Michael Hanslip Coaching

If you want to go faster, you have to pedal harder

Dial twirling - how to set those knobs on the suspension

MTB suspension is very sophisticated these days. If you read my last entry on air pressure in suspension, you'll know I ventured into the setting of the knobs without fully exploring the topic. That is here...

Even on my Slash with Flight Attendant, I still need to set all the electronic knobs properly and get the air pressure right. Flight Attendant really only flicks the platform switch to one of three positions (open, pedal or locked) as I ride based on slope, bumps and pedalling input. On more regular suspensions, it is all manual and the setting up is still the critical thing to an enjoyable ride.

Take the Fox Float X shock or the Grip2 fork. They have 4 adjustments which few other models or brands offer: high and low speed for both rebound and compression. In contrast, entry level forks might have zero adjustments although they usually have a rebound adjuster because that has to be adjusted for air pressure to behave anywhere near properly.
Assuming you read and followed the previous entry to get your air pressure correct, what's next?

First, let's look at what this high speed and low speed stuff is all about. It refers to the shaft speed of the suspension rather than the forward velocity of the bike. When jumping a bike, the face of the jump loads the rear suspension a lot. A big jump face will just about bottom out the shock. As the wheel leaves the lip there is suddenly zero resistance to the shock fully extending. It will do so with full speed - this is high speed rebound. The low speed happens when you go through a big bowl-shaped depression in the trail. As the bike travels down into the bowl, speed of the bike increases. On the other side it goes up the side of the bowl, slowly compressing the shock (this is LSC's territory) and as you roll out of the bowl at the top back onto flat terrain the load comes off smoothly assuming a gradual transition from up to flat - this is low speed rebound. Low speed compression also happens from pedalling but mostly it is the gradual increase in load from gentle terrain changes. High speed compression is running into a rock at high speed. The front wheel instantly wants to move up the height of the rock. There is so much oil flow attempting to go through the low-speed circuit that it is overwhelmed and the bypass IS the high-speed circuit.
Many HSCs are governed by a shim stack. These are merely thin steel washers that are pushed out of the way by the oil flow through the tiny holes they cover. This is why, as I mentioned in the last entry, you require some HSC to get any LSC. If the washers aren't forced down onto the holes by the HSC adjuster, then the oil can just flow through the holes with little to no damping going on. Once the HSC is set the oil will be forced to go through the LSC circuit. I should have mentioned that this circuit is typically governed by a needle in a hole. The needle has a taper (much like a sewing needle) and the adjuster moves the needle up or down, pushing more or less in the hole. More needle in the hole means less flow (more LSC). Less needle in the hole means more flow (less LSC).

In regular riding conditions you'd like the suspension to ride quite high in the travel range. At or just below sag. This leaves more reserve for bumps and preserves the bike's steering geometry which gets really messed up as the suspension compresses. This calls for a decent amount of LSC (but not so much that the bike feels wooden, slow or sluggish to answer bumps in the trail). LSC might be quite different front to rear because rear suspension has a leverage ratio between wheel travel and shock travel usually around 3:1. Forks area always 1:1.

HSC is the last thing you play with. Once air pressure, rebound and LSC are set, HSC can step into control the movement of the suspension when it hits stuff. Too much HSC will feel rough and make hands sore. Too little HSC relies on the air spring to ramp up and can make the suspension not respond to repeated impacts as well as it might.

Finally, once this is all set, go out and ride the bike and pay attention to what is happening. Keeping notes helps. If it feels right most of the time, but bottoms out when you go faster or rougher - the solution is probably a travel token. If it springs too much off jump lips, that is rebound. If it sits too low in the travel, that is LSC or air pressure. Every problem typically has two remedies. But one preferred remedy. Because everything affects everything else in some way, the best solution for your suspension depends on the impact either adjustment will make to the other things.

Which is where ShockWhiz is quite helpful. Because it looks at compression and rebound, for different kinds of events in isolation, it can recommend a single fix for any problem having considered everything else that might be impacted by its recommendations. A rider is doing well if they can look at one thing per run.

When you do make changes, only change one thing at a time and not more than 1 or 2 clicks on the dial. If you change two things and one is an improvement while the other is worse, the end product might be "feels the same". You'll forego the improvement. Keep notes. Bracketing can also help quickly narrow in on what works. If there are ten clicks, first try 3 clicks and then 7 clicks. One should feel better than the other, try either side of the one that is preferred - eg, you prefer 7 clicks so next steps are to try 6 and 8. If you prefer 6, try 5 and 7 (again). One of these three should be your pick. Another great option is to take the manufacturer's suggestion - they usually offer starting points based on air pressures (which are based on body weight). I find them very close.
RockShox has a setting page on their website if you want to play with that. If you have a Trek, they also have a settings page on their website which goes to tyre pressures as well as suspension settings.

You need to experiment a bit, and pay attention to settings in general, in order to get the most out of our suspension and by association, your bike.