speedo vs tac - Jeep Wrangler Forum
Jeep Wrangler Forum

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

Join Wrangler Forum Today


Reply
 
Thread Tools

Please support our sponsors and let them know you heard about them on WranglerForum.com
Old 07-24-2010, 06:47 PM   #1
Jeeper
 
Wench's Avatar
 
Join Date: May 2010
Location: Lincolnton, NC
Posts: 475
Send a message via AIM to Wench
speedo vs tac

I dont know if this was ever covered...searched the forums and didnt see anything.

Here goes:
My speedo is off by 5mph due to smaller tires I put on my jeep for hwy travel. I was checking my tac to see where my RPMs should be with 4.10 gears in my diffs. My question before I go any further in this matter is this:
Does the speedo in my jeep dash interfere with my tac giving me my true RPM reading?

Like I say my speedo registers 5 MPH over what my actual speed is. (example - if my speedo says im doing 60, im really doing 55)

any help on this matter will keep my from cracking open the diffs tomorrow and counting teeth...

__________________
You can lock it..even put a different t/c in it..but its still not a RUBICON!
Wench is offline   Quote Quick Reply
Old 07-24-2010, 07:56 PM   #2
Jeeper
 
TexasSam's Avatar
 
Join Date: May 2010
Location: Texas Coast
Posts: 90
There are some tire/gear charts on here that tell you the rpm at diff. speeds. What size tires did you have and what size tires do you have now? Also speedometers are not exact the can be off a few mph from the factory.

TexasSam is offline   Quote Quick Reply
Old 07-24-2010, 08:35 PM   #3
Jeeper
 
Wench's Avatar
 
Join Date: May 2010
Location: Lincolnton, NC
Posts: 475
Send a message via AIM to Wench
Quote:
Originally Posted by TexasSam View Post
There are some tire/gear charts on here that tell you the rpm at diff. speeds. What size tires did you have and what size tires do you have now? Also speedometers are not exact the can be off a few mph from the factory.
I use a rpm calulator. All i need to know is if my stock speedo dictates what my tac reads. If my speeds says im going 60 but im really doing 55, will my tac be reading off the speedo(60) or my actual speed(55).
__________________
You can lock it..even put a different t/c in it..but its still not a RUBICON!
Wench is offline   Quote Quick Reply
Old 07-24-2010, 08:35 PM   #4
Member
 
Join Date: Oct 2009
Location: San Jose Calif.
Posts: 1,006
Check your MPH with a GPS
03 RUBI is offline   Quote Quick Reply
Old 07-24-2010, 08:47 PM   #5
Jeeper
 
TexasSam's Avatar
 
Join Date: May 2010
Location: Texas Coast
Posts: 90
No your tac will not be off because your speedo is. Rpm will be diff. at 60 because of shorter tire and you will turn more rpm than before at a true 60mph.

Sorry if I am misunderstanding your question.
TexasSam is offline   Quote Quick Reply
Old 07-24-2010, 08:51 PM   #6
Jeeper
 
Wench's Avatar
 
Join Date: May 2010
Location: Lincolnton, NC
Posts: 475
Send a message via AIM to Wench
Quote:
Originally Posted by 03 RUBI View Post
Check your MPH with a GPS
thats how i know my speedo is off :P
__________________
You can lock it..even put a different t/c in it..but its still not a RUBICON!
Wench is offline   Quote Quick Reply
Old 07-24-2010, 08:52 PM   #7
Jeeper
 
Wench's Avatar
 
Join Date: May 2010
Location: Lincolnton, NC
Posts: 475
Send a message via AIM to Wench
Quote:
Originally Posted by TexasSam View Post
No your tac will not be off because your speedo is. Rpm will be diff. at 60 because of shorter tire and you will turn more rpm than before at a true 60mph.

Sorry if I am misunderstanding your question.
thanks! my gears are 4.10 according to my rpm calulator
__________________
You can lock it..even put a different t/c in it..but its still not a RUBICON!
Wench is offline   Quote Quick Reply
Old 07-24-2010, 09:30 PM   #8
Nerf gun assassin

WF Supporting Member
::WF Administrator::
 
distortedtj's Avatar
 
Join Date: May 2005
Location: yep right there.
Posts: 21,332
Send a message via Yahoo to distortedtj
All TJ/LJ rubicons come stock with 4.10 gears.
distortedtj is offline   Quote Quick Reply
Old 07-25-2010, 06:34 AM   #9
Jeeper
 
Neil F.'s Avatar
 
Join Date: Nov 2007
Location: Marlton, NJ
Posts: 5,708
Images: 1
RPM is you engine speed.
__________________
2003 TJ, 33" BFG AT, 2" BL, 2" BDS spring lift, Truck Lite headlights, Homemade sunrider top.
Neil F. is offline   Quote Quick Reply
Old 07-25-2010, 08:39 AM   #10
Jeeper
 
cabin_guy's Avatar
 
Join Date: Jun 2010
Location: In the woods, Muskoka Ontario
Posts: 41
Images: 2
Why would you put on smaller tires for highway travel? Ratio's make my head spin but don't smaller tires mean higher revs, and therefore worse milage?
cabin_guy is offline   Quote Quick Reply
Old 07-25-2010, 08:56 AM   #11
Jeeper
 
Wench's Avatar
 
Join Date: May 2010
Location: Lincolnton, NC
Posts: 475
Send a message via AIM to Wench
Quote:
Originally Posted by cabin_guy View Post
Why would you put on smaller tires for highway travel? Ratio's make my head spin but don't smaller tires mean higher revs, and therefore worse milage?
I am getting 260 miles out of 1 tank of gas. I had 33 inch M/T on it and was only getting about 200. I put 31 A/T on it and the ride and milage is alot better.

and yes rubicons came with 4.10 gears but I bought mine used. The diffs dont look like they have been opened but I was just making sure noone re-gear it before I got my hands on it

__________________
You can lock it..even put a different t/c in it..but its still not a RUBICON!
Wench is offline   Quote Quick Reply
Reply

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Jeep Wrangler Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools

Posting Rules
You may post new threads
You may 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
Speedo Housing Leak njkeagle TJ General Discussion Forum 16 10-21-2009 04:14 PM
Speedo Gear Spazzychaz TJ Tech Forum 8 07-09-2009 08:11 PM
Speedo gear: Issue semi resolved!!! Timberman TJ Tech Forum 0 02-26-2009 09:33 PM
Super 44 and new speedo gear juspimpin TJ Tech Forum 4 05-26-2008 11:34 AM
Which speedo gear? nicolas-eric TJ General Discussion Forum 12 10-05-2007 01:57 PM



Download our Mobile App

» Network Links
»Jeep Parts
» Featured Product

All times are GMT -5. The time now is 08:19 AM.



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