An old friend and mentor asked me what I was going to do with myself after I returned from 10 years in UK motor racing, as I was unhappy in my job as an engineer working for a local automotive manufacturer.

He mentioned that the Harley Davidson Softail suspension design offered an opportunity for me and my skill set , and suggest I have a good look at how I could enhance it.

I studied what was available on the market, and initially thought about designing a new fully adjustable shock absorber unit to suit. What became obvious to me quickly was that the majority of Softail owners were keen on lowering their bikes, as the "slammed" hot-rod look was very popular and suited the Softail style. I decided to use my hydraulics experience and apply it to the rear wheel ride height.

The after-market offered "airbag" type kits from numerous manufacturers that had varying degrees of quality and reliability, so I decided to design a hydraulically powered ram system, that neatly packaged under the bike. If I could re-use the Harley OEM spring and shock units, rather than scrapping them, this would offer better value, then I should be on a winner.

Instead of handlebar mounted switches, I decided to make the system operate by remote key-fob (with a small transmission mounted toggle switch as backup).The design and packaging created huge challenges as there was very little room to fit the components, and along with heat and vibration to deal with, suspension forces where huge!

The components had to made from high quality aerospace specification steel and aluminium alloys in order to safely carry the loads, and required a lot of calculation and optimization, including bench/rig loaded testing, extended road testing and hot weather testing.

The whole system had to be virtually invisible when viewed from the outside as the Softail owners were critical of extra 'clutter' The design had to fit all Twin-Cam model Softails, so two different transmission designs and the addition of ABS all had to be catered for in the package. Installation time is a significant extra cost to the purchaser, so I ensured the system didn't require much motorcycle disassembly, the rear wheel and tank don't need to be removed.

The finished product has achieved all it's design objectives, so I present it for sale confident that purchasers will enjoy all benefits Slamtail offers.

Ken Rutherford.


Ken Rutherford is the founder, Chief Designer and Director of Slamtail Suspension.

Born in Melbourne, Ken is a Mechanical Design Engineer and has extensive experience in mechanical & hydraulics design.

Initially working as a Technician for Koni Shocks, Ken spent 10 years working in motor racing in the UK, which included designing Hydraulic "Active Ride Systems" in Formula 1, and Senior & Chief Designer roles, developing chassis/suspension in World Rally, World Super Touring Cars, and DTM (German touring cars series). He resides in Melbourne with his family.


  • Nelson Piquet, Benetton Ford V8 B190 (1990)
  • Michael Schumacher, Benetton Ford V8 B191 (1991)
  • Michael Schumacher, Benetton Ford V8 B192 (1992)
  • Colin McRae, Subaru Impreza Turbo WRC (1997)
  • Gabriele Tarquini, Honda Accord STC (1998)
  • Tom Kristensen, Honda Accord STC (1999)
  • Laurent Aiello, Audi TT DTM V8 (2000)