Fork maintenance... on my bicycle

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UselessPickles

Making Grand Canyon replicas from air boxes...
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I've recently gotten into mountain biking (well, in SE Michigan, more like slightly hilly dirt trail riding). I'm enjoying it enough that I'm actually farkling my bicycle! First was the hydraulic disc brakes, and now a suspension fork that's more high-tech than my motorcycle's suspension.

reba_fork_apart.jpg


The fork has adjustable travel via internal spacers, and I wanted to remove the spacers for full travel, so I had to disassemble, clean and reassemble. I'm now up to 120mm of travel, which is almost as much as the FJR's fork (135mm). Only special tool necessary was a pair of snap ring (retaining clip) pliers. Probably much easier than FJR fork maintenance.

Got the suspension on ebay with only 50 miles of use, but about $200 cheaper than brand new. It has adjustable spring rate and preload via air pressure (it's an air spring system), adjustable rebound damping, adjustable low-speed compression damping, and an adjustable threshold for how much force is necessary during low-speed compression to bypass into the high-speed compression damping (high-speed damping not adjustable). The low-speed compression can be adjusted all the way to fully locked (for efficient pedaling). There's even remote dial+lever to adjust the low-speed compression from the handlebars, and to instantly switch between your preferred setting and complete lock-out.

Can't wait to get it installed and try it! It must be amazing compared to the "recreational" non-adjustable suspension that came with the bike. That thing has tons of stiction.

 
The drawback to air spring systems is that it requires a perfect fork seal which is hard to maintain in a dirt environment. As long as you are willing to do the maintenance and keep on top of things it all works well.

 
The air spring portion itself is completely contained within the upper tube. There's no exposed moving seals (for the spring itself), so I don't see how dirt could get in there and cause a leak without major abuse and multiple skipped service intervals.

The seal between the lower and upper tubes is not there to maintain air pressure. It's only there to keep dirt out for the purpose of allowing the lower tubes to slide along the upper tubes smoothly without scratching. Dirt would have to get past that seal, down in to the inside of the lower tube, then up into the seal at the bottom of the lower tube to start affecting the air spring. I suppose it will happen eventually with a neglected/abused fork, but it seems to be well designed to minimize the possibility of contamination.

 
I'm confused. No surprise there but...

How does the low and high speed dampening know what speed you are going? Is it simply a matter of switching it manually?

Being a semi avid rock climber(crasher mostly, just ask Kaiser) here in NorCal, I needs to know more. Brand and model of forks maybe.

Thanks,

Mark

 
Low and high speed damping are referring to the speed of the suspension movement; not the ground speed of the vehicle.

I guess it's not exactly low and high speed compression damping on this fork. There's one compression damping adjustment, and only one compression damper in the fork. But there's also a "floodgate" that will bypass the compression damper (resulting in low compression damping) if pressure builds up too much in the damper. The threshold at which the floodgate opens is adjustable. Since the speed of the fork travel produces pressure in the damper, the compression damper is only effective at lower fork speeds (if the floodgate is adjusted to open fairly easily).

One of the ways you can take advantage of this is to use higher compression damping to reduce brake diving, pedal bobbing, etc (all undesirable low-speed fork movements), but adjust the floodgate to allow the suspension to soak up bumps. Bumps cause a sudden fast movement in the fork, which will cause a pressure spike in the damper and open the floodgate.

It's a 2010 Rock Shox Reba SL. The thing cost more than my entire bike when it was brand new, and it's not even considered to be an expensive/high-end suspension fork (I think it's considered to be "mid-range"). I could have easily spent more on upgrading bicycle suspension than what it costs to get GP suspension to overhaul the FJR's front fork and send you an ohlin's rear shock. I think it might be easier to fall into farklitis-induced financial ruin with a mountain bike than an FJR.

 
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