Front End Support – Fork Air, Volume & Compression
Between our BikeCo Pro Tune services as well as working with some of the fastest racers in MTB we get a lot of questions regarding suspension tuning. Modern forks offer more ways than ever to dial in your ride. Getting the right front end support with fork air, volume and compression improves tracking, ride quality, dive, and how your bike performs in the chunk.
Recently BikeCo Pro Rider Cody Kelley was in town working with Joe Binatena on the 2019 Alchemy Arktos 29. It was an interesting opportunity to sit down and listen to Cody and Joe discuss setup.
“During the off-season I had a chance to mess around with setups. Chasing your buddies around on their trails is a blast and not too different than racing. I was finding that to get the fork to give me support in the steeps as well as if I got offline in a new section I wanted it stiffer and stiffer.
Since we don’t pre-run the race courses much you have times that you surprise yourself during an enduro. A more supportive front end is good in the steeps to keep your hands up. It also keeps the front end from burying into a hole or front end of a rock.
So ripping around with friends I was going up 2psi, up 2psi, and so on. I ended up running well into the 90psi range! And it felt sorta ok – except I noticed I wasn’t using the last 30 or 40% of travel anymore. Well that can’t be super good right?
The last few weeks I really spent some time getting more support out of the front end from volume spacing and compression dials. Balancing more volume spacers for more ramp with the high and low speed compression on the Grip2 I can get the support level I want at a PSI that allows full travel when I need it. I’ve really gotten into fine tuning with the fork dials to get my setup right.” Cody Kelley
Pushing on Cody’s fork is an eye-opener. I’m around 60lbs heavier than Cody and his fork feels even a touch stiffer than mine! The more aggressive ramp rate was notable in the first little bit of travel.
Why? Well believe it or not, Cody Kelley is a shit-ton faster than me. The added ground speed requires more supportive suspension to eat up holes in terrain that Cody’s almost skipping across, that I’m riding into and out of! On a race run pro enduro riders like Cody are pumping in and out of holes in the steepest terrain you can think of.
That super subtle fork that uses 80% of the travel on your XC / Trail loop is going to stall into features. Suddenly you’re ahead of the front wheel. Not great.
Along with more support as ground speed increases rebound settings must increase too. For top level racers it’s common for the rebound to be so fast for the race run that it’s tough to ride at sighting speeds. More than once I have seen Joe work with our pro riders during practice assuring them at full pace the bike will do what they want. And every time after the sighting pace is done and the speed is opened up they love it.
So what are the basic principles at work getting more support from your fork?
It takes a certain PSI pushing against the piston to support a given weight. In Cody’s early example of adding PSI to the system he was generating more support from a stiffer air spring psi while lowering the amount of sag. This is part of the reason he wasn’t using as much travel. He was starting out “taller” or “not as deep” in the stroke at sag.
Volume spacers increase how quickly the air spring’s pressure ramps. Less volume spacers, more volume total, provides a more linear feel. More volume spacers, smaller total volume, produces a more progressive or bottomless feel. As you increase volume spacers your starting PSI, or uncompressed PSI will lower.
However, remember that at a set sag the piston PSI will be the same. So 25% sag with no volume spacers or a maximum amount of spacers: at sag the air pressure ramps to the same PSI. Don’t fall for the “more volume spacers improves small bump compliance because it starts at a lower number.” Inaccurate. We have a lot of solutions to improve small bump – but simply adding volume spacers isn’t it. Check out our Pro Tune Suspension, etc for more!
Ideally volume spacers are used to balance desired sag and ramp rate, or bottomless feel. Faster riders may choose to run a bit less sag percentage. Still, venturing too far outside of the 20-25% sag range will start to affect grip even for rippers.
High and Low Speed Compression:
Just like Cody mentioned the external high and low speed compression controls are great for dialing in finite setup. Compression dials slow or speed the flow of oil through the damper which in turn modifies the shaft speed.
The video below illustrates hydraulic dampening basics. On the left is a “fast” setup with multiple ports allowing fluid flow. On the right is a single opening which only allows “slow” fluid transfer. The middle splits the difference…
Most riders tend to run the compression controls open. Getting a base tune with the compression with a click or two on the system will give you a wider setup range as you can back off a bit for more compliance.
Are You in the Ballpark?
Quick conclusions here – and there’s plenty more reading on our other blogs about these as you’ve seen!
Are you running too slow or too little support for your ground speed? The bike will want to dive into holes, compress too much in turns. All and all feel too squishy. Upside is it probably feels amazing riding slower across washboard type stuff. Wait, that’s not much of an upside.
Running more support than your speed requires? Your bike probably sacrafices some trail tracking. It will likely feel chattery and won’t squat deep enough into corners to load up correctly.
Need more help with your setup? Work with the experts here at BikeCo to get the best suspension products and tunes for your riding style!
Build your own custom Alchemy Arktos 29 with BikeCo’s online custom builder here