I am trying to buy a set of 18" rims for my S10 blazer but I can't figure out what all the numbers mean could someone tell me what a 7.5J x 18-ET21 rim is and will it fit my truck????

 

never heard of a measurement like that
is the truck 4wd or 2wd?
2wd needs 4.5 inches of backspacing and the bolt pattern for both 2wd and 4wd is 5x4.75

 

Yah I agree with packofqtips I've never heard of a reading like that. Try looking a little more on sizes and readings and post them here

 

Amateurs! That's how a lot of sites list measurements, especially Discount tire. 7.5J x 18-ET21 is a 7.5" wide rim, 18" diameter, 21mm offset. not sure on the -ET though. I know it can't be a negative 21mm offset since that would have a huge lip and stick out. Being only a 7.5" wide wheel that sounds like a FWD offset and might be OK if you have a 4x4 but you didn't mention that or bolt pattern of the wheel you got those specs off of.

If you have a 4x4, look for 18" rims that fit a 93+ Camaro/Firebird/Corvette