My Rides

Tuesday, June 9, 2015

Avalanche Downhill Cartridge Upgrade - Fox 36 29 (160mm)

WOW!  Plush on small bumps, and fast bumpy downhills, and really controlled on bigger stuff.

To me, an engineer and "clydesdale" (overweight) rider, I want to maximize the efficiency of my bike.  That means, letting the wheels move out of the way of as many obstacles as possible to preserve as much forward momentum as possible.  Additionally, since my hands support more weight than the typical rider, reducing hand/wrist fatigue is an added benefit - I can go faster on a late ride bumpy downhill...

As I've ridden my stock Fox 36, I've noticed 2 things I expected would be better:

  1. Small bumps at moderate pace produce more handle-bar displacement than I'd expect (not a big deal) - I feel like my Cannondale Lefty DLR 80 (80mm travel) was better at this
  2. Fast downhills over "washboard" or rocky sections (2-3" high) are harsh - on longer rides (>2 hours) I slow to give my hands/wrists a rest, and ultimately carry less speed overall. 
Avalanche Downhill Racing offers a replacement damper cartridge, which offers rider (weight, riding style) tuned damping.  It's best to read how they describe the damper and it's differences to stock, or read similar posts related to motocross shocks (there seem to be more of them).  To me, what it comes down to is:

  • Orifices through which oil can flow are larger, allowing the potential for less damping/resistance as the shock travels.  Meaning:  The shock can be dynamically more compliant (take less force to move it) than stock.
  • Mid to high-speed damping control is more complex - set via shims that flex/bend to control the oil flow through those orifices - and customized to your preferences.  The hydraulic pressure causes them to flex/bend, and the stacking of the shims adjust how they bend - and thus how (dynamically) compliant the fork is at different speeds.  In my case, set to be softer and more "regressive" at high speeds - meaning I get a lot more compliant ride over small to medium bumps.  
When you order from Avalanche you specify your fork model, year, etc., your weight, riding style and riding experience.  As I've pondered this, I think the riding style lets Avalanche target the general shape of your damping vs. speed curve, and your weight and riding experience let them estimate the range of fork speeds you'll experience - so that the tuning "scales" the curve to the range of fork speeds you'll routinely experience.  

First impressions
I've been on 3 rides that include a variety of moderately challenging trails.  While I had set the pressure in the shock to 75-80 psi before (30% sag), I followed the recommendation and set it to 90 psi (22% sag).  Some rides have started with slow rocky climbs.  While not a huge deal, I notice the front is more active - soaking up those small bumps.  I also noticed significantly less dive under braking - in fact I notice the rear shock rebounding (where before I only noticed the front shock activity under braking - they interact, of course).  

When the climb levels out, and I hit some moderate speed rocky sections, it just soaks them up - everything's just more effortless.  The rear, which I've described before as "disappearing", I now notice more.  The UCSC trails have a narrow flow-ey trails with roots.  On root-ey trails, I think I can hear the "blow-off" of the floating valve as I crash over roots.  I find I have to worry a lot less about my line, and can maintain more speed.  I keep the bike on the optimal line, keep my speed up, and the wheel just flows over whatever is there.  

On messy rocky downhills (slow to moderate speed), with rocks 3-6", and drops & steps 8-10", there's just a ton more control.  I can carry a lot more speed in because I'm feeling more in control, and my hands aren't so strained from "just holding on" that I can modulate the brakes, change my line etc.  

The other thing that surprised me was how much better the bike felt on bigger drops 10-14".  I still take these slow - landing the front wheel before the back wheel is over.  With the new damper, the front end seems to compress less (it doesn't - the travel indicators tell me that), but there's less "pitching forward" feeling.  I suspect that the higher low-speed damping is slowing the rate of "pitching forward" so, by the time the front is fully compressed, the whole bike is a bit further down the trail.  This is also noticeable on "whoops" (smooth down then up) - I used to feel the whole front end compress, the tire folding up.  Now it just feels like business as usual - a whole lot less fuss, and more controlled feeling.  

On a very fast rocky downhill, I found myself pedaling through sections I previously just "held on" through.  A whole lot less harshness at the wheel made it up to the handlebars.  Where I'd slow up for a few seconds between harsh sections to shake my hands out, I now sped through to charge into the next rough section.  

Into my 2nd ride, I reduced the rear shock's (Cane Creek DB Inline) high speed compression to minimum, and increased the low-speed and high speed rebound.  On my 3rd ride, I softened up the low-speed compression as well.  On a single track downhill with some small jumps, I noticed the front hard to "lift off" so I reduced rebound damping 1/4 turn.  The tuning sheet with the shock said to decrease low-speed compression 2 clicks to reduce harshness, so I did that to see if it could be even more plush on the fast rocky downhill.  I think it felt a little better (certainly no worse, and no noticed increase to brake dive).