Test driving Freightliner’s rack and pinion steering
May 1, 2007
LOUISVILLE, Ky. - Last year at the Mid-America Trucking Show, Freightliner announced it would offer rack and pinion steering on its Century Class, Coronado, Columbia, Classic and Classic XL models. Th...
LOUISVILLE, Ky. – Last year at the Mid-America Trucking Show, Freightliner announced it would offer rack and pinion steering on its Century Class, Coronado, Columbia, Classic and Classic XL models. This year, the truck-maker returned to the show with a truck equipped with rack and pinion steering that I had the opportunity to drive.
Freightliner is the first heavy-duty truck maker to offer rack and pinion steering. The system was first tested at the Pikes Peak Hill Climb where racer Mike Ryan pilots a Freightliner Century Class S/T.
“The lighter weight and extreme precision required to race up a 14,000-foot mountain are the same qualities needed by on-highway trucks to increase payload and maneuver through traffic or in cramped loading docks,” said Jonathan Randall, director of product marketing with Freightliner.
The system consists of a rack (a horizontal shaft) and pinion, which intersects the rack at a 90-degree angle. The pinion is controlled by the steering wheel and causes the rack to move to the right or left, controlling the movement of the wheels. Freightliner said the system provides more accurate and responsive steering. It’s also 45 lbs lighter than integral gear systems with spring suspensions.
The system also has fewer parts and pivot points making it more reliable, the company said, and also delivering a more accurate response to the steering input.
“Every joint has play in it, so with every joint you take away you get less play and better handling,” said Christoph Hofmann, director of product strategy with Freightliner.
Currently, Freightliner is the only major truck manufacturer to offer rack and pinion steering.
Hofmann said 400 rack and pinion steering equipped Freightliners have been involved in extensive real-world testing and the feedback from drivers has been positive. He also said there have been no durability issues experienced during testing. So far, the system has racked up more than 80 million real-world miles, with some reaching the 450,000 mile mark.
I had the chance to try the system myself at the Mid-America Trucking Show. I drove a Freightliner with rack and pinion steering along a route that included a short stretch of Interstate as well as some bumpy city streets near Louisville.
The benefits of rack and pinion steering were evident from the moment I began driving through the Kentucky Fairgrounds parking lot. The truck’s steering system was extremely responsive, immediately reacting to every input from the steering wheel. It delivered a passenger car-type feel from behind the wheel.
On the bumpy city streets there was less of what Hofmann refers to as “bump steer” – the effect an integral gear steering system experiences when passing over a pothole or bump. This is because the rack remains parallel to the axle at all times, Hofmann explained. The wheel did not move in my hands when we traversed bumps.
“You don’t get any torsion when the axle moves because the rack is always parallel to the axle,” he pointed out. “When the axle lifts up, you don’t get any bump steer.”
It can be unnerving to drive a tractor-trailer, particularly in windy conditions, that experiences understeer or excessive wheel movement with no little or no effect on the front wheels.
This has been an experience I’ve encountered on several Class 8 trucks in the past.
Rack and pinion steering does away with this sensation by allowing you to always remain in control, providing peace of mind. And while I didn’t have to perform any sudden avoidance maneuvers, it stands to reason the instantaneous responsiveness of rack and pinion steering would also provide safety benefits as well.
The system is now available and comes at a small premium which may ultimately be offset by the increased payload afforded by the 45 lb weight savings.