I just tried to get 245/40/18R tires installed on my 2010 SS HHR. I was told as of March of this year due to safety reasons (lawyers) they will only install 235's on stock rims. Anything wider require aftermarket rims. I imagine other tire shops will be doing the same. I have always had great service from DT so I didn't bother to shop around.

 

I just got new tires and rims from them. I didn't notice what tire size they gave me but I can check when I get out to the car

 

Probably has to do with the width off the rim. You never should have been able to mount a tire that requires a 7 inch wide rim on a 6 1/2 inch wide rim legally. They most likely just noticed the liability.

 

I just checked mine 245x40x18 nice riding tire. when I bought them they told me that was the biggest tire they could put on, otherwise it would rub

 

People run that size on the SS. Avoid deep snow, and you should be cool.

 

I was talking safety , not rubbing.

If you put a 8 inch tire on a 6 inch rim (or any mismatch you want) you are risking death. That is not even getting into odd wear patterns caused by a flexed contact surface and sidewall.

 

I don't know where they are coming up with some of these limits.

I just put 245/40/18 on my stock "SS" wheels. They look like they were made for it. Nice Flat sidewall (No bulge), no issues with mounting, nothing.

Maybe I could agree if you were pushing the limits with the 255/35/18's, but the 245/40's?

I just don't get it.

 

The ENGINEERS that design tires design them for specific size rims.

ENGINEERS are not known to come up with arbitrary numbers. The numbers I used were made up for illustrative purposes, I thought that was clear.

What makes you think that flat sidewalls is good? Or an indicator of proper fit?

I was just trying to explain why they won't let you have what you want. They don't want to get sued by your mommy if The tire explodes and kills you, or by the installers mommy if the tire blew his head off.

 

Great points Don, the rim width and tread width both have their limitations for a safe driving experience.
You don't want to find out at speed in a tight left hander that the tire will roll off the bead and cause loss of control and bent sheet metal.

 

The reason is, tire size X was specifically designed to fit rim size Y, is because when there is a failure of either and the owner gets blamed, they start pointing their finger else where. Somebody needs to be responsible in the eyes of the law and because no one wants to be, the put one in place. The latest craze is to put low profile with too narrow of a thread width. While they think it looks cool, the tire comes off the beed way to easy during hard cornering. Too wide of a tire and the thread shifts, causing excessive loading of the side wall. This will cause the side wall to fail, so to protect the general public who don't want to be involved in a collision, they put laws in Place to protect them.