Yes. By approximately 2.5%. When you're speedometer reads 60MPH, you'll actually be doing about 61.5

 

To keep the same ration you would 245/35-18 tires. To run 245 tires you need 8.5" wide rims. I have found very few rims available in 5-110. I do thorough investigation and have found multiple sites that say they have 5-110 rims in 18x8.5 configuration. When doing further research(going to the manufacturers web site) I find that the manufacturer doesn't even make rims in the 5x110 pattern. They do make them in a 5x108 or 5x112, however both will not fit our cars.

I have also looked at getting bolt pattern adapters. The thinnest I could find were 19mm. If I did choose to go this route I would do the 5x4.5" pattern. This pattern allowed me to look at wheels for 2008 Honda S2000 which also requires a large positive offset like ours does. Unfortunately with he 19mm spacer you would need a 54-61mm offset to even come close to having the wheels sit under the the car correctly. What ever offset you are looking at, subtract 19mm from it and that is how much farther they would sit out with the spacers. I wasnt prepared to have my rims and tires stick out an additional 1.3" from the fenders.

I have since decided that going with18x8 rims is the most fee-sable route. Also, after doing a lot of some math, 235/40-18s are the best tire size choice for getting your speedometer right.

Hope this helps, just my 2 cents.

 

as a side note mixing tires can affect abs and such...you say what about tire wear? Well.. the tires wear at approx the same rate so they all are being reduced in size at the same time...when the abs sees a different wheel speed at different corners that doesn't go away what do you think it will do? It will think one end of the car is spinning.....different sized tires will remain different sized tires all the way thru the wear cycle...

 

My fronts wear considerably faster than the rears......

 

And THAT is why you should rotate them.

 

And that's how I found out...... I didn't do the wearing, I got the car used.

 

I am by no means an HHR pro. However, there seem to be some rather large holes in logic here.

Changing rear tire sizes should have any effect on traction control... FWD here. Not that it would anyway even if we were talking on the fronts.

Tire sizes should not effect ABS at all. There is a tone ring and sensor near the hub that spins... reads 0 & 1s like digital code. Think about all the truck guys putting on big knob tires and all the hood suvs rollin 26's. No issues and shouldn't expect any.

Speedometer... again, FWD and speedo pick up is going to come off the trans output shaft. Rear tire size should make no effect.

Guys have been putting bigger wheels in the back for ages. Sure with no electrical sensory bs like we have now. However, I don't see the doom and gloom by doing so.

That being said, I wouldn't do it, because I think that change in side wall size will be more noticable then the slight fender gap.

Want to rid the fender gap? Lower the rear more, or weight it down.

But by all means, if I'm way off on the HHR, please correct me.

 

I agree with what he said.

 

thinking of running conti dws 245x40x18 should lower wheel center by .15" has anyone tried this size on ss wheels?

 

first off, the stock tire size on the hhr ss is 225/45/18 not 225/40/18s, that's cobalt sizing. second, I've ran 245/40/18s in the front with stock in the back and also 245/45/17s on cobalt ss/na 17x7 rims. 245/40/18s fit perfect but your speedo will be off as will the odometer. I have tried offsetting my mph with hp tuners but the odometer still reads incorrectly, not something I can adjust.

245/40/18 dws are awesome tires and I wish I wouldve purchased them instead of the 17s especially since they've raised the price on them by like 30 a tire. imo I'd go with the eagle gt's over the dws now due to the pricing... dws are one of the highest rated all seasons tho. also, a 255/40/18 will fit the stock rims(and the speedo will be correct), but will bulge a lot like my 245s on the 17x7 rims.

just remember, wider tires are worse in the snow than narrower tires of the same height.
hope this helps