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Speedometer vs odometer?

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poptopjr

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Winterville, NC
I bought my truck with over-sized tires (305/70 16) and have checked the speedometer numerous times and found it to be accurate. Is it possible for the odometer to be off while the speedometer is accurate?

I am asking because I'm trying to track fuel mileage. With a 22 gal tank, I am only getting about 300 miles per tank. I then had about 21 gallons and go again. All things considered 14mpg isn't terrible, but I was expecting better after all I have read.

Thanks for any info.

Keith
 
They should work with the same info, so should be correct if speedo is correct. How accurate is the speedo and did you check it with GPS or something? With that large of tires the speedo should be off a little unless the VSSB module was modified. Those tires are probably 2" taller than stock, which should make both the speedo and odometer read low.
 
With 245s my speedo was fast as well as my odo. With 265s my speedo is right but my odo was still a little fast. Now I'm running 235s and my speedo is slow and my odo is only a little slow. To the OP your probably lugging the engine a little and without the vssb mod it will make it a little worse.

Oh and my truck when I got it came with 245s
 
You cant have a 22gal tank. There is only a 26 gal. or 34 gal. tanks for short and long boxes and 40 gal for the subs.

With 245 my speedo was ahead, with 265 it is correct and with the 285 it is slower than real.


Cu,
Sven
 
My 91 gas (last year of the old sytyle circuitry as far as Dash clusters go. IIRC no VSSB on these) the Odometer is accurate, and the speedo is reading fast.

all of our others are pretty well spot on. Stock rubber on everything.

also, Chevylover is right, 26 and 34 are the only ones. (for pickups anyways, chassis cabs are different) check your in tank suction tube for being bent. my 96 runs out of fuel at 1/4 tank and takes only twenty something gallons to fill it, and it had a gas cap when I got it, so It sucked the tank up and crushed the suction tube.
 
Last edited:
I used GPS to track speed. I have also been through a few of those "this is your speed" deals the cops leave around town. All have been spot on. Stock tire size is a 265 so buddy is correct, 2 inches off. As far as tank size the owners manual that came with it said it is a 22 gal. Not sure how to check it really. But in the end the size of the tank is no matter. I fill till I see fuel in the neck and check the mileage, it is pretty consistent 14 1/5 to about 14.9. Once or twice over 15 but that is it in over a year.

Are you sure a 22 gal tank couldn't have come in a K1500?

Thanks again.
 
One thing I have found is the speedometer and the odometer are not very accurate to each other. I set mine to where the odometer is within 1% of actual(travel 100 miles according to GPS and odometer will be within 1 mile), but the speedometer is ONLY correct at 70 1/2 MPH. When it says 63 I am doing 60, 58 is 55, and 49 is 45. Also a 305 tire is wide and WILL hurt your milage as that is quite a bit of rolling resistance to fight going down the road.
 
poptopjr said:
I used GPS to track speed. I have also been through a few of those "this is your speed" deals the cops leave around town. All have been spot on. Stock tire size is a 265 so buddy is correct, 2 inches off. As far as tank size the owners manual that came with it said it is a 22 gal. Not sure how to check it really. But in the end the size of the tank is no matter. I fill till I see fuel in the neck and check the mileage, it is pretty consistent 14 1/5 to about 14.9. Once or twice over 15 but that is it in over a year.

Are you sure a 22 gal tank couldn't have come in a K1500?

Thanks again.
Click to expand...

there 26 gallons unless you got an aftermarket one
 
The speedometer error should grow with speed, although the electronics do weird things like TheFerm was saying. In general 35mph is going to be accurate, but at 50mph error might be 3mph, and 70mph might be 5mph off, but then 100mph might only be 6mph off.

So the GPS comparison at highway speed will be most telling. It is possible the VSSB module was modified to correct the speedo. If you pull it out from behind the glove box you could make sure the solder and links all look good and are mirrored opposites as explained on this site:
http://www.tbichips.com/drac/
 
My odometer is off 3% yet the Spedometer is spot on with 285s. Speed and mileage confirmed with two GPS units on my last 1000 mile run er, 1030 mile run.
 
well, and civilian GPS is only accurate to like 1 meter, less accurate by requirement, so you have to take that into account over a long period of time too it could tack on or lose a few meters each stop and go.
 
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