i just got my staggered set of 18's on do i need to retune to compensate for the larger rim/ tire size?

 

I'm pretty sure, yes.

 

if you have a hand held, sct or diablo, you can change it through the there, i think it is in the optional parameters section

 

alright thanks alot guys

 

I assume by tune you mean adjust your speedo reading ????
It's Not necessary if new rear Rim/ Tire combo is same diameter as stock.
What was stock and You didn't say what size tire on your 18's

 

It's not a "tune" per sey. You just need to use the handheld to change the tire revs per mile (assuming they changed). It's not a function of wheel size. It's a function of tire size. So if your tire circumference hasn't changed, you don't need to do anything. And you only need to base it on the rear tires.

 

alright well im running 255/45 up front and 285/40 out back so thats really close to stock.

 

Either use the specs from the tire manufacturere, tirerack or you can try this...

http://www.1010tires.com/tiresizecalculator.asp

 

You don't need to change a thing with those sizes. Those are as close to stock as you can get.

 

Most handhelds have an option to correct it in inches. Mark a white line on the very bottom of your tire with chalk, then have someone slowly move the car forward until the chalk makes one complete revolution. Measure that in inches, and punch it in your tuner. Should correct it if it's off.