i'm trying to locate a good deal on a set of BT45s.

I'm looking at DMTA (http://www.dmtaonline.com) and they stock the following:

BT45 REAR 140/80V17
BT45 REAR 140/80V18

what's the v17 & v18 mean? which should i get?

also, they only stock a 110/80 and 110/90 for the front. would it be a bad idea not to stick with the recommended 110/70?

the final number is the diameter of the wheel it is designed to fit. You want 17s.
Ideally you would want the 70 but if you have to choose take the 80 its closer and you can drop the forks the 5mm to make up the difference.

* The 17 is the size of your rims.  (Diameter in inches?)  The 18 won't fit.

* The 110/80 should fit fine, it will just be a little more round than the 110/70.  I wouldn't try the 110/90 though - that's getting a little TOO round (and too tight under the fender).

* V is the speed rating.  Look again for H-rated (up to 130 mph) tires.  They may have stock sizes in the H-rated section.  (V-rated tires are "safe" at even higher speeds, but they're overkill for the GS500.)

thanks for the info guys, i dug up the h-rated ones and they carried the proper 70 series front and rears.  new shoes are on the way!!