Ask a Mechanic | Understanding & Tuning Compression Dampers

Welcome to our Ask a Mechanic column where our expert mechanic Daniel Slusser answers your bike maintenance questions. If you have a question for Daniel, please post it on our Facebook Wall or e-mail Daniel directly at daniel.slusser@artscyclery.com. Today’s column will review how to adjust high and low-speed compression on a Fox 36 RC2.

Question

I read your article on fork tuning and had a question about adjusting the compression on my Fox 36 Talas RC2 160. I’ve tried turning them in a bit to try and keep the fork from diving under braking but then the fork just starts to feel harsh so I keep them mostly dialed out. How do you go about finding the right setting? From: Manny

 

Answer

Compression damper tuning can be tricky, but don’t let it dampen your spirits. Before you can properly adjust a compression damper you need to have a correct concept of what the adjustments do and the interplay between high and low-speed compression adjustments.

First, let’s discuss the basics: Low-speed compression damping adjusts how quickly the fork can react to slow speed compressions (i.e. pedal bob, brake dive, rolling terrain and pumping). High-speed damping adjusts how quickly the fork can react to high speed compressions (i.e. impacts with rocks at high speed, landing jumps, braking bumps, etc.). In order to access the high speed circuit you must first “break through” the low-speed compression circuit. I choose the words “break through” because you should think about low-speed compression damping as the threshold for accessing your high-speed compression damping. It is only after the fork compresses so fast that it overcomes the low-speed circuit that the high-speed damping begins to activate. Because of this, it is a good idea to tune your high-speed damping first.

Those two knobs on the right can make for a great ride if adjusted properly.

Before we do all that, we need to get your air spring set properly. Back off both compression adjustments all the way and set your air pressure so that you achieve 30% sag (that is using 30% of the fork’s travel which in this case is 43mm or 1 5/8″) when mounted on the bike in a downhill attack position. It is better to err on the side of too much sag than not enough at this point.

With your air pressure set we can now tune the high-speed adjustment. Go to a trail that you know well as a testing location and use the rebound damping setting you are normally comfortable with on your RC2. An easy way to see if you are using too much high-speed compression damping is that you will not be able to bottom the fork or access the full travel. On the toughest trails you ride, the fork should bottom out on the biggest hit you face, or else you aren’t getting the travel you paid for. So, to keep it simple, use as much high-speed compression as you can while still getting full travel on those big hits. If you can’t decide between two settings, pick the lighter one so you will have a smoother ride. After you become a World Cup downhiller you can choose the firmer setting.

Now it is time to tune the low-speed compression. You will likely need very little. If you use too much, the fork will feel harsh all the time (as you experienced) and you will loose small bump sensitivity. Don’t worry too much about brake dive and pedal bob since it it better in my mind to deal with a bit more than you would prefer if it means being able to hammer through the rocks. Now, if you live in a place like Santa Cruz, where trails are smooth overall but punctuated by jumps and drops, you will want to use more compression damping. If, on the other hand your trails are like those we deal with here that have lots of small to medium sized rocks everywhere, you will want very little compression damping. With that said, experiment using the bracketing procedure I described in the other article for rebound damping but applied to your low-speed compression damping. That should get your fork feeling just right. Again, err on the side of too little, rather than too much low-speed compression.

Enjoy the ride and don’t let over thinking your fork’s adjustment ruin the ride for you. All riding should leave you feeling decompressed. The Fox 36 is a great fork even with poor settings.

Daniel Slusser is a professional bicycle mechanic with over ten years of experience. He holds a bachelor’s degree in business administration from HSU and a master’s degree in history from Cal Poly University. When he is not riding, wrenching, or writing he enjoys spending time with his wife and two children.

2014-03-05T16:15:32-08:00