I am switching from 16's to 17's on my 2010 LT. I bought some 17X7 rims and I would like to know the widest tire I can go and still keep the speedo fairly close...will a 235/45-17 work ok?

 

http://www.anycalculator.com/tiresize.htm will help you compare speed changes between different tires. From what I saw, the difference is negligable - with a .015" diameter difference. 60 = 60 mph.

I would not expect there to be any clearance issues - but I may be wrong on that. Others can probably comment better on the clearance issues. Clearance also depends on the offset of the new rims. So post the offset specs if known, as it will help others figure out how well it will work for you.

Be aware that dropping to a 45 profile tire might lead to a bent rim or such with potholes (I had a lot of bent rims when dropping from a 50 to a 45 series tire on my other car - mind you, it's rims are rather "soft").