Recalibrating speedometer with tire change

[Strommen95]

@Strommen95

OK, I hear you.... I'll stand corrected... especially after input from Joe Z. you linked to.... 8-)

Guess my comments were pointing to... if you change tire size dramatically and the trannies shift points will be off til the transmission relearns over time, if possible for relearn if change is minimal... or you do a re-gear. Am I ok saying it like that?

After upgrading tire size, shifts will be off for a bit of time, yes. This is because of the extra "load" of the tires. The bigger the tire, the worse the shifting will be initially, but the ECU will adjust to the added load of the tires. For 33s, OP will barely notice a difference once the ECU adjusts. With 35s, hitting 8th is greatly reduced compared to 33s. Depending on driving habits, might not see 8th at all with 35s. Personally, 35s is where I would regear and definitely would for anything above that. We have so many engine choices now though that this has become a gray area to broadly answer.

In short, it's accurate to say upgrading tire size will negatively affect shifting but it's temporary. With much larger tires, the long term negative impact is the added weight of the tires, not the ECU potentially having a wrong calibration.

For the record, gearing needs to be properly calibrated for the ECU, which often gives people a false impression tire size needs to be calibrated correctly too. To put it at simply as possible, gearing is part of the mathematical equation for the transmission to determine speed, so it's vital for gearing to be accurate.

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[Red_shift]

@Strommen95

I deleted earlier posts that may confuse readers....

Thanks, I was getting a bit confused. It seems the bottom line is that not much will change that should concern me. I was really hesitating about doing anything like the Procal. I'll see if the dealer will do a recalibration for free, but I doubt it.

 

[2nd 392]

Dealer—Free, wake up your dreaming!

 

[halsjeep]

Not to threadjack but I asked the same in another thread. Getting a 4XE and thinking of upgrading from the stock 275/55 to 275/60. Not much of a difference at all but should I worry about shift points/recalibrating the speedo for such a minor upsize?

I have a 4xe Sahara and recently went to the Nitto Grappler 275/60. I asked the dealer about calibrating and the told me to order ECRI calibration tool. I had a little trouble with it the first time I guess because the ABS system in the 4xe is different that a regular Wrangler. With that said the tech support has been phenomenal. They made a couple of programming changes and everything is good. With that said i don't think going from 275/55 to 275/60 made that much of a difference. It looks like i higher speeds the speedo may have been off by 1-2 mph. I would say unless you want to change other settings like TPMS or lights I wouldn't worry about it.

 

[Strommen95]

Weird… my JL shifted all wonky when I went from 315/70/17 to 37/12.5/17. Didn’t shift normally until I corrected the tire size with JScan

The last time one of these types of threads was brought up, it was theorized that tire calibration might help or speed along the ECU's learning period. Which, sounds plausible to me. So while tire size isn't part of the strict shift logic for the tranny, it's very possible that a new calibrated tire size correlating with additional "load" may help the ECU adjust much faster.

My experience with 33s when I put them on a few years ago, before I had a Tazer, was that my Jeep shifted like crap and was sluggish. After a few days, shifting returned to like stock. When I did get a Tazer, I played around with settings and didn't notice any difference with shifting. This was after the tranny already adjusted to the new tires, not during the adjustment period.

 

[KrzybonesJLU]

My two cents and I’ll make the answer straight forward for you because people make it so complicated and argue..

Your speedo will read slower by 3-4 mph and your true mileage will be off. If that is something I’m you can live with then don’t recal. Yes the transmission (shift points) will self adjust accordingly to this size. But if you do anything larger then 285 70 then you should do a recall in addition do a regear.

My opinion you should just do the recalibration. If you can find a dealer to do it and can spend the coin then do it. But ounce you go down this rabbit hole.. it isn’t going to stop. So if you have plans in the future for mods like LED changes, tp threshold changes, adding DRL’s or even turning off the start/stop feature that people can’t get over for what ever reasoning they have... then you should consider getting a super chips, tazer and or Jscan. Not going to get into which is better because they all will tend to your most common needs.

Hope this helps welcome to the community and happy trails!

 

[Red_shift]

My two cents and I’ll make the answer straight forward for you because people make it so complicated and argue...
....

Hope this helps welcome to the community and happy trails!

Straightforward and simple work for me, thanks. The effects you describe in going with the 285's are enough that I'll have to think about whether the 1/2" difference in ride height is even worth it. Mostly I'll be on pavement and forest service roads, with an Ursa Minor camper top. Was just thinking that all-terrains would make for a better experience for longer trips than the mud-terrains, and if I was going to make that change I might as well go slightly larger in size.

Can't wait to get out and about in a Jeep! Thanks for the welcome!

 

[Strommen95]

Straightforward and simple work for me, thanks. The effects you describe in going with the 285's are enough that I'll have to think about whether the 1/2" difference in ride height is even worth it.

As someone that's had 285/70/17 for several years, your speedo will be off by 1MPH at highway speeds, less so in local driving. Really isn't a difference. Most vehicles speedometers read 1-2 MPH too fast from the factory.

 

[KrzybonesJLU]

Straightforward and simple work for me, thanks. The effects you describe in going with the 285's are enough that I'll have to think about whether the 1/2" difference in ride height is even worth it. Mostly I'll be on pavement and forest service roads, with an Ursa Minor camper top. Was just thinking that all-terrains would make for a better experience for longer trips than the mud-terrains, and if I was going to make that change I might as well go slightly larger in size.

Can't wait to get out and about in a Jeep! Thanks for the welcome!

if that’s all you’ll be on then you’ll be fine with getting stock size AT. I’ll admit I do like the look of larger tires even if it just 33’s.

 

[GSLSE21B]

Hptuners MPVI2 can be used for tires , gears , engine and transmission

 

[Tushar]

I used ECRI for reprogramming my speedo for35's. They have this cool feature where it uses GPS & tells you the exact tire size you are running based on what it senses. Having said that i still feel my shift points still take long to shift to higher gears. But i guess rehearing to 4:56 would fix that.

 

[JT1]

There isn't enough actual difference in tire height to worry about adjusting. Your speedometer will likely be right on, the digital readout might read 1-2 miles low. Don't waste time or energy on it.

 

[scottijohn63]

After upgrading tire size, shifts will be off for a bit of time, yes. This is because of the extra "load" of the tires. The bigger the tire, the worse the shifting will be initially, but the ECU will adjust to the added load of the tires. For 33s, OP will barely notice a difference once the ECU adjusts. With 35s, hitting 8th is greatly reduced compared to 33s. Depending on driving habits, might not see 8th at all with 35s. Personally, 35s is where I would regear and definitely would for anything above that. We have so many engine choices now though that this has become a gray area to broadly answer.

In short, it's accurate to say upgrading tire size will negatively affect shifting but it's temporary. With much larger tires, the long term negative impact is the added weight of the tires, not the ECU potentially having a wrong calibration.

For the record, gearing needs to be properly calibrated for the ECU, which often gives people a false impression tire size needs to be calibrated correctly too. To put it at simply as possible, gearing is part of the mathematical equation for the transmission to determine speed, so it's vital for gearing to be accurate.

I just did a 2.5" MOPAR Lift and 35" tires on my Sahara, I regeared to 4.88 and used ECRI to adjust my tire size and gears.

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