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Discussion Starter · #1 ·
I've searched and can't find a solid answer.

I just put in 4.56 gears on a 6-speed manual 2015 Wrangler.

I have a Procal but haven't tried to do this yet.

Quick questions:

Does it make any difference at all? Does the Jeep care in the least about the gears or does this only matter for an auto transmission?

Can it even be done? Is this even available to be programmed in a manual?

Is there any reason to do it or not do it?
 

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Programming the computer for your gears and tires has one effect with a manual. It makes the speedometer and odometer accurate.

Obviously, in an automatic, that is important so the computer can take care of the shifting correctly. But that part of the software isn't there for the manual so the computer doesn't care.

I did it with my manual equipped JK because I like to be able to glance down and see the actual speed I'm driving.

Legally, I think there is probably some law about keeping the odometer accurate. If it reads low and you try to sell the Jeep you can be accused of fraud or something like that.

The programmer will have selections for gears and tire size no matter what transmission you have. The vehicle computer stores the data in the same place for both since it's used to run the speedometer and that part of the code is the same for all versions.
 

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Anything worth doing, is worth doing right.
— Hunter S Thompson
A manual isn't as dependent on it, but your speedo will be off. If you already have the procal it should be done. For everyone else, with the low cost of the Jscan app now there's really no reason not to calibrate it.
 

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...

Legally, I think there is probably some law about keeping the odometer accurate. If it reads low and you try to sell the Jeep you can be accused of fraud or something like that....
Yep. Tire size matters to the odo and the law.
The odo/speedo is permitted to be 10% + 2 mph optimistic but 0% pessimistic. That's why most OE speedos/odos are off from the factory, erring on the side of caution.

When/if I sell my uncorrected Jeep that's riding on 33s I'll be legally obligated to check the box that says "odometer does not indicate correct mileage". I'm off by about 3% according to a gps.
 

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Discussion Starter · #5 ·
Sorry guys... I realize I was a bit unclear.

I've had the big tires on for months now. I've reprogrammed for them so my speedometer is correct.

It's only the gears I've just changed. So the speedometer is still correct.

I'm wondering if it makes a lick of difference to program for the gears.
 

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No reason to be sorry, I'm used to doing both at the same time so it's my mistake.
I'd be interesting in more experienced opinions too, if there is any "real" reason to do it. Personally I'd still do it so the Jeep knows exactly what's going on.
 

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Interesting thought. I don't think it would make a difference on a manual, as long as the speedo pick-up is at the wheel sensor and not on the trans like some cars do. I transmission swapped my old car with a manual a while back to change up the gear ratios. The donor trans used a speedo pick-up driven by the differential, but mine utilize the ABS sensor for speed, so it didn't care about the gear change at all.
 

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I'm wondering if it makes a lick of difference to program for the gears.
No.

If you've corrected for the tire size, declare victory and celebrate.
 
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Sorry guys... I realize I was a bit unclear.

I've had the big tires on for months now. I've reprogrammed for them so my speedometer is correct.

It's only the gears I've just changed. So the speedometer is still correct.

I'm wondering if it makes a lick of difference to program for the gears.
Now that you mention it, the axle ratio doesn't figure into the speed calculation. So no, really there's no reason to adjust for different axle ratios once the tire size is right.

I did tires and gears at the same time and programmed both together. But I could probably set the gears to anything and it would still work fine.

Of course, the automatic needs the gear ratio since it affects the tailshaft speed and that affects the shift points. But for a manual, it really doesn't matter.
 

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I would suggest checking your speedo against a GPS to ensure it is accurate after the regear. If the speedo is receiving its signal from sensors at the wheel, you should be good, but if the speedo uses a sensor at the trans output, then the regear would affect the calibration.

As others have said, having an accurate speedo is important, but more important, in my mind and from a legal standput, is the accuracy of the odometer. By going to numerically higher gears, your speedo and odometer would read faster speeds and higher miles than actual if the sensor is prior to the diff, so it is to your benefit for resale to correct the odometer for the gearing.


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I would suggest checking your speedo against a GPS to ensure it is accurate after the regear. If the speedo is receiving its signal from sensors at the wheel, you should be good, but if the speedo uses a sensor at the trans output, then the regear would affect the calibration.

As others have said, having an accurate speedo is important, but more important, in my mind and from a legal standput, is the accuracy of the odometer. By going to numerically higher gears, your speedo and odometer would read faster speeds and higher miles than actual if the sensor is prior to the diff, so it is to your benefit for resale to correct the odometer for the gearing.


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JKs with manual transmissions do not have a sensor at the transmission or transfer case at all. The last Wrangler to have a t-case speed sensor was the TJ/LJ. All the speed data comes off the ABS sensors now.

That's why it's so important to have the gear and tire properly put in for the 2012+ automatic. The 5 speed automatic does not have a tailshaft speed sensor. The computer needs to take wheel speed, figure out the effect of the axle gears as well as low range on the t-case so it knows how fast the transmission tailshaft is actually spinning so it knows exactly when to shift.

The 2007-11 automatic (42RLE) does have a tailshaft speed sensor built into the transmission so the transmission controller is never affected by changes in tire size, axle ratio, or even low range. It gets the information it needs directly from the transmission so it always knows when to shift.
 

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MPG after re-gear

How are you liking the re-gear? What effect did it have on performance and mpg? What gearing did you have previously?
 

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How are you liking the re-gear? What effect did it have on performance and mpg? What gearing did you have previously?
I used JScan to change tire size and gear ratio.

I'm not the OP, but I just re-geared my 6spd 10A. I went from 4.10s to 4.88s and they are freaking awesome. Yes, I sometimes pull out in second since first is really short now. Went wheeling two weeks ago and crawling was so nice.

I run 35x10.50R17 tires with my new gears. Perfect combo in my opinion. Glad I went to 88s; now if I get the bug to move up to 37s, I'm likley to not hate how 37s affect driving.
 

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I used JScan to change tire size and gear ratio.

I'm not the OP, but I just re-geared my 6spd 10A. I went from 4.10s to 4.88s and they are freaking awesome. Yes, I sometimes pull out in second since first is really short now. Went wheeling two weeks ago and crawling was so nice.

I run 35x10.50R17 tires with my new gears. Perfect combo in my opinion. Glad I went to 88s; now if I get the bug to move up to 37s, I'm likley to not hate how 37s affect driving.
Glad to hear this. I'm on stock 4.10s with a 6-speed and 35/12.5/R17, and really want to regear my Recon. I find it difficult to start out on steep hills, and reversing up an incline is impossible without roasting the clutch. I was afraid 4.88 would be going to far, but most people seem to love it. How does she do on the highway?
 

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Glad to hear this. I'm on stock 4.10s with a 6-speed and 35/12.5/R17, and really want to regear my Recon. I find it difficult to start out on steep hills, and reversing up an incline is impossible without roasting the clutch. I was afraid 4.88 would be going to far, but most people seem to love it. How does she do on the highway?
I waffled back and forth a lot before I made my decision.

From everything I have read it appears that 4.56 works for autos with 35s, and 4.88 is best with 6spd. I'm very happy with 4.88s.

I pull out in first barely using the gas, and like I said sometimes I pull out in second now.

As to the highway, the jeep is around 2750 at 70. I don't drive out west, so I'm usually between 65-70 most times on the highway. Even 75 is still under 3000 rpms. I drove a 4 banger Jeep for years so 3,000 doesn't worry me.

I really like accelerating up hill now! Downshifting is a thing of the past. Your recon is likely as heavy as my 10A, so I suspect you will have a similar experience.
 

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Discussion Starter · #16 ·
How are you liking the re-gear? What effect did it have on performance and mpg? What gearing did you have previously?
I went from 3.73's to 4.56's and am very happy with the change. I'm on 35's and got exactly what I wanted out of it.

Basically... it feels normal again. I think I've got another thread here with more details about this but the bottom line is that I'm glad I did it.
 
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