about 13.7". And that's with the lip rolled. You would either have to notch the frame to the inside or bulge out the quarters/do flares. As mentioned by others 325 (13" to 13.2") is the max you can go w/o major mods and it has to be centered/backspaced perfectly for the 325 to work. Here's a pic of a 345 touching on both sides.
-Joe
Last edited by 71 OLDS; November 9th, 2023 at 10:02 AM.
We tried with a 345 on my 71 442 and it literally goes from the frame rail to the lip. With a 12" wheel a 345 is 13.8" to 14.1" wide. The measurement from frame rail to the lip on my 442 was about 13.7". And that's with the lip rolled. You would either have to notch the frame to the inside or bulge out the quarters/do flares. As mentioned by others 325 (13" to 13.2") is the max you can go w/o major mods and it has to be centered/backspaced perfectly for the 325 to work. Here's a pic of a 345 touching on both sides.
-Joe
Thanks for posting. That's the information that i was looking for. What size tire and wheel did you end up using?
The car is in paint and body jail with lots of custom projects being done. It currently has 305/40/18s on the rear and 265/40/18s on the front but I did purchase my autocross wheels and tires. For the rear it's 11.5" wheels w/325/30/19s and on the front it's 11" wheels with 315/30/18s. The rears won't need any mods but lots of work will need to be done to get the 315s to turn lock to lock on the front. Here's a few pics with the 305/265:
Here's a pic of the new 19x11.5 rear wheel w/o the rocket sticker. Hope to have some pics with the new wheels/tires mounted in the next few weeks since all the front fender mods will be starting soon.
Last edited by 71 OLDS; November 11th, 2023 at 12:18 AM.
November 8th, 2023, 11:50 AM
