Maybe a classic newbie question but before I put on bigger tires I would like to understand...

Based on the mph calculation program on this site, 30" tires at a certain RPM, gear, etc, will result in your speedometer reading 77 mph. 32" tires at the same RPM, gear, etc, will give you a reading of 88 mph.

Ok, so if its true that taller tires will cause your speedometer to show a higher speed than you are actually traveling, would this also cause your odometer to record more miles than you have actually travelled?

Wouldn't this decrease the time you have on your warranty as well as decrease the perceived value of your x?

Please let me know what you all think on this topic.

Thanks!

You have it backwards.

One revolution with the bigger tire moves you farther.

The speedometer will show a lower speed with the larger tires. It might show 65 mph but, you goin 69 mph. I'm not sure about the mileage. The easiest way to check your speed and mileage is with a GPS.

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?

If the speedometer is not accurate than neither is the odometer. If you have a 1 inch taller tire then the original then it will be off by about 4%. Not exactly but close to it and it will tell you that you are going slower than you really are and the odometer will be off by 4% less miles than you have actually traveled.

Upgrading to taller tires will make your speedo read lower than actual. The same goes for the odometer. If anything you will extend your warranty, resale, etc because your odometer will read lower mileage than the truck actually has. Once you make the upgrade, calculate the error using mile markers on the highway. Also, don't forget to adjust the mileage numbers when calculating you MPG, or else it seem worse than actual.

In an idle moment this weekend, I figured out that if I had upgraded to 31s when I first got the truck, I would have effectively extended my 100,000 mile extended warranty by 3,000 apparent miles or approximately ten weeks, whichever comes first.

Thanks everyone!

Math is not my strong point, being from a square state and all. :p

John

Silverxglider -

And, if you'd mounted 33's instead of those little bitty 31's...

You would have gotten another 16,279 miles extra coverage, or, if 3k = 10 weeks for you, then you would have also extend the warranty another 54 weeks (Over a year)