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I am currently restoring my 1970 Cutlass. I am looking to get these rims. What size and backspacing would work? Also what tires would anyone recommend!
Preferably I would like my back tires thicker then the front. Any help would be great!
I'm guessing you were looking at these, but the link didn't work correctly.
Do a 15x8 in the rear with a 255/60/15 and a 15x7 in the front with a 235/60/15.
They don't have more than one offset for these, but they should fit the car just fine.
I like the Cragar SS rims myself.
A pair of 15x8 with 4.5 backspacing for the rear with 255/60/15 BF Gooderidge T/A's
A pair of 15x7 in the front with 235/60/15 .
That will fill the rear nicely. A new set of cargo coils or air shocks will lift it up just enough if you like a little more height in the rear as well.
Just my opinion,
Hope this helps
Eric
Welcome to the site, I merged your 2 threads. I would go with the 15x8 rear and 15x7 front. You may be able to get 275-60-15 in the rear.
There is no may about it. The 1970 - 1972 S body style has the largest rear wheel openings of any A body produced. A 15x10 will fit with a 295/50/15 with no mods with the right back spacing.
I like the Cragar SS rims myself.
A pair of 15x8 with 4.5 backspacing for the rear with 255/60/15 BF Gooderidge T/A's
A pair of 15x7 in the front with 235/60/15 .
Eric
I would second this combo. As for backspacing, I hate using that since backspace is dependent on wheel width. What you want is as close to zeor OFFSET as possible. Do the math to calculate what that means for backspace on your selected rim width. Don't forget that since backspace is measured from the inboard edge of the wheel and not the tire bead seating surface, it also depends on the exact shape and material of the wheel. Aluminum wheels tend to have a larger lip on the rim than steel ones.
In this diagram, note the difference between measurement "B", the wheel width, and "D", the backspace.
There is no may about it. The 1970 - 1972 S body style has the largest rear wheel openings of any A body produced. A 15x10 will fit with a 295/50/15 with no mods with the right back spacing.
What would the correct backspacing be for the 15x10 with 295/50/15? I'm coming up with 5", but hoping someone could verify. Thanks!
What would the correct backspacing be for the 15x10 with 295/50/15? I'm coming up with 5", but hoping someone could verify. Thanks!
It's actually 5.25" - 5.5", depending on the shape and thickness of the wheel lip. The 10" width is the inside dimension between the bead seating surfaces, and the wheel has an additional lip outboard of that, as you can see in the drawing above.
I have seen numerous posts by 1970-1972 Cutlass owners saying they are using 15x7 wheels with 235 and 15x8 with 255 tire widths (a few posted above in this thread). I have been researching myself what size tires fit properly on what size wheels, and those smaller wheels didn't come up as optimum for the respective tires where I found info. I am sure they work, because many have said so! Plus, who wants to buy new wheels if you don't have to!? However, should we be concerned in any way? Do the tires seat good on the wheels? Seems the smaller wheel widths might be pulling the walls inwards a bit farther than "recommended"!
I am looking into new wheels with a staggered 15" look with rear 255/60R15 and front 235/60R15, or possibly stick to my 14" SSIIIs wheels with 245/60/R14 all around. A lot to think about buying new wheels!
The following link is to a table I found to be identical at two separate sources. (Source: https://www.tyresizecalculator.com/c...rim-size-chart)
Any thoughts on all this? From this chart, the min wheel width for 235 width tire should be 7.5" and 255 should be a 8.5". The site does have a disclaimer to verify sizes with the tire/wheel manufacturer, so its always best to use the manufacturer specs!
Last edited by SXy71; April 25th, 2021 at 09:25 PM.
Reason: Updated what I am trying to decide!
First, you have a website with no information whatsoever on who developed it, where the data came from, or what was done to verify the data. Why do you believe them?
Second, the fact that you've seen the exact same information at two separate sites (and likely many more) is called COPY/PASTE. In the aerospace industry we have a saying: " a lie told twice is corroborated."
Is there a reason why you think that some nameless website is more accurate than information provided by the tire manufacturers?
BF Goodrich says that their 255/60-15 tires should be mounted on rims between 7.0" and 9.0" wide. They suggest that 275/60-15 tires should be mounted on rims between 7.5" and 9.5" wide. But hey, what do they know. They only design and manufacture these tires.
Ah, thanks Joe for the much better source - BF Goodrich individual tire size specs! I had missed that "rim width range" in the rather hidden pull-down menu when I was at that very BF Goodrich site earlier. And yes I know and agree, they should know best! What really makes me look stupid - besides your (strangely condescending) comments - is that the site I referenced even had a disclaimer to verify sizes with the manufacturer! I went ahead and added that disclaimer to my original post.
So yes, a BF Goodrich T/A Radial 255/60R15 should fit on a rim width from 7 to 9", and a 235/60R15 on a 6.5 to 8.5!
Ah, thanks Joe for the much better source - BF Goodrich individual tire size specs! I had missed that "rim width range" in the rather hidden pull-down menu when I was at that very BF Goodrich site earlier. And yes I know and agree, they should know best! What really makes me look stupid - besides your (strangely condescending) comments - is that the site I referenced even had a disclaimer to verify sizes with the manufacturer! I went ahead and added that disclaimer to my original post.
"Strangely condescending" is due to my amazement at repeated posts across nearly every forum I read, where people will swear by some information they read on the web from some nameless source. Sorry, I'm an engineer. I deal with hard data and verified sources. The fact that someone posts something on the interwebs doesn't make it true, and if you do enough research on the web, you'll find that many, many sites simply copy incorrect info from each other. When researching, use source material (ie, Oldsmobile factory literature, manufacturer's data sheets, etc) and not some third party site. Just the other day I had a disagreement with someone on the production numbers for my 62 wagon. That person was quoting some "standard catalog of American cars" or something and got a number that was 1/10 as many as Oldsmobile production data.
I am converting to 15 x 7 wheels ('70 Cutlass conv't.) as well. Currently have 225/70R14 tires. (26.4" diameter x 8.4" wide). Not looking to do staggered sizes front/rear. Considering 235/60R15 (26.1" diameter x 9.3" wide) tire or 245/60R15 (26.9" diameter x 9.6" wide) tire - both show compatible with 15 x 7 JJ wheel. Looking for a stock appearance (with larger 15" wheel of course) and good handling for cruising. Which tire size? Neither should cause any fender rub issues. The 245 tire size is over one inch wider than current tires. Is the 235 tire size the "better" choice? If so, why? Or is either tire a fine choice? Thanks.
That's a great point regarding the tire profile. According to the B.F. Goodrich site, the 245/60R15 has a sidewall profile of 5.8" vs. a sidewall profile of 5.6" for the 235/60R15 vs. a 6.2" sidewall profile for the current 225/70R14. I'll have to take that into consideration.
I previously had 15x8 Torq Thrusts on my ragtop - 245-60-R15 all around so I could rotate and change a spare if needed, but had 1" aluminum spacers on the rear drums to push the rear tires out a bit more for a stagger look without the mismatch. Excellent compromise for a street car if you want to keep it simple. the BS was 4.5" on those wheels so plenty of inner clearance from fender wells and suspension but they otherwise filled the wells up nicely.
I recently moved up to 17x8 TT's to take advantage of better tire options. Another great option if you have the notion!
I previously had 15x8 Torq Thrusts on my ragtop - 245-60-R15 all around so I could rotate and change a spare if needed, but had 1" aluminum spacers on the rear drums to push the rear tires out a bit more for a stagger look without the mismatch. Excellent compromise for a street car if you want to keep it simple. the BS was 4.5" on those wheels so plenty of inner clearance from fender wells and suspension but they otherwise filled the wells up nicely.
I recently moved up to 17x8 TT's to take advantage of better tire options. Another great option if you have the notion!
Do you have any photos of your 17x8s that you can share? I have always liked those wheels. What size tire are you running on them?
I'm running 245-50-17 Falkens all around - this combo is literally within a few thousandths of the prior 245-60-R15 so there was no change in geometry or speedo accuracy. Plenty of sidewall height and BS remains same at 4.5" as well. Last photo depicts the prior 15's showing the stagger from the rear spacers
Last edited by 70sgeek; October 14th, 2021 at 01:15 PM.
Thanks for posting the photos. Those look great! Perhaps it is the shape of the wheel itself and the depth of the rim that really makes this work. It does not look like a huge wheel with a thin tire. It looks completely natural on the car.
I think 14 and 15" tires are scarce in variety and generally old tech in design anymore. I've been wanting to move up in wheel size for awhile to take advantage of greater tire selection and it was too long in the making. I run the Koni Street shocks (the orange set) and the new tires don't feel any harsher than the 15" BFG's they replaced. As far as handling - they're stickier for sure - good road feel and smoother in ride quality for the most part. I don't (purposely) take my ragtop out in the rain so haven't had opportunity to try them out in wet weather, but I'm pretty sure they'd be more than competent in it.
August 10th, 2017, 12:35 PM
