In the 175SR14, the "S" is the speed rating (S=112mph, H=130mph).

The 240's did come with 175SR14 (which has a 78 aspect ratio), however, the OP was asking about his 280Z, which came with the 195's. A 175/78-14 and 195/70-14 have the exact overall height (24-3/4") and as a result the same revolution's per mile (815.35).

This is getting interesting.

I'm considering adding a '70-'72 240Z to my budding collection. Assuming a stock 240Z with either 14" OEM steel wheels or 14" slotted mags, I'm thinking the 195/R70-14 would be preferable to the OEM 175/78-14.

Correct?

In the 175SR14, the "S" is the speed rating (S=112mph, H=130mph).

The 240's did come with 175SR14 (which has a 78 aspect ratio), however, the OP was asking about his 280Z, which came with the 195's. A 175/78-14 and 195/70-14 have the exact overall height (24-3/4") and as a result the same revolution's per mile (815.35).

Actually, the pure millimetric 175-14 size was typically said to have an implied 80% aspect ratio, not the 78% that was becoming common in US alphanumeric tires. A small difference (2%), but a difference none the less.

This is getting interesting.

I'm considering adding a '70-'72 240Z to my budding collection. Assuming a stock 240Z with either 14" OEM steel wheels or 14" slotted mags, I'm thinking the 195/R70-14 would be preferable to the OEM 175/78-14.

Correct?

A qualified yes. First, the original 175-14 size - as well as the modern re-labled equivalent 175/80-14 - is almost non-existant these days, so past a few odds and ends like Vredsteins, you won't be running the original size anyway.

The other part to consider is the rim width. The factory steel rims here in North America through about 8/71 build were only 4.5" wide. I'm not aware of any companies who approve of pinching a 195/70-14 down to fit a rim that narrow. For '72 and later, the factory rims were 5" wide, which is generally the narrowest that a 195/70 is spec'd to work on. This is a bit of an issue for people with the early cars and rims, as the factory size is almost unavailable, yet the next obvious size is too wide for the rims. For those cars I'd recommend 185/75-14 as the best alternative.

Step up to a 6" rim and things open up. The 195/70 still fits fine, yet 6" is wide enough for up to a 225/60. Same is almost true for a 7", although most 195/70s will be a bit stretched on a rim that wide.

I'm pretty certain that I've listed this before, but it seems appropriate to do it here as well. The following sizes are all about the same rolling diameter as the 175-14 (plus or minus 2-3%, which is generally considered a negligible difference). Please note that many of these sizes are no longer available, or at best hard to find. I've not added the P (Passenger) that some may have at the beginning, nor have I added any speed ratings.

Also, due to varying offsets, lowering amounts, different air dams, etc., I'm not trying to say that all of these sizes will definitely fit all S30s. This is just for reference.

175R14 (80% aspect ratio)

DR78-14

185/751R4

DR70-14

195/70R14

205/65R14

ER60-14

225/60R14

175/70R15

185/65R15

205/60R15

225/55R15

205/55R15

225/50R16

245/45R16

205/50R17

225/45R17

245/40R17

225/40R18

245/35R18

As a final reference, I have 195/70TR14 on 14x6 wheels on my '71 240Z. Works great on a mostly stock car.

Arne,

Thank you for all the excellent information! This raises another set of questions, perhaps more of academic interest, but I think the kind of stuff we Z lovers thrive on.

Can anyone comment on the differences in performance, handling, etc. between a stock 240Z with original 175/14 tires back in, say 1972, and the same car now with 195/R70-14 tires?

Would it feel much like the same car as far as stability, steering and handling? Would braking be affected? How about driving on wet roads or at high speed? Would the overall ride be different, say smoother? Would a passenger notice any difference?

Thanks again Arne, Enrique, Gary, Jim and Mike!

Any non-60 series 14" street rubber that you can buy today (with the exception of Hoosiers) are strictly minivan fodder. No true performance capabilities by today's standards.

That said, your typical 195/70-14 all-seasons tire of today is still a better all-around tire than anything that you could buy in the early '70s, with the possible exception of the Michelin XVS/XWX lines, and maybe the Pirelli CN36.