Speedo Reading

[Leon Todaro]

I'm curious....if my 1971 E has 205/60 15's what speed am I really going when the speedometer reads 60 MPH. I believe the original tires were 185/70 15's. Right? I know there are some math experts out there. My strengths lie elsewhere. Thanks in advance for the calculations....

[Chuck Miller]

Leon,

Your spedo is reading about 2% fast...

Try this easy calculator....

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

Hope this helps,
Cheers,

[SWBS]

Leon,

Your spedo is reading about 2% fast...

Try this easy calculator....

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

Hope this helps,
Cheers,

That's a nifty tool. What it actually means however, is that your speedometer reads 2% faster than it did with the previous tires. Since the speedo could be a tad off to begin with, time your car through a measured mile (freeway markers will work nicely) at a steady speed, and then divide the resulting seconds into 3600. The answer is your MPH.

Jim

[Leon Todaro]

Jim, I'll try it. Chuck, great tool. It's a wonderful age we live in. Thanks guys. And as usual this site is a wealth of info........

[Neunelfer]

With the proper tire measurements and the new 915 (from a 75 car) can guys like Palo Alto and/or West Holloywood recalculate my speedo? I'm running the 225/50-15 Yoks. I'm off by 6-8mph or more.

[Chuck Miller]

Eric give them a call ... but I heard 'no' a long time ago.
I heard that they can build up a 'reduction box' that you mount inline to a spliced cable that can get you right on the money....
But again, that was a long time ago... would be nice to know any new info ...

A 225 x 50 x 15 should put your speedo a little over 5% high...

Cheers,

[Neunelfer]

Let you know what they say.

Yeah... did the calc. 5.3%

[Neunelfer]

OK... scoop is: You must take their "Ratio Test"

http://www.paspeedo.com/ratio.htm

Then send it in and they'll calibrate. About $125.