I’m no expert but, over the years in my job, I’ve built up a good understanding of how suspension works, That, coupled with endless fiddling with mountain bikes suspension (an order of magnitude more complex than anything you’ll find on a car or van), I’m fairly confident I understand the issues with our vans.
I believe the problem is with the speed of the compression damping.
Our UK roads are atrocious! The vast majority of our bumps are what’s termed “square edge” – there is no slow gentle ramp-up to the top of the bump, instead it’s generally a sharp steep face.
What this does is force the suspension damper to accelerate very quickly or to put it another way, when the wheel hits the square bump it tries to move upwards along its travel extremely quickly.
This is what’s know as High Speed Compression. – The high speed is not vehicle speed but damper speed.
Imagine a bicycle pump with your finger over the end. Compress the pump slowly and you’ll feel force but it will be smooth and relatively easy. Try to compress it as fast as you can and you effectively hit a solid resistance.
This is exactly what’s going on in the damper.
Manufacturers have to design a one-size-fits-all system for average roads. Given that average road is a European road then it’s easy to see how our roads massively skew that average.
There’s no chance of getting an optimum solution.
So what’s required is a damper with a greatly reduced High Speed Compression rating.
This isn’t without it’s problems as the opposite of this is rebound damping which needs to be adjusted accordingly.
Unlike mountain bikes (Hi and Lo speed compression and rebound adjustment) van dampers don’t or rarely come with adjustable settings.
Even if they do/did it’s unlikely it’ll cover what’s required. The point being, without dedicated damping circuits, changing the overall setting affects all aspects of the damper.
The whole point of this is I’ve yet to find any manufacturers data that supports any re-design of the internal valving to reduce damping rates as required.
None of the so called suspension experts to my knowledge have done any proper testing with damper instrumentation to demonstrate one brand is better than stock etc. Perhaps I’m wrong? They just fit some shiny new stuff and tell you it’s better.
An interesting experiment would be to remove the dampers altogether and try it on a bumpy road so see what the delta is?
Spring rates could be lowered but I think this might just shift the problem to pitch and roll.
I find motorways are fine but if I’m just wandering around country roads at relatively low speed then I reduce the tyre pressures. Makes a big difference.
