Sponsored

Ring & Pinion Gears 38s to 40 Tires

JCJL

Active Member
First Name
James
Joined
Sep 30, 2019
Threads
4
Messages
39
Reaction score
29
Location
Indiana
Vehicle(s)
Jeep Gladiator LE Rubicon White & Jeep Gladiator LE Rubicon Granite Crystal
Occupation
NAVY
What are you guys running with 38s & 40s

I was going to go 5,13 or 5,38


It's not about driving fast just want TQ/Power to the ground.

Don’t get me wrong I drive my Jeeps on the Interstate

So you Professionals tell me what Gears to go with
Sponsored

 

RavensEyeOffroad

Well-Known Member
First Name
Nick
Joined
Sep 16, 2019
Threads
75
Messages
1,469
Reaction score
1,411
Location
Kentucky
Vehicle(s)
'21 Mojave
Build Thread
Link
What are you guys running with 38s & 40s

I was going to go 5,13 or 5,38


It's not about driving fast just want TQ/Power to the ground.

Don’t get me wrong I drive my Jeeps on the Interstate

So you Professionals tell me what Gears to go with
sheer power is going to be 5.38.
auto trans?
 
OP
OP

JCJL

Active Member
First Name
James
Joined
Sep 30, 2019
Threads
4
Messages
39
Reaction score
29
Location
Indiana
Vehicle(s)
Jeep Gladiator LE Rubicon White & Jeep Gladiator LE Rubicon Granite Crystal
Occupation
NAVY

Sponsored

OP
OP

JCJL

Active Member
First Name
James
Joined
Sep 30, 2019
Threads
4
Messages
39
Reaction score
29
Location
Indiana
Vehicle(s)
Jeep Gladiator LE Rubicon White & Jeep Gladiator LE Rubicon Granite Crystal
Occupation
NAVY
at 4:05 in the video he shows his gauge display and he is doing 80 mph @ maybe 3100 rpm's. 5.38 gears 40" tires.
I believe 488s would be a better fit, i am reaching out to some builders to get feedback
 

Jeep Rookie

Well-Known Member
First Name
Dave
Joined
Jul 6, 2019
Threads
1
Messages
104
Reaction score
62
Location
Utah
Vehicle(s)
None yet
May want to use the calculator floating around here...
37s (36.5) with 5.13s turns 2226@70
39s with the same 2165@70
Stock Rubi 2035@70 with much less rotating mass.
Sound like your first two are much better choices.
 

RH 67

Well-Known Member
First Name
Dave
Joined
Jul 25, 2019
Threads
18
Messages
695
Reaction score
481
Location
SoCal
Vehicle(s)
2020 Black Rubicon Gladiator, Alfa Romeo Quad
Occupation
Retired DOD, Army SF, SS.
I`m going to 37`s and was worried about gearing also, that was until i drove a Gladiator with 4:10`s and 37`s. To put it mildly i was shocked at how well it performed, at first i did notice a slight loss in power but after a couple of hours of driving i was not even thinking about being on 37`s and the truck felt normal.

I would use caution on going too low with the gearing.
 

Sponsored

RH 67

Well-Known Member
First Name
Dave
Joined
Jul 25, 2019
Threads
18
Messages
695
Reaction score
481
Location
SoCal
Vehicle(s)
2020 Black Rubicon Gladiator, Alfa Romeo Quad
Occupation
Retired DOD, Army SF, SS.
Can you expand on this statement?
Going too low your going to take away top end and mpg and take away what makes the Gladiator a good daily driver. I believe that 4:58`s would be close to a stock Rubicon with 4:10`s and 33`s. No need to have the motor revving any higher than it needs to be.
 

Jeep Rookie

Well-Known Member
First Name
Dave
Joined
Jul 6, 2019
Threads
1
Messages
104
Reaction score
62
Location
Utah
Vehicle(s)
None yet
Just an observation...
JCJL is looking at 38-40" tires.
You must consider the significant increase in rotating mass, rolling resistance, aerodynamics, etc.
Also you must consider the extra stress on the engine, tanny, and transfer case caused by the above.
The Penstar motor's torque increases with rpm which would help immensly in this case.
Geared lower (5.13 min) properly will reduce drivetrain stress and give him the grunt he is after "and" have a happy freeway runner utilizing 8th gear as it is intended to be. A lugging motor is not efficient.
Again, Just my thoughts...
 

MrKnowitall

Well-Known Member
First Name
Guenther
Joined
Oct 4, 2018
Threads
0
Messages
468
Reaction score
343
Location
Detroit
Vehicle(s)
14 JKU-R
Going too low your going to take away top end and mpg and take away what makes the Gladiator a good daily driver. I believe that 4:58`s would be close to a stock Rubicon with 4:10`s and 33`s. No need to have the motor revving any higher than it needs to be.
Putting 40s on a Jeep takes away from it being a good daily driver. That said, 5.38 isn't too low at all. If the question isn't whether or not you have to re-gear (entirely too subjective) but rather what ratio to go with, then I suggest the tallest available gear that you can live with at the maximum expected speed. Here's the calculation:
40" tires Revs per mile X Axle ratio X top gear X max desired speed / 60mph gives you
521 x 5.38 x 0.64 x 80 / 60 = 2392rpm.
Alternately I like multiplying the original ratio by the square of the tire size change:
OE Gear x (OE Tire rpm / mod tire rpm)^2 so
4.10 x (628/521)^2= 5.95. Using that in the 1st calc, you'd still only be turning 2650 at 80mph- that's less than my 6spd JKR does, not that anyone makes a gear that big.
With the resistance (air and rolling) of 40s, and all the weight (from add-ons) that any jeep on 40's will have, you'll won't every bit of that rpm, unless you want to just give up on 8th gear. You won't save a nickel in wear or fuel by going with 5.13 or 4.88s.
 
Last edited:

hjdca

Well-Known Member
Joined
Oct 27, 2019
Threads
9
Messages
1,639
Reaction score
2,324
Location
Southern California Mountains
Vehicle(s)
Jeep Gladiator Rubicon manual Sting Gray
Build Thread
Link
2035 rpm in high gear works for the Rubicon because of 33 inch tires. When you increase the size of the tire, you cannot just increase the rpm linearly. You will also need more hp to turn those bigger tires at the same rpm, so, the rpm has to go up more to get more hp. So, instead of 2035 rpm, you will want 2200 or 2300 to give you that extra hp to be efficient at that speed.
 

RH 67

Well-Known Member
First Name
Dave
Joined
Jul 25, 2019
Threads
18
Messages
695
Reaction score
481
Location
SoCal
Vehicle(s)
2020 Black Rubicon Gladiator, Alfa Romeo Quad
Occupation
Retired DOD, Army SF, SS.
2035 rpm in high gear works for the Rubicon because of 33 inch tires. When you increase the size of the tire, you cannot just increase the rpm linearly. You will also need more hp to turn those bigger tires at the same rpm, so, the rpm has to go up more to get more hp. So, instead of 2035 rpm, you will want 2200 or 2300 to give you that extra hp to be efficient at that speed.
That`s the beauty of the 8 speed.
Sponsored

 
 



Top