It's not the impact loading I'm worried about, like oldejack said, mountain bike equipment is designed firstly to be lightweight, and is designed to carry about 200lbs max per shock. Motorcycle shocks are designed for easily double that. While the spring rate is nearly the same, the shaft and piston size on my R1 shocks is about 25% bigger than the figures you quoted, and my mind tells me there must be a reason they do that.
I'm not trying to shoot your idea down, I just don't want to see anyone get hurt.
Where do you get your 200lbs max per shock from?
Remember these bikes have linkages and such that magnify the force seen at the shock. Maybe this will help,
look at it like this. The max force the shock will see is when the spring is fully compressed (assuming the spring doesn't bind due to my external bottom out bumpers, neglecting damping force) now i'm using 350lb/inch springs but these shocks can run as high as 550lbs/inch spring rates.
Im going to switch to metric now
550lbs/inch = 96000 N/m
500lbs/inch = 88000 N/m
My shocks have 3" stroke so total spring compression aprox 0.0762m
spring rate*stroke = max force on spring perch = 7315.2 N
R1 shock has a 500lb/in spring rate, R1 stroke aprox 3"
max spring force 6160 N/m aprox
Make no mistake these damper units are designed for the loads i plan on exerting on them.
Possible reasons why there's a large difference in diameter
- Fatigue life, motorbikes are expected to last for 100000km+ push bikes not so much
- leverage ratios are quite high on motorbikes
- oil volume
Remember im using push rods and rockers i have full control over the leverage ratio the shock sees. The dampers even have
steel bodies(not typical for mountain bike shocks) which with help with reliability.
Thanks for the critique and i can see where your coming from but i'm convinced enough to give it a go!