IS THIS THE CURE FOR THE ‘K-SERIES BACK’?

For more than 50 years Kenworth’s venerable K-series cab-over has been a solid and dependable prime mover used for many tasks. Paul Matthei speaks with Wickham Freightlines Workshop Manager, Steve Lord, about a technical solution the company has developed to significantly improve the ride in its K200 prime movers.

Kenworth’s immensely popular K-series has been a stalwart of the cab-over class for over half a century, and for good reason. Its propensity for reliability and longevity has enabled a multitude of operators to make a decent profit using it as a tool of the trade. The formula is simple, literally, in that Kenworth has stuck with a tried-and-true cab structure that has been gradually evolved rather than radically changed over the years.

The biggest change in the model’s history occurred when the K108 morphed into the K200 just over a decade ago. Kenworth engineers put a massive effort into improving cab ergonomics for the driver including raising the cab and fashioning a flat floor between the seats for easier bunk access and a safer, more user-friendly set of steps and side catwalk for improved cab entry and egress.

However, they stopped short of fully addressing the K-series Achilles Heel, which is ride quality. Sure, various measures such as parabolic front springs have been added which have made a dramatic improvement over earlier

models. But the fact remains that the K-series ‘kick in the back’ is still evident on rough roads, of which, Australia has aplenty.

As a loyal Kenworth customer over five decades, Wickham Freightlines knows as well as any this shortcoming of the K200. But rather than simply accepting the fact, the company decided to design and build its own solution in the form of an airbag cab suspension system.

Interestingly, in addition to a kaleidoscope of Kenworths, the company also runs a smattering of Scanias which are widely regarded as among the most comfortable prime movers in the business.

According to Workshop Manager, Steve Lord, the goal was to replicate, as near as possible, the ride quality of the Scania in the K200 by installing a twobag rear-of-cab air suspension system.

“Any cab-over Kenworth will whack you in the back on lumpy roads, so we wanted to design a cab suspension system to take that characteristic kick right out of them,” says Steve.

“We used as many Kenworth components as possible, including airbags, shocks and ride-height valves, so that replacement parts could be easily purchased from Brown and Hurley or Gilbert and Roach.”

Steve says the company has a number of talented fabricators who are able to construct just about anything, so the challenge of designing and building the necessary infrastructure for the cab suspension was met with relish by them.

Upon completion of the first iteration, the team installed an accelerometer to test its effectiveness and compared this with the results from one of the company’s Scanias.

“The results were actually quite similar, we were very happy with that,” Steve says, adding that the original K200 cab suspension project was started in 2018 after the company’s Operations Director Graham Keogh suggested he wouldn’t mind seeing some form of cab suspension on the K200s.

“He mentioned this just before he went on a trip with Kenworth to the USA,” says Steve. “So being a bit of a thinker myself and having been in the game a long time, it started me thinking about how we could execute this and everything sort of snowballed from there.”

Steve explains that he set a time limit of three weeks to have a prototype K200 cab suspension built while Graham was away in the States, to give him a pleasant surprise when he returned.

“The boys and I pulled out all stops and worked long days to ensure the prototype was finished, painted and sitting on a frame ready to install in the truck when Graham got back,” says Steve, proudly adding, “He was blown away when he saw it and was very excited to see it being fitted into the truck, which took about one day, and then around two days for testing.

“We didn’t outsource any of it, the fabrication boys did a fantastic job using

“HE WAS BLOWN AWAY WHEN HE SAW IT AND WAS VERY EXCITED TO SEE IT BEING FITTED INTO THE TRUCK, WHICH TOOK ABOUT ONE DAY, AND THEN AROUND TWO DAYS FOR TESTING.”

Installing a two-bag rear-of-cab air suspension system.

The prototype worked really well, the driver loved it and said it felt like a completely different truck to drive.

spare steel that we had laying around and the end result was most impressive.”

Steve says the first couple of days of testing included making sure nothing was going to rub due to the cab movement, with the concept operating exactly as they had envisaged.

“The prototype worked really well, the driver loved it and said it felt like a completely different truck to drive,” says Steve.

He adds that the finished product was fully engineered and mod plated so that it became an integral and, most importantly, legal part of the vehicle.

“It was actually a relatively simple concept, we didn’t try to redesign the whole truck but just focussed on an area of the K-Series that we believed could and should be improved,” says Steve.

Some three years on, the original design has been updated to MkIII status, with various improvements including individual height control valves for each airbag instead of a single unit connected to both bags, along with structural design ameliorations to make it more aesthetically pleasing.

“The twin height control valves help keep the cab level by enabling the airbags to independently react to changes in the lean of the cab, such as when cornering,” says Steve.

Testament to the success of Wickham’s cab suspension, which is now fitted to four of the company’s K200s that have since collectively travelled well over one million kilometres, Kenworth asked the company if it could borrow one of the test units to evaluate the cab suspension as part of its K220 development.

Word has it that the forthcoming K220, reportedly due for a June 2022 release, will feature Kenworth’s version of cab suspension that will be yet another important evolutionary milestone in the lengthy K-series timeline.

All up, it’s a great example of a transport company with the initiative and wherewithal to fix an inherent foible in a prime mover; with the successful outcome leading to a similar fix in the new version for the benefit of all operators who subsequently purchase that particular model of vehicle.

TESTAMENT TO THE SUCCESS OF WICKHAM’S CAB SUSPENSION, WHICH IS NOW FITTED TO FOUR OF THE COMPANY’S K200S THAT HAVE SINCE COLLECTIVELY TRAVELLED WELL OVER ONE MILLION KILOMETRES, KENWORTH ASKED THE COMPANY IF IT COULD BORROW ONE OF THE TEST UNITS TO EVALUATE THE CAB SUSPENSION AS PART OF ITS K220 DEVELOPMENT.