big tires/milage math???

[MT Tatman]

I put 33' tires on, and I know that I can add 10% to my speedometer to get an accurate idea of my speed. For example, 50mph on the dial is 55mph on the road, What about my odometer reading? According to my odometer we went 315 miles on 11.5 gallons of gas....that seems way high, but if I take 10% off, it is 24.5 mpg....is this correct math???

 

[Infamous82]

What vehicle and did you change the gearing for the 33's?

 

[flyinhawaiian01]

Probably easier to just calculate actual speed from a phone's gps to your speedo, then reduce your mpg by the percentage you're off.

GPS speed / speedometer = number to multiply your mpg by

Example:

60mph on gps
53mph on speedo

60/53=~1.132

Odometer at end of tank: 230 miles
fuel filled: 18.22 gal

230/18.22=12.623mpg

corrected:
12.623 * 1.132 = 14.289mpg

 

[MT Tatman]

Thanks, I'll try that. The rig is an '85 4runner with original gearing, I haven't changed that yet.

 

[nevada]

Thanks, I'll try that. The rig is an '85 4runner with original gearing, I haven't changed that yet.

its cheap and easy to change the speedo gear.
instead of guessing every time, just swap the gear.

 

[nevada]

I put 33' tires on, and I know that I can add 10% to my speedometer to get an accurate idea of my speed. For example, 50mph on the dial is 55mph on the road, What about my odometer reading? According to my odometer we went 315 miles on 11.5 gallons of gas....that seems way high, but if I take 10% off, it is 24.5 mpg....is this correct math???

you would be adding the 10%. you are traveling further than it shows. the odometer is driven by the speedometer.

but, somehow I don't think you are getting 27mpg with 33's...

 

[penbergm]

If your getting 27+ mpg with 33's, tell me what kind of pot your truck is smokin'. I get about 18 mpg.

 

[MT Tatman]

That's exactly my point......there is no possible way for me to be getting anything over 20mpg in my rig now. Something strange is afoot. I need to top off the tank and do another mileage check. I think a number was written down incorrectly. If I did 215 miles (not315) on 11.5 gal., that would be right around 18mpg.

 

[nevada]

That's exactly my point......there is no possible way for me to be getting anything over 20mpg in my rig now. Something strange is afoot. I need to top off the tank and do another mileage check. I think a number was written down incorrectly. If I did 215 miles (not315) on 11.5 gal., that would be right around 18mpg.

that's sounds more like it. and even then still maybe a little high.

though, my 85 has 5.29 gears, and 35s. my last fill up showed 20.8. not bad. but, not typical. usually its in the 15-17 range...

 

[flyinhawaiian01]

That's almost exactly what I get with 35's and 4.88's. I actually got 22mpg once on a roadtrip, loaded down with camping gear (and 2 bundles of firewood!), but I was following my buddy's 4 runner and he couldn't get over 55mph without the death wobble!

250 miles out of the tank is about max for most of us, that equates to around 20-22mpg, I bet you just wrote it down wrong, or your odometer skipped a bit on the hundreds digit! Mine will do that if I hit the reset button quickly and not all the way down!

 

[MT Tatman]

Okay, we did a mileage check, using the highway mile markers vs. my odometer. Seems like a 10% difference is about right. We register 10% less miles than we travel, and we got about 14mpg. This was in my typical mountain terrain, but mostly on the highway, over mountain passes, and high altitude. I expect about 15 on average until I re-gear.