Speedo off
- Thread starter Sugarbear
- Start date
MountainRambler
New member
Most GPS systems are not that accurate it is quite possible for your speedo to be +/- 3MPH different from your GPS. Make sure you double check your tire diameter measurement on the outer, middle, and inner parts of the tire. :thinking:
jeeeep
Hooked
you measured from the ground up to the edge of the tire, not the center height? I ended up adjusting the size down until I got a match on GPS then checked it with a mile marker test line (I found one on a side freeway), if I recall I ended up entering a size down of almost 2 inches
I've also tested against those electronic speed signs - the ones that let you know how fast you are going.
I've also tested against those electronic speed signs - the ones that let you know how fast you are going.
cozdude
Guy with a Red 2-Door
So on my 315/75r16 mud grapplers I measured 35.25 at 28 psi. Make sure you have your tires pressure right where you want it, then measure from the ground to the bottom of the tread where it meets the sidewall. This will give you the most accurate measurement.
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steve_r2
New member
Speedos are calibrated higher usually by the manufacturer so your nav is probably giving you your true reading in comparison.
Here's an article on it:
http://www.thecarexpert.co.uk/how-accurate-is-a-car-speedometer/
Here's an article on it:
http://www.thecarexpert.co.uk/how-accurate-is-a-car-speedometer/
GPS's are actually pretty damn accurate or at least, mine are and it should be a good indicator as to whether or not your speedo is off. As mentioned, you need to measure from the ground to the edge of the tread or to the center of the wheel and X2. Both will give you the correct number you need to plug into the programmer. DO NOT put in what is written on the side wall or what it "should" be based on a chart or online calculator.
Brankz
New member
Can you post a pic of your tire? 34.5 it's like the smallest 37s.
My next tire may be 315/75/16
MountainRambler
New member
Upon further study I made a bad assumption :doh: GPS are accurate within +/- 3 feet for your position, when it comes to speed Wayoflife is exactly right they are pretty damn accurate. GPS speed calculations are accurate to within +/- 0.1 MPH at constant velocity. Sorry for the bad information, Next time I'll double check before posting.
cozdude
Guy with a Red 2-Door
here you go brankz. this is mine with the same dimensions
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Sugarbear
New member
