08-03-2021, 04:50 PM
I discovered that all the dampers on my 1932 Tourer were very tired, especially the rears that were still running wooden friction discs, had totally lost their lignum vitae central bushes and with tired coil springs were providing virtually no damping at all.
I happen to know Dan White, a long time suspension engineer and keen Austin 7 owner who, with another suspension expert, runs Suspension Supplies Ltd (SSL). He offered an interesting explanation as to why friction dampers worked better in the early years of motoring. Roads surfaces then were graded for horse drawn vehicles, with typically 20mm granite gravel giving a well shod horse good grip. This surface meant that a vehicle's suspension was constantly receiving low amplitude, high energy inputs (vibrations), keeping it 'on the go' and, as a result, friction dampers were less prone to suffering from stiction. With today's smooth (if only!) tarmac roads, the suspension is receiving fewer inputs and therefore stiction has become a much more obvious problem, whether one is running wood, Tufnell or a Ferodo type friction material. Lubrication of the discs helps to overcome stiction but, invariably, there is then inadequate damping.
Looking to solve the problem, SSL have identified a modern friction material with virtually no stiction, enabling one to set a damping force that controls suspension movement but one that is also smooth and progressive. They currently make friction discs in this material for Bugattis, Bentleys, Rileys and also Austin 7s.
I decided to fit a set to my Tourer and although, thanks to Covid, I have not covered many miles since doing so, the result is most encouraging. What was most noticeable when assembling the dampers and adjusting the damping force was the absence of stiction which made it very easy to set and repeat the desired figure simply using a spring balance. I should add that stiffer coil springs were necessary at the rear to achieve the required damping force; double coil springs might possibly be another approach.
I hasten to add that I have no financial interest in SSL but thought that their insights might be of relevance to this discussion.
I happen to know Dan White, a long time suspension engineer and keen Austin 7 owner who, with another suspension expert, runs Suspension Supplies Ltd (SSL). He offered an interesting explanation as to why friction dampers worked better in the early years of motoring. Roads surfaces then were graded for horse drawn vehicles, with typically 20mm granite gravel giving a well shod horse good grip. This surface meant that a vehicle's suspension was constantly receiving low amplitude, high energy inputs (vibrations), keeping it 'on the go' and, as a result, friction dampers were less prone to suffering from stiction. With today's smooth (if only!) tarmac roads, the suspension is receiving fewer inputs and therefore stiction has become a much more obvious problem, whether one is running wood, Tufnell or a Ferodo type friction material. Lubrication of the discs helps to overcome stiction but, invariably, there is then inadequate damping.
Looking to solve the problem, SSL have identified a modern friction material with virtually no stiction, enabling one to set a damping force that controls suspension movement but one that is also smooth and progressive. They currently make friction discs in this material for Bugattis, Bentleys, Rileys and also Austin 7s.
I decided to fit a set to my Tourer and although, thanks to Covid, I have not covered many miles since doing so, the result is most encouraging. What was most noticeable when assembling the dampers and adjusting the damping force was the absence of stiction which made it very easy to set and repeat the desired figure simply using a spring balance. I should add that stiffer coil springs were necessary at the rear to achieve the required damping force; double coil springs might possibly be another approach.
I hasten to add that I have no financial interest in SSL but thought that their insights might be of relevance to this discussion.