Dealer adjusted tire size-Question.

[Reddog]

I reset my tire size with the Taser and it is dead on using radar speed check and GPS data. You have to tweak the tire size if you want it dead nuts correct. But frankly, is there anyone left in America who still drives the speed limit?

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[davesparky6]

The dealership used a wiTech 2.0 scan tool. For them to do a tire size change, they have to pay for a one time subscription that give them a code that will unshadow the function in their wiTech. Of course that cost is passed on to the customer.

Problem with the dealership wiTech tool vs. Jscan or similiar, is that it is usually a one and done programing and you run into the issues the OP has. With Jscan or similar, you can play up and down multiple times with the tire size to fine tune the actual speed plus also have the option of programming a error adjustment (%) to the speedometer signal on the cluster.

Problem of not getting it dead nuts accurate is you will occur a faster odometer count. 3 MPH fast over 60K miles means you will incur that mileage count almost 1800 miles quicker. Not a big deal if already out of warranty, but could be an issue if in warranty and you lost those margins to letting the speedometer read fast.

So…. Would it be worth selecting the tiniest of tires on Jscan, using a GPS app, and doubling your warranty?? Asking for a friend….

 

[Trollboogie]

1 up for the ECRI. It has a GPS function for an accurate speedometer calibration. I used it for my first Mojave, then my 24 when I traded in the old one. Just buy another unlock for about $50. You can even let friends use it. They just purchase an unlock for their vin. You remove it after the calibration. It however doesn't have the live functions like a Tazer does.

 

[Maximus Gladius]

I reset my tire size with the Taser and it is dead on using radar speed check and GPS data. You have to tweak the tire size if you want it dead nuts correct. But frankly, is there anyone left in America who still drives the speed limit?

I drive on the fast side of the”close enough”

 

[Hootbro]

So…. Would it be worth selecting the tiniest of tires on Jscan, using a GPS app, and doubling your warranty?? Asking for a friend….

Sure, if you want crappy shift points.

Max in Jscan is 44" and min is 26". In theory, that would be a 38 mph spread error if running those sizes.

 

[Verne]

The ECRI unit uses your own manual measurements in addition to a GPS speedo to calculate your actual rolling tire size and calibrate the speedo. Mine's pretty much dead-nuts accurate with 37s and verified against other GPS methods.

The one think you have to keep in mind is if you are using a GPS app on your phone to check your speed vs your rig, you cannot have the phone plugged into apple play or hooked up to Bluetooth. If you do, the phone will use the speed on the dash. You have to unplug and unpair your phone and then use the gps speedo to check. If mine is plugged in, it’s dead nutts on the dash and Waze. If not, its off by 2-3 mph

 

[Trollboogie]

The one think you have to keep in mind is if you are using a GPS app on your phone to check your speed vs your rig, you cannot have the phone plugged into apple play or hooked up to Bluetooth. If you do, the phone will use the speed on the dash. You have to unplug and unpair your phone and then use the gps speedo to check. If mine is plugged in, it’s dead nutts on the dash and Waze. If not, its off by 2-3 mph

Yes, don't plug your phone in or let it connect wirelessly while programming . The ECRI uses Bluetooth on your phone to communicate to the ECRI module.

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