im thinking about picking up some 17x7 wheels, just wondering what tire size i should get to keep the speedometer as close to the right speed as possible, thanks

 

235/40-17 would be right on.

 

i got a question... what does the 7 mean in 17x7?
More importantly, are there any tire widths that are too wide for a 240 or shouldn't be used due to tractin etc? Anyone know a source that might give some limits to rim size or width or whatever on a 240?

 

...the 7 is 7inchs width. go to NICO and check out there tire forums. or go to tirerack.com and u should find sum info

 

this site got all the tire sizes and offsets needed to clear most coilovers
http://www.az**********/faq.html
and its a great FAQ page

 

nice faqs

 

For most purposes, the difference in speedometer reading is not going to be significant. It really isn't very difficult to know what speed you're going either. For example, lets assume that you were off by 10%. That would only be 6 mph at 60 and 10 mph at 100. Clearly that's pretty simplified but it doesn't get much more complicated.

If you really want to play around with different sizes, you can use the calculator at: http://www.web-cars.com/math/tiresize.html

Good luck,
Matt