Can A Change In Tire Diameter Be Accurately Calculated ??

[TAB]

Short answer, yes, easy, just need to figure out the delta in circumference.   Reality, give how tire size. Hanges dramatically with wear, presure and tempure.   Then there is the whole accuracy of the system itself.  Its not really possible to get an accurate number.

[Bidah]

Sure you can calculate like has been described.  I had those tires on an older Suburban.  If I recall correctly the difference I found was 7% (grain of salt here).  I took the mileage that the tires had been on the vehicle, and added that amount.  Not that anyone cared, I just got to thinking one day...

[billt]

I don't want to think about the math right now, but I do have a question. If I understand correctly, you put a larger tire on, and your speedometer now says you're going slower than you really are? My truck basically has the metric version of 35" tires. My speedometer says I'm going somewhere between 2 & 4 mph faster (depends on speed) than I really am. That has been my experience with all larger sized tires.

I'll clarify. The larger the tire, the slower your speedo will read compared to your actual speed. (You'll actually be traveling faster than indicated). To help visualize, think the difference in rotational speed with monster truck tires going 60 MPH, compared to tires on a Toyota Camry. Right now if my speedo say's I'm going 60 MPH, I'm actually traveling faster.

[mkm]

I'll clarify. The larger the tire, the slower your speedo will read compared to your actual speed. (You'll actually be traveling faster than indicated). To help visualize, think the difference in rotational speed with monster truck tires going 60 MPH, compared to tires on a Toyota Camry. Right now if my speedo say's I'm going 60 MPH, I'm actually traveling faster.

I believe yours is doing that because I have no reason to doubt you. I just find it strange because mine does just the opposite. With larger than factory tires, my speedometer says I'm going faster than I am. If it says I'm going 70 mph, I'm really going about 66 mph.

[MikeBjerum]

Let's go back to the start here.  Why do you care how many "actual" miles?  For sale purpose you just report odometer.  That is what is asked for, and if you stray from that you open a can of worms.  For maintenance, etc., it is too minor to worry about.

[Sponsor]

[Timothy]

New cars and trucks, my 03 Ranger for example, have a speed sensor in the differential and compensates for tire diameter thru the control module.  If the module has not been programmed to the new tire size it will skew the numbers.

[billt]

Let's go back to the start here.  Why do you care how many "actual" miles?  For sale purpose you just report odometer.  That is what is asked for, and if you stray from that you open a can of worms.  For maintenance, etc., it is too minor to worry about.

Curiosity mostly. I'll never sell the truck because now that I'm retired I don't drive enough to justify buying a new one. I've had my 2015 Jeep Grand Cherokee for a year and a half now, and I just turned 3,800 miles. And over 500 of that was a trip to Lake Havasu City, Kingman, and back. Barring theft or a collision, I won't be buying any more new cars.

[alfsauve]

I use a GPS function.  First with a handheld, now with my phone.    You can compare mph at various speeds and if you have an accurate known track, maybe mile markers, you can compare distance. 


In both Pathfinders it tells me that my odometer is reading about 3mph higher at 65mph, than my actual speed.  Given the percentage difference, I can probably apply that to the mileage as well.

[billt]

You would think by now, the way cars have advanced, they would have a speedometer adjustment on them for different size tires. Aftermarket tires are so popular today.

[Solus]

You would think by now, the way cars have advanced, they would have a speedometer adjustment on them for different size tires. Aftermarket tires are so popular today.

That is why I wonder if it was set for the specific tires ordered with the car or for an "average" of the available options