Recalibration issue

[Crownline]

Long story short, purchased a new vehicle that the original dealer (four hours away) put new tires on without recalibrating. Got Jeep Cares involved and our local dealer performed the recalibration. Got it home and it's still around 4 or so mph off. If speedo says 66, gps apps say 70. If we're going slower, it's about 3 mps off, etc.

Took it back to local dealer and said it's not right. They supposedly looked at it again and said it is right and it's normal for the speedo to be 3 or 4 mph off even AFTER recalibration. What??? NO!!!! I have no idea what tire size they are using as my husband talked to the service guy himself (not the actual guy who did the work). Opinions??

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[BDinTX]

Stab in the dark here but if the new tires are the metric 35” BFG KO2 (315/70R17) and they plugged in 35” instead of 33.4” that could be your discrepancy.

 

[Crownline]

Stab in the dark here but if the new tires are the metric 35” BFG KO2 (315/70R17) and they plugged in 35” instead of 33.4” that could be your discrepancy.

That's exactly what happened, BUT the guy said there's nothing they can do about it, bc there isn't an option for anything between 34.5 and 35. Which is true, there isn't. But the program or whatever they use says is that's the case, to call them (MVP, Mopar) and they will create a new contract with a specific tire size so it's accurate.

Oh, and the dealership guy claims putting anything but 35" is illegal.

 

[beaups]

If gps app shows faster than speedo then dealer plugged in too small of a size, not too big. Are your pressures possibly set way too high?

 

[Crownline]

If gps app shows faster than speedo then dealer plugged in too small of a size, not too big. Are your pressures possibly set way too high?

Tires are all around 35 psi.

I believe you have it backwards (see my attachment), but I'm no expert. I do know when my husband suggested putting it to 34.5, the service guy said then it would be reading higher...which I'd be fine with if it was closer.

 

[beaups]

Tires are all around 35 psi.

I believe you have it backwards (see my attachment), but I'm no expert. I do know when my husband suggested putting it to 34.5, the service guy said then it would be reading higher...which I'd be fine with if it was closer.

The lower you set the tire size in the bcm, the lower the speedo will read as the bcm will calculate less distance traveled per rotation due to the lower circumference it believes you have. He has the value set too low. My guess is it’s still set for 33’s.

 

[Crownline]

I'm still confused bc this is telling me otherwise.

 

[beaups]

I'm still confused bc this is telling me otherwise.

It’s telling you the same thing. You are really going 70 but your car is telling you 66 still because it doesn’t know you have larger tires. If he increases the tire size correctly in the bcm it will raise the speedometer from 66 to the correct reading of 70 in the example you provided.

 

[Crownline]

So if I mess with that, to get it back even, (speedo and actual to match) I have to put in a new tire size of 33. Just so confused!

Bc if I raise it above 35", the difference is even more. So I'm not understanding how you're saying he put in a too small of a tire size.

 

[beaups]

So if I mess with that, to get it back even, (speedo and actual to match) I have to put in a new tire size of 33. Just so confused!

Bc if I raise it above 35", the difference is even more. So I'm not understanding how you're saying he put in a too small of a tire size.

The tool you are screenshotting is simply showing the speedometer errors created by having a tire size that doesn't match what the vehicle expects. The larger tire you put on, the more the actual vehicle speed will be higher than what the speedometer shows. Your wrangler has 35's on it and it thinks it has 33's, so you are getting exactly what you screenshotted in that calculator. The tech needs to "correctly" program the BCM for 35's.

Think about it this way: If you put 66" tires on your wrangler (lol) and the speedometer read 50mph you'd actually be travelling 100mph. Tech would need to raise the size in the BCM to 66" (prob not possible) which would increase the speedometer in that scenario to show the correct reading of 100mph.

 

[Crownline]

But they did do it for 35" and it's 3 or 4 mph off!

 

[beaups]

But they did do it for 35" and it's 3 or 4 mph off!

They didn't do it correctly. I've only ever done calibration myself w/Tazer but I do recall reading others having this issue and that the dealer didn't do it correctly.

 

[cornercanyon]

What tires and size do you have on? BFG KO2 (315/70R17)'s?

 

[Crownline]

• 14

Nitto Ridge Grappler 35×12.5R20

 

[KarlN]

install a Tazer mini, measure the actual tire height, load the calibration info. in as instructed and get it exact. I'm less than 1 mph off at 80 now.

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