2nd Gen Non-Engine/Transmission Bigger tires vs screwy odo

[BLUEDOT 72]

I have gone up 2 sizes (from 245 orig. ) to 265 then to 285. I have been *****ing about my mileage since early on and it didn't really dawn on me that I was probably getting better than I thought because I was using the Odometer reading for calculations. Recently, I started using a little Garmin GPS mileage between tanks and it says that my mileage is greatly improved. And the people at Garmin tell me that the GPS odometer s "right-on"!.



When my speedometer reads 60 MPH, both of my Garmin GPSs(2 models) read identical at about 66. 2 MPH. ( I am actually using the little E-trek for a speedometer)



My questions are: Has anyone had any similar GPS experiences that they have faith in?



Can I get my Speedo/Odo calibrated to the larger tires? (12valve, 1998, 4x4,2500,manual transmission,106,000miles)

 

[dsherman]

GPS P

I have two of the same gps plus there dead on

 

[NETim]

faily recent thread on this very thing

There was a discussion about this very thing recently. I've never done it, so I'm not up on the details but apparently you can buy different size gears (more/less teeth) for your speedo drive from the stealer and correct for different size tires.



Tim

 

[JGK]

BLUEDOT 72,



There is about an 8% correction factor between your 285's (assuming they are 285-75s) and the original 245's. So a little quick math isn't too bad to figure what you're true speed and mileage is. For instance, at 50 MPH you're really doing about 54. At 75, more like 81.



If you fill up at 400 miles, you really went about 430 to 440.



I thought about changing the gears in the speedo, but for me it's just easier to do the math and put the money elsewhere. Besides, your truck won't chalk up the miles quite so quickly!



-Jay

 

[lmills]

I had the same thoughts when I put 285's on mine. I thought I lost mileage till I realized the odometer was way off. I checked and double checked to find out it was off 10%. I now just do the math in my head while driving.

 

[R D Brown]

I also have a Garmin and the speed readout is the same as the speedometer on the truck. No tire size changes.

 

[C. Harlan]

it's just easier to do the math and put the money elsewhere. Besides, your truck won't chalk up the miles quite so quickly!

Why waste more miles?? If I was to have had my speedo recalibrated over 100k back, Jeez..... I would have LOTS more miles than what the clock says. right now, I am at 175,300, and I could not imagine what it would be! For example, when I went to Denver from San Antonio, it only logged about 889 miles to the outskirts of denver, and like 940-975 up to Breckenridge, CO..... I know in reality, its almost 1100 to Denver, and another 70-80 miles to the Good Ski Area... . Just a thought to keep in mind, and make your truck look newer!



-Chris-

 

[lmills]

That's why I decided to leave mine alone. Heck, next time I plan to go with larger than 285's. Besides I have the 4. 10's and this helped out on lowering my RPM's and increased fuel mileage. I don't plan to sell the truck, so the odometer being off doesn't bother me. I will just have to drive a little further to hit the 1,000,000 mile mark.

 

[vssman]

It's really easy to change the gear on the vss unit (Back when the company that made them was in the US, I was the Manufacturing Engineer for that product). The gear is about an $8. 00 part. If you don't twist the unit as you pull it out, you can even reuse the o-ring. If your not sure how to calculate for the right amount of teeth, give Rickson wheels a call. They have all of the right gears. Tip: Above a certain number of teeth requires the unit to be rotated and installed in a different position. It's really easy.