Inaccurate Odometer

[sohllis]

For some time, I thought I was getting lower than average gas mileage and while there was some fact in that, I also discovered the odometer isn't recording my mileage correctly.

I've owned my TJ for just over a month now and decided to reset one of the trip readings to 0. The drive from my place of residence to work place is 16 miles however, the trip reading shows I drove 8.

I have a couple questions.

Is this an issue of the speedometer needing to me calibrated due to bigger tires? Is a dealership the only place to do this?

Lastly, is this now a legal issue with the dealership I purchased it from? I purchased under the impression it only had 77,000 miles when in all actuality it could have over 100,000 depending on how long ago these big tires were installed. Actual mileage is a significant factor to which can usually drive the price and value of a vehicle north or south. Thoughts? Should I consult an attorney?

 

[JMT]

TJ’s have a speedo gear on the transfer case. When you change tire size you can change that gear out with the appropriate gear. The gear costs about $30 and it’s a 10-15 minute fix. Here’s a chart that shows the correct gear for various gear ratios and tire size.

https://www.extremeterrain.com/wrangler-jeep-tj-speedometer-gear-chart.html

However, the discrepancy you are describing is far larger than any I’ve ever heard. For exampke, I run 33’s and for every 5 miles on the odometer I actually drive 5.8 miles. To figure my MPG I calculated a ratio, 5.8/5=1.16. Then I just multiply the #miles driven on odometer by 1.16 to get actual #miles and divide by #gallons to fill up.

You’re ratio would be 16/8=2. I don’t see how that’s possible unless you have crazy giant tires. Something else seems wrong. What size tires are you running?

 

[Mr. Bills]

What year is your TJ? Is it a Rubicon? The reason I ask is that the NP241 transfer case in the TJ/LJ Rubicons do not use speedometer gears, however there are available electronic speedometer calibrators for it.

 

[Alex01]

As far as your question about being mislead by mileage goes... If you had 29 inch tires stock and the owner swapped the tires to 33 the day he bought it your jeep would be under reporting its millage by 13.79% which would currently give you real millage of 87,618. If your saying your jeep is reporting mileage at a rate of 50% of actual mileage, 8 miles reported on a 16 mile drive, then when you were on the freeway going 70 mph the jeep would say your traveling 35 mph. I believe you and the dealer would have noticed this on the test drive. I'm not an attorney but somehow you would need to prove that the dealer sold it to you in this condition.

Putting a new speedo gear in is just about the easiest job you can do (I have a non rubicon np231). It is one bolt, you pull out the current gear, attach the new one, change the o-ring, put the 1 bolt back.

 

[alittleoff]

When I got my Jeep, it had a lot of mod work done to it, and showed 19 mi. on it. But the speedo gear wasn't changed. I looked online and saw that I needed a 36 tooth, if I remember right, to correct the speedo. At a GPS speed of 55, mine displays 53, good enough for me.

Steve

 

[Chris]

Check out this thread:
How to recalibrate your speedometer after changing tire sizes