Anyone running bigger tires without the calibration done? Experience?

[XraytecH]

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[Kaiser]

Here's my recent real world experience....I have a sport S with max tow (4.10 gears). I swapped on a set of JL Rubi take off 285/70/17 ("33 inch tires"). I purchased jscan and diligently went in to recalibrate...based on the actual on vehicle measurements of the 285/70/17s I was goint to set it to 31.75" ....what did I find in Jscan?.....tire size was set at 31.93" from the factory. So basically I had zero need to recalibrate. I went ahead and set it to 31.75" just because I was in there. After the fact I started a thread on here and someone confirmed that 31.93" was the factory setting. Not sure if that is just for max tow or rubi models with the 4.10 gears.

Well, here's what I just found on my '21 Max Tow Sport S, hooked up the J-scan and the factory had the wheel size set at 30.65!!! Speedo has been reading 2 MPH low according to my speedo app running 285-70R-17 BFG AT KO2s. I don't get it.

 

[sdk131]

Well, here's what I just found on my '21 Max Tow Sport S, hooked up the J-scan and the factory had the wheel size set at 30.65!!! Speedo has been reading 2 MPH low according to my speedo app running 285-70R-17 BFG AT KO2s. I don't get it.

That is a mystery for sure! Very interesting!

 

[Jaydebe]

I ran my 37's on the stock JTR for about 2k miles; Living in the mountains of WV and traveling too.

I didn't think it as an issue unit I added the Tazer and it was night & day IMO. First, my speedo was usually off by 1.5-5mph (it was not a constant), so that's weird.

The shifting was much better. I expect a similar difference when I finally get my regearing done. It was peppier and definitely found 8th again. Something I didn't see for almost 2k miles.

Which also gives you better mpg's. About 1.5-2 more.

 

[Kaiser]

That's good!
The BFGs I mentioned measure 15.5" from the ground to the hub center (front wheel) with 37 lbs air I've been running so I tried setting the size to 31"
Speed is dead on with my app now and also noticed the 8 speed shifted a bit sooner, very happy with that, wasn't terrible but had been bugging me a little. Probably not as dramatic a change as yours Jay but noticeable. Looking forward to what the MPG looks like now.

 

[JeffInFLA]

Well, here's what I just found on my '21 Max Tow Sport S, hooked up the J-scan and the factory had the wheel size set at 30.65!!! Speedo has been reading 2 MPH low according to my speedo app running 285-70R-17 BFG AT KO2s. I don't get it.

I just swapped my stock 245/75R17 (measured to be ~30.5” tall) with 285/70R17s (measured to be 32” tall). Hooked up Jscan... checked the tire size after the swap and it read 31.93”. I’d never looked at the tire size setting prior to the swap but it seems my Gladiator has always thought it had 32” tires on it (well, close ‘nuff).

 

[ScottLars]

I just swapped my stock 245/75R17 (measured to be ~30.5” tall) with 285/70R17s (measured to be 32” tall). Hooked up Jscan... checked the tire size after the swap and it read 31.93”. I’d never looked at the tire size setting prior to the swap but it seems my Gladiator has always thought it had 32” tires on it (well, close ‘nuff).

I did the same but after checking distance and speed with GPS ended up at 32.75". Now it's spot on.

 

[JeffInFLA]

I did the same but after checking distance and speed with GPS ended up at 32.75". Now it's spot on.

Which app are you using for comparison?

 

[ScottLars]

Which app are you using for comparison?

JScan. I think the more important measurement is dynamic circumference. I did a rollout measurement in the driveway and it worked out the the 32.75" that is listed in JScan.

 

[RiverMtnBeach]

Well, here's what I just found on my '21 Max Tow Sport S, hooked up the J-scan and the factory had the wheel size set at 30.65!!! Speedo has been reading 2 MPH low according to my speedo app running 285-70R-17 BFG AT KO2s. I don't get it.

Yeah, seems like factory calib is all over the place. Mine was at 29 something. I actually had a problem/annoyance towing after calibrated for 35s, held gears all the way to redline even at half throttle when accelerating. Completely unnecessary unless you’re at WOT. Calibrated up to 36 something and that solved it. For some reason the Maxtow likes shift points when the tires are SMALLER than it’s calibrated for, so that larger setting from the factory might be a work-around they snuck in there.

 

[JeffInFLA]

JScan. I think the more important measurement is dynamic circumference. I did a rollout measurement in the driveway and it worked out the the 32.75" that is listed in JScan.

Sorry, I was asking if there was a specific GPS app you were using. I just went for a ride using Waze and another GPS speedometer app on my phone... All matched. I’ll keep an eye on it but I think I’m good to go.

 

[ScottLars]

Sorry, I was asking if there was a specific GPS app you were using. I just went for a ride using Waze and another GPS speedometer app on my phone... All matched. I’ll keep an eye on it but I think I’m good to go.

I used Google Maps and a GPS app I use for boating, Navitronics. The speed on any GPS is always tough to match with just due to delay. I mainly used the distance traveled reported by the app and compared with trip meter in JT was always coming up short on trip meter until I got tire size set to 32.75. There's also factors of tire brand/type, tire pressure, etc.
As long as you got it matched, that's all that matters.

 

[Brahmajoe]

I used Google Maps and a GPS app I use for boating, Navitronics. The speed on any GPS is always tough to match with just due to delay. I mainly used the distance traveled reported by the app and compared with trip meter in JT was always coming up short on trip meter until I got tire size set to 32.75. There's also factors of tire brand/type, tire pressure, etc.
As long as you got it matched, that's all that matters.

What air pressure did you run for this measure ment

 

[ScottLars]

What air pressure did you run for this measure ment

36-37 psi

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