Speedometer Gear Calculations? - Jeep Wrangler Forum
Jeep Wrangler Forum

Go Back   Jeep Wrangler Forum > TJ Jeep Wrangler Forum > TJ General Discussion Forum

Join Wrangler Forum Today

Thread Tools

Please support our sponsors and let them know you heard about them on WranglerForum.com
Old 05-31-2011, 12:53 PM   #1
Join Date: Feb 2011
Location: Corpus Christi, TX
Posts: 342
Speedometer Gear Calculations?

How many of you guys have used to trip meter/odometer vs. milemarkers or gps distance to calculate your speedometer error? Is this a known accurate method for the TJ? I recall someone saying that this may not be accurate but I would think that it works fine.

My other quandary is that by my calculations, a 31 tooth speedometer gear would be better than a 32 tooth speedometer gear for my TJ (AX 15, 3.55 gears, 31" KM2s). Every single chart I see indicates that a 32 tooth would be right for me. The one assumption that I'm making is that my Jeep currently has a 33 tooth gear since it came with the Sahara package which had 30" tires standard...I could be wrong and will pull the gear tonight to check.

Anyway, I drove a 50 mile stretch of highway between San Antonio and Corpus Christi and my trip meter read 47.4 miles when it should have been 50 miles on the dot; that's just over 5% error and theoretically a 31.284 tooth gear would be perfect (we all know that's impossible). It would seem like a 31 gear would work great, with less then 1% error and an indicated reading of 70.6 mph while doing 70 mph.


KP Texan is offline   Quote
Old 05-31-2011, 07:47 PM   #2
pavement princess

WF Supporting Member
::WF Moderator::
kjeeper10's Avatar
Join Date: Feb 2011
Location: Connecticut
Posts: 41,824
Not much of a difference with my 31 inch tire. Considering actual dia. Is only 30.5
Chart calls for a 27 tooth and Mopar does not even make one for my application

3.5' lift, 37x12.5x17 MTR. Rock Krawler custom length X-Factor arms,Teraflex,Synergy,Rancho 5000X shocks. Krawl Offroad
- General lift discussion thread. Have a question, need help, issues, selecting a kit, ask here
- My 2007 2 Door Build
Click HERE to become a WranglerForum Supporting Member!
kjeeper10 is online now   Quote
Old 05-31-2011, 08:08 PM   #3
Join Date: Feb 2011
Location: Corpus Christi, TX
Posts: 342
My current setup is just inaccurate enough to annoy me. I just pulled my gear and I was right about it being a 33 tooth. Now I guess I'm looking for a 31 tooth unless anyone sees a flaw in my calculations!
KP Texan is offline   Quote
Old 06-05-2011, 12:15 AM   #4
Join Date: Feb 2010
Location: British Columbia Canada
Posts: 5
The charts for my jeep showed I needed a 41 tooth gear.
Thats 5.13 gears and 35x12.5x15 tires, however, it was still off according to a gps.
My tires don't measure 35" tall, more like real close to 34" so I put in a 40 tooth gear and did another gps trip, its almost perfect now.
Now I have a spare 41 tooth gear for my next tire swap.
64krusty is offline   Quote
Old 06-17-2011, 10:05 PM   #5
Join Date: Feb 2011
Location: Corpus Christi, TX
Posts: 342
I just installed my 31 tooth gear and my calculations were correct! At 70 mph on gps, I now have in indicated 71 mph on the speedo. I also did a 10 mile run and it was less than 1/10th of a mile ahead in error. Big difference in accuracy over my old gear! Now I can actually run some decent fuel mileage calcs....

KP Texan is offline   Quote

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
speedometer Gear? JeepGuyLJ TJ General Discussion Forum 10 04-23-2011 02:01 AM
Speedometer gear issue crackle TJ Tech Forum 4 09-15-2010 09:38 PM
Speedometer gear help mike_b_ar YJ Tech Forum 10 01-19-2010 08:07 PM
Speedometer gear confusion Triple88a TJ Tech Forum 45 06-18-2008 08:19 PM
Color and # of stock Speedometer gear? Yellow 30? jonbugh TJ General Discussion Forum 5 03-11-2008 04:31 PM

Download our Mobile App

» Featured Product

All times are GMT -5. The time now is 02:10 AM.

User Alert System provided by Advanced User Tagging v3.1.0 (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.

Jeep®, Wrangler, Liberty, Wagoneer, Cherokee, and Grand Cherokee are copyrighted and trademarked to Chrysler Motors LLC.
Wranglerforum.com is not in any way associated with the Chrysler Motors LLC