We installed 4.88s from a 4.10. (37” tire). Review, tips, and notes inside!

[JT1]

Remember that around town a re-gear does nothing. Re-gearing changes the lowest overall range and the highest overall range. Everywhere in between, the TCU is free to select a gear up or down to meet the need.

So once you are rolling over 10 mph, and the transmission is in 1st through 7th, the axle ratio is irrelevant.

except my truck has a third pedal, so that processing is done by the driver. And around town the regear absolutely does things... the time spent accelerating in every gear goes down.. I can accelerate faster in 6th gear now than I could in 4th before the regear.

Sponsored

 

[dcmdon]

except my truck has a third pedal, so that processing is done by the driver. And around town the regear absolutely does things... the time spent accelerating in every gear goes down.. I can accelerate faster in 6th gear now than I could in 4th before the regear.

Yes, but that is because you are now going slower. When less power is required to maintain speed.

How fast you can accelerate in any gear is not relevant. What is relevant is how fast you can accelerate at a given speed.

And that is going too vary based on teh speed.

Whatever speed gets you near peak power RPM in a given gear is going to suffer if you re-gear.

 

[JT1]

Yes, but that is because you are now going slower. When less power is required to maintain speed.

How fast you can accelerate in any gear is not relevant. What is relevant is how fast you can accelerate at a given speed.

And that is going too vary based on teh speed.

Whatever speed gets you near peak power RPM in a given gear is going to suffer if you re-gear.

I'm not going slower.. this is a manual, you understand that there are no automatic downshifts. Acceleration in a given gear is important. Prior to the regear 5th AND 6th were 100% useless and 4th going uphill in a headwind struggled. 70mph. Now I can climb hills in a headwind and accelerate in 6th. 2400ish rpm both scenarios.. shorter lever arm, physics and all that.

 

[Bonanza]

Remember that around town a re-gear does nothing. Re-gearing changes the lowest overall range and the highest overall range. Everywhere in between, the TCU is free to select a gear up or down to meet the need.

So once you are rolling over 10 mph, and the transmission is in 1st through 7th, the axle ratio is irrelevant.

Not quite. Starting and stopping frequently uses the first number of gears quite a bit. Even going WoT has the engine accelerate in gear til redline, and the gearing does come into play at all times. Notably, the gearing requires less depression of the gas pedal, which is a welcome change. It also changes how long the Jeep stays in a certain gear, how often it shifts, etc.

Right now, I’d suspect the 5.13s would’ve been more appropriate for my driving habits. But it’s hard to know for sure.

 

[Wheelin98TJ]

Remember that around town a re-gear does nothing. Re-gearing changes the lowest overall range and the highest overall range. Everywhere in between, the TCU is free to select a gear up or down to meet the need.

So once you are rolling over 10 mph, and the transmission is in 1st through 7th, the axle ratio is irrelevant.

Not sure I follow.

The axle ratio is always relevant. Regearing to a deeper gear ratio increases torque multiplication.

 

[dcmdon]

Not sure I follow.

The axle ratio is always relevant. Regearing to a deeper gear ratio increases torque multiplication.

Yes, but if you need an overall lower ratio, you just go down a gear.

At some point 7th with an X rear end is the same as 6th with a Y rear end. Same overall reduction ratio.

 

[Wheelin98TJ]

Yes, but if you need an overall lower ratio, you just go down a gear.

At some point 7th with an X rear end is the same as 6th with a Y rear end. Same overall reduction ratio.

The axle ratio is still relevant.

The rig with gears will win the red light drag races around town.

 

[Escape.idiocracy]

Yes, but if you need an overall lower ratio, you just go down a gear.

At some point 7th with an X rear end is the same as 6th with a Y rear end. Same overall reduction ratio.

The location in which the torque is increasing is different.
I understand what you are saying, however the real world application is going to come into play….


pulling - 5k # trailer @50mph speed can be maintained by the transmission dropping gears to meet the demand. However, when the demand requires the torque that 3rd gear can provide motor speed is now too high and over heats…… by having the torque multiplier in the rear end and not in the transmission the trans now only drops to 5th gear, and motor rpm’s are significantly lower to produce the same speed.

The above is an explanation…… I’m not going to get into the weeds and pull up crawl ratio calculators etc to further show the “why” nor am I saying the above is a perfect explanation. Just trying to help explain the difference with torque and where it is being multiplied…..

 

[dcmdon]

The location in which the torque is increasing is different.
I understand what you are saying, however the real world application is going to come into play….


pulling - 5k # trailer @50mph speed can be maintained by the transmission dropping gears to meet the demand. However, when the demand requires the torque that 3rd gear can provide motor speed is now too high and over heats…… by having the torque multiplier in the rear end and not in the transmission the trans now only drops to 5th gear, and motor rpm’s are significantly lower to produce the same speed.

The above is an explanation…… I’m not going to get into the weeds and pull up crawl ratio calculators etc to further show the “why” nor am I saying the above is a perfect explanation. Just trying to help explain the difference with torque and where it is being multiplied…..

Often when discussing with someone, they fail to explain themself and things stay vague.

Thankfully, that's not a problem. You did a great job explaining your position.

You are still mistaken though. Where the torque is multiplied makes no difference to the engine.

If your transmission is reducing 3 to 1 and your differential is reducing 4 to 1

ABSOLUTELY IDENTICAL

to the engine as if the transmission was reducing 4:1 and the diff 3:1.

The overall reduction is 12:1. Period.

Either of these examples will make the same power, generate the same heat, and use the same amount of fuel.

As far as your statement that "motor speed is now too high and over heats". That's also incorrect because the heat generated by a motor is directly proportional to how much power it is being asked to produced.

Power = torque x RPM.

In other words, a motor putting out 100 ft lbs of torque at 3000 rpm is making the same power as a motor putting out 300 ft lbs of torque at 1000 rpm. Both will make similar heat.

 

[dcmdon]

The axle ratio is still relevant.

The rig with gears will win the red light drag races around town.

Absolutely. It will launch harder. It will therefore be faster almost all the time.

But sometimes you get bit by this logic. Back in 2004 Subaru came out with the STi to compete against the Mitsubishi Evo. The Evo was quicker to 60. But that didn't really tell the story.

Up until 57 mph, the Subaru was actually faster. But because the Evo had just a bit taller gearing it could get to 60 in 2nd gear.

The Subaru bounced off its rev limiter at 58 mph and required a shift to 3rd JUST before 60.

So to get to 60 the higher geared Evo required 1 shift. The lower geared Subaru required 2.

The Evo required a shift into 3rd at 64 mph. At which point the Subaru retook the lead.

So you see, sometimes lower gearing bites you in the butt. And sometimes it helps. It all depends on what you are looking for.

Another example. I used to road race a 125 and 250 cc 2 stroke GP bike. We would usually gear the bike so it hit redline in top gear at the fastest point on the track. But sometimes gearing it like that would put you in a place where you had to upshift immediately before an important corner,. Shifting into that gear, to only hold it for a split second was slower than if you went down a tooth on the rear sprocket (gearing up) so that you could hold the lower gear into the corner.

I hope this makes sense.

 

[Vtur]

There's difference between tranny vs axles gear ratio. Axles regearing shifts the power band through out all gears.

 

[Escape.idiocracy]

Often when discussing with someone, they fail to explain themself and things stay vague.

Thankfully, that's not a problem. You did a great job explaining your position.

You are still mistaken though. Where the torque is multiplied makes no difference to the engine.

If your transmission is reducing 3 to 1 and your differential is reducing 4 to 1

ABSOLUTELY IDENTICAL

to the engine as if the transmission was reducing 4:1 and the diff 3:1.

The overall reduction is 12:1. Period.

Either of these examples will make the same power, generate the same heat, and use the same amount of fuel.

As far as your statement that "motor speed is now too high and over heats". That's also incorrect because the heat generated by a motor is directly proportional to how much power it is being asked to produced.

Power = torque x RPM.

In other words, a motor putting out 100 ft lbs of torque at 3000 rpm is making the same power as a motor putting out 300 ft lbs of torque at 1000 rpm. Both will make similar heat.

Can you explain why two diesel gladiators equally equipped one with factory gears and one with 5.13’s when towing the 5.13’s run cooler oil temps?
I would like to understand, and what you posted above reads in a manner that makes sense, but the real world application is showing differently…

I’m not trying to be a smartass… I would like to understand.


I am interested in this:
“As far as your statement that "motor speed is now too high and over heats". That's also incorrect because the heat generated by a motor is directly proportional to how much power it is being asked to produced.”


lower gears give higher torque at the wheel and higher acceleration and lower car speed. Higher gears gives lower torque at the wheel and lower acceleration and higher car speed.


If I am putting a lower gear ratio in, this is increasing the applied torque to the ground…. Therefore reducing the strain on the motor…. “Doing more with less”….

Make it make sense for me

 

[jeepstertim]

4.10 w 35's should be right in the sweet spot...should be able to hold 8th at 2000rpm w 75-77mph

Unless you're fighting a head wind....

 

[dcmdon]

lower gears give higher torque at the wheel and higher acceleration and lower car speed. Higher gears gives lower torque at the wheel and lower acceleration and higher car speed.


If I am putting a lower gear ratio in, this is increasing the applied torque to the ground…. Therefore reducing the strain on the motor…. “Doing more with less”….

Make it make sense for me

I only have a few minutes to write, but we can discuss more later. So lets start with your example.

You put a lower gear ratio in and for a given throttle setting you are able to apply more torque (force) to the ground. But you aren't doing more with less. You are doing less with less. Because when you lower the gearing, the speed of the wheel decreases.

So (for a given throttle setting) you may be able to push harder, but you are pushing slower.
So, yes, you are reducing the strain on the motor. Because you are going slower,.

Lets look at 3 equal trucks pulling a trailer.

One has 3.83 gears and is driving along in 7th gear up a steep hill. It is working hard to maintain 70 mph at 2500 rpm.

Two has 4.56 gears and is easily going up the same hill with the same trailer at the same RPM. But its only going 59 mph. (70 x (3.83/4.56)=59)

Lets look for a moment at aerodynamic drag. The power necessary to overcome aerodynamic drag increases as a cube function. The power necessary to overcome mechanical drag as well as the drag of lifting something up a hill, increases as a square function.

So if all the drag were aerodynamic, the decrease in power between 59 and 70 would be (59/70)^3 = .599

If all the drag were mechanical the decrease in power would be .703

So if we guess at a middle value of .65, then it means that in reducing the speed from 70 to 59, you have made it so the motor only ha to make 65% as much power as it does at 70.

guess what happens when you reduce power output by 35%?? Heat goes down. Everything runs cooler.

Now lets take truck number 3.

Its got 3.83 gears just like truck #1. But when he reaches the hill, he downshifts to 6th so that his overall gearing is the same as Truck #2 with the 4.56 gears. His motor is also Turning 2500 rpm and he's also going 59 mph.

EVERYTHING is identical in the 2 trucks as far as the engine is concerned. Same RPM. Same torque produced at the crankshaft, same torque at the rear wheel, same speed at the rear wheel, same power output.

Does this make sense??

If it doesn't, then I'm failing and need to come up with a different angle.

 

[dcmdon]

Regarding running cooler with lower gears. As I showed above the speed that you drive has a huge impact on necessary power produced.

So if you pull even a tiny bit slower with the lower gears, it can make big difference. I'm not going to explain the math, but here is the change with only a 3 mph decrease in speed from 70 mph.

aero power
(67/70)^3 = .87

mechanical power
(67/70)^2= .91

So with a 3 mph decrease in speed, you have decreased the amount of power the engine must make by about 10%.

Crazy huh??

Sponsored