Damping for trials

[Niro]

I have a follow up question in my search for new rear shocks for vintage trials competitions.

What does "Damping" mean and what is the actual different in riding with "standard damping" or with "light/ super light damping"? 

Thanks. 

[turbofurball]

This link talks about car suspension, but explains what dampers are.

 

Compared to the vast majority of motorsport trials bikes perform best with a low level of damping, on modern bikes it's typically adjustable to suit individual riders' weight and / or preference.

Edited June 28, 2022 by turbofurball

[feetupfun]

Lighter damping in the shocks makes for less effort from the rider when un-weighting the bike, or getting a bigger lift with the same effort.

Your 247 will handle fine in trials sections with either standard damping or light damping in the shocks. Standard trials damping is slightly better if you are also going to use the bike for trail riding. Lighter damping is slightly better if you only use your bike for trials riding.

Suspension damping is the conversion of kinetic energy into heat for the purpose of controlling the up and down motion of the wheels and the up and down motion of the bike. Bike shocks use oil moving through small passages to absorb the kinetic energy. The heat energy gained by the oil is transferred to the atmosphere.

Edited June 29, 2022 by feetupfun

[Niro]

Thank you! Valuable information. 
I think I will choose the lighter damping version, since I am riding only trials with the bike. 

[Ftwelder]

3 hours ago, Niro said:

Thank you! Valuable information. 
I think I will choose the lighter damping version, since I am riding only trials with the bike. 

It's very important to have the correct spring rate, one that does not require much pre-load to achieve 25~ 30% sag with rider on pegs. I started with a 45# spring and should have started with 60# with a low leverage system and 157 KG of bike/rider.

[Niro]

12 hours ago, Ftwelder said:

It's very important to have the correct spring rate, one that does not require much pre-load to achieve 25~ 30% sag with rider on pegs. I started with a 45# spring and should have started with 60# with a low leverage system and 157 KG of bike/rider.

You mean 60LB? 
and by "low leverage" you mean light damping? 

[feetupfun]

Leverage is the ratio of axle travel to shock travel. On a 247 the ratio is about 1.1:1, so if the shock travel is 100mm then the axle travel is 110mm.

The bigger the leverage ratio, the stiffer the springs need to be to achieve the right sag. Also, the heavier the rider, the stiffer the springs need to be.

For example I'm 94 kg and on a 1.1:1 rear end, 45 pounds per inch springs are about right.

40 pounds per inch springs on a Cota 247 would probably suit riders weighing between 70 kg and 85 kg.

[Niro]

Is 1.1:1 considered low leverage?
 

Falcon shocks offered me 50lb springs. I'm around 80kg with gear. 
Is 50LB will be much of a difference from 40LB? 

[feetupfun]

10 hours ago, Niro said:

Is 1.1:1 considered low leverage?
 

Falcon shocks offered me 50lb springs. I'm around 80kg with gear. 
Is 50LB will be much of a difference from 40LB? 

1:1 is zero leverage (Sherpa T pre-1970)

1.5:1 is high leverage for twinshock trials bikes (Godden Majesty 250/320, Fantic 240). Some twinshock MX and enduro bikes are even higher leverage.

1.1:1 is a typical for trials bikes made 1970-1975.

With Falcons and your weight, if you get the 50 lb springs you will have zero risk of bottoming out the rear end during landings but the the rear end wont work quite as well as it could in rocky stream-bed sections. 40 lb springs would give a more supple rear end in stream bed. You should use the lightest springs you can get away with because if you aren't using all the suspension travel, the suspension action is not as good as it could be.

If I was your weight, I would try the 40 lb springs first.

[Niro]

Would you say that the NJB Ultimate shocks are better option because they allow the rider to adjust the shock length? 
Is the length is critical as the spring pre load?

[turbofurball]

You only need adjustable length if you're changing the ride height of the bike, or to change the fork angle a little

[Ftwelder]

9 minutes ago, Niro said:

Would you say that the NJB Ultimate shocks are better option because they allow the rider to adjust the shock length? 
Is the length is critical as the spring pre load?

I bought the NJB ultimate because of the adjustable body length which is independent of the the preload adjustment. The damping is very light and seem to be quite good.

Coil spring exact length is not critical as long as it's both short enough to be installed and long enough to prevent the spring coils from contacting each other known as binding. 

 

 

[Niro]

Thanks guys. Great information. 
I think I will stay with one length spring, either NJB or Falcon.