Fuel Milage Poll

This I absolutely disagree with. Ask you gotta do is spin a wheel end by hand once to see it takes quite a bit of force, and watch how quickly it stops spinning to see it would be a measurable fuel benefit to lifting it off the ground.

 

On a truck rolling down the road it does not make that big of a difference. http://www.hendrickson-intl.com/CMSPages/GetFile.aspx?guid=534eb52c-558a-4bd4-987c-27e6e26af6c1

 

There are just too many variables for me to even try calculating on a cellphone. But here are some thoughts:

At steady speed it would not be a benefit.
At slow acceleration rates, it would be so small it would be meaningless.

So we'd be looking at noticable gains only when empty/very light & accelerating rapidly.

The improvement in rotational inertia would be roughly 20% (1/5), but rotational inertia is still just a small fraction of the energy expended bringing 30,000lb truck & empty trailer up to speed.


My best guesstimate -- and it is just a guess -- would be instead of say 2.5mpg in the 1/2-mile you spent racing from 0-60 you might get 2.525mpg. So if you got 7.5mpg cruising at 60mph -- on a 30-mile trip with 5 stop signs you would get:

5 miles / 2.525 mpg = 1.98gal
25 miles / 7.5 mpg = 3.33gal
-----
30 miles / 5.31gal = 5.65mpg trailer lift axle up


Axle down:
5 miles / 2.5 mpg = 2.0gal
25 miles / 7.5 mpg = 3.33gal
-----
30 miles / 5.33gal = 5.63mpg trailer no lift axle

So best case scenerio 5.65 vs 5.63 -- or .02/5.65 = 0.00354 (0.35% -- or 35 basis points).

Again that is a rough guesstimate of pretty much the worst case scenerio, but it should be in the same order of magnitude. So I would be extremely skeptical of any claim of more than 0.5% improvement ($350/year with a $70,000/year fuel bill)-- and even that would be only for local stop & go work with a hot shoe driver.

 

It does take energy to spin up to speed, but once there it will keep going for quite a while unless you have disk brakes or serious bearing issues. I've come upon accidents well after they've happened only to see a wheel still spinning in the air.

Seriously, next time you jack up an axle, give the wheel assembly a good spin. If it comes to a stop in under a minute you've either got puny arms or a serious bearing problem.

 

Tho I've never timed it, I can take an educated guess that i have never once had a wheel still spinning after a minute. On any truck I've ever owned.

 

Year 2000
Make Peterbilt
Model 379 exhd
Engine 60 series
Trans eaton 18
Gear Ratio 3.90
Tire Size 11r 24.5 Westlake and bridgestone
Type of loads hopper always 80,000
Normal Cruising Speed 65-75 either one is 1500rpm
MPG 5.5 to 6.5 depends on wind and speed
only 12,xxx miles on rebuild so not broke in yet

 

Wide based tires cost like 1k a piece. Certainly couldn't buy 2 for 1k. If you find a place that sells wide michilans (line energy d or t) for 525 a piece, let me know.

That being said, your formuala only take into account lab conditions AND assumes bearing resistance halves as well as rr. Your formula is flat our incorrect for this type of application. The force required to move an object at a certain weight has many variables not taken into account. The math is much more complex.

Where are you getting that a tag would be 3% better then lift anyway? I just got off the phone with KR (who you dont trust, but has real world experience), Michilan and fontain trailers. They all confirmed at highway speeds a lift saves fuel and lowers resistance. KR said your right, the resistance would go up on the drive with the lift up, but it doesn't go anywhare near double and having the lift down is more resistance. Michilan agreed. Fountain actually has test data confirming this. (seeing as this is an option on their trailers.)

 

My point exactly. The other poster said it only beifits loads that start and stop a lot do to inertia build up, but the lift still helps at high way speeds.

 

Why would you respond to "fuel mpg poll" if you dont even know your mpg.

 

I must have puny arms lol.

I dont have micro blue on my truck yet though