Originally Posted by iyamdman
Your Post was really great. All the info I was looking for. I am thinking of getting an 05 GT Limitied.
I want to figure out the best tire/rim size for me.
I am nervious going with a <45 tire since they don't take pot holes and road debrie well. Also, it will roughen up the ride.
What I want to do is get a handeling increase by increasing the tire patch, not by having a narrower tire height.
I think this would mean using a 17" x 8 rim with a 245/40 tire.
My question is does the 245/40 tire have a similar side wall height as the stock 215/45?
Also, what do you think of the daily drivability of the 245/40/17?
Don't be afraid of a 35 series profile tire. I run a 255/35/18 tire and I use it for everyday driving. "Yikes! A 35 series?!" Hold on.. I will show you how a 255/35/18 will actually have the same, if not, more sidewall than a say a 215/40/18. The whole matter is that the series profile is nothing more than a percentage based on the width of the tire.. so the wider the tires, the taller the sidewall (it's all proportional). So the first number is the width in Millimeters, the second number is the percentage of the width of the tire for the profile height, and the third number in the tire size is the rim size. Anyway, here's a simple calculation for the two tires:
255mm x 35%(series) = 89.25mm profile height of the tire
215mm x 40%(series) = 86.00mm profile height of the tire
So you see, just because it's a 35 series doesnt mean it's going to be a thin tire, in fact from this comparison, it's actually thicker. The trick is to find a tire that can fit not only your rims, but under your fenders (if you plan to go that wide).
So for your question "does the 245/40 tire have a similar side wall height as the stock 215/45?". Well, here we go:
245mm x 40% = 98mm profile height of the tire
215mm x 45% = 96.75mm profile height of the tire
So as you can see, it's actually bigger - not by much, but it counts, I can go into the effects of overall tire diameters later.
Today's lower profile tires have better technology such as stiffer sidewalls, reinforced sidewalls, and even run-flats. These are all the matters of keeping your rims from bending. One that I do caution people is that you NEED to check tire pressures frequently to keep them properly inflated so that the tire can support the weight of the car and the abuse of potholes. I will have to put up a new post about "how to properly inflate a set of aftermarket tires."
If you want to go with better handling, you can still do a 225/45/17. It's less weight (comparing to a 245/40/17), your car's stock alignment will still be in compliance and there's a lot of great tire choices in this size. Having a really good performance spec alignment will make use of all 225mm. If you want to have a wider size, you can run a 245/40/17 and run a flatter (less camber) alignment to make use of the acceleration and braking traction. Both are good tire choices (see my side notes on each tire size). The 225/45/17 with an 8" wide rim will definitely be performance driving since you will be able to feel the feedback as you need from the car.
For 18" rims, a 225/40/18 is very doable for daily driving (yes, even for potholes, provided that you drive a little slower over them when you see them and keep your tires properly inflated). For more of a flatter setup and less camber, 245/35/18 is a good choice as well. I run a 255/35/18 on a 18"x8" rim because, well, I am just being Xenonk
and I am crazy like that.
As for the rim fitment, that's up to you.. if you plan on running a 245mm tire, run a 8" wide rim. If it's a 225mm, you can run a 7.5". I am going to update my wording on the rim to tire fitment issue to express my thoughts on what works for performance, and what just works for slower-non-performance daily driving.
Hope that clears things up.