Sport model Program question. 285/70/17

[oubbascooba]

I’ve been having 285/70/17 non-LT ridge grapplers for 17k now. I have a question for those running NON-LT 285s and reprogrammed the tire size around 48 lbs per tire. Do you always hit 8th gear or is it 50/50?

I haven’t reprogrammed my Sport with 3.45 to match my tire size. I’m like 50/50 on 8th gear at 70 mph and it downshifts a lot. If no hills or drag I’ll hit 8th. But the slightest factor, it will drop to 7th, or just never see 8th.
For those that programmed to the right size and running a non-LT in the 48ish lb range, do you see 8th more frequently?

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[Ratbert]

You'll have difficulty hitting 8th if you haven't adjusted the computer's settings for the larger diameter.

You're seriously running at 48 PSI? Is there a reason?

 

[oubbascooba]

You'll have difficulty hitting 8th if you haven't adjusted the computer's settings for the larger diameter.

You're seriously running at 48 PSI? Is there a reason?

48 lbs per tire. Tire Weight. Just clearly stating I’m not running an LT ply tire, and that even a light off-roading 285/70 is still kicking me out of 8th gear. Most LT 285/70 are like 60lbs a tire. I don’t do major off-roading and don’t need a “beefy” LT tire. No rocks here in south Louisiana. I’m running 33 psi. Plus the standard load tire rides better and is softer.

 

[DaltonGang]

You'll have difficulty hitting 8th if you haven't adjusted the computer's settings for the larger diameter.

You're seriously running at 48 PSI? Is there a reason?

I think he meant to say what the tires weighed.

 

[DaltonGang]

48 lbs per tire. Tire Weight. Just clearly stating I’m not running an LT ply tire, and that even a light off-roading 285/70 is still kicking me out of 8th gear. Most LT 285/70 are like 60lbs a tire. I don’t do major off-roading and don’t need a “beefy” LT tire. No rocks here in south Louisiana. I’m running 33 psi. Plus the standard load tire rides better and is softer.

My JLUSS hits 8th gear on the freeway, all the time, with 285/70/17 tires.

 

[Ratbert]

48 lbs per tire. Tire Weight. Just clearly stating I’m not running an LT ply tire, and that even a light off-roading 285/70 is still kicking me out of 8th gear. Most LT 285/70 are like 60lbs a tire. I don’t do major off-roading and don’t need a “beefy” LT tire. No rocks here in south Louisiana. I’m running 33 psi. Plus the standard load tire rides better and is softer.

I foolishly assumed you were talking about PSI since tire weight shouldn't have an impact on it at all. From what I understand, the TCM shifts purely based on output shaft speed, not load.

That is, tire weight is irrelevant. LT vs non-LT is irrelevant. What matters is tire size and gear ratios. The fix is to tell the computer about the larger tire size.

 

[The Fixer]

Honestly, we haven't had an issue with my wife's JLU Sport. 3.6/auto - hasn't been reprogrammed, been running 285/70 KO2s for the last two years. Highway mileage is still great, and we see 8th gear on the highway without issue - we are on the East Coast basically at sea level like the OP.

I also ran my 2.0/auto Sport with 285/70s for a few years without reprogramming as well. I did reprogram with JScan once I went to 315/70s.

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