RST 200K 20" fork ... modified?
Before I start tinkering, thought I'd ask if anyone has modified this fork.
I'd like to increase the travel and use a lighter spring.
Currently, there is enough stanchion for about 40mm more travel.
Instead of a top cap, the top of the coil screws into a plate mounted inside the stanchion.
Found these springs at McMaster:
Last edited by client_9; 01-31-2013 at 07:26 AM.
I have not tried modding this specific fork but have worked on plenty of others.
First easy thing to try to decrease the spring rate by 1/2, just leave the spring off from one side, most fork designs still function fine with a spring on just one side. Looks to me like with this fork design you might be able to add more travel by adding a 10mm-20mm thick round spacer with a hole drilled through it, placed on top of the top spring hat or below the lower spring hat, then use a correspondingly longer bolt to retain the fork together. Looks to me like this design uses the actual coil spring to hold the stanchions and lowers together, just be certain that whatever you do is tight/strong enough to not loosen an allow the lowers to seperate while riding! Check for parts that may loosen periodically! If it is the inner elastomer spacer that provided the bottom-out stop function, you may need to trim it shorter but be sure the fork still bottoms out before the tire can contact the crown at full compression.
Good place to try shopping for replacement springs is to just go to a local old-fashion hardware store, they often have selection of generic compression springs. Probably easier to match-up sizes and spring rate with the new springs onhand rather than staring at catalog page. Looks like the threaded fit with ends of the spring into the top/bottom retainer is fairly critical to function of this fork design.
Thanks for the info!
Yep, I already figured out I can run a threaded shaft from stanchion top to bottom of lower leg to keep it all together.
Got the idea by looking at my Fox fork. A little reverse engineering!
I have some springs and elastomers on the way from McMaster.
My daughter is 50 lbs. What's funny is, I've seen this 20" RST fork on adult recumbent bikes.
Like here: RST 200K - Basically Bicycles--Recumbent Bikes & Recumbent Trikes Turners Falls, Massachusetts