I picked up a set of used wheels with 245/45/17 tires. When i looked them up on tire rack they suggest 275/40/17. Is that what should be on there?

http://www.tirerack.com/wheels/Wheel...All&sort=Brand

 

How wide are the wheels? That's required to determine the correct tire size.

In general terms, the 245/45-17 fits on a wheel 7.5" - 9.0" wide. The 275/40-17 fits on a wheel 9.0" - 11.0" wide.

Consider the fact that the stock tires on the WS6 and SS coupes were 275/40-17 on 17x9.0" wheels.

 

Is there any way for me to measure while on the car? If not, i have two new tires going on soon and I'll measure. I just bought the size that were on already.

 

The wheel width is measured inside the rim, where the tire beads sit. Typically, the outside (overall) width of the wheel is about 1" more than the width inside the rim. Measure the outside width of the wheel, and subtract 1" to get the actual width, as measured inside the rim. Problem is that the tire sidewall bulge can interfere with the outside measurement.