Transfer case re-gearing (3 Viewers)

[cruiseroutfit]

The only difference is that you don't drive on your transmission. You actually need tires. And the size of those tires will affect you ratio on the pavement.

All that math only applies to the OEM tire size.
What is the number one reason we all want to regear everything on our rigs after we get bigger size tires?
Everything falls out of spec with 33", 35", 37" etc.

If everything stays the same, then how come there will always be a difference between 33's and 37's?
Yes the drivetrain will remain constant in it's ratios, but the tire sizes will affect everything in all gears 1 through 4, high or low.

There is a good reason people have installed 4.88 and 5.29 gears once they got a bump in the tire size.

Right but you will always have a 3.3:1 transfer throughput regardless of tire size. The math does not change based on the tire, in fact it is not even considered when deciding throughput ratio of the transfer case. Tires don't "theoretically" change the transmission ratio, transfer case ratio or axle ratio. They don't change.

Of course there will be a final ratio difference between 4.88 and 5.29, the math says so (trans 1st x t/c low x diff) and there will be a realized difference based on tire (2πr). But to say "you would only get that 3.3:1 ratio with 31" tires." isn't true. You get 3.3:1 out of your t-case with 21"

And yes, I can provide the math to support what I said, upon request.

Please do.

 

[richardlillard1]

Agreed. It stays constant.
But at the output shaft, not on the pavement where it counts.

Some people might think they would get a full 5.29 ratio, but in reality when coupled with >37" tires, that ratio will go down to a more OEM spec.

The low gear (higher numerically) compensates for the tire size increase, it does not add anything unless you run OEM size tires. Then you will really feel the new gearing.

In essence we try to keep the engine RPM in a certain range where the power/torque output is optimal for the condition we are in. That will be accomplished by regearing either the transmission (difficult to do), transfer case (easier) or axle gear (still easier).

Huh? Is this some common core math crap?

I don’t know about your math, but my 5.29s make the driveshaft spin 5.29 times faster, or 1.19 times faster than the stock gears did.

My speedo is also off by about 10% whatever speed I am actually going when I check it with GPS. So not really closer to factory.

 

[cruiseroutfit]

Agreed. It stays constant.
But at the output shaft, not on the pavement where it counts.

Every change at the output shaft, also makes it's way to the pavement. I'm lost here???

 

[Dragos80]

Right but you will always have a 3.3:1 transfer throughput regardless of tire size. The math does not change based on the tire, in fact it is not even considered when deciding throughput ratio of the transfer case. Tires don't "theoretically" change the transmission ratio, transfer case ratio or axle ratio. They don't change.

Of course there will be a final ratio difference between 4.88 and 5.29, the math says so (trans 1st x t/c low x diff) and there will be a realized difference based on tire (2πr). But to say "you would only get that 3.3:1 ratio with 31" tires." isn't true. You get 3.3:1 out of your t-case with 21"



Please do.

If everything stays the same, why do we even bother to regear anything?


It drops the engine RPM as stated above. Puts the engine power.
The whole reason for regearing anything is to raise the RPM to a better power output, in order to cope with the lower revving tires and increase centrifugal mass.

Agreed with your point. the tranny and transfer case will see no change.
The engine will behave differently due to the tire size increase which translates to adding more overdrive. As if we always drive in a higher gear.
Regearing will in other words downshift us to a more responsive harmony with the engine and tires.

 

[cruiseroutfit]

If everything stays the same, why do we even bother to regear anything?

I'm not saying everything stays the same... I'm saying it absolutely changes and here is my math.

Low Range Transfer Output stock: 2.44804:1
Low Range with HRUD and 3.1:1 Low Range Gears: 3.31672

Math, not theory.

Nice! So with both the UD high and low range low gears installed you get 3.3:1 low range gearing.

You were the one arguing the above point, not me Note he was referencing "Transfer Case Gear Ratio Chart".

Engine RPM, altitude, tire size, attitude, supercharger, driver weight, load, grade, humidity, etc... all don't change the Transfer Case Gear Ratio

 

[Douglas S]

If everything stays the same, why do we even bother to regear anything?


It drops the engine RPM as stated above. Puts the engine power.
The whole reason for regearing anything is to raise the RPM to a better power output, in order to cope with the lower revving tires and increase centrifugal mass.

Agreed with your point. the tranny and transfer case will see no change.
The engine will behave differently due to the tire size increase which translates to adding more overdrive. As if we always drive in a higher gear.
Regearing will in other words downshift us to a more responsive harmony with the engine and tires.

Please stop.

 

[richardlillard1]

Please stop.

This is getting to be up there with that viscous coupler thread.

 

[orangefj45]

Georg, have you ever stocked the 36221-60121M?

Terrain Tamer has this gear in stock. We can have one here in 2-3 weeks.
Can get via DHL in a few days .....

Georg @ Valley Hybrids & Cruiser Brothers

 

[half k cruiser]

You're spot on, with any change to the high-range ratio, you are proportionally changing the low range ratio as well.

Final T-Case Gearing Chart with different options, whipped this up quick so feel free to check my math.

View attachment 1613583

My brain hurts from trying to decipher that, so i'm going to take your word for it.

 

[iptman]

Terrain Tamer has this gear in stock. We can have one here in 2-3 weeks.
Can get via DHL in a few days .....

Georg @ Valley Hybrids & Cruiser Brothers

Which gears are these?

 

[orangefj45]

Which gears are these?

I was responding to a question Kurt posted earlier in the thread.

We have the high range OD & UD gears as well as the low range 3.1:1 gears in stock.

Georg @ Valley Hybrids & Cruiser Brothers

 

[Dragos80]

Please stop.

This is getting to be up there with that viscous coupler thread.

Don't be afraid of math.
Let's take 4th gear ratio, stock axle gear ratio and OEM size tires. In that case you can talk about the true ratios.
0.753 OD, 4.11 axle ratio, 31" tires

This combo gives you a final ratio of 3.095 in HI.


Add 33" tires and you suddenly need 3.29 final ratio due to larger size tires.
Add 35" and that requires 3.49 ratio

Since you cannot easily change the transmission gear ratios, you will look elsewhere (axles or x-case).

for a 33" tire you would require a roughly 1.06 increase in gear ratio to maintain every design aspect in the OEM parameters. This would be preferred in the case of the engine power band and transmission lock up speed.

For a 35" tire you would need a 1.3 increase in your gear ratio.


Your 10% UD HR is slightly more than what's needed for a 33" tire, but less than what would be needed for 35" tire.


Using the "10%" UD ratio we get 0.753 4th gear, 4.11 axle ratio and 1.09677 HR = 3.394 ratio using the OEM specs (meaning 31" tire).

When you use a 33" together with this 1.09677 UD HR, it will net you a 3.1886 ratio, which is slightly less than anticipated > 1.03 real UD.
For a 35" tire you get a 3.006 ratio which would be the equivalent of 0.97 HR x-case.
For a 37" tire the "10%" UD HR would get you the equivalent of 0.9188 ratio which, as in the case of a 35" tire, still overdrive.


In conclusion a 10% underdrive transfer case ratio in HI would only be better for a 33".


Yes, 10% UD would still be better than stock everything, but not enough for 35" tires and larger.
One would need to combine this x-case regear with an axle regear... 4.26/4.55/4.88


For those of you having trouble understanding the numbers above, think about larger tires as having a 5th or 6th gear in your transmission which always gets your engine to lower RPM when you need it in higher RPM range.
As if you are always in the wrong gear.

People who run 35" swear by the 4.88 ratio.
That's 18.7% higher than stock, which is also higher than 10% UD.

 

[bryson]

Don't be afraid of math.
Let's take 4th gear ratio, stock axle gear ratio and OEM size tires. In that case you can talk about the true ratios.
0.753 OD, 4.11 axle ratio, 31" tires

This combo gives you a final ratio of 3.095 in HI.


Add 33" tires and you suddenly need 3.29 final ratio due to larger size tires.
Add 35" and that requires 3.49 ratio

Since you cannot easily change the transmission gear ratios, you will look elsewhere (axles or x-case).

for a 33" tire you would require a roughly 1.06 increase in gear ratio to maintain every design aspect in the OEM parameters. This would be preferred in the case of the engine power band and transmission lock up speed.

For a 35" tire you would need a 1.3 increase in your gear ratio.


Your 10% UD HR is slightly more than what's needed for a 33" tire, but less than what would be needed for 35" tire.


Using the "10%" UD ratio we get 0.753 4th gear, 4.11 axle ratio and 1.09677 HR = 3.394 ratio using the OEM specs (meaning 31" tire).

When you use a 33" together with this 1.09677 UD HR, it will net you a 3.1886 ratio, which is slightly less than anticipated > 1.03 real UD.
For a 35" tire you get a 3.006 ratio which would be the equivalent of 0.97 HR x-case.
For a 37" tire the "10%" UD HR would get you the equivalent of 0.9188 ratio which, as in the case of a 35" tire, still overdrive.


In conclusion a 10% underdrive transfer case ratio in HI would only be better for a 33".


Yes, 10% UD would still be better than stock everything, but not enough for 35" tires and larger.
One would need to combine this x-case regear with an axle regear... 4.26/4.55/4.88


For those of you having trouble understanding the numbers above, think about larger tires as having a 5th or 6th gear in your transmission which always gets your engine to lower RPM when you need it in higher RPM range.
As if you are always in the wrong gear.

People who run 35" swear by the 4.88 ratio.
That's 18.7% higher than stock, which is also higher than 10% UD.

 

[Dragos80]

Tell where exactly I am wrong then.

 

[MTKID]

Don't be afraid of math.
Let's take 4th gear ratio, stock axle gear ratio and OEM size tires. In that case you can talk about the true ratios.
0.753 OD, 4.11 axle ratio, 31" tires

This combo gives you a final ratio of 3.095 in HI.


Add 33" tires and you suddenly need 3.29 final ratio due to larger size tires.
Add 35" and that requires 3.49 ratio

Since you cannot easily change the transmission gear ratios, you will look elsewhere (axles or x-case).

for a 33" tire you would require a roughly 1.06 increase in gear ratio to maintain every design aspect in the OEM parameters. This would be preferred in the case of the engine power band and transmission lock up speed.

For a 35" tire you would need a 1.3 increase in your gear ratio.


Your 10% UD HR is slightly more than what's needed for a 33" tire, but less than what would be needed for 35" tire.


Using the "10%" UD ratio we get 0.753 4th gear, 4.11 axle ratio and 1.09677 HR = 3.394 ratio using the OEM specs (meaning 31" tire).

When you use a 33" together with this 1.09677 UD HR, it will net you a 3.1886 ratio, which is slightly less than anticipated > 1.03 real UD.
For a 35" tire you get a 3.006 ratio which would be the equivalent of 0.97 HR x-case.
For a 37" tire the "10%" UD HR would get you the equivalent of 0.9188 ratio which, as in the case of a 35" tire, still overdrive.


In conclusion a 10% underdrive transfer case ratio in HI would only be better for a 33".


Yes, 10% UD would still be better than stock everything, but not enough for 35" tires and larger.
One would need to combine this x-case regear with an axle regear... 4.26/4.55/4.88


For those of you having trouble understanding the numbers above, think about larger tires as having a 5th or 6th gear in your transmission which always gets your engine to lower RPM when you need it in higher RPM range.
As if you are always in the wrong gear.

People who run 35" swear by the 4.88 ratio.
That's 18.7% higher than stock, which is also higher than 10% UD.

Well, when you put it that way... yep, I’m still afraid

 

[lumbee1]

Don't be afraid of math.
Let's take 4th gear ratio, stock axle gear ratio and OEM size tires. In that case you can talk about the true ratios.
0.753 OD, 4.11 axle ratio, 31" tires

This combo gives you a final ratio of 3.095 in HI.


Add 33" tires and you suddenly need 3.29 final ratio due to larger size tires.
Add 35" and that requires 3.49 ratio

Since you cannot easily change the transmission gear ratios, you will look elsewhere (axles or x-case).

for a 33" tire you would require a roughly 1.06 increase in gear ratio to maintain every design aspect in the OEM parameters. This would be preferred in the case of the engine power band and transmission lock up speed.

For a 35" tire you would need a 1.3 increase in your gear ratio.


Your 10% UD HR is slightly more than what's needed for a 33" tire, but less than what would be needed for 35" tire.


Using the "10%" UD ratio we get 0.753 4th gear, 4.11 axle ratio and 1.09677 HR = 3.394 ratio using the OEM specs (meaning 31" tire).

When you use a 33" together with this 1.09677 UD HR, it will net you a 3.1886 ratio, which is slightly less than anticipated > 1.03 real UD.
For a 35" tire you get a 3.006 ratio which would be the equivalent of 0.97 HR x-case.
For a 37" tire the "10%" UD HR would get you the equivalent of 0.9188 ratio which, as in the case of a 35" tire, still overdrive.


In conclusion a 10% underdrive transfer case ratio in HI would only be better for a 33".


Yes, 10% UD would still be better than stock everything, but not enough for 35" tires and larger.
One would need to combine this x-case regear with an axle regear... 4.26/4.55/4.88


For those of you having trouble understanding the numbers above, think about larger tires as having a 5th or 6th gear in your transmission which always gets your engine to lower RPM when you need it in higher RPM range.
As if you are always in the wrong gear.

People who run 35" swear by the 4.88 ratio.
That's 18.7% higher than stock, which is also higher than 10% UD.

Excellent post and I came to the same conclusion myself. I will be installing 4.88's in my axles to compensate for the 315's. The axle regear is cheaper than the TC gears.

 

[junior80]

I've gone cross-eyed.

 

[TexasJack]

Here is my take on it:

 

[MTKID]

Here is my take on it:
View attachment 1614144

Finally, a formula I can follow! N=40’s

 

[richardlillard1]

Any of you ever see that movie “A Beautiful Mind” with the mathematician who saw numbers and equations in random magazine articles and stuff?

This is nothing like that, because that guy understood math, but I remember I got up in the middle of the movie to pee so I missed a few minutes in there.