Need technical support! (differential in tire diameters)

[BARNEY O]

Can anyone tell me how much differential in tire diameters from front to rear there could be or ratio before it would trigger the ESP system?
Doing the math on the Passion, the difference from front to back is .256" in diameters. On the Brabus the difference is .346"
I'm looking at something a little more aggressive like 1.181"
Fronts 195x50x15 (22.677" dia.)
Rears 225x50x15 (23.858" dia.)
Would appreciate someone's expertise on this issue.

Regard,s Barney O.

[rfernatt]

I don't know, but jwight witnessed the results firsthand with a set of snow tires that drove ESP/ABS nuts. He may be able to provide some guidance based on that experience.

I can say that 195/50s all the way around work great on 15x6 rims. And, you can rotate.

[jwight]

All I know is what didn't work; some other folks added a lot of info on how to keep different size combos from setting off the computer. Hopefully they'll chime in here.

[BARNEY O]

Originally Posted by jwight

All I know is what didn't work; some other folks added a lot of info on how to keep different size combos from setting off the computer. Hopefully they'll chime in here.

Do you recall the snow tire size?

[BobDiaz]

Why is there a difference in the tire sizes from front to back?

Does anyone know why?


Bob Diaz

[jwight]

Originally Posted by BARNEY O

Do you recall the snow tire size?

Here's the original thread: New snow tires and Rial rims - big problems! [Solved]

"Stock tire size in front, the rears are 175/65 vs. 175/55 so a little taller."

That was enough to throw the computer off.

[jimvw57]

I would assume the tire size difference between the front and rear is to compensate for the extra weight of the rear engine, but that would be a guess.

[BARNEY O]

Originally Posted by jwight

Here's the original thread: New snow tires and Rial rims - big problems! [Solved]

"Stock tire size in front, the rears are 175/65 vs. 175/55 so a little taller."

That was enough to throw the computer off.

Jwight,

Crunching the figures of the 2 tire sizes you listed there was a diameter difference of 1.378" and it caused problems. This helps somewhat,now I know a 10 % ratio difference appears to be too much.Still wonder about my 1.181" dia. difference? It's under 10% but not much !! Could 10% be the max the computer will allow?

[fortow]

Originally Posted by BobDiaz

Why is there a difference in the tire sizes from front to back?

Does anyone know why?

There are two size differences - diameter and width. Since this thread is concerned with diameter you may be referring to that.

The diameter difference is a result of the difference in width. The difference in width required a different aspect ratio to get the rolling diameters as close as possible, but not exactly the same.
As to the reason for different tire widths front and rear - that is done for several reasons. The primary one being to induce under-steer. That topic has been discussed frequently before. Related to that is the fact that the front is lighter and that the front tire need not be spec'd to carry as much weight.

[High Side]

So... what is the difference in diameter between the stock passion front tire and back tire? Or are they essentially the same, except for the width?