Actually, 175/70-14 is not very close to the original tire size diameter (using my original 1973 175/SR-14 spare for measurement).

My original spare is 25" in diameter, and a 175/70-14 is only 23.6" in diameter. I recently moved from 195/60-15 (24.2") to 195/65-15 (24.98")to get closer to a 25" diameter tire on my car, and now the speedo is dead on (based on GPS and the police radar sign they put beside the road to tell you how fast you are going).

So if you want your speedo to work properly, you'll need to get a tire as close to 25" diameter as you can. You could go with a narrower 195/50-17 (7.67" width), and get a 24.7" diameter, and still have a narrow enough tire to tuck into the rear wheel well without rubbing.

Actually, 175/70-14 is not very close to the original tire size diameter (using my original 1973 175/SR-14 spare for measurement).

My original spare is 25" in diameter, and a 175/70-14 is only 23.6" in QUOTE]

Sorry guys, I stand corrected

The original aspect ratio must be about 80 according to the calculator from 1010 Tires, which means a 205/50-17 is fine.

, if you are changing the tire size, and rim size, does this have any effect on your speedometer reading?? ( sorry didnt mean any disrespect, by jumping into your thread) example, if you are adding lower profile tires, the tires must spin faster to achieve the same speed as a larger sized tire?? I do believe.

, if you are changing the tire size, and rim size, does this have any effect on your speedometer reading?? ( sorry didnt mean any disrespect, by jumping into your thread) example, if you are adding lower profile tires, the tires must spin faster to achieve the same speed as a larger sized tire?? I do believe.

Yes, you are correct sir. The closer you are to the original diameter, the less pronouced it will be. This tire size calculator will tell you how far off your speedo will be with different tire sizes:

http://www.miata.net/garage/tirecalc.html

Also note that if you have a low mileage car (like Arne's, my two Z's and others), it will also accumulate miles faster than it really is!

Also note that if you have a low mileage car (like Arne's, my two Z's and others), it will also accumulate miles faster than it really is!

Which is one big reason my car is in the garage until I get new wheels and tires!!

Arne, I keep trying to tell you -- go with the "D" caps and 195/70-14 tires and you'll be all set!! I really like the hubcap look on my '72 and plan to keep them on the car. Put them on your car for the time being and if you just can't bring yourself to keep them on the car full-time, you could also go for the 15" wheels and tire set up I have on my car for the daily driver wheels. They look period correct, but I have never seen another Z with these wheels, so you will be unique in your part of the world :classic:

My stock wheels are too narrow for 195/70s, I'd have to go with 185/75-14 instead.

I did try one on the car, was frankly unimpressed. The red car just screams for something flashier than the dark gray hubcaps.

The original tires aspect ratio is 78% (175/78/14).

Old thread, but jus so I'm sure,

will 205/40/17 tire and rim combo work without rubbing?

Or would I need to adjust the offset and backspacing?

I heard go with zero offset and 4 or 4.5 inch backspacing.

Ordering one of these Azul Speedstar rims this weekend from WheelsNEXT.com

and like to make sure I do this right :rambo:

Speedstar in BLACK (GLOSS FINISH)

Speedstar in HYPERBLACK

Thyanx ~Z~