Tire sizes and speedometer mileage reading
 

I currently have 255/45/20 and 275/45/20 on my truck and the other day on round trip of 28 miles, my speedometer only clocked it at 25 miles in my truck. My other modern 2017 car with stock wheels gets the 28 miles as per google maps as well.
Would the size difference affect the mileage so much? Just wanting to hear any input on this.

Re: Tire sizes and speedometer mileage reading
 

Tire diameter will affect mileage readings from a little to a lot depending on the size. Download a free GPS speedometer app on your phone and use it to compare to what your truck speedometer says. They are very accurate. Even the amount of tread wear can result in a difference from new tires to well worn.

Tom

Re: Tire sizes and speedometer mileage reading
 

I completely blanked out on using our wonderful technology that we all have access to these days, thank you very much for the suggestion. Any suggestion on a good app for the android phones to use (tried and tested please).

Re: Tire sizes and speedometer mileage reading
 

Taller than stock tires will lower the speedometer (and therefore odometer) readings compared to actual speed. Shorter than stock tires raise the speedometer reading compared to actual speed. I agree use a speedometer app (there are free ones) to compare indicated speed to actual speed. I did on the drive home when I bought my truck and found out an indicated 35mph was actually 50mph.

Where the speedometer cable attaches to the trans there is a gear inside the trans. You can change this gear to get your speedo to be more accurate.

Edit: Took to long to type out my reply. iPhone user here but my app is “GPS Speed” by Alterplay Pty Ltd, that I trust, maybe they have an android version.

Re: Tire sizes and speedometer mileage reading
 

I have an iPhone and the one I use is called Speed Box. I just went into the app store and searched for GPS speedometers and picked one that looked easy.

Tom

Re: Tire sizes and speedometer mileage reading
 

Thank you, I got something will test it out shortly.