Most shock absorber makers offer a choice of 40 or 50 ib spring rating, I realise that the angle the shocks are mounted at, distance forward of the rear wheel spindle & weight of rider all make a difference but is there a guide as to which spring is most suitable.

For trials on early Bultaco sherpa go for 40 Lb./ inch springs unless you are over 16 stone. on the later type Sherpa with the lower shock mount moved up the swing arm you may be better off with the 50 lb./inch springs.

Have a chat with Robin Packham at Falcon shocks http://www.falconshockabsorbers.co.uk/ he's very helpful and knows his stuff.

Edited March 18, 201511 yr by p@ul250

If you have a modified rear end, you can work out the spring rate by calculating the leverage ratio on the shocks. 1960s trials bikes like the M27 and series 1 M49 have a leverage ratio of about 1:1 and use 40 or 50 pound springs depending on rider weight.

Work out the leverage ratio for a modified bike and multiply the original spring rate by that ratio to get the new spring rate.

Leverage ratio = wheel axle travel / shock shaft travel or

Leverage ratio = distance from swingarm pivot centre to wheel axle centre / distance from centre line of shock shaft to swingarm pivot centre measured at 90 degrees to shock shaft