Changing tire size could make both your speedometer and odometer off.

Use or borrow a GPS for a day,..they are right on the money MPH wise.
Beats the heck out of going to a speedo shop at $85.00per hour.

that's a good point about the odometer reading. We've switched from tall rubber to LP22.5's and I know our speedo's are off. Hmm. May have to rethink things here.

When I checked my mileage on my 2002 international, I discovered That for every 7 actual miles ran showed up as 10 on the odometer. This truck runs perfectly and mechanics always comment on how nice the the truck runs with over 700,000 miles. I believe the engine only has around 500,000 miles,
Obviously I, and the previous owner has been over maintaining the engine wth oil changes and any other maintainance based on mileage. :lol:

It isn't difficult to recalibrate the speedometer.

I agree with GMAN, sounds like a change in tire size wasn't accounted for somewhere along the line.

DaveP Look on your drivers side door jam on your IH it should have a sticker telling what size rims your truck came with.
Mike

Doghouse is correct. Borrow a GPS, they are dead on accurate.


DaveP, being off 2mph is not a big deal. Thats 20 miles off at the end of a 10 hour day of driving. Chances are, your speedometer is the one that's off and not the odometer that records the total mileage. I know my speedometer doesn't always show the correct speed but I know the odometer is right on. I've done the calculations while driving using a timed mile at 60 mph and also with my GPS.

Yeah, that's only 4000 miles (or more) off per year. No biggie, especially if you are basing your maintenance, costs, "IFTA, etc. off your mileage. :roll:

The speedometer and odometer are tied together. It takes a helluva lot more than "a timed mile" to show a fraction of a mile. I seriously doubt you are capable of seeing a 4% variance per mile with your naked eye. And we all know you don't keep track of miles, so by the time it would show up, you wouldn't be noticing it anyway. :roll:

Naw....just proffessional tourists..... :wink: 8) 8) :lol: