Will running a smaller diameter rear tire cause my speedometer to be off??

[ADE 1000]

I have started to weigh my options for snow tires this winter and I found a decent package that uses 235/60-16s all the way around. This tire size is pretty much the same diameter as the stock front 18" tires.

I know people have talked about running fronts all the way around with no issue, but I want to make sure I am not screwing anything up by running a smaller tire at the rear.

[Black Terror]

It will be off approximately 5MPH @ 70 MPH. Equivalent to 3.75 rear axle ratio vs. 3.55.

[Petrograde]

smaller rims are ok as long as you keep the overall tire height as close to stock as possible.

[Mike Poore]

I have started to weigh my options for snow tires this winter and I found a decent package that uses 235/60-16s all the way around. This tire size is pretty much the same diameter as the stock front 18" tires.

I know people have talked about running fronts all the way around with no issue, but I want to make sure I am not screwing anything up by running a smaller tire at the rear.Better make sure they're gonna clear the brake calipers.

[stumpy]

Your speedometer, and odometer, would read higher than actual. However, you could have an even bigger problem with the anti-lock brakes if the difference in diameter from front to back is too great.

[CRUZTAKER]

It'll work....I ran 16" marquis wheels with snows on all four corners the first year I had the car. As long as the circumfrence is the same all around, or even a tad taller in the rear, the ABS won't care. Now the traction control will however once over about 40 mph, but who cares, turn it off. With quality snow tires, one doesn't need the t/c anyhow.

And yes, the speedo will be off, and the odo will rack up a few extra miles, but again, who cares? You'll figure out the speed your driving after awhile, and besides, it'll always read higher than which you are really traveling, so it also may avoid speeding tickets!

On a dry day, you'll swear you had 4:10's installed, and start smoking people left and right.

Happy wintering!

[Murader03]

I run the smaller front tires on all four courners. Allows for better tire wear due to rotation. The speedometer/odometer will run about 3% FAST as verified via a GPS receiver. The ABS should not be that big of a problem, but if you have traction control, the smaller tires on the back wil cause the TC light to come on. Just turn the TC off and although the light will remain on, nothing else should be affected as you drive. :flag: :beer:

[Cobra25]

What happeneds if you run the rear tires in front & rear. ?

[ADE 1000]

Thanks for the responses guys.

I will probably still try to find a rear tire that is the same diameter as stock, but its good to know that I can run a smaller tire in the back without any major issues.

[ADE 1000]

What happeneds if you run the rear tires in front & rear. ?

There have been some posts discussing this lately and the consensus is that aside from some slight rubbing at full lock it should work fine.

[Murader03]

What happeneds if you run the rear tires in front & rear. ?

Again, if you have traction control, it will see the rotation differences from front and rear, and activiate the TC above 35 MPH. Again, just turn it off. Otherwise, what was said above about the slight rubbing......

[MMM2003]

Hey:

This is a great little Tire size calculator. You can use it to compare two sizes and it will tell you exactly what difference you see will in RPM and Speed.

Tire size calculator (http://www.miata.net/garage/tirecalc.html)

Hope this helps.

Peter aka MMM2003


I have started to weigh my options for snow tires this winter and I found a decent package that uses 235/60-16s all the way around. This tire size is pretty much the same diameter as the stock front 18" tires.

I know people have talked about running fronts all the way around with no issue, but I want to make sure I am not screwing anything up by running a smaller tire at the rear.