redneck2thamax

I just recently bought a 99 dodge ram 2500 4x4 which i believe has just a leveling kit on it. it is sitting on 315's right now. my speedo is off because the bigger tires were put on. how can i calculate my MPG correctly since i have the bigger tires.
thanks

badme

try this

http://offroadexchange.com/speedo.htm

blackcloud

I am running your same set up, I read on here a while back that for a 315 or 35 (same size) you take your odometer reading and times it by .06 to get your actual miles traveled. Then you add the two numbers and divide by gallons used

For example your odometer says 400 miles you take 400 x .06 = 24

Then you would divide 424 by gallons used, in my truck 424 miles i would have used about 21 gallons. 424 divided by 21 =20.1 mpg

redneck2thamax

where does the .06 come from? i found some where some one said to take your speedo reading like what it says your at say 50 and divide that by what your really at 56. and youll get something like .8 something. and do that with a lower speed and then get an average of the .8's and the divide your mileage by that and that will then give you your actual mileage. does that work?
thanks

sheriffav8r

Superchips 3705 will give you a good tune and adjust your speedo for tire size.... Or get another tuner that has this feature.... JM2C

FOXY005

You can get the conversion factor by dividing the actual diameter of your new tire size by the actual diameter of the stock tire.

Example New Tire Diameter = 35"
Stock Tire Diameter = 33"

35" divide by 33" = 1.06 Conversion Factor

So for each 100 miles traveled it would be multiplied by 1.06

Example 100 miles traveled x 1.06 = 106 Miles - Actual Mileage traveled
500 miles traveled x 1.06 = 530 Miles - Actual Mileage traveled

blackcloud

Same thing that i said just one less step, and a better explanation

FOXY005

Yeah, but the 33" & 35" I used were just examples.
I do not know his actual tire diameter sizes, he would have to get those from the manufacturers spec. and I do beleive they vary from one manufacturer to another. Might only be a fraction of an inch but the conversion factor could vary just depending on how many decimal points you want to round it to.

redneck2thamax

oh ok cool so now all i need to do is find out the original tire size.

VWPAT

Actually you can go to a Dodge dealer and have them hook their computer up to it, and change the tire revolutions as it pertains to the speed sensor. This will correct your speedometer, without having to hand calculate everything. The best way to do it, is to do a test drive with the tech in the truck with you, hooked up. You should have a GPS to watch actual speed. The tech can alter wheel speed until he gets the speedometer reading the same speed as your gps. A superchips unit can do the same thing.

old 300

If you have access to a GPS drive down the road @ 60mph on your speedo and see what the gps says. I have 285/70-17's for the winter and @ 62.5/100km/hr the gps says 66.25 or 106 km/hr. According to my figuring thats 6% so when I check my mpg I multiply the miles from the odometer X 6%. The other way is to watch the mile markers on the freeway and take an average over 10 or 50 or 100 miles, whatever works for you.

redneck2thamax

alright cool ill have to try that i think when im at 60 on the gps it said i was doing 70 but when im down at 45 its doing 50.

sheriffav8r

Go to tirerack.com and find your tires. Check out the specs and get the tire diameter....