I want to put 17" rims up from my 16" rims. Do i need to change the computer for the speedo and tach, or can i just bolt them on and drive. Also how much would it cost if i were to have the computer changed?

 

yes, you will need a recalibration if you change wheel size. dallas mustang offers a speedo calibrator for about $100, or you can change it yourself with a programmer or a custom tune for around $350 (but you get lots of other stuff changed at the same time that make you go fast(er) )

 

Or you could just adjust tire height to compensate.. IE my 275/35/18's read the same as my old 16's did...

 

yepper, just get the right size tire to keep the same tire height

 

so if i go up from my 225/55r 16 on the base and put on Gt rims (i think they are 245/45 r 17) should they just bolt on?

 

just ask the tire store what the "revolutions per mile" is for the tires you have and the tires you want to change to with the different wheels and get as close as you can to the same revs/mile and you'll be OK. the determining factor is the circumference of the tire, not the diameter of the wheel that matters when it comes to the speedometer reading.