Regearing, where does the power come from?

[Ted404]

The one thing you must think about when changing tire size is you kind of already re geared it. It’s called roll out. If your one turn of your drive shaft from the factory moves you 1 foot (not real numbers) when you add 10% in tire size you will add roll out distance the gearing simply corrects this distance closer to factory. Now your Speedo is correct again too and in cases like mine you get to use 7,8 gear again on the highway. Not to mention lower strain on your motor and transmission

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[BLK HOLE]

Pretty simple...ever ride a bike and try to start off in high gear? Hard AF and works the hell out of your legs. What happens when you put it in low gear then?

Same thing when you put 37s on it and then regear it.

 

[Zachanadandy]

Pretty simple...ever ride a bike and try to start off in high gear? Hard AF and works the hell out of your legs. What happens when you put it in low gear then?

Same thing when you put 37s on it and then regear it.

Or you could just take off in 1st Gear? Nobody is suggesting you drive around in high gear all the time. Early JKs had a 2.86-1 1st Gear so even a Rubicon with 4.10s had a final drive ratio of 11.7-1 on 31s. Our 1st Gear is 4.7-1 so even on 4.10s the final drive ratio is 19.27-1. You'd have to run a 51" tire to match the "strain on the engine and transmission" faced by a stock JK Rubicon every day starting from a stop. Conversely a JT with 4.10s and 37s has the same initial drive ratio as a JK Rubicon on 22.5" tires. This transmission has changed the equation so massively that it's hard to get people new to Jeeps and modifying them to understand. Nobody in a JK was being told they needed 7.5-1 gears in their axles to run 37s, but that's what they'd need to match the 8spd with 4.10s.

 

[BLK HOLE]

Or you could just take off in 1st Gear? Nobody is suggesting you drive around in high gear all the time. Early JKs had a 2.86-1 1st Gear so even a Rubicon with 4.10s had a final drive ratio of 11.7-1 on 31s. Our 1st Gear is 4.7-1 so even on 4.10s the final drive ratio is 19.27-1. You'd have to run a 51" tire to match the "strain on the engine and transmission" faced by a stock JK Rubicon every day starting from a stop. Conversely a JT with 4.10s and 37s has the same initial drive ratio as a JK Rubicon on 22.5" tires. This transmission has changed the equation so massively that it's hard to get people new to Jeeps and modifying them to understand. Nobody in a JK was being told they needed 7.5-1 gears in their axles to run 37s, but that's what they'd need to match the 8spd with 4.10s.

You're free to do whatever you want...but adding larger tires to a stock config adds strain and reduces the gearing. You're free to argue whether or not that its minimal, thus doesn't matter to you, or not...but there's no denying that its there. I chose to regear. It was nice having 8th back when on the freeway.

JK transmissions suck.

 

[bleda2002]

Or you could just take off in 1st Gear? Nobody is suggesting you drive around in high gear all the time. Early JKs had a 2.86-1 1st Gear so even a Rubicon with 4.10s had a final drive ratio of 11.7-1 on 31s. Our 1st Gear is 4.7-1 so even on 4.10s the final drive ratio is 19.27-1. You'd have to run a 51" tire to match the "strain on the engine and transmission" faced by a stock JK Rubicon every day starting from a stop. Conversely a JT with 4.10s and 37s has the same initial drive ratio as a JK Rubicon on 22.5" tires. This transmission has changed the equation so massively that it's hard to get people new to Jeeps and modifying them to understand. Nobody in a JK was being told they needed 7.5-1 gears in their axles to run 37s, but that's what they'd need to match the 8spd with 4.10s.

The 8 speed also has 2 overdrives so regearing gives you effectively a new first gear, and still maintain an over drive. Just have to decide what's more useful, a better first gear, or a higher over drive. You seem to drive down hill a lot, so a better over drive works. I can't live with 12 second 0-60 or 7 second 0-30 so better low gears works for me to get shave nearly 3 seconds from 0-30 and have more grunt when towing.

 

[Zachanadandy]

You're free to do whatever you want...but adding larger tires to a stock config adds strain and reduces the gearing. You're free to argue whether or not that its minimal, thus doesn't matter to you, or not...but there's no denying that its there. I chose to regear. It was nice having 8th back when on the freeway.

JK transmissions suck.

I'm not arguing nobody should regear, but having been down the path of gearing too low and killing the freeway mileage (5.38s and 38s suck on the freeway, even 4.10s were better), I point out the simple math. Are 4.56s a better match for 37s than 4.10s? Maybe as low as 4.88s? Absolutely, but unless you're running 40s or never drive freeway speed is stay away from the 5.xx ratios personally. A. There's no need and it's more gear than anyone really needs B. It limits freeway driveability. If you're only going to 35s I absolutely wouldn't spend the money on a regear. Our JLUR felt like it was geared too low on factory 4.56s and 35s on the freeway.

 

[BLK HOLE]

I'm not arguing nobody should regear, but having been down the path of gearing too low and killing the freeway mileage (5.38s and 38s suck on the freeway, even 4.10s were better), I point out the simple math. Are 4.56s a better match for 37s than 4.10s? Maybe as low as 4.88s? Absolutely, but unless you're running 40s or never drive freeway speed is stay away from the 5.xx ratios personally. A. There's no need and it's more gear than anyone really needs B. It limits freeway driveability. If you're only going to 35s I absolutely wouldn't spend the money on a regear. Our JLUR felt like it was geared too low on factory 4.56s and 35s on the freeway.

I had 5.13s and 37s (now 39s) and it was glorious. Got 17mpg...get 16.5 now.

 

[Zachanadandy]

The 8 speed also has 2 overdrives so regearing gives you effectively a new first gear, and still maintain an over drive. Just have to decide what's more useful, a better first gear, or a higher over drive. You seem to drive down hill a lot, so a better over drive works. I can't live with 12 second 0-60 or 7 second 0-30 so better low gears works for me to get shave nearly 3 seconds from 0-30 and have more grunt when towing.

I'd have to see the time slips to buy either of those numbers. Had the td3 in our 2019 JLUR and confirmed multiple times it would still 0-60 in just under 7s on 38s on 4.10s, and lost 1-2 tenths on 5.38s due to the extra shift right before 60mph. Are you telling me your JT was somehow slower to 30mph than that because there's no way your shaving 3 seconds off a 3 second 0-30mph time short of a bomb blowing the Jeep past 30mph in less than a second. 12s 0-60? Maybe in reverse.

 

[BLK HOLE]

I lost over a sec 1/4 mile time going to 5.13s. (done using an app)

 

[bleda2002]

I'd have to see the time slips to buy either of those numbers. Had the td3 in our 2019 JLUR and confirmed multiple times it would still 0-60 in just under 7s on 38s on 4.10s, and lost 1-2 tenths on 5.38s due to the extra shift right before 60mph. Are you telling me your JT was somehow slower to 30mph than that because there's no way your shaving 3 seconds off a 3 second 0-30mph time short of a bomb blowing the Jeep past 30mph in less than a second. 12s 0-60? Maybe in reverse.

0-30 7 seconds on tazer, 0-60 12 seconds on tazer with 4.10s and 39s. 0-30 is now low 4s and 0-60 low 9s on 39s with 5.13s. Multiple runs, multiple times, flat ground. 7 seconds on 38s means you only lost half a second going from 32.5 to 38s that's amazing honestly. I am not kidding when I said the JT on 39s couldn't get out of its own way on 39s and beadlocks.

Final straw for me was in the mountains trying to get to the cabin in TN and having to use 1st gear as it was the only one that would actually climb the grade.

 

[Zachanadandy]

0-30 7 seconds on tazer, 0-60 12 seconds on tazer with 4.10s and 39s. 0-30 is now low 4s and 0-60 low 9s on 39s with 5.13s. Multiple runs, multiple times, flat ground. 7 seconds on 38s means you only lost half a second going from 32.5 to 38s that's amazing honestly. I am not kidding when I said the JT on 39s couldn't get out of its own way on 39s and beadlocks.

Final straw for me was in the mountains trying to get to the cabin in TN and having to use 1st gear as it was the only one that would actually climb the grade.

The JLU was the 2.0t, and the td3 added the performance trans tune as well as the 93 octane tune. That alone did more for performance than the regear by a long shot and was $2300 cheaper. I'd be interested to see if something like the livernoise tune wakes up the 3.6L anywhere near as much. On paper the gains are about the same. Unfortunately they don't have a tune fit the new gpec5 pcms yet.

 

[Badunit]

I am always amazed at the difference of opinion on gearing. I am of the opinion that almost every truck is geared too high from the factory while other people will feel the factory gearing is the best even after upgrading their tires to a much larger size. Even my Ram with its 800 ft-lb of torque was a dog the way it was geared from the factory. Re-gearing woke it up with no decrease at all in mpg.

I'm re-gearing my JT to 4.56 while running the stock 33's, which is equivalent to 5.13 with 37's. My JT is my daily driver and this is the lowest I can go without limiting my top speed. I've been tracking my mpg for the past 3000 miles and will continue to do so after re-gearing so we'll see what difference it makes. I am also waiting patiently for the GPEC5 to be unlocked and tunes to become available.

 

[Pilsner]

I've gone through the math and it should be ideal for my 75% off pavement (FS and logging roads), 15% in town, 10% highway, and 0% crawling use for the vehicle. I want good torque from 0-50 mph and 3k rpm max at about 75mph in 6th. It only looks like a radical change because these things are geared so wrong from the factory.

You really shouldn't do that. That's WAY too much gear. I don't know why FS roads would require a regear at all. They are not "geared so wrong" from the factory with stock sized tires. I really mean no offence, but you don't seem super experienced here and I suggest you take advice and do some research before making that change.

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