Is that ok to run? that's closer to stock (sidewall height FR bias) than the 255/40 all the way around, right?

or is it better to run 255/40 all the way around, and then 245/45 all the way around?

I have a lot of tires I have to burn through, so trying to find out the best way

 

No no, go 40 series all the way around. I wouldn't even consider 245/45s at all...ever....

 

255/40/17 all around with a stiffer front anti-roll bar. This seems to be the preferred setup for the racing guys.

 

I dont race, and wont be getting a bigger sway bar any time soon...

So how come 225/45 is ok up front with 255/40 out back?

Ill probably end up trying it out anyways, have 4 rs3s (255) and 4 re01rs

 

The car over-steers , to compensate you need to put narrow tires in front and wider in rear
OR
If you run 255 all around the car will oversteer and you compensate with a larger front sway bar

 

The diameter of the 225/45 is equal to the diameter of a 255/40, I am wanting to say they are both 25". But the diameter of 245/45 is almost .5 inch larger than that of a 255/40. Iirc there is a .8 inch difference between 245/45 and 245/40. The 245/45 has a lot of sidewall. Tire rack has the exact diameter measurements under the spec section of the tires if you want to double check. These measurements will vary based on tire manufacturers. Hope this helps

 

Because the second number in a tire size is called the aspect ratio or profile. This is a ratio of sidewall height to section width. Therefore, a 225/45/17 is the same overall height as a 255/40/17. If you did want a slightly more narrow tire up front for clearance or something, then you'd run 245/40/17 F 255/40/17 R.

 

Hm I was thinking that the 225/45 was taller than 245/40 or 255/40, but looks like the diameter is pretty much the same

 

A 225/45/17 IS taller than a 245/40/17. Just like a 255/35/18 is taller than a 285/30/18.

 

You should look up how to calculate the diameters manually and then it makes more sense. For a 225/45/17 it is 225 (mm) * .45 (which is basically like saying 45% of 225) and you get 101.25. This is the size of the sidewalls in mm...so basically 4 inches or so. When calculating the overall diameter it is the wheels diameter 17" + the sidewall (4") *2...giving you 17+8 which is roughly 25 inches.

A 245/45/17 would be 245*.45 which is 110.25mm sidewall...this is an extra 20mm which means the overall diameter would be almost a whole inch taller...the tire would be taller in the front than the 255/40/17 in the rear.