Speedometer Reading High
08-26-2008, 04:02 PM
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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知 actually going 25 or when it says 70 I知 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.
08-27-2008, 07:50 AM
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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.
08-27-2008, 08:08 PM
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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.
08-28-2008, 08:10 AM
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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.
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08-28-2008, 04:59 PM
#8
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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
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