BONES BACON ON SUSPENSION: AIR PRESSURE VERSUS DAMPING

September 2, 2015
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By Bones Bacon

Clickers? “Oh yeah, I forgot my forks had those things. I used to play with those things all the time. I carried a screwdriver in my boot and would stop by the side of the track and make adjustments during practice.” This is what people tell me all the time when they are asking questions about adjusting the air pressure in their TAC or PSF forks. Before I talk about changing air pressures, I always ask, “Did you try your clickers?” It seems like a question that it is almost too basic to ask, but people tend to get so carried away with adding pressure to this chamber and removing pressure from that chamber that they forget the basics of fork design. It is, however, true that the latest generation of air forks have opened up a lot of new areas of concern about adjusting your forks, not the least of which is getting arm pump from using your air pump too much.

Telling the difference between the need for a spring-rate change and the need for a damping change can be tricky, but let’s give it a shot. This is a wake-up call for air fork owners. Pretend that your air forks are now spring forks. Are you going to change your fork springs at the track between motos? Of course not. Instead, you will make damping adjustments to get your bike dialed in.

Let’s get the basics out of the way first. When you arrive at your local track, you unload your bike and put it on a stand. Since you have already pre-determined your best air pressures, which mimic the spring rate, and have established a pretty good overall balance on your bike, you are ready to work on getting your forks fine-tuned. Once you have made sure that your shock sag is spot-on and the fork air pressures are where you want them, it’s time to go out and ride.

On the track, you notice that when you are coming into high-speed, rough braking bumps before a corner or, even worse, down a steep hill into a choppy corner everything goes haywire. When you chop the throttle to set up for the turn, the back end kicks up, your arms get stretched beyond reason, and the overall feel of the forks is stiff and harsh. What should you do? If you are considering going back to the pits to lower the air pressure in the main chamber, stop! Don’t do it! Instead, take the screwdriver out of your boot and stiffen the compression a couple of clicks. Your forks most likely need more damping control to stop them from diving too deep into the stroke too easily. Many times in this situation, going stiffer on damping will make the forks feel plusher. Why? Because they will stay higher in their stroke and have more usable travel to work with. It might be possible to fix this common problem with more air pressure, but that will change the fork in the situations where you like what it feels like.
Here is another example where damping trumps air pressure as a cure. The balance on your forks feels good; they aren’t diving under deceleration, and they are absorbing the small chop; however, back in the pits, you notice that you aren’t using all of the fork’s travel. In this situation you might be tempted to lower the air pressure in the main chamber to allow the fork to be soft enough to get a full stroke—stop! Don’t do it! Air pressure will change the full spectrum of the fork’s action, but you are only concerned about one part of the fork’s travel. Lower the oil height in the forks to increase the air-space volume. This will give the forks a little softer feel down in the stroke.

Here is one last example of where a damping change makes more sense than an air-pressure change. Ben Townley used to tell me that all his tracks at home in New Zealand were very fast, very hard-packed and very choppy. In this situation, a fork has to respond to bumps much quicker and may need to settle into the corners more, especially if there are no ruts to grab the front tire on the entrance. The best strategy? Grab the screwdriver stashed in your boot. Soften the compression clicker a little and loosen the rebound. The tire will now follow the bumps instead of skipping across them.
Keep good notes on the changes you make for each type of dirt and track condition. That notebook could be your best friend on race day. Remember, unless you’ve eaten enough cheeseburgers during the week to gain 10 pounds, you should stick with your current air pressures and focus on the clickers.

Jim “Bones” Bacon has tuned the suspension of the biggest names in motocross, including Jeremy McGrath, Ricky Carmichael and Ryan Villopoto. If you have a suspension question, send it to mxa@hi-torque.com.

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