8.5+ mpg
 

These past few trips I've been getting fantastic fuel mileage, checked at the pump of course(although my satellite is very accurate, and dash is about 2% out). Two trips ago was 8.5 MPG.

If my satellite is correct for the last trip I just did, I got 9.1 MPG! I'll be checking it tomorrow when I fill up to go on a trip. I'll let you guys know!

A few things I'm doing right:

58-60 mph
light loads(last trip averaged 20k)
no idling(satellite shows .3%)
easy take-off, coasting coming up to a ramp
~1300 rpms at cruise speed
105 psi in the tires
exhaust manifold is insulated using insulation from summit

A few things i'm doing wrong:

39" trailer gap due to my front axle being a pig(5th wheel should be even further back)
Michelin XDN2's on the drives

Actually this whole year has been good, I got 7.6 MPG in January(in Canada) and haven't got much lower since.

I can honestly remember about 3-4 tanks I got in the 8.7-8.8 range. Some were heavy as well.

Very impressive MPG numbers. What is your engine, transmission and ratio?

What is special about the Michelin XDN2 tires?

volvo 425 hp, very well maintained, rebuilt 3 years ago, new air/air 1 year ago

13 speed .73 final gear

3.73 gear ratio

XDN2 24.5 lo pros

The XDN2's are probably the worst tire out there for fuel mileage. Huge grips, no shoulder to speak of.

http://www.tirecraft.com/commercial/MichXDN2.asp

I also have a straight through muffler on.

As someone new to trucking, may I ask what exactly is meant by gear ratio and final gear ? What exactly do the numbers that you've posted indicate ?

Re: 8.5+ mpg
 

XDA Energy, would get you around another 0.25mpg.
I'd get it, but unfortunately, it only comes at 22.5 size! :sad:
I'm averaging about 7mpg right now, but due to hit, my AC is always on, and idling up to about 35%. Normally, it's around 20-25%.
Oh, and my speed is around 65mph also.

First I will explain gear ratio because in order to explain final gear, I need to explain gear ratio first.

All a gear ratio is is a number explaining how many times your "input" is multiplied, or how many times it turns.

In other words, my driveshaft spins exactly 3.73 times for every time my tires turn.

Final drive ratio is the ratio of the last gear(final gear) in my transmission. it is .73 or an "overdrive" gear because it is below 1:1

so for every time my engine spins .73 times, the driveshaft turns 1 time.

As you can guess, the lower "numerical" gear in your transmission, the higher numerically it is.

For example, "low" gear is around 16:1, so the engine spins 16 times for every time the driveshaft spins.

Re: 8.5+ mpg
 

You continue to impress me with that big ACERT, you must've got a monday engine or something!

I am considering switching to 22.5's, I really wish I could get super singles but they're not legal in the prairie provinces.

Right now, at 60 mph I spin 1348, and if I switched to 515 revolution per mile tires I'd be at 1400. Just about perfect. My volvo engine needs a little more RPMs

The reason I bought XDN2's, I was still on the overnight run from winnipeg to minneapolis. I really needed them in winter, because there are no salt shakers out during the night. So now I'm stuck with them until they wear out.

Thanks for explaining the concept so well, Allan. Does that mean, therefore, that the higher the gear ratio, the more power that is generated ? Is that why heavy haulers, like the Volvo I drive, have a gear ratio of 4.11, as it means more power ?

As for the final gear, does a higher number result in a higher RPM at final gear ? My truck cruises at its final gear ( 18-speed ) at around 1450-1500 rpm, at 100 km/h. Does a high final gear lead to better pulling power on hills when in the final gear ?

Also, is it possible to get the gear ratios and final gear lowered to save on fuel, or raised for more power output ?