I have a question reguarding my 07 silverado classic 2wd. 5spd 4.3l reg. cab truck. The truck came factory with 17" wheels but someone put on 20" chevy performance rims and tires. Does the speedo need to be recalibrated or does it electronicly fixes itself?

Thanks for any help.

 

id imagine it would be fine.

 

It depends on which 17's came with truck from the assembly line. If the truck came with 245/70/17 it has a rolling diameter of 30.5" tall. If the truck came with 265/70/17 then it has a rolling diameter of 31.6" tall. The OE 20" have 275/55/20 that have a 31.9" rolling diameter.
If trucks OE size is 245/70/17 @ 60 mph with 275/70/17 you are really going 57.3 mph.
If trucks OE size is 265/70/17 @ 60 mph with 275/70/17 you are really going 59.9 mhp.