fuel-mileage, why not 6x2 trucks..??

Alright. You won.

A single drive with a dead axle is considered as tandem, and has the same weight limit. Yes, the differential lock very much needed, also the separate airbag valve. And the off road is a different animal. I am talking about highway operation, and a little yard work.

 

44,000 kgs is the norm here on 6 axles, we have reduced to 40,000 kgs on 5 axles. Yup 315's are the norm for singles but 385 super singles are very popular on lift axles aswell as steers.

We are allowed heavier weights on axles here so you'll have to do the maths on which configuration is most suitable for your type trucks and regulations, Centre lifts are fine but have poor traction, rear lifts have superior traction even compared to 6x4's, it's all down to weight distribution and the axle must be able to dump all the air, they don't use anything else in Nordic countries and even the 6x4 sometimes has a lifting rear drive to increase traction.

We run single wheels or supersingles on our tags to save weight and drag, you also will have a lighter axle, a diff less and a short prop less. We are running r620 scanias with both 6x2 and 6x4 configurations and the fuel difference is 1mpg. When the axle is down it is no different to a 6x4 and the fifth wheel can be positioned anywhere.

Trailer clearance was an issue with older trailers with short necks on the chassis, you need to slide the fifth wheel back to accommodate them, newer trailers generally aren't an issue and your chassisless boxes def won't be an issue , our trailers run with a kingpin approx 6 feet from the front of the trailer and often fridge units are no more than 18 inches approx from the back of the cab and I've never seen them hit the cab even going up steep ramps on ferries. On low profile trucks with low fifth wheels often a smaller tyre is fitted to the tag for extra clearance but generally isn't a problem.

A weight shifting device is pretty standard here and is a good job but you'll also need to take all the weight off the tag too.

A centre lift would work on your tractors as the fifth wheel is positioned just like a 6x4 but they do suffer from traction problems but for normal highway work they are fine

 

True 4 wheel trucks are rubbish off road and so are mid lifts but place the fifth wheel behind the drive and the difference is amazing, our tags have far better traction than our 6x4's believe it or not. Tags have to lift to stop the drives from being lifted off the ground especially I notice US trucks I've seen have very short suspension travel

 

Actually the manufacturers are claiming 2-3% fuel saving with rolling tag axle. Which is not much, but easily can add up. Direct drive transmission other 2-3%, super singles 4% and I am close to 10%. That is a bunch of free money.

 

I our world a single screw with a tag is considered a single drive w/ a tag not a tandem. We consider a twin screw or 3 axle to be 2 drives unless otherwise noted. And if your tag is off the ground it does not get 34,000 it only gets 12,000. So if you have a light load you could legally run with your tag up, as long as your axle out is good. And yes with a tag or drop on the ground it has the same weight handling ability as any other tandem.

 

The 1mpg difference I've seen it happen, I ran a couple of times to holland with a tag tractor, same load of wheels, same trailers and that has been the return however I'm just thinking the diffs in ours are much bigger and heavier so that could make a difference. It sure does all add up,for safety you could keep duals on the drive and supersingle on the tag, that would improve rolling resistance, be aerodynamic conscious, watch the speed, all adds up to more cash in your pocket, I like the way you think, it's a sensible approach and you are takin steps to futureproof your business cos the price of fuel is only going one way; up! 10% is a significant saving at the end of the year.

 

Of course, I will buy an aero truck with full aero package. It will be KW680, or Pete 579. But you have raised an interesting question. Safety with supersingles. I was thinking about it myself. To have duals on the drive and SS on the tag perfectly make sense with lift up tag axle. But do I need this extra safety with rolling tag? I mean, good to have, but necessary to have and loosing on the rolling resistance? Definitely I will have active tire pressure monitoring system, since the SS-s are more sensitive for the right pressure and I am more vulnerable than with the duals. And, thanks God I never had problem on my steer tires (although I buy only Michelin on steer) , but guys can do surprisingly well even in the case of steer tire failures. Although depend on the road too. On a flat highway with a full lane wide paved shoulder it is quite different, than on two lane snowy, mountain roads. For example, what Icee used to demonstrated the retarder for me. By the way, I was not right, there are different retarders, but so rarely used, almost nobody knows about it. And it is a very smart thing, but on my driving area I do not need it. But at least I do my decision based on my knowledge, not by accident. Thank you guys.

 

Why are you saying a single will only get 12000 lbs??? It is 20,000 in every state.

 

I'm wondering why people who are very concerned about fuel mileage don't simply slow down? Every 1mph speed reduction is 1/10mpg increase. Slow down 10mph and save 1mpg - for free. And the slower you go the less important aerodynamics are. I have a Peterbilt 379 with a C13 CAT set at 500hp, 10 speed and 3:55 rears pulling a very non aero trailer that will get 7.5 -7.7mpg at 60mph. If I decide to do the 6x2 conversion I should get 8.5 to 8.7mpg. I suppose it would be slightly better with an aero truck but not much. TMC has Pete 387's and 379's that are specked identically running the same speeds and pulling the same trailers and there is only a 2 - 3/10ths difference in MPG. Since I already own the Pete free and clear it's not worth buying another truck to save $2500 a year in fuel. Also at some point what you like has to enter the equation.

 

As I posted in another thread, look at these videos for the answers.... http://www.michelintruck.com/michelintruck/toolbox/videos-demos.jsp#xonetires