Assistance/Advice Needed for JScan - Changing tire size.

[wwcenturion]

Ideally, I would like to hear from people who have done this recently using the JScan app. I just purchased the JScan license (for the app), a Vgate iCar Pro Bluetooth 4.0 (BLE) OBD2 Fault Code Reader OBDII Code Scanner Car Check Engine Light for iOS/Android (see below), and the security cable (also below).

I'm see conflicting instructions for the process. I just want to change the tire size. Can anyone who has done this with this app and hardware (recently) tell me exactly what to do so I don't mess something up? Much appreciated.

I plan to measure shoulder height of the tire using a level and tape measure. I don't think I need to change the gearing ratio, just the tire size.

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[wwcenturion]

So I guess I'll answer my own question. Connected everything this evening. Used the Jscan app to purchase the license for my Gladiator "Maxitowmus." My 37s are actually 36.25" so that is the setting in the app that I used. I did not have to reset the ECUs manually or perform the WoT steps I've seen posted in other places. Just followed the directions in the app and everything worked perfectly. Speedo is now correct, tranny switches to higher gear a little easier, and I'm looking forward to potentially seeing a slight boost in MPGs.

 

[Aonarch]

Ideally, I would like to hear from people who have done this recently using the JScan app. I just purchased the JScan license (for the app), a Vgate iCar Pro Bluetooth 4.0 (BLE) OBD2 Fault Code Reader OBDII Code Scanner Car Check Engine Light for iOS/Android (see below), and the security cable (also below).

I'm see conflicting instructions for the process. I just want to change the tire size. Can anyone who has done this with this app and hardware (recently) tell me exactly what to do so I don't mess something up? Much appreciated.

I plan to measure shoulder height of the tire using a level and tape measure. I don't think I need to change the gearing ratio, just the tire size.

So I used a level and measured my tire height loaded at 36 psi and my speedo was still off.

I then remeasured and rounded up. Still off.

I then just punched in the manufacturers claimed height unloaded, presto!!! Speedo is accurate.

YRMV

 

[Kevin_D]

You'll find you can fine tune the speedometer reading by changing the tire size up or down as needed.

Kevin

 

[OHJeeper]

So I used a level and measured my tire height loaded at 36 psi and my speedo was still off.

I then remeasured and rounded up. Still off.

I then just punched in the manufacturers claimed height unloaded, presto!!! Speedo is accurate.

YRMV

I know this is an old thread, but I found it doing a search on JSCAN and Tire Size.

I was thinking about the issue of measuring the tire "under load". I recently put on new tires and measured the diameter under load, put it in JSCAN and it was still reading low. Fussed with it a few times, incrementing by 1/2" each time until I finally got the right setting and, whadya' know: it was the same size listed on mfg's specs...

Then I got to thinking how this could be, and it dawned on me. If you take a piece of string and measure the circumference of any circle (tire, coke can, beer bottle, etc) it has a certain length. For argument's sake, let's say 10" is whatever you measured.

Now, take that string and put the two ends together: I don't care if it's a perfect circle, a random shape, a square, oval... whatever shape you make it, it's STILL 10"...

Thinking of a tire... when it's on the rim and not under load, it's (roughly) a perfect circle... When you put it under load, the bottom flattens so it's not round anymore, but the CIRCUMFERENCE has not changed... to run a complete revolution of the tire takes the same distance as a perfectly round one does. BUT the height of the tire is smaller because when you measure from the pavement to the top of the tread that "flat spot" shortens the diameter, but NOT the circumference (or, perimeter since it's not a perfect circle).

Someone tell me I'm crazy, but I think the measurement should be take when the tire is NOT under load, or, in my case and @Aonarch's (and others I'm sure) just use the specs given by the manufacturer...

 

[Kevin_D]

But, many tires say they’re bigger than they really are. A 37”-spec tire, measured with no load, will most often measure something less than 37”.

Kevin

 

[OHJeeper]

But, many tires say they’re bigger than they really are. A 37”-spec tire, measured with no load, will most often measure something less than 37”.

Kevin

I agree, you can't just buy a 37" tire and expect it to be 37"... but the tire mfg will usually list their "true" size (36.5, 36.41, etc)

 

[ShadowsPapa]

You'll find you can fine tune the speedometer reading by changing the tire size up or down as needed.

Kevin

And in reality one shouldn't use the speedometer but should go by the odometer.

but the tire mfg will usually list their "true" size (36.5, 36.41, etc)

Not always accurate - there's "rolling" size that can vary.
Best way is to START with their size and adjust from there. Apparently Jeep folks don't care about real accuracy and call it good enough if the speedometer matches.
Took two changes to get mine right - and I started with their "true size". I finally got it right by comparing odometer readings to a dedicated GPS and phone app (which is really GPS)

 

[Aonarch]

And in reality one shouldn't use the speedometer but should go by the odometer.



Not always accurate - there's "rolling" size that can vary.
Best way is to START with their size and adjust from there. Apparently Jeep folks don't care about real accuracy and call it good enough if the speedometer matches.
Took two changes to get mine right - and I started with their "true size". I finally got it right by comparing odometer readings to a dedicated GPS and phone app (which is really GPS)

Yes I admit the odometer match method is the one you should use.

I just flirt with the upper limits of acceptable speeding in my area, so I wanted my speedo dead on. I should probably check how accurate my odometer is though.

 

[FloridaJT6MT]

So that OBD works with your JT? I only ask because JScan doesn’t have that one listed as recommended for the JT. This is straight from their website.

I’d love to buy this one because it’s like a third of the cost of the two they recommend.

 

[kooltoys]

keeping in mind that the speedomter being incorrect will add or subtract from the actual mileage of your JT. warranty, resale,etc

 

[ShadowsPapa]

Yes I admit the odometer match method is the one you should use.

I just flirt with the upper limits of acceptable speeding in my area, so I wanted my speedo dead on. I should probably check how accurate my odometer is though.

If your odometer is correct, the speedometer will be.
One thing I've found odd is that the "analog dial" speedometer consistently reads higher than actual speed even with everything else matched exactly dead-on. The digital numerical display in the center is more accurate on mine.
If the speed sign in town says I'm at 35 the dial will read 35-37 and if I'm doing 55, the dial on the right says about 56-57. When I haver the ACC set to exactly 65 the dial reads 66 but the numeric digital display matched GPS or ACC setting.

I’d love to buy this one because it’s like a third of the cost of the two they recommend.

I have the Vgate you displayed - and it works with jscan but due to the speed requirements of certain things in the Jeep system, jscan can't do SOME things with that adapter. For most people that adapter which is what, about 25 bucks? will do fine. It works with tire settings and other things.
I just found a couple of areas it didn't let me reach (and sorry, I can't recall which! It's possible I was just snooping around trying to see what damage.......... er, what I could learn when I got the error message. ) so I turned around and bought the more expensive one.
I don't dare let my wife know because she always gets all over me for trying to save a couple of bucks. She'd ask "so why didn't you buy THAT one to begin with, ya big dummy?, you know better than that".

Anyway, that Vgate iCar pro works fine for most things. Tire size settings will be fine with it.

 

[FloridaJT6MT]

If your odometer is correct, the speedometer will be.
One thing I've found odd is that the "analog dial" speedometer consistently reads higher than actual speed even with everything else matched exactly dead-on. The digital numerical display in the center is more accurate on mine.
If the speed sign in town says I'm at 35 the dial will read 35-37 and if I'm doing 55, the dial on the right says about 56-57. When I haver the ACC set to exactly 65 the dial reads 66 but the numeric digital display matched GPS or ACC setting.



I have the Vgate you displayed - and it works with jscan but due to the speed requirements of certain things in the Jeep system, jscan can't do SOME things with that adapter. For most people that adapter which is what, about 25 bucks? will do fine. It works with tire settings and other things.
I just found a couple of areas it didn't let me reach (and sorry, I can't recall which! It's possible I was just snooping around trying to see what damage.......... er, what I could learn when I got the error message. ) so I turned around and bought the more expensive one.
I don't dare let my wife know because she always gets all over me for trying to save a couple of bucks. She'd ask "so why didn't you buy THAT one to begin with, ya big dummy?, you know better than that".

Anyway, that Vgate iCar pro works fine for most things. Tire size settings will be fine with it.

Ok, thank you. So that makes sense why they don’t recommend it for the JT. I’ll just buy the more expensive one they recommend because the functions that don’t work with the cheaper one would probably be what I end up needing at some point,

 

[ShadowsPapa]

Ok, thank you. So that makes sense why they don’t recommend it for the JT. I’ll just buy the more expensive one they recommend because the functions that don’t work with the cheaper one would probably be what I end up needing at some point,

You know what my wife would tell you to buy............ LOL. She's usually pretty smart that way.

 

[MrFahrenheit]

So that OBD works with your JT? I only ask because JScan doesn’t have that one listed as recommended for the JT. This is straight from their website.

I’d love to buy this one because it’s like a third of the cost of the two they recommend.

The one your picturing is the 'Vgate iCar pro LE' The one he bought was the 'Vgate iCar pro BLE'

The 'BLE' is the same one I have that works just fine. Similar but different models names on the adapters.

This is the one I bought from Amazon:

https://www.amazon.com/dp/B06XGB4873

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