6x2 Fuel Savings Average 2.5% in Track and Fleet Tests, NACFE Study Finds

[kscarbel]

Heavy Duty Trucking / January 22, 2014

The 6x2 configuration with a single drive axle in its rear tandem is likely to save highway truck operators an average of 2.5% in fuel compared to the dual-drive 6x4 that currently dominates the market, says a report of a study released Tuesday by the North American Council for Freight Efficiency.

The study, which involved axle and truck manufacturers and five large fleets, also found that fuel savings would pay back the costs involved with acquiring 6x2 systems in about 20 months.

Current upcharges of $1,000 to $2,000 per vehicle are likely to disappear with volume production if many fleets switch to 6x2 truck-tractors, and residual values would probably increase as their monetary benefits became better known.

Lack of traction with two drive wheels instead of four – a common fear among drivers and owners - can be managed with controls that shift weight from the 6x2 tandem’s “dead” axle to its “live” drive axle, says the report, “Confidence Findings on the Potential of 6x2 Axles.” Weight-shifting mechanisms should “automatically” be chosen with any 6x2 purchases, NACFE recommends.

One negative finding involves tire life.

“Some in the industry assume that the driven tires of a 6x2 will wear twice as fast as the tires on a 6x4, since only half as many tires are providing thrust,” the study states.

“But data from tire manufacturers and several fleets indicates that the useable tire life on a 6x2 drive axle is actually about one third that of the 6x4 drive tires.”

Loss of 6x2 drive-tire life can be offset by using less costly trailer tires on the dead axle, the report says. Trailer tires usually offer lower rolling resistance than drive tires, which will save a bit more fuel.

Dana Holdings Corp. and Meritor Inc., which build truck axles and offer 6x2 as well as 6x4 drive tandems, sponsored the study and supplied much data for it, said NACFE's executive director, Mike Roeth. But they did not bias the study's findings for or against 6x2s.

Further support came from Bridgestone Corp., Michelin North America Inc., and Performance Innovation Transport-FP Innovations.

The report says an NACFE contractor ran track tests using two Kenworth tractors with Dana axles and a Volvo with Meritor axles, which with 6x2 axles together saved 2.3% in fuel after being modified from a 6x4 configuration.

It cites findings in tests by Daimler Trucks using a Freightliner Cascadia tractor and Volvo Trucks using Volvo VN that together got 1.9% better economy when converted to 6x2s from 6x4s.

Results of in-service, on-highway testing by five fleets yielded better results – an aggregate economy gain of 3.5% -- the study found.

Those tests, which also pitted 6x2s against 6x4s, included Kenworths operated by Con-way Truckload, Macks run by United Parcel Service, Volvos run by Nussbaum Transportation, and Freightliners and Internationals run by two fleets that wished to remain anonymous.

Duration of each fleet test ranged from one to 12 months.

Averaging the economy gains of the three test groups – NACFE contractor, truck manufacturers and fleets – yielded the 2.5% stated in the study’s conclusions. Readers should consider the operations of the participating fleets, which are described within the report, in deciding which results might be closest to what they might see, NACFE says.

“Given all the data in this report, Trucking Efficiency [NACFE] predicts a rather aggressive adoption of 6x2 axles on new truck production over the next few years, possibly doubling every year: 2% in 2013, 4% in 2014, 8% in 2015 and 16% in 2016,” the report states.

Greater popularity in coming years will gradually raise resale values of 6x2 tractors, so fleets wanting to convert to them should consider lengthening their trade cycles to capture some of that dollar increase.

The report also recommends that drivers be trained to properly operate the equipment, and that fleets should go all-out in a conversion so drivers, mechanics and other employees get accustomed to the new fleet spec.

The complete report can be downloaded at www.nacfe.org/projects.

http://nacfe.org/wp-content/uploads/2014/01/NACFE-2013-Study-Executive-Report-FINAL-030913.pdf

http://www.truckinginfo.com/channel/owner-operators/news/story/2014/01/6x2-fuel-savings-average-2-5-in-track-and-fleet-tests-nacfe-study-finds.aspx

[KECorbin22]

Have had quite a few come thru our shop, dead axle in the rear. Drivers complain about getting hung on uneven ground and loosing traction on takeoffs, in wet conditions. One driver said he got stuck on scales at a DOT check station, Officers had to come out and push him off.

[kscarbel]

We've talked about 6x2s before (http://www.bigmacktrucks.com/index.php?/topic/34359-nacfe-report-lays-out-6x2-axle-advantages-and-drawbacks/). I think complaints in the U.S. market are related to the primitive 6x2 arrangement being promoted here. It doesn't even come close to comparing with the much more refined 6x2 designs in Europe and elsewhere.

Whether the dead axle is forward (pusher) or aft (tag) of the drive axle, they should be steered (single tire) and liftable.

In Europe, they do run some non-steered (liftable) tags. But those trucks are running at 44 metric tons (97,003 lb).

Page 6 (11) https://til.scania.com/groups/bwd/documents/bwm/bwm_0000027_01.pdf

• 6x2/4 - Six wheels, of which two are driven and four are steered – by means of an additional steered axle ahead of the drive axle (twin-steer)
• 6x2*4 - Six wheels, of which two are driven and four are steered – by means of an additional steered axle aft of the drive axle

[kscarbel2]

Some global market examples of Scania 6x2, 6x2/4 and 6x2*4 configurations in on-highway and vocational.

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[mack mhe9]

Looked at doing this my self. Single drive with a pusher axle. I would like to know more about the way the Europeans plum there air systems. And what drive axle would hold up in hills of the northeast?

[2stacksuperdog]

O&G industries ran a bunch of R-models that were single axles w/ lift axles and pulled 20ft dumps. I think they were good for 27 or 28 ton with permits at 80K

[Green Dash]

I'm curious how a properly spec'd 6x2 would compare to a "live" tandem in various situations where traction is lost. We had some CH's at work that were equipped with automatic power dividers? (I'm not sure what Mack called them, but the axles were live but had no activation switch.)

Anyhow, the system had stopped working on a few of them and the trucks were now getting stuck in situations where a single axle would not have even spun a tire.

[rsb502]

I like the concept but it needs to be tailored to the work and to the conditions including roads traveled. As stated above some trucks with a rear tag or lift axle and the driven axle in the front will get stuck going over curbs, etc. In The US there are a lot of driveways that you have to drive over a sloped curb to enter and with a rear tag you would high center, losing traction on the drive axle in position two, with the axle in position three its negates the issue and having a true liftable axle that could be raised when a curb or other pobstacle was coming would also help out. I have read some on the traction control systems and weight management in the US 6x2 systems and they have to detect a wheel slip from the driven axle before they reduce pressure on the non driven axle. If you are already spinning its too late to compensate and I think thats why the tire wear is so bad, the tires are literally spinning before the system reacts and you can only dump air from suspension thru a 1/4" line so fast. There has to be a way to run maybe 5 psi less pressure in the non driven axle than the driven axle, or to use some sort of bias valve to run higher pressure on the driven axle. Herein lies the big issue in the US, we are legal for 20,000# per axle and 34,000# per tandem not to exceed 20,000#, the systems they are using are trying to distribute the load evenly across the tandem and they dont have to, set it up like it is 3 individual axles on a tractor having all axles allowed 20k, or factory spec whichever is less and I think it would work just fine. I set up the air ride on a tag axle for a friends tractor after he pulled his front drive and used a small bendix pressure regulator to drop the suspension pressure to the tag axle by 10psi from the leveling valve mounted on the rear axle and it worked fine. We mounted the lift switch outside in the side box per dot spec and he picked it up when he didnt need it and never got a ticket for being over on any one axle, the only thing he had a hard time with was the weight on his steer since the tag ran less pressure than the drive it put more on the steer. I thought the simple solution was to run a 14,600 or 16000# axle on the steer and make sure you had enough tire to hold it, then you were under your 20,000# per axle and had traction.

[RowdyRebel]

Key phrase I picked up on was "on-highway". Dumping the air to that dead axle means more weight & increased traction available to the single drive axle when you're on solid ground. If you are at a job site and you dump the air, the drive axle sinks further into the soil without gaining any traction...so now you're even more stuck than you had been before the dead axle suspension air was dumped. If the company drivers would've called for a wrecker every time they got stuck, those 6x2 trucks would've proven unprofitable and expunged from the fleet within a few weeks. As it was, they had to deal with them for a couple years before the company saw the foolishness in that idea. In a vocational truck that leaves the pavement from time to time, one wrecker bill for a pull-out is going to wipe out several months worth of fuel savings. Even if you DON'T call a wrecker, when you're also spec'ing light weight drive line components, every time you try to move the truck and it doesn't move you increase the likelihood of twisting a drive shaft, snapping an axle, etc. I just don't see any payback to running a 6x2 setup in a vocational truck once all of the other variables are factored in. In a highway truck? Perhaps...but I drive a Mack and try to avoid highways whenever possible.

[mack mhe9]

And this is my problem. My money's made when im 90 thousand pounds but its Bly a few trips. The rest of the year I'm pretty light and the fuel savings would be nice. Then tree season your up in the muddy fields but that's a month and a half of the year. I just need two trucks one for light loads and one for heavy.

[kscarbel]

Noting the examples above of Scania 6x2 vocational chassis (rear-loader refuse and tipper), I can assure you that when equipped with a driver-controlled inter-wheel differential lock, the 6x2 is quite capable off road.