Speedo Question - Jeep Wrangler Forum
Jeep Wrangler Forum

Go Back   Jeep Wrangler Forum > TJ Jeep Wrangler Forum > TJ Tech Forum

Join Wrangler Forum Today


Reply
 
Thread Tools

Please support our sponsors and let them know you heard about them on WranglerForum.com
Old 05-27-2013, 10:24 AM   #1
Jeeper
 
bmlbrewer's Avatar
 
Join Date: Aug 2012
Location: Lamar, Colorado
Posts: 348
Speedo Question

So I know if you swap out tires and don't do the speedo gears, the speedo will show slower than you're actually going, but if my Speedo shows 4 mph faster than I'm actually going. To my knowledge, 33's are the biggest tires that have ever been on the Jeep, and that is what I'm runnin now. Is there anything that could cause this that isn't the speedo gears? I'm just curious, and making sure its nit a sign that something is wrong with my Jeep.

bmlbrewer is offline   Quote Quick Reply
Old 05-27-2013, 10:29 AM   #2
Jeeper
 
Join Date: Dec 2012
Posts: 2,631
If your running 33's, your speedo is way off. It will give off wrong readings when calculating MPG. Below is a link to give you an idea or even order the proper speedo gear if needed. I'm debating on doing mine BUT I run 31's so its borderline waste of money for me.

Jeep Parts, Jeep Accessories & Jeep Soft Tops From The Jeep Parts Experts - Quadratec

RevCo666 is offline   Quote Quick Reply
Old 05-27-2013, 10:33 AM   #3
Jeeper
 
bmlbrewer's Avatar
 
Join Date: Aug 2012
Location: Lamar, Colorado
Posts: 348
Quote:
Originally Posted by RevCo666 View Post
If your running 33's, your speedo is way off. It will give off wrong readings when calculating MPG. Below is a link to give you an idea or even order the proper speedo gear if needed. I'm debating on doing mine BUT I run 31's so its borderline waste of money for me.

Jeep Parts, Jeep Accessories & Jeep Soft Tops From The Jeep Parts Experts - Quadratec
I really don't care about my MPG... That's not why I drive a Jeep. When the tank is empty, i fill it up. It's just that I noticed when compared against the GPS and speed cameras on the side of the road, my speedo says 4 mph faster that my actual speed. I know that this is contrary to normal, and was just trying to figure out what could be the possible cause.

But thank you. I appreciate the quick response and the link. I'll save it for if I ever decide to change my speedo gear.
bmlbrewer is offline   Quote Quick Reply
Old 05-27-2013, 10:41 AM   #4
Jeeper
 
Join Date: Dec 2012
Posts: 2,631
Quote:
Originally Posted by bmlbrewer View Post
I really don't care about my MPG... That's not why I drive a Jeep. When the tank is empty, i fill it up. It's just that I noticed when compared against the GPS and speed cameras on the side of the road, my speedo says 4 mph faster that my actual speed. I know that this is contrary to normal, and was just trying to figure out what could be the possible cause.

But thank you. I appreciate the quick response and the link. I'll save it for if I ever decide to change my speedo gear.
No worries, but maybe the wrong speedo gear was installed which is possibility since your saying its faster then it should be... Could save on a speeding ticket by looking into your gear.
RevCo666 is offline   Quote Quick Reply
Old 05-27-2013, 10:51 AM   #5
Supporting Member

WF Supporting Member
 
Water Dog's Avatar
 
Join Date: Mar 2011
Location: Roseville, CA
Posts: 5,581
Images: 11
Sometimes people put in speedo gears thinking they have a certain size tire, when the tires don't actually measure out to what they think they have. Put a tape measure on the diameter of your tires, pull the speedo gear and confirm that it is the right gear for your tire size....Or get a speedohealer, but they're kind of pricey.
__________________
Dennis
Water Dog is offline   Quote Quick Reply
Old 05-27-2013, 11:25 AM   #6
Jeeper
 
bmlbrewer's Avatar
 
Join Date: Aug 2012
Location: Lamar, Colorado
Posts: 348
Quote:
Originally Posted by RevCo666 View Post

No worries, but maybe the wrong speedo gear was installed which is possibility since your saying its faster then it should be... Could save on a speeding ticket by looking into your gear.
Ah. That does make sense. I just didn't know if it could be wiring or something too. It doesn't really bother me that it reads faster bit just means I can convince myself I'm going faster because when going the right speed, the speedo says I'm speeding. And if I'm in a 40 mph zone, as long a the needle is somewhere between 40-50 I know I'm ok. I like the flexibility. Haha
bmlbrewer is offline   Quote Quick Reply
Old 05-27-2013, 11:34 AM   #7
Jeeper
 
n00g7's Avatar
 
Join Date: Apr 2013
Location: Northern VT // Western Wisconsin
Posts: 1,914
4mph at what speed? There are a lot of factors involved... how much you inflate your tires, the actual tire diameter, etc. I feel like 4 mph at highway speeds is an acceptable margin of error.
__________________
That moment when you look at a really nice JK and think to yourself, "Well I SUPPOSE I could see myself trading in my TJ for one of those, but for those ugly ass door handles."
n00g7 is offline   Quote Quick Reply
Old 05-27-2013, 11:44 AM   #8
Jeeper
 
bmlbrewer's Avatar
 
Join Date: Aug 2012
Location: Lamar, Colorado
Posts: 348
Quote:
Originally Posted by n00g7 View Post
4mph at what speed? There are a lot of factors involved... how much you inflate your tires, the actual tire diameter, etc. I feel like 4 mph at highway speeds is an acceptable margin of error.
4 mph at 40-45 mph. The speedo shows 50 when I'm actually going 46.
bmlbrewer is offline   Quote Quick Reply
Old 05-27-2013, 11:50 AM   #9
Jeeper
 
PStov98TJ's Avatar
 
Join Date: Dec 2012
Location: Long Beach, Mississippi
Posts: 2,021
Sounds like it's just under 10% off in the positive direction. Which is opposite of what mine is off with 33's.

But I'd have to agree with others that the wrong speedo gear was installed. If the PO had KM2's on it, they are notorious for running a full inch smaller than the advertised diameter.

And I could be off base on this one, but could a lower gear ratio than stock cause this as well?
__________________
OME 2.5" coils and Nitro Shocks, Metalcloak front track bar, JKS Quick discos, 33x12.50 Goodyear MTR's w/Kevlar, 15x8 Pacer wheels, thedirtworx rear tire carrier
PStov98TJ is offline   Quote Quick Reply
Old 05-27-2013, 11:57 AM   #10
Jeeper
 
n00g7's Avatar
 
Join Date: Apr 2013
Location: Northern VT // Western Wisconsin
Posts: 1,914
Quote:
Originally Posted by bmlbrewer View Post
4 mph at 40-45 mph. The speedo shows 50 when I'm actually going 46.

Have you tried at highway speeds/ slower? If it's a constant 10% off on the high side I'd have it taken care of as you'll over report your mileage. If it was under reporting I probably wouldn't bother and then just drive the speed limit instead of over lol.
__________________
That moment when you look at a really nice JK and think to yourself, "Well I SUPPOSE I could see myself trading in my TJ for one of those, but for those ugly ass door handles."
n00g7 is offline   Quote Quick Reply
Old 05-27-2013, 12:02 PM   #11
Jeeper
 
PStov98TJ's Avatar
 
Join Date: Dec 2012
Location: Long Beach, Mississippi
Posts: 2,021
Quote:
Originally Posted by n00g7 View Post

Have you tried at highway speeds/ slower? If it's a constant 10% off on the high side I'd have it taken care of as you'll over report your mileage. If it was under reporting I probably wouldn't bother and then just drive the speed limit instead of over lol.
This is a good point too. If you ever go to sell the jeep, the miles will be greater than actually traveled and take away some of your resale value.
__________________
OME 2.5" coils and Nitro Shocks, Metalcloak front track bar, JKS Quick discos, 33x12.50 Goodyear MTR's w/Kevlar, 15x8 Pacer wheels, thedirtworx rear tire carrier
PStov98TJ is offline   Quote Quick Reply
Old 05-27-2013, 02:36 PM   #12
Jeeper
 
Join Date: Dec 2012
Posts: 2,631
Quote:
Originally Posted by pstov98tj View Post
this is a good point too. If you ever go to sell the jeep, the miles will be greater than actually traveled and take away some of your resale value.
x2
RevCo666 is offline   Quote Quick Reply
Old 05-27-2013, 03:26 PM   #13
Jeeper

WF Supporting Member
 
yoopone's Avatar
 
Join Date: Dec 2010
Location: Suburban Chicago and the UP of Michigan
Posts: 597
It is really easy to crawl under the Jeep and pop that gear out. Won't take longer than 15 minutes. You can check out what you have. Also the gear has to do with your final drive ratio also. So the chart would give tire size on one axis and gear ratio on the other axis to come up with a final speedo gear size. If you were over registering miles by 10% I would get the correct gear in there.
__________________
1989 YJ
1997 TJ
1999 TJ
2006 TJ
2005 TJ Rubicon
yoopone is offline   Quote Quick Reply
Old 05-27-2013, 03:54 PM   #14
Jeeponator

WF Supporting Member
 
Michigunman's Avatar
 
Join Date: Aug 2010
Location: Cumming, GA
Posts: 1,257
I would have to disagree with the using actual measured height. A lot of factors can impact that. I would stick to what they are spec'd at.

In my case 285/70x17 KM2's convert to 32.71". The place I bought them contacted the manufacturer and they said they should be considered a 33". They definitely measure a little less mounted on the Jeep. With that said I have the 41 tooth speedo gear as recommend per the Quadratec chart and it's dead on.
__________________
Michigunman

Just because you can doesn't mean you should.
Michigunman is offline   Quote Quick Reply
Old 05-27-2013, 05:39 PM   #15
Supporting Member

WF Supporting Member
 
Water Dog's Avatar
 
Join Date: Mar 2011
Location: Roseville, CA
Posts: 5,581
Images: 11
Quote:
Originally Posted by Michigunman View Post
I would have to disagree with the using actual measured height. A lot of factors can impact that. I would stick to what they are spec'd at.

In my case 285/70x17 KM2's convert to 32.71". The place I bought them contacted the manufacturer and they said they should be considered a 33". They definitely measure a little less mounted on the Jeep. With that said I have the 41 tooth speedo gear as recommend per the Quadratec chart and it's dead on.
I think yours is on because you are only talking a 1/4" from your measured diameter. If it's closer to an inch off, it deffinitely won't be right...don't ask how I know..!
__________________
Dennis
Water Dog is offline   Quote Quick Reply
Old 05-27-2013, 07:37 PM   #16
Jeeponator

WF Supporting Member
 
Michigunman's Avatar
 
Join Date: Aug 2010
Location: Cumming, GA
Posts: 1,257
Quote:
Originally Posted by Water Dog View Post
I think yours is on because you are only talking a 1/4" from your measured diameter. If it's closer to an inch off, it deffinitely won't be right...don't ask how I know..!
I never gave an actual measurement. The 32.71 is just converting from metric to inches. Actual measurement is less than 32". I don't know of any tire that actually measures it's spec'd height when mounted and installed.

__________________
Michigunman

Just because you can doesn't mean you should.
Michigunman 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




Download our Mobile App

» Featured Product

All times are GMT -5. The time now is 11:26 PM.



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