Ijust got my new tires235/50r17 front and 275/40r17 for the rear. But when i compare them to what I have 275/60r15 they are a couple of inchesshorter than what i HAVE KNOW. I was thinking of going to 18" rims for the back and then i can go with bigger tires. I S THERE any problem having 18 on the back. I am going with Firestone Firehawk Wide Ovals. Theyu rate good on the tire rack site. They don't have bigger ones in 17,s. Thanls billjl

The specs on your current wheels would help in recommending tire sizes you might find appealing. Diameter, Width, backspace/offset.
M&H makes some taller 17" drag radials that could work.

My wheels are Cragar SS front 17x8, rear 17x9.

Hope I'm calculating this correctly, if not someone will certainly point it out:

275/60 = 165mm of sidewall height (275*60%)
275/40 = 110mm of sidewall height (275*40%)
15" wheel = 381mm
17" wheel = 431.8mm

You gained only 50.8mm of height switching from 15" wheel to 17" wheel, but lost more than that going from a 275/60 to a 275/40.

That's not a bad thing, as long as the whole car is going down - closer to the ground should equate to all-around better performance. But they might not fill the wheelwell the same as the old ones.

How about a 275/50-17 Drag Radial for the rear? Same diameter as your 275/60-15.
http://www.mandhtires.com/store.php?crn=70&rn=294&action=show_detail