Found a small change in tire size messes with engine performance.

[YBABRAT]

Original owner expected Falken M/T to be the same as factory Falken A/T in tire size, so they never bothered with calibration.

I ran 6k with the improper calibration which effected shift points and fuel economy. Now that I recalibrated using my Tazer JL Mini, staying in over drive gears in inclines that require some power is less common. I now get more linear function with automatic and better power characteristics. Getting better fuel efficency while not having to be cautious.

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[jadmt]

been preaching that for years...the number jeep uses for a rubicon with 285/70-17 from the factory is only 31.9" (not sure if tazer tells you the data the factory uses but AEV pro cal does) The inventor of the pro cal told me that the most accurate way to set the calibration is to park on a flat cement surface and measure from center of hub to the floor and double it. My speedo and tripometer are spot on using this method.

 

[Criztaztrophe]

been preaching that for years...the number jeep uses for a rubicon with 285/70-17 from the factory is only 31.9" (not sure if tazer tells you the data the factory uses but AEV pro cal does) The inventor of the pro cal told me that the most accurate way to set the calibration is to park on a flat cement surface and measure from center of hub to the floor and double it. My speedo and tripometer are spot on using this method.

I'm not saying you're wrong. But why wouldn't you just measure from the top of the tire to the ground? Any reason in particular? I've always just done that.

 

[Chemistry76]

The tire deflects at the ground, deforming the tire. It is not a perfect cirle. The radius below the hub, to the ground, is shorter than the radius from the hub to the top of the tire.

 

[jadmt]

I'm not saying you're wrong. But why wouldn't you just measure from the top of the tire to the ground? Any reason in particular? I've always just done that.

the inventor of the pro cal told me that is the most accurate way to do it. the guy who invented the pro cal is the brother of the owner of AEV and is about as smart as they come. I figured if he invented it he knows how it is supposed to work. When I measure from the top of the tire my speedo and trip are not 100% accurate like they are going from center of hub down. I have used this method of 4 jeeps and a power wagon. it will be easy for you to compare just use a stand alone gps and go for a 20 mile drive and see which way is closer on your tripometer. I can drive 100 miles and my gps and tripometer will be less than 5/10's off.

 

[Criztaztrophe]

Good enough for me, I'll switch to that method! Like Forest Gump said... Im not a smart man... something about chocolate.

 

[grimmjeeper]

The tire deflects at the ground, deforming the tire. It is not a perfect cirle. The radius below the hub, to the ground, is shorter than the radius from the hub to the top of the tire.

 

[YBABRAT]

A number of factors... sidewall strength, tire pressure with temp changes, are some. Just because it has the same numbers as oem, the type of tread and firmness of compound also effects deflection.

 

[YBABRAT]

been preaching that for years...the number jeep uses for a rubicon with 285/70-17 from the factory is only 31.9" (not sure if tazer tells you the data the factory uses but AEV pro cal does) The inventor of the pro cal told me that the most accurate way to set the calibration is to park on a flat cement surface and measure from center of hub to the floor and double it. My speedo and tripometer are spot on using this method.

Yes tazer tells what tire diameter is set by ecu. You can adjust up and down in small increments.

 

[calemasters]

Original owner expected Falken M/T to be the same as factory Falken A/T in tire size, so they never bothered with calibration.

I ran 6k with the improper calibration which effected shift points and fuel economy. Now that I recalibrated using my Tazer JL Mini, staying in over drive gears in inclines that require some power is less common. I now get more linear function with automatic and better power characteristics. Getting better fuel efficency while not having to be cautious.

I went from 33s to 35s. I did not notice any issues. But I did later recalibrate just so I could get into heaven.

 

[autotragic]

With my Tazer I set what I thought would be "close enough" and then watched my GPS speed compared to the speed on my dash. I ended up with 34.5" after a couple of tries. I cannot get a 100% accurate match, it's off by 1 mph either way but the factory calibration was off 3 mph so 1 mph off is still better than what they did.

 

[grimmjeeper]

With my Tazer I set what I thought would be "close enough" and then watched my GPS speed compared to the speed on my dash. I ended up with 34.5" after a couple of tries. I cannot get a 100% accurate match, it's off by 1 mph either way but the factory calibration was off 3 mph so 1 mph off is still better than what they did.

That's really the best way to do it. Measuring the tire (hub to ground) is a good start. But a check against a GPS will let you dial it in.

 

[roaniecowpony]

The tire deflects at the ground, deforming the tire. It is not a perfect cirle. The radius below the hub, to the ground, is shorter than the radius from the hub to the top of the tire.

So, if I have a track vehicle, do I measure from the center of the track and double it?

 

[roaniecowpony]

Hmmm. Where does all that tire tread circumference go?

 

[Camaroboi13]

I went from 33s to 35s. I did not notice any issues. But I did later recalibrate just so I could get into heaven.

So THAT’S what my problem is

eh, I just drive a diesel so it doesn’t care what size tires I have on it. When my Speedo says 65 I know I’m doing 74… keeps the mileage lower that way too

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