Okay, don't want to think, but can someone tell me how the speedometer and odometer are affected by different tires?

Say you have tire A with 800 revolutions and tire B with 820 revolutions and comparing that with our stock CLS tires (I think it's like 816 revolutions).

If you are at 60 mph, on our stock tires, we should be going 60 mph. What about tire A and B? If speedo says 60mph, are they slower or faster than what it says?

Also, if you drive 1 mile on the stocks, you go 1 mile. How about A and B...which one would be less?

 

Just use this...

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

 

don't forget, the CLS stock tires are already too fast vs. real speed/odo readings which translates in higher mileage

 

what is the specs for the stock tires... I can't remember for some reason....

 

OK.. Nevermind... I got them

 

Also the stock tires are only "fast" on some cars. My were dead on, as are many. Might just be a few that have been off.

 

my stock tires are off by about 2-3%....they are too fast and they clock milage at 2-3% higher rate than it should

 

How did you determine that yours were on? I checked mine on a lot of interstate runs (200-400 miles segments), and found them to be off app. 1 1/2%.. And then confirmed that with comparing the speedo with my GPS.. YMMV

 

I believe the tire companies will tell you that +or- 2% off from standard is ok. I believe that standard is 819 revs per mile. On the minus side, your speedo mileage would not register as many miles as standard and on the plus side, your speedo would be adding more miles than the calibration.

 

So, if 819 revs per mile is considered the standard, does a tire that specs at 800 revs per mile basically mean that our odometer will read more miles than it should? (bad thing)....and our speedometer would read slower?

Or was it the other way around?

Or am I still screwed up?

 

If it was less than 819 revs per mile, you wouldn't be putting on as many miles on your speedo.

 

Standard devided by new, times speedo (or odo) reading equals the real spead (or miles).. less revs per mile means you are going faster, have driven farther than your dials indicate.

 

The reason stock CLS/TLS tires are "fast" is because the original CL/TL were calibrated for a tire that is 25.68 inches in diameter whereas the type s tires are 25.5 inches.

In general:

smaller tire = more revolutions per mile = going slower than speedo says = going less distance than speedo says

all of these relationships are linear so you can take the ratio of size or revolutions to determine what percentage your speed or distance will be out.

 

Had a cop friend clock me with a radar gun, used the radar on the side of the road, had several friends pace me with the cruise set to the same speed, & took 2 1200 mile trips to NYC which I have taken 12 times before in others cars, & used the mile markers. Maybe mine was the blacksheep

Doesn't matter now anyway since I have the Toyos I'm know I'm a little fast.