First off I'd like to say that the xB is one of the coolest cars out there. I love the car and i'm gonna be keeping this car forever.

Now to the serious part...I just wanted to have a few questions answered because i'm somewhat uninformed about the offset, why it's important etc. and other things involved with the wheel and tire setup:

1) What is "offset" and why it's so important in optimizing the best setup for your rims.

2) What are some of the differences between the sizes of tires, for example, 225 or 215 etc., and how does it affect ride quality.

3) I already have my 18" Velox VX-8's chillin' in my garage and i just wanted to know what the best setup is for tires so i don't have to do any tweaks on my fender and what not. (i'm also going to have my spy springs installed too)

THanks for you guys support. Now i'm ready to hear you guys' responses.

The offset of the wheel determines where the backpad sits relative to the center of the wheel. It is important because even though a wheel may be 18×7.5, the offset may make it sit too far inside and hit the suspension, or stick too far out and extend past the fenders. You can see a detailed explanation here: http://www.tirerack.com/wheels/tech/offset.htm

Tire sizing is just that. The first number in a tire size will give you the tire width in millimeters. For example a 185/60R15 is 185mm wide. The 2nd number gives you the aspect ratio for the side wall. On a 185/60R15, the side wall will be 111mm (185 ×.60). "R" refers to the size of the opening in the tire. On a 185/60R15, the opening in the tire is 15" thus designed to fit a 15" rim. To keep your odometer and speedometer relatively accurate, you will want to keep the overall wheel height within 3% os the stock height. To figure this out, you need to do the following:

Take the width of the tire, and multiply it by the aspect ratio divided by 100. This will give you the side wall height. Example: on a 185/60R15 tire, 185mm ×60 ÷ 100 = 111mm.

Multiply this figure by 2. When figuring the overall height, you have the sidewall on the top and on the bottom. So now we are at 222mm (185/60R15 example).

Now we need to add the middle portion. Since it is in inches, and the sidewall measurement you have is in millimeters, you will have to convert. 1" = 25.4mm so multiply the last number in the tire size by 25.4. For the 185/60R15 example, you will do 15×25.4= 381.

Now you take the 381mm (opening in the tire) + 222mm (side wall ×2) and you get 603mm which is your overall wheel height. If you want this figure in inches, divide by 25.4 to get 23.74". You will want your new tire to end up ±3% to this figure.

The easiest way would be to create a formula in Excel so you can just hammer in different sizes and it will spit out the height automatically.

So... on your Velox 18's.. what is the width and offset? This will determine the optimum tire size.

the width is 7.5 and the offset is 40