Tire sizing reprogramming question
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Laughing Gas
Joined: Feb 2004
Posts: 1,080
Likes: 1
From: Elsinboro, NJ
Tire sizing reprogramming question
Ok so calibrating the tire size with AE was a breeze. Only had to try four different sizes before the GPS and Speedo ran true to each other.
Now for the question: I had to set the size of the tires on AE to 32.25" to get the speedo to run in time with the GPS. Accurate to 90 MPH. Now I Have 315 75 R16 wheels and 3.73 gears. I'm pretty sure a 315 would equate to a 34.60" right? Just wondering why that I had to actually program almost three inches smaller to get it to calibrate.
Thoughts?
Now for the question: I had to set the size of the tires on AE to 32.25" to get the speedo to run in time with the GPS. Accurate to 90 MPH. Now I Have 315 75 R16 wheels and 3.73 gears. I'm pretty sure a 315 would equate to a 34.60" right? Just wondering why that I had to actually program almost three inches smaller to get it to calibrate.
Thoughts?
Post Fiend
Joined: Mar 2007
Posts: 26,966
Likes: 50
From: Texas
Because the speedo was off from the factory. If you had corrected to the correct size, then you would have remained off by the same factory settings.
I drove a couple hundred thousand miles on my truck before I got a GPS and discovered my speedo had been off since day one.
I drove a couple hundred thousand miles on my truck before I got a GPS and discovered my speedo had been off since day one.
Cargo Master
Joined: May 2010
Posts: 3,047
Likes: 10
From: Snohomish, WA
I have found that every truck I have recalibrated required smaller than actual size. I always measure the actual height, then start 2" less than measured. I usually get it pretty close or right on that way.
Posting Guru
Joined: May 2007
Posts: 1,141
Likes: 0
That is about right 315 are only 33.5 inches tall, you can check your AE buy putting a mark of white paint on the rear tire at the bottom dead center,and mark the ground, drive truck till one full revolution, measure distance and divide by 3.146. 315 only measure 33.5 at the most depends on the brand, my 285-16 michelins are programmed at 31.75.
