Recalibrate for Larger Tires

[Wrangler73]

I replaced the 255/75/17's on my 2021 Willys with 285/70/17's. I dont notice any shifting difference at normal driving, but have a small 6X12ft trailer to pull a Polaris Ranger on (2 door - 1500 lbs) and noticed a large difference in shifting. You will be on the highway going 75 and look down and are at or above 3K RPM. Would this have anything to do with the larger tire change?? I was told I shouldnt need to recalibrate for the bigger tires as it "wasnt enough of a difference". The Ranger was bought after the tires were changed so I didnt get to pull it with the old tires.

Bottom line, based on your experience would the shifting patterns be affected more under load? I dont pull the trailer or Ranger often, but definitely notice the high RPMs but not sure if its the way it's supposed to work under towing, or maybe the tires?

Would paying a shop to recalibrate make any difference?

Thanks

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[lowmpg]

Your 255's had 630 revolutions per mile, the 285's have 617 revolutions per mile, so yes you need to have the vehicle calibrated for that level of change. You speedometer, odometer are both off as well.

Fun calculator to see how the tires change things: https://tire-calc.com/comparison/255-75-r17-and-285-70-r17/

 

[Wrangler73]

Thanks....is that done with a Tazer? Trying to figure out what I'm asking for to be done.......

 

[lowmpg]

Thanks....is that done with a Tazer? Trying to figure out what I'm asking for to be done.......

Yes you can do it with a Tazer. You simply need the vehicle to know what size tires it has, that's all. Pretty sure a dealer can do it. Do some searches here for folks that did larger tires. Tazer isn't the only option.

 

[slowcrawlerZJ]

You can use a Tazer Mini or Tazer Lite. Also Rough Country sells a programmer for calibration. The Tazer Mini will allow many more options for your Jeep besides just calibration. I’d go one of those routes before taking it to the stealership.

 

[Strommen95]

The difference between 255 to 285 sized tires is very small. Small enough that the additional load has no real bearing on the transmission. If you use a GPS comparing speeds of 245/75/17 and 285/70/17, you'll likely find the speedometer to be more accurate with 285s. The factory calibration reads a bit fast, at least for Sports.

Tire calibration does not do anything for transmission shifting. It's not part of the transmissions shift logic. The transmission, through gear ratio knows the speed of the vehicle and has nothing to do with the speedometer being accurate or not. Extra weight or load will affect transmission shifting. Weight or load has nothing to do with calibration. Many will report their transmission struggles with bigger tires, not understanding the additional load is hurting shifting and not proper calibration.

What will help your transmission upshift, specifically with tires bigger than the 33s you have or when towing, is regearing. Your engine is revving high when towing because it's not safe for the transmission to upshift further with the additional load. Shorter gears, which is stronger gearing, will be able to handle the additional load giving you 6th/7th/8th gear back and shifting would feel "normal". It wouldn't be totally normal when towing in your case but it'll respond much better than stock gears would.

A Tazer represents much more than just an accurate speedometer. It's worth getting and has many benefits.

 

[LCW]

Thanks....is that done with a Tazer? Trying to figure out what I'm asking for to be done.......

You can do it with JScan (app). a Bluetooth OBD II adapter and SGM bypass cable as well.

SGM bypass cable: https://www.amazon.com/dp/B08ZL4LRVK/

OBD II adapter: https://www.amazon.com/dp/B07JFRFJG6/

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