Sponsored
OP
OP
AnnDee4444

AnnDee4444

Well-Known Member
Joined
Jan 14, 2019
Threads
49
Messages
4,685
Reaction score
6,273
Location
Vehicle(s)
'18 JLR 2.0
AnnDee. Thanks. When I downloaded the spreadsheet into XLSX per the instructions, it kept the tables but lost the graphs. Do you have a suggestion for capturing a download with the cool graphs?
It looks like there's something I've done with the graphs that prevents Excel from opening them correctly. These were created in Google Sheets in order for them to be easily sharable, and I guess this is one of the downsides.

I don't have a solution for this yet, but I can suggest keeping it all in Google Sheets and copying it to your personal Google account, like this:

Jeep Wrangler JL Calculator: gear ratio, tire size, speed, etc. Untitled
Sponsored

 

pnut

Well-Known Member
First Name
M
Joined
Nov 19, 2020
Threads
17
Messages
377
Reaction score
548
Location
Michigan
Vehicle(s)
2022 Wrangler 392 XR
Any idea if this is valid for the forthcoming 392? Meaning the trans is the same as the auto one listed? Thx.
 
OP
OP
AnnDee4444

AnnDee4444

Well-Known Member
Joined
Jan 14, 2019
Threads
49
Messages
4,685
Reaction score
6,273
Location
Vehicle(s)
'18 JLR 2.0

J0E

Well-Known Member
First Name
J0e
Joined
Sep 1, 2018
Threads
55
Messages
1,353
Reaction score
1,121
Location
Hawaii, MT, SLC, NYC
Website
bt39.com
Vehicle(s)
2021 JLR, 05 LJR on 43s
Build Thread
Link
Occupation
Drywall construction - reel estate
Here's a spreadsheet I built to calculate gear ratio, tire size, speed, etc. The yellow colored cells are how to control the inputs (either drop-down or number fillable), all other cells are un-editable.
bt39.com/GearWheelSpeed might be easier to use.

If you are having trouble using the spreadsheet because another user is currently editing it, you can download your own local copy in Excel format:
I use session ID so everyone has their own data and there are no collisions. I can add anything you like to be displayed by default, although with the edit link you can change any parameter.

I plan to add graphs, that's pretty useful.
 
Last edited:

Sponsored

The_Skyo

Well-Known Member
Joined
Oct 8, 2021
Threads
3
Messages
67
Reaction score
106
Location
Vancouver, BC
Vehicle(s)
2022 JLUR 6 spd 4.88
This chart is fantastic despite there not being many comments here. For me it raises some questions though.
I currently drive a Focus ST (manual) with a 2L turbo inline 4. I can shift into 6th on flat ground at about 80kph (50mph).
I recently ordered a manual rubicon with 4.10 gear ratio. With the option of 4.88s giving nice crawl ratios I'm a little torn by what I see in this chart.

At 50mph with 4.10 (33" tires likely staying so it fits in my garage with a roof tent) I'd be at 1500rpm. With the 3.6 not being so torquey at low RPM since it has no turbo it sounds like people try to stay above 2000rpm. 4.88s would bring me up to 1789rpm at 50mph and 2147rpm at 60mph which sounds useable.
Does it really kill my MPG if I got 4.88 on stock 33" tires? I don't often go above 75mph around here and people have complained that the gears are too tall and they sound much taller than the Focus I drive so 4.88 actually sounds like it's closer to what I'm used to. Any first hand experience with both here?
 

damageinc321

Well-Known Member
First Name
Mark
Joined
Feb 4, 2021
Threads
31
Messages
150
Reaction score
138
Location
Indiana
Vehicle(s)
2018 wrangler rubicon unlimited
I recently had a forum member question why a manual with 37s & 5.13s is actually 70 MPH @ 2500 RPM while this calculator shows 75 MPH@ 2500 RPM. Here are some tips:
  1. This calculator is using the numbers for a true tire size. The number you enter is what the calculator will run. Many tires are actually less tall than the advertised size, sometimes up-to an inch shorter. Also, all tires sag when loaded, which I think could also have an effect.
  2. A "5.13" gearset has 8 pinion teeth & 41 ring gear teeth. This actually calculates to a true ratio of 5.125:1 (41 / 8 = 5.125). This hardly makes a difference, but is worth noting. I'm also not even really certain what the quoted "0.72:1" 6th gear ratio actually is.
  3. Even after speedometer correction, inaccuracies are more apparent at higher speeds.

Other than that, the rest is math. I'm rounding to the nearest hundredth below, but the calculator is doing the true calculations. Here's how it works:
A true 37" tall tire without sag will travel 116.24 inches per revolution (pi*diameter)
which is also 9.69 feet per revolution (116.24 / 12)
and finally 545.08 revolutions per mile (5280 / 9.69)

To calculate the overall ratio, multiply the axle ratio by the 6th gear ratio: 5.125 x 0.72 = 3.69 overall ratio
At 2500 RPM, the axle & tire will turn 677.51 revolutions per minute (2500 / 3.69)
The tire's 677.51 RPM @ 545.08 revolutions per mile (from above) is 1.24 miles per minute (677.51 / 545.08)
Which is also equal to 74.58 MPH (1.24294 x 60)​
I have 37s 3.6 auto with 5.13 gears and I'm using tazer for recalibration. I used actual tire size and 5.13 for gear ratio but my speedo is off by 1 mph , should i enter 5.125 ? Would that fix it?
 

word302

Well-Known Member
Joined
Sep 13, 2017
Threads
11
Messages
5,146
Reaction score
5,718
Location
Oregon
Vehicle(s)
JLU
I have 37s 3.6 auto with 5.13 gears and I'm using tazer for recalibration. I used actual tire size and 5.13 for gear ratio but my speedo is off by 1 mph , should i enter 5.125 ? Would that fix it?
Don’t adjust your gear ratio, adjust your tire size.
 

grimmjeeper

Well-Known Member
First Name
Roy
Joined
May 6, 2021
Threads
10
Messages
3,341
Reaction score
18,158
Location
Castle Rock, CO
Website
www.grimmjeeper.com
Vehicle(s)
2021 Wrangler, 1987 Comanche, 1997 F250
Build Thread
Link
Occupation
enginerd
I have 37s 3.6 auto with 5.13 gears and I'm using tazer for recalibration. I used actual tire size and 5.13 for gear ratio but my speedo is off by 1 mph , should i enter 5.125 ? Would that fix it?
The more accurate your inputs the more accurate your results will be.

Adjusting your gear ratios to be more exact will have a minor effect. If you're really OCD about digits of precision go ahead and put the numbers in. But adding digits of precision like that won't make big changes in the results.

The biggest thing that affects your results is getting an accurate tire size. Getting the true rolling diameter of a tire is difficult. It's affected by inflation pressure, weight on the tire, even tread wear. And then you have to deal with how the air pressure in your tires varies as you drive and the tire heats up.

Tires can be more than an inch off from the advertised size and that's a huge impact. I had some 35s (315/70R17) that had an advertised diameter of 34.4" but an actual rolling diameter of 33.5". Getting the tire size accurate made the calculations pretty close but only within a margin of error.

Then there's the other side of it. Even if you have accurate inputs in the calculator you're dealing with a vehicle that has factory spec gauges. They are only "close" to what is actually going on. Your tach can be off, your speedometer can be off. So you can't know for sure what's going on. Hell, the speedometer needle in my Jeep is 1-2 MPH off from the digital display. And they're both running off the same signal.


Honestly, the best way to use charts and calculators is as a rough estimate. They will tell you a good ballpark number but they will never be 100% precise compared to what you see in the real world. Rounding ratios to 2 decimal digits is well within the variance of the gauges in your Jeep.

If you obsess over 6 digits of precision in this environment you're just going to frustrare yourself.

And when it comes to programming your Jeep, use the 5.13. Tweak the tire size to make the speedometer accurate.
 
Last edited:
OP
OP
AnnDee4444

AnnDee4444

Well-Known Member
Joined
Jan 14, 2019
Threads
49
Messages
4,685
Reaction score
6,273
Location
Vehicle(s)
'18 JLR 2.0
Somewhat related but not that useful... calculated tire diameter vs. rolling tire diameter


Also not that useful... if you want to calculate the exact gear ratio: ring teeth / pinion teeth. A "5.13" for example is 41 / 8 = 5.12500000000000000....

Two decimal points

Jeep Wrangler JL Calculator: gear ratio, tire size, speed, etc. Gear.PNG



Four decimal points

Jeep Wrangler JL Calculator: gear ratio, tire size, speed, etc. Gear 2.PNG
 

Sponsored

MCJA

Well-Known Member
First Name
Matthew
Joined
Oct 12, 2019
Threads
7
Messages
287
Reaction score
596
Location
Olympia, WA
Vehicle(s)
2020 Wrangler Unlimited Rubicon EcoDiesel
Going uphill in 7th gear in a rainstorm on the third Thursday of the month, my speedometer is off by 0.28713 MPH. My vehicle is loaded with myself, my wife, a dog, a parakeet, 2 bags of groceries and a tuba. What equation should I use to calculate the distance between the Earth and the Moon? I need 8 significant digits. No less.
 
OP
OP
AnnDee4444

AnnDee4444

Well-Known Member
Joined
Jan 14, 2019
Threads
49
Messages
4,685
Reaction score
6,273
Location
Vehicle(s)
'18 JLR 2.0
Going uphill in 7th gear in a rainstorm on the third Thursday of the month, my speedometer is off by 0.28713 MPH. My vehicle is loaded with myself, my wife, a dog, a parakeet, 2 bags of groceries and a tuba. What equation should I use to calculate the distance between the Earth and the Moon? I need 8 significant digits. No less.
The moisture from the rainstorm likely caused your wheel-speed sensors to read incorrectly. Since the parakeet's wings aren't very big, use the tuba to blow the sensors dry. Have your wife watch the dog to make sure he/she/they don't eat your groceries or the parakeet.



Oh, and use this formula: https://en.wikipedia.org/wiki/On_the_Sizes_and_Distances_(Aristarchus)#Half_Moon

Moon-Earth_distance%2C_Moon_phases.gif
 

Ratbert

Well-Known Member
First Name
John
Joined
Jun 20, 2020
Threads
87
Messages
7,343
Reaction score
9,684
Location
COS region, CO
Vehicle(s)
AEV JL370 JLURD , AMG GLC43
Build Thread
Link
Occupation
Software Engineer
Clubs
 

Baldo72

Active Member
First Name
Luca
Joined
Mar 2, 2022
Threads
3
Messages
43
Reaction score
77
Location
USA Charlotte NC
Vehicle(s)
2022 JL Rubicon, Alfa Romeo Giulia, 1972 JEEP CJ5
Got my Rubicon XR yesterday at Gupton...as it was swimmy to begin with and funky to drive with the XR package on prior to the tires to set in...I was wondering if you have any suggestions on what is the best PSI for On-Road and Off-Road for the XR factory tires? new to the Wrangler world and looking for some help. These 35's came inflated at 50PSI when i picked up yesterday...
cheers!!!

1.jpg
 

word302

Well-Known Member
Joined
Sep 13, 2017
Threads
11
Messages
5,146
Reaction score
5,718
Location
Oregon
Vehicle(s)
JLU
Got my Rubicon XR yesterday at Gupton...as it was swimmy to begin with and funky to drive with the XR package on prior to the tires to set in...I was wondering if you have any suggestions on what is the best PSI for On-Road and Off-Road for the XR factory tires? new to the Wrangler world and looking for some help. These 35's came inflated at 50PSI when i picked up yesterday...
cheers!!!

1.jpg
I’d start with 30PSI and chalk them.
Sponsored

 
 



Top