How to correct speedo for tire size change ?
Captain
Joined: Sep 2013
Posts: 586
Likes: 17
From: Nevada
Just for reference, a 33" tall tire has a circumference of about 8.6 ft.
If my math is right that tire would be 50.5 inches tall.
If my math is right that tire would be 50.5 inches tall.
Last edited by frankie_b_jr; Jul 9, 2016 at 12:15 PM.
Registered User
Joined: Jul 2016
Posts: 9
Likes: 0
So I got a speeding ticket, 14mph over, 49 in a 35 zone.
I saw the Officer on his bike waiting for speeders with his speed gun.
Thing is I was watching my speedo at the time and it was only
showing 2-3 mph over.
I double checked it later, side by side with my brithers truck which is dead on and my truck is way off.
My truck came with 245/75-16
I now have 265/75-16
So how do I correct this ?
I saw the Officer on his bike waiting for speeders with his speed gun.
Thing is I was watching my speedo at the time and it was only
showing 2-3 mph over.
I double checked it later, side by side with my brithers truck which is dead on and my truck is way off.
My truck came with 245/75-16
I now have 265/75-16
So how do I correct this ?
Captain
Joined: Apr 2016
Posts: 647
Likes: 3
From: Alabama
That's a BIIIG tire! Don't think that'll fit my truck.
You're right. It must not be revolutions per mile as was suggested.
8.6 ft circumference equals a diameter of 32.87 inches.
A 50.5 inch tall tire would have a circumference of 13.2 feet.
Administrator
Joined: Apr 2010
Posts: 87,403
Likes: 4,214
From: Clayton MI
It is, you are correct. Need to program the PCM for larger tires. The 97 and younger trucks, its just change a gear. 
Registered User
Joined: Jul 2016
Posts: 9
Likes: 0
There is two on them trucks. One on the rear-end and one on the side of trans under driver door. When I buy dodge truck now that's the first thing g I go ahead and replace is the speed sensor on side of tranny and the tps sensor