05 Dodge Ram 1500 Rim/Tire Questions

[Raminator157]

Recently I purchased stock 17 inch rims and bought cooper winter tires. 265/70R17

I had the stock 20 inch rims with GOODYEAR WRANGLER HP 275-60-20

It seems like I am going slower then what the speedometer says. Was my trucks computer programed for 20 inch rims? I figured if I put stock smaller rims with stock winter tires I would not have an issue.... Help?

 

[DeRocha]

Your stock (20") tire diameter is 32.9" while your 17" snow tires are 31.6" (obviously a difference of 1.3"). Therefore when you have the winter tires on you will be going a few mph less than what the speedometer shows.

Speedometer______ Actual
...(mph)...........Speed (winter tires)
.....35.................33.62
.....40.................38.42
.....45.................43.22
.....50.................48.02
.....55.................52.83
.....60.................57.63
.....65.................62.43
.....70.................67.23