Tire size - 1979 GMC K15

[Steve W]

I have to replace the tires on my GMC 4x4 K15. I inherited the truck from my Dad and did a full body re-build. The door decal states that the factory tires are H78/15 and I now have 235/75/15 mounted. The problem I have is a speedo that shows 50mph when I'm actually doing 60mph. The mechanical part of the speedo appears to be OK.

The tire shop recomends a 30" tire or stay with the 235/75's. I currently get 16m/gal a want to keep that.

Any suggetsions would be appreciated.

Steve

 

[nerfherder78]

You should have speedo gears that can be changed based on your rear end gears and tire size. I havent done this to my truck yet so Im not exactly sure what it involves, you might be able to ask a mechanic or a transmission shop about it.

Hope this helps,
Craig