Calibrating the Speedo for a slight change in tire size
10-22-2014, 11:55 AM
#1
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Calibrating the Speedo for a slight change in tire size
Hey guys, I could use some help.
I own a 2012 FX2, the 5.0 engine, stock size tires that came on mine were the Michelin LTX 265/60-18
A few days ago I changed them out and upgraded to a Michelin LTX 275/65-18. Dealer did the change and reprogrammed the speedo to compensate for the tire change (charged me $55 to do it). However, GPS, radar signs, and with help from a buddy, my truck is reading 3mph lower then actual speed when traveling 60mph.
Took it back to the dealer today and all they could tell me was, the correct size was programmed, and they double checked. I was told this is the same tire the FX4 and 4x4 use from factory.
What can I do to correct this?
On a side note, I also noticed my MPG gage (which has always been fairly close to real world) is reading 2-3mpg off from my calculations.
I own a 2012 FX2, the 5.0 engine, stock size tires that came on mine were the Michelin LTX 265/60-18
A few days ago I changed them out and upgraded to a Michelin LTX 275/65-18. Dealer did the change and reprogrammed the speedo to compensate for the tire change (charged me $55 to do it). However, GPS, radar signs, and with help from a buddy, my truck is reading 3mph lower then actual speed when traveling 60mph.
Took it back to the dealer today and all they could tell me was, the correct size was programmed, and they double checked. I was told this is the same tire the FX4 and 4x4 use from factory.
What can I do to correct this?
On a side note, I also noticed my MPG gage (which has always been fairly close to real world) is reading 2-3mpg off from my calculations.
Last edited by Sheepdog00; 10-22-2014 at 12:36 PM.
10-23-2014, 07:56 AM
#2
Senior Member
It's not an exact science, there are so many variables between vehicles, 2-3 mph variance is not unheard of. Speedometers are known for speedometer error of +/- 2 mph. But if you know what the difference is, short of them not being able to dial it in, you know what you need to do to compensate.
10-23-2014, 01:03 PM
#3
An aftermarket programmer that does tire size might get you closer. Usually the dealer has very few adjustments they can make. If their settings for your tire size arent correct theres not much they cwn do. Also. There will be some size variance between brands of tires, even in the same size
10-23-2014, 05:34 PM
#4
Senior Member
They can program in a slightly different size tire and get it accurate. Example yours is reading 3 mph slower then you are traveling, have them program in a 275 70 18 or a 275 75 18.
10-26-2014, 04:40 PM
#6
Senior Member
My FX4 with the stock Pirellis is pretty well as good as it gets on the speedo versus a GPS. My XLT however with its stock 275 65 18 Wrangler AT/S tires reads a good 3 mph faster than actual speed. Pretty good degree of variance between two stock tire equipped 2013's. One of these days... like maybe Tuesday I am going to hook HP tuners up and fix that on the XLT... among other things lol.
10-26-2014, 04:48 PM
#7
Senior Member
My stock 265/70/17's red a few km more than actual speed. With the move to 285/70/17 (33") it is dead on accurate. The truck drives well and I don't feel the need to program it.
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10-26-2014, 04:55 PM
#8
Odd how so many get different results with tire size changes, I had 265/60/18 (30") and went up 2" in size to a 275/65/18 (32") and my speedo is dead on accurate compared to gps.
Go figure.
Go figure.
