Speedometer Reading High
Thread Starter
Registered User
Joined: Sep 2006
Posts: 29
Likes: 0
From: Alameda, CA
Speedometer Reading High
Truck is a 1996 2500 4wd. Standard size tires. Speedometer reads five miles fast across the board. So when it says 30 I’m actually going 25 or when it says 70 I’m going 65. Checked this on several of the radar signs that show how fast you are going. Is there an easy way to fix this? I have lived with it for years and just wondered. Figured you guys would know.
Registered User
Joined: Dec 2007
Posts: 207
Likes: 0
From: SW Missouri
My 97 reads 3-4mph high as well. When the stock 245/75-16 tires need replaced I'm going to install 235/85-16's. There a bit taller so the speedo should be closer and unlike 265/75 tires they are not wider than stock. I'm hoping for a little increase in fuel economy due to the reduction in rpm's. There are different speedometer gears you can get for the transmission. Someone will probably chime in but they will likely want to know your axle ratio.
Registered User
Joined: Nov 2007
Posts: 378
Likes: 0
From: Outside of B'ham
offroad,
I did the same thing with tires. 235/85 was just right to fix my speedo. Only problem is, the odometer still shows the same distance traveled. I was off by two MPH at 70. With taller tires, I was right on with the speedometer. Now, by my calculations, that is 2.85%. So, you will travel 2.85% further compared to what your odometer reads. Always add that correction when you calculate to get more accurate mpg reading.
I did the same thing with tires. 235/85 was just right to fix my speedo. Only problem is, the odometer still shows the same distance traveled. I was off by two MPH at 70. With taller tires, I was right on with the speedometer. Now, by my calculations, that is 2.85%. So, you will travel 2.85% further compared to what your odometer reads. Always add that correction when you calculate to get more accurate mpg reading.
Registered User
Joined: Dec 2007
Posts: 207
Likes: 0
From: SW Missouri
offroad,
I did the same thing with tires. 235/85 was just right to fix my speedo. Only problem is, the odometer still shows the same distance traveled. I was off by two MPH at 70. With taller tires, I was right on with the speedometer. Now, by my calculations, that is 2.85%. So, you will travel 2.85% further compared to what your odometer reads. Always add that correction when you calculate to get more accurate mpg reading.
I did the same thing with tires. 235/85 was just right to fix my speedo. Only problem is, the odometer still shows the same distance traveled. I was off by two MPH at 70. With taller tires, I was right on with the speedometer. Now, by my calculations, that is 2.85%. So, you will travel 2.85% further compared to what your odometer reads. Always add that correction when you calculate to get more accurate mpg reading.
Trending Topics
Registered User
Joined: Nov 2007
Posts: 378
Likes: 0
From: Outside of B'ham
I also have 3.55's and I am reading 1800 RPM at 70 MPH. At 2000 RPM, I show about 75 MPH. The mileage is neglible. In October of last year, I went to the beach in the truck. I ran at 70 MPH going down. Road around town for three days and came home on the same fill up. I went 750 miles on about 32 gallons of fuel. You do the math 
Ronnie
Ronnie
Thread
Thread Starter
Forum
Replies
Last Post
mullishacrew
1st Gen. Ram - All Topics
4
Mar 18, 2012 12:41 PM
75woody
3rd Gen High Performance and Accessories (5.9L Only)
4
Jul 17, 2007 11:16 PM
jmccart
3rd Gen High Performance and Accessories (5.9L Only)
2
Mar 18, 2007 10:03 PM
dieselnewbie
3rd Gen Engine and Drivetrain -> 2003-2007
10
Apr 14, 2004 02:16 PM