Tall tires

[larryw]

I have a set of the Shelby "Cal 500" 14x6" slotted wheels. They appear to be a zero offset, best I can tell. I'd like to try a tall tire to drop cruising rpm a bit.

A set of 225/70/14 tires at 26.5" tall will run about 785 revs/mile (tirerack), vs about 840 revs/mile (guessed-can't find specs) or so for a 225/60/14, about a seven percent difference. On the tach it would represent about a 200 rpm drop at 3000.

I made a cardboard section of a 225/70/14 from tirerack's specs and taped it to the rim. It seems to clear nicely with the car supported at the balljoint (suspension loaded), but I cannot force the spring into full compression to see what would happen at a bump.

Anyone know if I'll have problems?

[alternativez]

I suggest you try to keep the tire diameter closer to stock. I tried the slightly taller tire on my '76 BMW 2002 for the same reason, better highway cruising, and to match the speedo of the engine/electronics of the '91 m42, 5 speed, R&P, LSD swap, basically turning the '02 into a '91 318is. However, in my case, I was having some rubbing issues with a 195/60/15 and feeling like I was driving a truck, so I dropped to 195/55/15, and also switched from a lousy Yokohama 520 to a fine Michelin, still a bit taller than stock, but only slightly. The steering lightened up, I tear around corners now with a rejuvenated "sport sedan" because I'm not rubbing, and the traction is far better. Everything is a compromise. Taller tires sacrifice some acceleration, but more importantly, they change the suspension dynamics, perhaps adding some body roll due to higher center of gravity. I doubt I've lost much mpg, but I've gained a livelier car, which has inspired me to play with the suspension. The original tire diameter is 24.26, or so, for the early Z, not sure what car you have, so unless you really like the look of the taller tire, over 2" taller than stock with lots of sidewall, I suggest 225/60/14 would be maybe a more comfortable size. There are several good threads on tire/wheel sizes. Explore those. Check out Chachacourt's thread on the RB-R, great thread discussing clearance, etc. Everyone has personal preferences; for example, I'm thinking 215/45/17 front, 24.62", 225/45/17 rear, 24.97," which wouldn't appeal to everyone. It's an area for research. Tires' real measurements, like shoes, don't always match their statistical meaurements; you have to try them on for size. Also, tire sizes dictate availability of certain tires, so you might want to look at your tire preferences and then think size options. One thing you will hear is, do what you think and what you like. Good luck. My .02.

Edited July 15, 2011 by alternativez

[Jeff G 78]

Why not use a 3.36 rear end gear from an auto or swap in a ZX 5 speed? Tall tires will make your car look really funny and they will probably rub. I tried a similar size back in 1986 and they rubbed over bumps.

[LeonV]

I was running slotted 14" mags with 225/60-14 size tires on them and they fit very nicely. However, the tire selection is poor so I upgraded to 16" Panasports.

[Walter Moore]

The auto transmission cars came with a 3.54 differential. The 3.36 was in the early 240 4-speed cars.

If you change your tire size or rear differential, remember that your speedometer will be wrong unless you change the speedometer drive gear.