Cutlass Fan

Can someone tell me the stock tire size on a 1965 Cutlass convertible. I looked in both the owners manual and the shop manual and can't find the size in either one. I am thinking it was either 750 x 14 or 775 x 14. At present it has bfg 205-70r14 but I think they somewhat smaller than original.

Happy Trails

I don't really know anything about this topic, but I did find a few online sources that indicate the standard equipment tire size was a 7.35x14. I didn't do an exhaustive search, but I also didn't find a source that lists a different standard equipment tire size.

hurst68olds

7.35x14 aprox. 195/78/14

taller than your 205/70/14s but not as wide

'67 was the first year for 70 series tires on an OLDS a-body & they were F70-14 approx. 215/70/14

joe_padavano

To expand on the above, the 7.35x14 was standard, but 7.75x14 was optionally available, per the SPECS booklet:



This table provides dimensional information:



The 7.35x14 had an OD of just under 26" and a section width of 7.3". As noted above, 205/75-14 is the closest available modern tire, though about 3/4" wider in section. The optional 7.75x14 had an OD of 26.7" and a 7.75" section width. 225/70-14 is the closest available modern tire; slightly smaller in OD and about an inch wider in section.

Cutlass Fan

Thanks for your help Joe & Hurst. and thanks for posting the list of standard equipment, very interesting. My 205/70R14's only have an effective diameter of 23 1/2" (11 3/4" center to floor) even though the diameter is listed as 25.3. I know my speedo reads about 10% or more fast.

joe_padavano

This is an important point that most people do not realize. Published tire diameters are nearly always theoretical unloaded numbers. Tires deflect under load, and due to their construction, radials deflect considerably more than bias ply tires. The number that matters is the EFFECTIVE diameter under load. Tire manufacturers call this the "rolling radius". Truck tire manufacturers typically publish either this number or a "tire revs per mile" number, which is the same thing when you apply a little math. The bottom line is that I'd always go taller than original when changing from bias ply to radials.

Cutlass Fan

I've got nearly new BFG Radial ta's that were put on shortly before I purchased the car, so I guess I'll stay with them for now. I do wish they were a couple of sizes bigger as rpm at 70mph is close to 3400rpm with my 3.23 gears.

joe_padavano

Yeah, between torque converter slippage and tire rolling radius effects, that's somewhat higher than the theoretical 3000 RPM at 70.