Wheel Offset & Size

[ViperGTSR]

Can someone please post a link to a good defintion of offset?
I was looking at getting some rims on ebay, and was wondering about the offset and width :18" x 8" (Front) Offset 38 and 18" x 9" (Rear) Offset 45 with 5x114.3 bolt pattern, and tires are Dunlop Sport FM 901 245/40/18 (Front) and 265/35/18 (Rear)

Now that rear seems like a near impossibility for our cars but please enlighten me. Will the tires add to this confliction? I am looking for some good information specific to my needs, and some general info about offset, because while searching (damn search wont let u search a SINGLE number!) there were very few people that understood offset. thank you

[AMRAAM4]

Pics in center of the page can be clicked on to make larger.

http://www.gmpperformance.com/products/wheels_tires/wheels.htm

[ViperGTSR]

Thanks alot that was a great site!

[AMRAAM4]

no problem:thumbs:

[AaronGTR]

Offset is the distance in millimeters from the wheels mounting surface (at the hub) to the wheels centerline. This can be positive (towards the outside of the wheel) or negative (towards the inside of the wheel). Most new cars are positive. How much offset and how wide a wheel you can use depends on the clearance inside the wheel well. Tire size and if you have drop springs affects it too. Remember that a 18x7 and a 18x8 wheel with the same offset will be in different places because the centerline changes. Also the wider wheel requires a wider tire and that will throw your speedometer off more. For example, if you went to a 18x7 wheel with 225/40-18's the speedo would read 60.6mph at 60mph. If you went to a 18x8 you would need a 245/40-18 which would read 62.1 at 60mph.

Remember wider/bigger wheels and tires are heavier too. Stock is a 16x6.5 wheel with 225/50-16's. Most people do well with either 17x7's or 18x7's with a 38-42mm offset. Tires could be 225/45-17, 235/45-17, 225/40-18, or 235/40-18.