Quick question. My truck originally came with 275/65/R18 tires. Would 255/65/R17 cause my odometer to read higher speed and rack up mileage faster, or are these tires equivalent height to my stockers? I get confused with the ratios. Thanks very much!

 

Yes, you are going to change your speedometer and odometer, unless you can get it reprogrammed.

 

https://tiresize.com/speedometer-calibration/

 

EDIT....Sorry a couple minutes late.

 

Wow, I didn't realize there was that much difference! Thank you very much! I guess I won't be going this route. Was trying to save a few bucks on a Craigslist deal on wheels and winter tires, but I don't think I will. I'd prefer not to ForScan it, cuz I'll forget when I go to put my summer tires back on. Thanks again!

 

SO, I guess my next question is, do our trucks measure mileage based on actual tire rotation or the speed that the speedometer is reading? All this electronic crap really throws me for a loop. It used to be much simpler when there was just a cable attached to the transmission, unless of course it's still done that way...

 

The speedometer reading is determined on the tire rotation. Changing tire diameter (and thus revs per mile) without changing it in the truck will cause the speedometer to be incorrect as well as the odometer.

Or at least functionally that seems to be the case, because if you put a taller tire on, for example, without programming that into the truck, your odometer and speedometer both read 'low'

 

Based on the homework done by Matt, you will read 6% larger in miles (distance traveled) and speed (speed in MPH).
There is no difference now with electronic than the old cable driven by the gear inserted in the transmission.

Changing a size of tire in the old days, and today, both would alter speed and distance.

 

The link I provided shows how the speed changes, which also means odometer will accumulate incorrect mileage.

 

You can change it for free with FORScan..

This is the third time I've responded to this question today lol

Look into it via the sticky at the top of this sub-forum. It's worth the $25-$35 adapter to get you going. And that'll literally be the only money you spend to use it.