Site for tire sizes and spedometers
 

Here is site for those considering different tire sizes and how they will effect your spedometer....thought it may help!

www.miata.net/garage/tirecalc.html

Thanks for the post

That's some good stuff to know:THUMBSUP:

Thanks !!!

:OFFTOPIC: I recently installed 235/70/15 tires and rims on my beater that was stock 195/75/14. The site will be very helpful for getting the correct plastic gear that goes in the transmission. That calculation says my speedometer reading is 9.6% too slow and references a 60mph reading as actually traveling 65.7mph.

JB
Greenville, NC

Re: Site for tire sizes and spedometers
 

There is no "correct" plastic gear for 99 an up cars. Use Speedcal or correct thru ECU.

Re: Site for tire sizes and spedometers
 

This site gives same numbers as my trusty calculator, but keep in mind you're probably about 2-3% fast from factory, so some of the slightly larger than stock tire/wheel combo's are probably bringing you back into dead accurate speedo range....which is one reason I chose my slightly larger than stock diameter tires. Cody went one size larger than I did, and I bet he's either dead on or only slightly reading slow, no big deal, but enough to be careful if he runs thru his buddies radar gun.

Re: Site for tire sizes and spedometers
 

According to that site, my new 315/35-17's will not change my speedometer reading from my stock 245/45-17's.

It gives the stock Revs/mile as 785.0 for both. Tirerack.com, where I bought my tires, give the Revs/mile as 808.0 for the 315's and the 245/45-17 as 811.

Anybody have an idea which is correct?

Re: Site for tire sizes and spedometers
 

The difference between the two is like .004% or about 20 ft every mile. At 60mph that is only a 1/4 mph difference. Don't think you will be able to blame the speeding tickets on the tires.

Re: Site for tire sizes and spedometers
 

How about if I have 265/35/18 up front and 285/35/18 in the rear. Which one is the one that'll effect the speedo. I get 1.5% to fast with the 265 and 0.7% too slow with the 285. Do I just subtract on from the other. If that's the case 0.8% isn't too far off from factory wheels.

Re: Site for tire sizes and spedometers
 

That is pretty cool. I am getting new tires for my car, and it was very helpful!

Re: Site for tire sizes and spedometers
 

Can anyone that uses this post respond to my change? I went from 245/45/17 to 275/40/18. Does my speedometer read different more or less accurately now?
Thank you,
Mike

Re: Site for tire sizes and spedometers
 

Here is another somewhat similar tool I use. You enter trans gear ratio's, rear gear ratio, tire size and red line, it will then show you your rpm and speed for all gears.


Transmission Calculator

Re: Site for tire sizes and spedometers
 

i used to use that miata one until i found this one
http://www.1010tires.com/TireSizeCalculator.asp
much more detailed but it doesnt have that cool picture for comparison

Re: Site for tire sizes and spedometers
 

I love 1010Tires Calculator!!

Pic below shows STOCK vs
265-35-18
275-35-18
285-35-18
295-35-18
size widths

Re: Site for tire sizes and spedometers
 

Its saying if I go with 275's on the car at all that I will be going .08% too fast....what does that equate to in MPH? The 315's there's not any difference whoot!

Re: Site for tire sizes and spedometers
 

hi guys.

i would buy some 9x18 and 10x18 wheels.

now whats the best fit for tires?

i think abaout on the rear 285/35/18 and for the front 265/35/18 oder 255/40/18

some inputs from you?

Re: Site for tire sizes and spedometers
 

I've got 18X8.5 and 18X9.5 on my mach, tires are 245/40/18 and 285/35/18
I'd go 295/35/18 for the rear and either of the two front sizes you listed. both will work

Re: Site for tire sizes and spedometers
 

what is the stock rim offset on 2004 mach?

Re: Site for tire sizes and spedometers
 

I have 18s. I will often use my GPS as a speedometer b/c I am too lazy to do the math. :31:

Re: Site for tire sizes and spedometers
 

Just get a programer and change the tire size. Just more money for the addiction of owning a Mach.

LS:ORANGE: