speedometer calibration

[Rubiwoo]

Finally got my new wheels and tires mounted and installed onto the JTR. Used my Tazer JL Mini to adjust to what the tire manufacture says the tire diameter is 36.8. I'll do a measurement another day and time. set the cruise at 65mph and used google maps for that mph. Google maps shows me at 63mph.

My question is, do i adjust up or down for tire diameter to get closer to matching google and in car odometer?

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[Terminus33]

Increase diameter a couple points

 

[jay21mojave]

IMO... adjust tire diameter up.. when you measure I would bet you will find less than the mfg diameter. I'm not sure that the Google speed is accurate either. On my JKUs with 35s mine reads 3 mph fast vs WAZE. Keep us informed..

 

[kevman65]

I used my Garmin GPS and my radar detector, they both have GPS MPH.

The two are off to each other about .125 MPH, I set my speedo to the faster of the two.

 

[cdyoung9799]

Any time I change wheels/tires, I reset my speedo with my Flashcal. I've used a few GPS apps to check my speed, but I don't have the utmost faith in their accuracy down to the actual MPH. When I use these in my company work car, which is bone stock, they tend to show I'm going slower than I really am. There's a speed radar sign in a neighborhood close to my house that is always on, so I use that as a benchmark. Or I'll follow my wife in her car while we're on the phone so I can compare my speedo to hers. I usually just assume I'm 1-2 MPH over the limit at all times.

 

[Rubiwoo]

Bumped it up to 37.05 and using Google maps and a near by road speed indicator thing, I got it pretty close. Set cruise at 50 and the sign and google bounce between 49-50.

I suspect another small bump should be spot on.

 

[Rubiwoo]

So i was playing around with the tire size again yesterday and notice the vehicle getting sluggish. I went back to 36.78 (value provided by the Tazer mini) and the vehicle seems happy with that value. Tested with google again and the street speed sign and oddly, it now reads 49 when cruise is set to 50? Prior day was 2 mph fast. I'm just going to leave it and call it good..

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