Well I finally got around to changing the speedometer gear on truck.

I had the stock speedo gear with ProComp 33/12.5x15 Xterrains and had the truck calibrated by AAA. You can see the 2-9 mph variance as well as the actual miles being off by 15% which of course throws off your gas mileage.

http://users.superford.org/harry5150/images/board/speedo1.jpg

I replaced the stock 19 tooth tan gear below...

http://users.superford.org/harry5150/images/board/speedo4.JPG

with the a 17 tooth green gear.

http://users.superford.org/harry5150/images/board/speedo3.JPG

Here's the results. Not perfect but much better.

http://users.superford.org/harry5150/images/board/speedo2.jpg


Details

1997 Explorer Sport
2WD w/ 5 Speed Auto Transmission
33/12.5x15" ProComp Terrains
19 tooth Tan Speedometer Gear (before)/ 17 tooth Green Speedometer Gear (after)

That was pretty cool to see the varience between March and August. How much does it cost to get those tests?

Free of charge to AAA members. :)

I'm an AAA member and ive never heard of this where do i go or who do i call?

Go to AAA.com, register as a member and then go to member services. I believe it's in the auto maintenance section & it gives drive up locations.