Hi. I have a 09 which runs stock on 245x45xr18 (18x8 rims)
I am shopping around and found 225x40xr18 (18x7.5 rims)
Q1: Can i run thinner tires than stock?
Q2: Can i run the 225 on the stock rims, i know stretching isn't good but i dont mind.
Q3: Does running thinner tires setup alter the cornering capabilities?

Thanks.
Regards.

 

If it can work, which I'm not suggest it will or wont. But let's say that it does, you're going to sacrifice ride quality, and on 18's, it will look like sh!+ with less meat on them. If you were at 20's and had thinner tires it would at least fill the space better. Still a rougher ride, but would look better then low profile on 18's. Will it corner better, probably, but does that slight advantage outweigh the comfort you're giving up?

 

I am planning to lower the car with Coilovers. So im not concerned about the gap. And i live I the countryside and do 90% highway driving so comfort isnt a problem.
Awaiting reply

 

You're missing the point, it's not about gap in this case, it's about overall diameter of the wheel. You go low profile on a 20" rim, the overall diameter will likely be the same as the stock wheel and tire, therefore it fits the entire opening and looks right. You go low profile on an 18, now you've shrunk the diameter, thus the look will suffer. Not to mention you may throw off the speedometer a little with a shorter rotation circumference then stock. If you're going to lower it and thin the tires, don't skip the wheels...you should consider getting some 20"s, or stick with a stock size on the 18's, I promise every time you walk up to the car you'll see how odd it looks and you'll kick yourself.

 

https://tiresize.com/calculator/

There is quite a difference in those 2 sizes.

225/40/18

Diameter 25.1"
Width 8.9"
Sidewall 3.5"
Circum. 78.8"
Revs/Mile 804

245/45/18

Diameter 26.7"
Width 9.6"
Sidewall 4.3"
Circum. 83.8"
Revs/Mile 756

 

That's awesome, been on that site a lot, never explored the calculator.



So a 5" circumference difference equals a 6% decrease in linear length. That's cool how it even calculated the revolutions per mile. that difference of 48 RPMile, (also 6%) will result in noteworthy differences at the speedo and odometer. Not to mention, theoretically messing with the transmission a little too and to be quite honest, would likely make your car slower then the speedo actually says. (someone correct me if I got that backwards). So shift points may be off a little based on both torque and resistance...brakes will likely heat up a lot faster in emergency stopping situations since the wheel is rotating more then stock, and even ABS could malfunction some based on static calculations in the computer...I mean, the list of reasons not to do this are growing...