You do have it backwards.
The odometer counts each revolution of the tire as the distance around the stock tire (Circumference)...
When the tire's circumference is longer, you are going FARTHER than it thought you were.
The easiest relationship to picture is the mileage and the speed are off by the exact same percentage.
The key is that the speedometer will read a speed slower than your actual, and the odometer will read a mileage thats shorter than your actual.
If you are going 10% faster than the speedo says, you are also going 10% farther than the odometer says.
I think of it this way:
The wife sitting next to me see's I am not speeding too badly....and the dealer I trade it in to see's I have fewer miles on the trade in.
And I never tampered with the odometer.
I have 33" tires, and my speedo is off about 14%
If you need to confirm your speed, use the mileage markers along the road...hit the trip odometer button to reset it as you pass a marker, note which one....and after 10 miles or so, check your trip odometer reading against the mileage marker distance.
If you had 10 miles on the markers, and 9 miles on the odometer, you're off by 11%, etc. Your speedo and your odo would then be off by that amount, at all speeds.
(Divide the marker distance by the odometer distance, subtract 1, and multiply that by 100 to get the percentage.)
The percentage is the amount you add to the speedometer or odometer reading to get the real numbers.
10/9=1.11-1=0.11x100=11%
if the speedo says 100 mph, add 11%, and you are really going 111 mph, etc.
Or get a GPS.
Does that help at all?
_________________________
- TJ
2001 Xterra '03 VG33, SE 5 spd, 305/70/16's, Revolvers, UBSkidderz, Doubled AAL's, 3"SL/2"BL, winch/bumpers, skids, sliders, OBA, Snorkel, pine stripes....
Friends don't let friends drive stock.
http://www.gifsoup.com/view/501230/tj-tackling-crawlers-ridge-o.gif