My 93 9C1 came with 235/70-15s. There is only .3 of an inch difference. That should not effect you speedo too much and should fit right on 7 inch wheels. Hope this helps.
Mark: Snowman-33

 

I run 255/60R17's on my RMW and have no problems front or back.
These are 29" tires, about same size (hair taller).
Stock Impala rims, FWIW

 

They work fine. They will rub the sway bar at full lock. Ran them for years on two wagons.

 

I have them on my OCC right now, and the speedo reads closer to correct than the 225s did. No noticeable difference in the car otherwise.

 

These days, the quality & quantity of choices for 225/75R15 (28.28"), 235/70R15 (27.95"), 215/75R15 (27.69"), 225/70R15 (27.40"), and 205/75R15 (27.11"), are already bad, getting worse, & dwindling.

So far as I'm concerned, the ONLY OEM tire choice left for Caprices, Custom Cruisers, Roadmasters, & Fleetwoods is 235/75R15 (28.87").
235/75R15 is the OEM option for Cadillac Fleetwoods with V4P Tow, V4U Limo, B9Q Hearse, or B05 Armour.

 

275/60-15

Both the BFG Radial T/A (all season) and the Nitto 555 Extreme (summer ultra-high perf.) are 28.0" tall, have plenty of load rating and fit of 15X7" wheels fine. They should cost the ~ same. I have used the BFG 275/60-15 on a RMW on oem 15x7", they fit fine with no problems. Even on the Limo the load rating is sufficient and love them. I've used a larger wheel size Nitto 555 and they are a great tire for $.

 

Only oem options ?



Notice the original poster didn't say OEM size only. That is who I responded to dinky. Interesting constraint for Marky...only oem tire sizes, therefore for you I only recommend the oem brace. No welding. We all know you need all the friction you can get, however you can get it.

 

You can run the larger tires, but you will have to change either the 94-96 computer tire setting, or the VSS gearing in the 91-93 cars. As long as the tire fits under the wagon, 91-92 sedan, and RMS rear fenders, you can run them. If you do not change the computer or gearing, your speed input will not reflect the true speed of the car, causing miscalculations by the computer to the transmission, and/or engine, and instruments.

 

Scot, I don't get your stance against what I said. (dinky?)
SOME wagons [such as the one in my sig, that I drove for 240,000 miles] may have some issue running sizes such as
275/60R15
255/65R15
255/70R15
275/65R15
in their rear wheelwells, but that's the very reason why I lamented that they weren't OEM options; had they been OEM, GM likely would've clearanced the rear wheelwells to accommodate them.
There's nothing wrong with the above mentioned choices once the rear wheelwells are clearanced to suit them; I recommend them [provided quality options are available].

235/75R15 was the OP's original interest, happens to be an OEM option [if only for Cadillacs V4P, V4U, B9Q, and B05], and still offers many more decent choices than all the other tow-worthy sizes combined.

Have I given you some sort of friction in the past, scot?

 

P255/70R15 Kumho ROAD VENTURE APT KL51

For a couple bucks more you can go with P255/70R15s. Just about the same overall height as the P235/75R15 tires but wider contact patch.

I really like the Kumho ROAD VENTURE APT KL51s with their H speed rating for better heat resistance.

Here's some pretty good discussion of both tire sizes: http://www.impalassforum.com/vBulletin/23-wheels-tires/272270-235-75-15-a.html

Good info on the Kumhos: Kumho*Road Venture APT KL51