i2ichal2d

hey guys i kno teh stock sizes is 215/45/17 for fornt and 245/40/17 for rear. i was wondering why the side profiles are differnt and what u ugys recommend me replace the fronts with stocks? i am going to pick up soem rims soon my rear tires are going to be the same at 245/40/17, at the same time should i replace my fronts with a 40 side profile? or stick withe the same? can i see some pics please?

Jim@tirerack

You need to stay with the 215/45R17. The 215/40R17 is going to be a shorter tire and will not work on the car.

macdreballin

why wont it work im curious?

juice04

I think what Jim is saying that your car will run, but the new 215/40/17 tires will be extremely undersized - overall height that is.
The OEM 215/45/17 overall height is 24.6"
The new 215/40/17 overall height is 23.7"

That's almost a whole inch shorter on the overall height difference which will affect your odometer, speedometer, and how it rides/handles.

xviper

Because you are dealing with different widths. Therefore, you need to adjust the aspect ratio so that the overall diameter of the tire will be more or less the same as each other.

You're talking about the front tires here. Size differences here won't affect the speedo or the odo since the speed sensor is on the output shaft of the tranny and only the rear tire diameter will affect how it reads. As for changing the ride and handling, this is a given whenever you change tire specs.

Race Miata

I'm guessing here that you misunderstand the 40 or 45 number in a tire's dimension. The number is the profile as a percentage of the tire width, not the actual sidewall height. The 2 stock tires 215/45/17 and 245/40/17 have very similar sidewall height.

Read more at TireRack's Tire Tech page.

kent-k

will that setup affect the ABS? the computer will think that the wheel speeds are very different front to rear, right?

xviper

Only if the overall tire diameter is vastly different. I'm not sure just how much of a diameter difference it'll take to adversely affect the ABS.