[djamgils]

could be a stupid question but anyway.

the general amount of sag for a dh bike should be ~35% but do you measure this when standing in a "race" position or when sitting on the seat?

because with a VPP bike you have a sweet spot for pedaling around the 35%. and most of the pedaling is in the saddle if you would be climbing. But when you pedal on a dh track downwards it is possible that you are either standing or sitting.

And where does the 35% come from? experience or scientific reasoning? and with all the changes in dampers and linkages does the "old" 35% sag rule still work. because a lot of people need a lighter spring when they switch from for example a dhx to a ccdb

 

[Arkayne]

Fox says to set sag based on "normal riding position" which I'm assuming depends on what kind of riding you do. I set my sag based on a neutral standing position.

These shock companies spend $$ for 'scientific reasoning' and the 35% is simply a starting point which you can add or subtract depending on your experience.

 

[DirtyMike]

I have mine set for My normal riding postion, about 35% ish sag. Currently My normal riding postion is a race position so thats how my bike is set up, when the season is over for me, I will set the rear sag just a little higher for trail riding and more pedalling.

The idea of having more sag is that not only do you need upward travel, but you need downward as well, and what that does is allows your wheels to follow the terrain with more precision, and control.

 

[bushrider]

The ideal sag is determined by the frame design.
For example my cannondale Gemini DH is designed to run 40% sag.
If I ran 30-35% the head angle would be too steep and the BB would be too high for DH.

Different shocks require different springs as the shock its self has some spring force. eg. take the spring off your shock and try to compress it by hand. Its not easy with a fox or a manitou shock. With my Avalanche its impossible to compress the shock by hand, this is part of the reason you'll end up with the same sag with a lighter spring on an Avalanche compared to a fox shock. I've no expirience with a CCDB but I imagine its similar to the Avalanche in that way.

For a DH bike I would measure sag in the seated and attack positions and average the the two measurements and to find a spring that gives you an average sag of 35% or whatever sag the bike design calls for.

 

[ChrisKring]

Have a buddy check the sag in the "race position" Make sure to bounce the bike after you get on it to settle it into the natural position.

The only better way to check it is with a data logger like Push uses. But they are way too expensive. A tape measure works good.

 

[sperkins]

hey check out this link maybe it will be useful.
www.thebikinghub.com/mtb/an-introduction-to-mountain-bike-rear-shocks

 

[ChrisKring]

hey check out this link maybe it will be useful.
www.thebikinghub.com/mtb/an-introduction-to-mountain-bike-rear-shocks

I think that is more geared for XC than DH. You should set the sag on your dh bike in the riding position that you ride in. So if you ride mostly sitting down, by all means set the sag sitting down. Most people stand up though.