Turn signal issues and tire size reset?

[mojocho]

Is that with CarPlay and iOS?

It is VERY easy to demonstrate an instant variance between the speed syncing to the speedometer using Waze on iOS connected via CarPlay and the speedo going out of sync when not connected to CarPlay on a vehicle with incorrect tire diameter.

My guess is you aren’t on iOS and connected to CarPlay.

CarPlay also passes fuel level info from the vehicle—I get pop-ups when fuel is low in CarPlay and Apple Maps offers directions to the nearest gas station.

The close integration you speak of already exist in your vehicle—with iOS and CarPlay.

https://developer.apple.com/videos/play/wwdc2016/723/

Ah, I'm on Android Auto via Samsung phone. Maybe that's why mine is not integrated

Sponsored

 

[Delhux]

With both my old JKU and my current JT, I found that I did have to set the tire size a little larger than actually measured to get it accurate.

…

Also interesting, I have an 80A Edition, and Jscan originally showed the same setting of 32.74 as yours.

Out of curiosity, how much larger did you have to set your tire diameter? And were you using tazer or JSCAN?

I adjusted my tire diameter via JSCAN last week and prior to adjusting, found that the preset tire diameter was read as 32.74”.

Prior to this, I had found that my speedometer and odometer were both reading only 93% of actual (odometer would record 9.3 miles after covering an actual distance of 10-miles, speedometer would read approximately 70 MPH when actual speed was 75MPH).

My initial approach was to take an accurate measurement of the tires and work from there.

I measured and entered my tire size as 34” (I’ve read some disparity in user experience entering sizes via JSCAN and tazer—tazer almost seems as though it “adjusts” user-entered sizes, while JSCAN just goes with whatever dimension the user specifics).

I have only been able to test it up to 45MPH and have not done an odometer test, but it still seems like it is reporting my speed as approximately 1MPH below actual speed at 45MPH.

One thought occurred to me: since I now know the pre-existing tire diameter value (32.74”) AND the previous deviation from actual for both speed and distance (7%), would it make sense to simply enter the current tire diameter to the value which would make 3274 93% of itself?

That would be between 3500 and 3525 (closer to 3525).

That value would be larger than I would have expected to enter, but it seems like it makes sense given 2 of the 3 variables (original tire diameter settings and deviation from actual) are now known.

 

[steveorama]

Out of curiosity, how much larger did you have to set your tire diameter? And were you using tazer or JSCAN?

I adjusted my tire diameter via JSCAN last week and prior to adjusting, found that the preset tire diameter was read as 32.74”.

Prior to this, I had found that my speedometer and odometer were both reading only 93% of actual (odometer would record 9.3 miles after covering an actual distance of 10-miles, speedometer would read approximately 70 MPH when actual speed was 75MPH).

My initial approach was to take an accurate measurement of the tires and work from there.

I measured and entered my tire size as 34” (I’ve read some disparity in user experience entering sizes via JSCAN and tazer—tazer almost seems as though it “adjusts” user-entered sizes, while JSCAN just goes with whatever dimension the user specifics).

I have only been able to test it up to 45MPH and have not done an odometer test, but it still seems like it is reporting my speed as approximately 1MPH below actual speed at 45MPH.

One thought occurred to me: since I now know the pre-existing tire diameter value (32.74”) AND the previous deviation from actual for both speed and distance (7%), would it make sense to simply enter the current tire diameter to the value which would make 3274 93% of itself?

That would be between 3500 and 3525 (closer to 3525).

That value would be larger than I would have expected to enter, but it seems like it makes sense given 2 of the 3 variables (original tire diameter settings and deviation from actual) are now known.

I think you may be over thinking it a bit. It seems Jeep's default tire size in the system is 32.74" which is interesting if you consider the stock tires on the Overland is 255/70R18 or 32.1". The Rubicon and Mojave on the other hand come stock with 285/70R17 or 32.7". It looks like Jeep just used the larger measurement to make their life easier. The speedometer would only be off around 1MPH at 70 so no harm no foul.

Now as far as resetting the tire size using JScan IIRC, I believe their instructions are to measure the height of the tire under load and then use the closest 1/4" measurement. When I did mine, I went ahead and used the exact tire size 275/70R18 or 33.25" as my baseline to determine if I needed to go up or down. I did a test drive and I guess I just got lucky as I'm now right on the money for Waze and a local radar.

Edit: All of that is interesting as prior to resetting my tire size, my speedo was off by about 2-3mph at 70. Which lines up with the stock size of 32.1" vs the replaced 33.2". My setting also started at 32.74" per JScan so if that was true I would of never seen much if any speedo variance. So take all of that as you wish, but I think the best thing to do is establish what you're at now and determine if you want to go up or down and just do 1/4" increments until you nail it.

 

[Delhux]

One thought occurred to me: since I now know the pre-existing tire diameter value (32.74”) AND the previous deviation from actual for both speed and distance (7%), would it make sense to simply enter the current tire diameter to the value which would make 3274 93% of itself?

That would be between 3500 and 3525 (closer to 3525).

That value would be larger than I would have expected to enter, but it seems like it makes sense given 2 of the 3 variables (original tire diameter settings and deviation from actual) are now known.

Just as an update, this method worked perfectly.

In the future, I won’t bother with all the tire height measuring stuff. Instead, I will just drive 10 (or more) miles on the highway using mile markers and record the odometer discrepancy (OD%).

Then, I’ll use whatever programmer I’m using to verify the vehicle’s current diameter settings (DS).

Lastly, I will just divide DS by OD%, and enter the value into the programmer as the new tire diameter setting (NTDS).

DS / OD% = NTDS

For me, OD% was 93%, DS was 3274, and the new tire diameter setting was 3520.

With that entered into JSCAN, my speedometer and odometer are perfect—no need to do funky tire measurements or repeated tinkering in the programmer—just one mile marker drive, a quick read of the current diameter settings, and easy math to get a perfectly calibrated diameter setting.

 

[Tim]

Just as an update, this method worked perfectly.

In the future, I won’t bother with all the tire height measuring stuff. Instead, I will just drive 10 (or more) miles on the highway using mile markers and record the odometer discrepancy (OD%).

Then, I’ll use whatever programmer I’m using to verify the vehicle’s current diameter settings (DS).

Lastly, I will just divide DS by OD%, and enter the value into the programmer as the new tire diameter setting (NTDS).

DS / OD% = NTDS

For me, OD% was 93%, DS was 3274, and the new tire diameter setting was 3520.

With that entered into JSCAN, my speedometer and odometer are perfect—no need to do funky tire measurements or repeated tinkering in the programmer—just one mile marker drive, a quick read of the current diameter settings, and easy math to get a perfectly calibrated diameter setting.

Glad I found this. I installed new tires and updated my tire size to how they measured which was 33.8” for my 35x12.5s. Something was off as I had 1/8 tank of fuel according to the DIC but the truck only took 14 gallons until the pump clicked off whereas I usually get 17 or 18 gallons in at that point. I reset the trip and watched the mile markers and it was off by almost .4 miles in a ten mile stretch. When I did the math it works out that I should have my tire size set to 34.9” for the odometer to read correctly. Interestingly, my speedometer was within 1mph with the tires programmed to 33.8 so it will be interesting to see how changing it to 34.9 affects things.

 

[Delhux]

When I first discovered this, I was convinced the new diameter settings were way too high and I’d have a seriously miscalibrated speedometer and odometer. But, as I posted, it worked perfectly.

Let me know how it works, “your mileage may vary”…

Glad I found this. I installed new tires and updated my tire size to how they measured which was 33.8” for my 35x12.5s. Something was off as I had 1/8 tank of fuel according to the DIC but the truck only took 14 gallons until the pump clicked off whereas I usually get 17 or 18 gallons in at that point. I reset the trip and watched the mile markers and it was off by almost .4 miles in a ten mile stretch. When I did the math it works out that I should have my tire size set to 34.9” for the odometer to read correctly. Interestingly, my speedometer was within 1mph with the tires programmed to 33.8 so it will be interesting to see how changing it to 34.9 affects things.

 

[Tim]

So after I reset my tire size to 34.9“ (even though they measure to 33.8”) the odometer is perfect. I mean it is exactly correct on a 12 mile stretch of highway. Speedometer is also good. Transmission shift points are also way better. The truck now drives pretty much like it did on the stock tires. When the size was not correct the truck was really dogging it and holding onto gears way too long. I know the computer wasn’t correct with the tire size being wrong previously but my range and MPG also went way up. I went from 15.8 mpg to 19.1 and range on full tank is back up around 400 miles.

 

[Delhux]

So after I reset my tire size to 34.9“ (even though they measure to 33.8”) the odometer is perfect. I mean it is exactly correct on a 12 mile stretch of highway. Speedometer is also good. Transmission shift points are also way better. The truck now drives pretty much like it did on the stock tires. When the size was not correct the truck was really dogging it and holding onto gears way too long. I know the computer wasn’t correct with the tire size being wrong previously but my range and MPG also went way up. I went from 15.8 mpg to 19.1 and range on full tank is back up around 400 miles.

MATH FOR THE WIN!

I’m glad to hear it all worked!

Sponsored