Fox CTD rear shock set up on 140mm bike

andrew9

andrew9

Likes Dirt
Hi all!

My bike is a Univega RAM with 140mm rear travel, 160mm fork.
Most of my riding is on moderate Downhill trails that have lots of little doubles, rock gardens and berms. I’m 80kg with gear. I’m fairly new to suspension, only got my first non-rigid mountain bike three months ago.

I took my first ride on a new 2014 model Fox CTD BV, it replaced a Fox Vanilla R coil, which has a 650 spring. The Vanilla spring was too hard, but generally rode pretty nice, just a bit too high in the rear.

I had a bit of trouble with the new CTD, never got the shock to where I was happy.
Started at 160psi, about 20% sag which rode way too soft. Then went up to 180psi, felt smooth and plush on the rocky and undulating trails, but used up all the travel on even small 1-2 metre doubles, with very smooth transitions.
Bumped it up to 200psi, it was rubbish, lot of "kicks in the back" over bumps and steps in the trail, and still used up all the travel on some of the jumps, which are pretty tame.

I was descending in "Trail" mode, and switching the Trail compression dampening between 2 and 3 (medium and firm), I didn't try “Descend” mode for long, as it seemed softer than trail, as I understand it should bottom even easier, as the compression dampening would then be open?
How easy should it be to bottom a rear shock? 190psi was as firm as I it could go without it starting to "kick" and it'd still use all the travel on even a 30cm drop to flat, that seems too soft to me? I had the rebound pretty slow, so that shouldn't have been the cause of the kicking?

There is a 1.5m drop on that trail that I usually go off, but with how shock was performing, I was worried of bottoming out too hard and so I went around it today.

Any set up tips? or anyone want to share their ideal pressure on their 140mm bike that has a 200x57 shock?
Any tips or hints?
 
C

creaky

XMAS Plumper
I'm not familiar with that bike or the suspension design but did you buy an appropriately tuned shock i.e. compression and rebound tune for that suspension setup ? Bought new of 2nd hand ? The Fox CTD comes in a range of different tunes. If the whole tune is off then you may need to explain your experiences to NorthShoreDynamics (or similar) and get them to re-tune it to suit.

A couple of potential cheaper solutions to try first assuming that the shock is not stuffed:

1. If you pumped the pressure up from 160 to 200psi did you also increase the rebound damping (sorry Ducky, dampening) ? If not, then that would explain the "kicks in the back".

2. It sounds like you are getting excessive bottom out even with correct sag. Check if your model shock can accept 'volume spacers'. If so, get a decent size one and install. That will give you better bottom out resistance for the same level of 'plushness' in the initial shock travel. If your shock cannot use volume spacers then you can add extra 'float fluid' to achieve the same effect. Do some internet research to understand the above processes, they are relatively simple for the home mechanic.

PS. There is no 'ideal pressure' as different suspension designs have varying leverage ratios acting on the shock.

Good luck.
 
andrew9

andrew9

Likes Dirt
It's a new 2014 year shock, CLXW tune, it's a tune to suit an Intense Carbine, a different bike, but at least it's also 140mm. A tune is not available to suit this bike, so I had to guess what shock would be the best.

I had the dampening quite firm, I'm not sure if that was the problem, but I didn't adjust it at the same time as the pressure, I may have had it "out of sync" for a run or two by accident. Thanks for the good tip.
I didn't realize my shock could take volume spacers, turns out it already has a "0.6" I think I'll look into adding or swapping them, or try some extra fluid. I googled "CTD air spacers" and it sounds like I'm not alone with this scenario.

I wanted another coil shock, due to my "huck to flat" and "jump casing" style but this frame doesn’t have enough clearance around the bottom mount to fit any coil except the obsolete Vanilla.

Here’s a crappy photo with the Vanilla fitted, in case you’re curious
Thanks Creaky, big help
 

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T

TwoSix

Likes Bikes
Not sure if this is helpful, but Ive found running a higher pressure in descend mode favourable to a softer setting in trail. It is just more supple in descend mode off the top of its stroke. Maybe try 15% sag in descend mode and slow the rebound a little*

When I say a little I actually ran my rebound in the slowest setting on my lapierre zesty at 15% sag in open mode. Was a XL/XL tune but rebound was very fast in all the settings really
 
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styler

styler

Likes Dirt
Looks like the tune you have is

2014, FLOAT-K F-S, CTD-Adj BV LV, Intense, Carbine, 7.875, 2.250, 0.6 Spacer, VTL, RTM, 200, 16

velocity tune light.

Rebound tune medium.

I have a a focus thunder 130 which looks to have a very similar design rear suspension. The standard shock on this was a medium compression, light rebound. I found that the rebound control did not have enough control. I have since fitted a medium compression and a medium rebound with a firm propedal CTD and a 0.6 spacer which works much better then the original RP23. I would imagine the light tune you have would be way to soft as sometimes I think I would like to try a firm tune. I run about 12mm of sag on the shock and weight 85 kgs and find that works well.
 
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