4.88 Gears Not What I Expected

OverlanderJK said:
You don't need to program with a manual. I thought you had to but you don't.
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How does the computer know how far your vehicle travels in one tire rotation if it isn't based on correct tire size? I though reprogramming was the only way to get the speedo, tach, and fuel usage gauges consistent with the re-gear and increased tire size. :thinking:

Without correct programming, the speedo could tell you that you are only going 70 when in fact it might be closer to 80.
 
Sharkey said:
How does the computer know how far your vehicle travels in one tire rotation if it isn't based on correct tire size? I though reprogramming was the only way to get the speedo, tach, and fuel usage gauges consistent with the re-gear and increased tire size. :thinking:

Without correct programming, the speedo could tell you that you are only going 70 when in fact it might be closer to 80.
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I believe he meant gear ratio doesn't need to be programmed. The speed is done from the hub so gearing would not effect the speedo and with a manual there are no shift points to correct so I guess you would not need to program the gear ratio if it did not cause limp mode or some other weird issue :idontknow:
 
TFD said:
I have a 2015 jku rubicon. I'm running trail grapplers 35s. I'm re gearing in a couple weeks. Is 5.13 too much for 35s? I live above 5000 ft and do all my wheeling in the mountains.
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That would be pretty steep but if you don't drive fast on the highway or don't care about the high RPMs then go for it. 4.88 feels steep in the low gears to me with 35" TG.
 
Have an 08' auto. Went from 4:10 to 5:13 with 35". Couldn't stay in of with the 4:10. Wouldn't even hold 65. Now I can hold 65+ but if there is a hill or headwind you can tell. I think it's as good as I can get it. I did cal also.

Next rig will be 3.6L min
 
Spudcannons said:
I believe he meant gear ratio doesn't need to be programmed. The speed is done from the hub so gearing would not effect the speedo and with a manual there are no shift points to correct so I guess you would not need to program the gear ratio if it did not cause limp mode or some other weird issue :idontknow:
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I think you are missing my point. I'm not saying gearing changes the speedo (I don't know if it does); I'm saying rolling tire diameter does. Even if the speed is done by the hub, it has to be converted to MPH based on the effective rolling diameter of the actual tire. If the hub thinks each turn is the turn of a 32" tire when it really is a 35" tire, then the speedo will be off, true?

So, if he hasn't recalibrated then he may think he is going 70 mph at 3000 rpm when in fact he is going 80 at 3000 rpm, true? (I concede my numbers are just guesstimates, but I think you get my point)
 
Also, it's not just your tire size but the tire and wheel weight. As weight goes up, performance and MPG goes down. If more of the weight is in the tire, or towards the outside (away from the center cap and lug nuts) you will need more gear/power to accelerate. How heavy is the Jeep?

Don't forget that when you re gear you should go a little deeper than calculations to make up for the extra/added rotational mass of the larger and heavier wheel and tire.
 
TFD said:
It is my daily driver. 4.88 it is then. Thanks for the feedback
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I had 5.13's on my 14 JKUR with a 6 speed and 35's. I live in Denver. It was great going up hill into the mountains but yes the Roma were a little higher but not bad. About 27-2800 in 6th doing 70 mph. I've put on 37's since then and I'm at 25-2600 now. You'll find it's not a crazy difference but the power and ease is night and day. If you may be tempted with 37's then go 5.13. I'll also add wheeling at elevation the deeper gears will help
 
Sharkey said:
How does the computer know how far your vehicle travels in one tire rotation if it isn't based on correct tire size? I though reprogramming was the only way to get the speedo, tach, and fuel usage gauges consistent with the re-gear and increased tire size. :thinking:

Without correct programming, the speedo could tell you that you are only going 70 when in fact it might be closer to 80.
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With tire size yes, but not with gear ratio.
 
t8er said:
I had 5.13's on my 14 JKUR with a 6 speed and 35's. I live in Denver. It was great going up hill into the mountains but yes the Roma were a little higher but not bad. About 27-2800 in 6th doing 70 mph. I've put on 37's since then and I'm at 25-2600 now. You'll find it's not a crazy difference but the power and ease is night and day. If you may be tempted with 37's then go 5.13. I'll also add wheeling at elevation the deeper gears will help
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I was thinking about going with 5.13. I don't think I'll be going bigger than 35s until I have enough money to swap out the Dana for a prorock 44 up front. It'll probably take me three yrs to save up for the axle, coil overs and everything else involved.
 
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