Turn signal issues and tire size reset?

[Delhux]

Did you measure the actual size of the tires? Go from the center of the hub to the ground and then double it. That should provide a starting point that is real close to what is needed.

I did. That method gave me a measure of 16.875, which would put the diameter to enter at 33.75” (which is almost what I did, but I decided to try the closest measure the the actual tire height, which was just a hair over 34”).

I thought for sure the 34” was going to be too tall and end up giving me a vehicle-reported speed higher than my real speed, but it just narrowed the gap a bit. I think it may actually need to be set a 1/4” larger, but we’ll see…

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[jjdustr340]

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.

The other post about not plugging the phone in nailed it. I’ve seen it reported many times that certain apps use what the vehicle says instead of what the app says.

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

What I do when reprogramming tire size is get it as close as I can between the speedo and my app, then verify with one of those permanent “your speed” radars by the local school.

 

[Delhux]

The other post about not plugging the phone in nailed it. I’ve seen it reported many times that certain apps use what the vehicle says instead of what the app says.

SERIOUSLY, @md_adirondacks cracked this caper wide open! I never would have figured it out without that input.

What I do when reprogramming tire size is get it as close as I can between the speedo and my app, then verify with one of those permanent “your speed” radars by the local school.

Well officer, I was trying to see if 60 was actually 60…

 

[jjdustr340]

SERIOUSLY, @md_adirondacks cracked this caper wide open! I never would have figured it out without that input.



Well officer, I was trying to see if 60 was actually 60…

In my defense, the one I use IS in a 35 mph zone. Lol

 

[hekhl00]

Waze 100% pulls speed data from the car computer, unless it malfunctions or its connection isn't working. Try using it while the phone is not plugged in, that way you'll see your speed as read by GPS. That's actually a good way of setting it yourself if you have a Tazer or something like it.

I'm pretty convinced that your install shop never changed your wheel size in the computer and what you're seeing is your phone connection being inconsistent. Which plug are you using btw, the one in the front or inside the arm rest? The plug inside the arm rest is known for not maintaining a good connection and in mine never works at all past 5 minutes.

Sorry but what’s your source for this assertion? How would Waze or any other app pull that data over USB? That would require a very tight integration between the app and every single car computer it is plugged into. I can’t imagine that the USB port is that tightly integrated into the rest of the cars systems. Everything I’ve read regarding Waze indicates that the speed is a simple GPS calculation of time and distance. Same goes for Google maps.

 

[mojocho]

Sorry but what’s your source for this assertion? How would Waze or any other app pull that data over USB? That would require a very tight integration between the app and every single car computer it is plugged into. I can’t imagine that the USB port is that tightly integrated into the rest of the cars systems. Everything I’ve read regarding Waze indicates that the speed is a simple GPS calculation of time and distance. Same goes for Google maps.

I agree. Waze did not read the car's speedometer. This is first hand knowledge. I use Tazer. When going to the dealer, I'll unmarry it at home and then use Waze as my speed indicator on the highway drive. It will report the 5-7mph difference from my speedometer with my 37"tires.

That's with Waze plugged in via USB in the arm rest console.

Has the turn signal issue returned? You may have two different issues going on

 

[Kevin_D]

Sorry but what’s your source for this assertion? How would Waze or any other app pull that data over USB? That would require a very tight integration between the app and every single car computer it is plugged into. I can’t imagine that the USB port is that tightly integrated into the rest of the cars systems. Everything I’ve read regarding Waze indicates that the speed is a simple GPS calculation of time and distance. Same goes for Google maps.

This.
Why go to the trouble of Integrating to the car’s system when a simple calculation in the app will easily provide the data…

Kevin

 

[sharpsicle]

Many manufacturers intentionally set the speedo to read a bit higher than reality, presumably in an attempt to deter speeding. Most often this is progressive, meaning the slower you are driving the smaller the difference. I've seen cases in cars such as BMWs where it displays as much as 5mph higher than reality when getting to highway speeds. But since odometers need to be accurate for legal purposes, they really tell the true story. If thats the case, it means you'll never have the speedo and odometer match on a highway test run. I'm not surprised your 10-mile test came back the way it did. It's compensating for what it thinks is the built-in speedo variance (that you're manually trying to correct).

So, if true, either you live with the speedo reading high and odometer accurate, or speedo reading accurate but odometer reading low. Looks like a normal nanny-system speedometer case to me.

 

[Delhux]

I agree. Waze did not read the car's speedometer. This is first hand knowledge. I use Tazer. When going to the dealer, I'll unmarry it at home and then use Waze as my speed indicator on the highway drive. It will report the 5-7mph difference from my speedometer with my 37"tires.

That's with Waze plugged in via USB in the arm rest console.

Has the turn signal issue returned? You may have two different issues going on

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/

 

[Delhux]

Many manufacturers intentionally set the speedo to read a bit higher than reality, presumably in an attempt to deter speeding. Most often this is progressive, meaning the slower you are driving the smaller the difference. I've seen cases in cars such as BMWs where it displays as much as 5mph higher than reality when getting to highway speeds. But since odometers need to be accurate for legal purposes, they really tell the true story. If thats the case, it means you'll never have the speedo and odometer match on a highway test run. I'm not surprised your 10-mile test came back the way it did. It's compensating for what it thinks is the built-in speedo variance (that you're manually trying to correct).

So, if true, either you live with the speedo reading high and odometer accurate, or speedo reading accurate but odometer reading low. Looks like a normal nanny-system speedometer case to me.

No.

1) My instrument cluster was showing my speed as 5MPH slower than reality. I was actually driving faster than my vehicle reported.

2) Being off by nearly 3/4-mile after only 10-miles is not a small difference.

Your threshold for surprise needs to be both inverted and recalibrated.

 

[sharpsicle]

No.

1) My instrument cluster was showing my speed as 5MPH slower than reality. I was actually driving faster than my vehicle reported.

2) Being off by nearly 3/4-mile after only 10-miles is not a small difference.

Your threshold for surprise needs to be both inverted and recalibrated.

Whoa whoa, calm down man. You're describing a variance in the speedo to odometer. Not to mention, at this point the adjustments you've made are all over the place in an attempt to sync them up. I was simply giving you a scenario that exists elsewhere that explains perfectly why they may never match exactly.

To clarify, I'm trying to help you with this statement:

I’m just having a hard time understanding how the vehicle’s computer could or would be calculating the revolutions for the speedometer differently than the revolutions for the odometer

 

[sharpsicle]

Before we go off the rails a bit here, let's look at this post from earlier:

The first stop, I left the car off for about 5-minutes, when I started again the GPS and speedo were back in perfect sync.

However, I repeated the mile marker test and found that in a 10-mile test, the trip odometer reported 9.3 miles—even though Speedo and gps were lined up this time.

So, speedo is right, but odometer is low. Which means to get the odometer right, the speedo would need to read higher. Yes?

Let's go with what I said about seeing other makes with a 5mph variance at highway speeds. Let's assume you're going 75. That means that the truck thinks a displayed speed of 75 is a real speed of 70. Percent difference? About 7%. But since you've manually adjusted that to match the GPS, that 7% ends up translating elsewhere.

Your 10-mile test is recording at 9.3 miles. Percent difference? About 7%. This all makes perfect sense if you consider my scenario.

 

[Delhux]

Whoa whoa, calm down man. You're describing a variance in the speedo to odometer. Not to mention, at this point the adjustments you've made are all over the place in an attempt to sync them up. I was simply giving you a scenario that exists elsewhere that explains perfectly why they may never match exactly.

To clarify, I'm trying to help you with this statement:

I have no idea how you interpret “all over the place”.

I initially questioned how they could be different.

That was answered when it was identified that Waze was pulling speed data from the vehicle via Waze/CarPlay.

That was verified by a GPS-only test, and found that the GPS-only test was verified with identical results from the highway mile marker test.

Then, the tire diameter was adjusted via JSCAN and verified, again, that the initial diameter adjustment (increase from 32.74” to 34”) brought the vehicle speedometer to within about 1MPH of actual speed (vehicle still reporting slower than actual).

The adjustments have been linear, logical, and documented. How could you interpret it as “all over the place”?

 

[sharpsicle]

I'm trying to help you here. I'm explaining how they could be different. Your Waze-integration only explains MPH, it does nothing for odometer. I apologize if you didn't like my word choice, but that doesn't change what I'm describing to you.

 

[sharpsicle]

Maybe someone can help me out here and explain this one. If Waze is pulling speed data from the truck, how would this difference have occurred?

A few miles later I notice that my GPS/speedo seem out of sync. Sometimes the GPS is just wrong, so I restart the app and give it some time, but it stays inaccurate.

I notice that at 70 on the dash, it’s reporting 75mph on the GPS.

My opinion from everything being said here is:

1 - Waze is calculating speed based on GPS, not pulling from the vehicle
2 - Jeeps may be programmed with a progressive displayed-speed variance

Maybe I'm wrong, but those are the only points that explain literally everything here. And sadly, it wouldn't be the first time I've seen this variance in action.

EDIT: This seems more and more plausible as I read other forums. Check these threads out:

https://www.jeepforum.com/forum/f11/speedometer-calibration-3322537/
https://www.jeepforum.com/forum/f28/liberty-speedometer-error-519049/
https://www.jlwranglerforums.com/forum/threads/incorrect-speed.16185/page-2

They all talk about how even among the same model, there can be differences in how accurate the on-board speedo really is. The variance may not be intentional, but it's there, and from a Jeep perspective it would make perfect sense from a liability standpoint to always make sure the speedos read a little higher than ever reading lower.

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