Truck Topics

The Tandems & Drop Axle Debate

When it's time to spec out the drivertrain on new expedited straight truck, the owner-operator some choices to make.  Should he/she run with a single rear axle, tandems or a drop axle? 

Will the truck be used to haul heavy loads on a regular basis or will an extra axle be needless weight?  Will the improved ride of tandem axles justify the extra expense?

We asked several owner-operators about the reasons for their rear axle preferences and discovered that there is hard logic behind their choices. 

Mini-Glossary
Rear axles may be drive, tag or pusher types.  
Tag axles are unpowered and go behind drive axles.
Pusher axles are unpowered and go ahead of the drive axles.

Phil and Diane Madsen's new truck was recently profiled in an Expediters Online.com article.  At that time, Madsen said of his choice to equip his new ride with tandem axles: 
"We wanted to go with tandem axles because of our experience with the fleet owner trucks that have been so equipped.  The difference between tandems and a lift axle has been profound -  it's just a much smoother ride.  Without question, it's the smoothest running truck we've ever driven."

"Also, with the large sleeper, we needed tandem axles; otherwise, we would have a payload capacity of about a thousand pounds."

Veteran expediter Carroll Bean plys his trade in a 2003 Western Star with a twin screw arrangement.  He says, "When I ordered my present truck, I wanted the tandems because they make it a more re-saleable truck.  With the long wheelbase, a buyer can leave it the way it is and have a number of applications available or the frame can be shortened with no problems - a buyer could use it for a dump truck if he wanted."

"If you're designing a truck for expedite only, I would have to say that a lift axle is probably the way to go.  I also believe that an owner is better off with a pusher axle over a tag axle. 

"With a tag, if it sits too far back, when it's lowered it will pivot and put more weight on your steer axle.  With a pusher, you've got that axle in front of your drive axle and you take some weight off both the drive and steer axles."

He continues, "On my last truck with a lift axle, I put almost 600,000 miles on that truck and I never bought a set of rear tires."

"I only had to drop the axle on that truck maybe 25% of the time and some of those times I dropped it because the weight of the axle itself would put me overweight." 

"Don't forget, the lift axle can always be removed."

One fleet owner tells us, "I like my trucks to have a capacity of 13,000 lbs. because that's what the carriers prefer.  When I buy a heavier Class 8 truck, I'll put a pusher axle on it for that reason.  Now, do I find that it pays for that investment?  I do not, but I do it anyway to make that truck available for more loads.

"For example, I have two Freightliner Columbia's, both of which weigh in the neighborhood of 22,000 lbs. with fuel and drivers, so that gives them a cargo capacity of only 10,000 lbs.  I'll put a pusher axle on those trucks, basically for that reason."  

"Those trucks have recently been moved from Con-way Expedite to other carriers so we'll see how they do at their new carriers."

Glen Rice is the former owner-operator of the 'Lil Deuce Coupe', a luxurious, show-quality expediter truck that was destroyed in a tragic accident several years ago. 

The 'Lil Deuce Coupe', Glen's last truck before his retirement, was equipped with a pusher axle that he says saw very limited use:  "I would drop the axle just to run across scales and keep ém happy," he says.

"I can tell you that the drop-down axles (pusher or tag) don't ride very well because they are not usually equipped with shock absorbers and people put too small of a tire on there.  Also, the axles rattle and bang and it's very easy to lock up the brakes.  That's why I recommend a true tandem axle."

"With a tandem, I think the truck rides better, especially when you have a load of say, 10,000 lbs. in the box.  I believe the truck rides better even when empty because you have the extra 1,200 lbs. or so of the axle weight."

"If you're stuck in snow or mud, you have the option of the interlock on the rear axle to help get you moving. I also think the tandems offer more safety because you have more tire footprint on the road for improved traction."

He adds, "Volvo engineers told me sometime back that your fuel mileage can suffer with tandems - they quoted about .5 mpg - but you can get that mileage back by running non-lug or steer tires." 

Fleet owner Dave Corfman says that he has mixed feelings about equipping an expediter truck with tandem or drop axles:
"One thing to consider is the carrier and the type of freight they have.  With some companies, they might have primarily lightweight or medium-weight loads and the truck's weight capacity won't be an issue.  Other carriers might have more LTL-type freight or double loads and then the truck owner needs to be able to carry some weight."

He continues, "Or, if you have a truck with a reefer and/or a monster sleeper, those really cut down your weight capacity, so you're forced into extra axles.

And, the downside of those extra axles? 

"Cost.  You have more tires to buy, Federal Excise Tax to pay, increased tolls and lowered fuel economy to contend with."

Summing up, Corfman says that he can see the benefits of the tandem or drop axles under the conditions that he noted, but, "if a guy is going to add a tag axle to his truck because he thinks he can make a lot more money, he's dreaming."