Rear spring rate for Greyborgs latest frame

P

Peter Sternersson

100 W
Joined
Aug 14, 2012
Messages
147
Location
Ljungby, Sweden
Just came back after an aweful ride on my newly built greyborg frame.
I bought a new spring for my Fox shock, took the stiffest I could find at 550lbs/inch.
But it bottoms out like crazy, ruined my rear light cause the tire got so far up.

I made a extension on the upper mount to make the spring act stiffer, moved the hole about 70mm back I think.
Also, I have cut the swing 25mm shorter, and tre frame 50mm shorter in front.



Soo, what spring rates do you folks out there run on a greyborg frame with the latest swing arm? (or bikes with similar geometry)

It feels like a 1000lbs-1200lbs spring mounted at the correct upper hole would not be to exaggerate. But then you have to go look at dirt bike shocks I guess?
 
Look at Stealth, they use a dirt bike shock with 700-750LBS springs
Regular bike shocks are not really made for that kind of weight stress - our bikes are very heavy.

http://www.dnmshock.com/products.php?func=p_detail&p_id=14&pc_parent=3
 
I ended up buying a 250cc dirt bike shock with a 1000lbs spring on it.

Had to weld on a new upper mount and cut the seat post a bit to make room for it.
It´s a bit hard, 850-900lbs might work better, but I will try riding some on it before changing spring.

 
Took it out for a spin in the woods, and the damper doesn´t do much dampening, it feels like its just the spring there, bouncing around.
However, I had the compression setting on the damper at its lowest, thinking this would make it softer.
Took another short spin with the compression turned up, and it felt better, will try more tomorrow if the rain permits.

Maybe a softer spring and harder compression is the way to go.

Looks kind of nice though...

 
Yup 1000 could be on the hard side. Also you sure can't compare a cheap dirt bike shock with a FOX :)
What are those cut outs on the right side of the motor? Looks like some sort of venting but cant see the stator...
 
Surely the shock doesn´t meet the quality of a Fox, but I dont think it´s the cheapest crap you can find, it´s a "Fastace" damper for about 185 USD.

The shiny things you see are aluminium "wings" that creates a sucking through the holes milled behind them. Lowered the temperature with about 10-15 degree C, and they are just a quick and dirty fix with not a really good fit.
I´m waiting for my 3D printer to arrive and then I will make wings with a better fit.
 
Turned out the bouncy spring was user error :roll:

There was an adjustment for the rebound as well, and this was set to the lowest. With it turned up a bit, the damper feels much better, but still a little hard.

I´m having charger issues that I will deal with first, but come summer, I might buy another softer spring for it...
 
Soft springs and strong rebound damping makes a good ride, as long as the travel is long enough. Mercedes has been doing it for years. I've considered doing something on my full suspension Steintrike, as the ride is hard 'cause it is made for overloading with 50 kilos or so of luggage.
otherDoc
 
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