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Welcome back to the Bikerumor Ask A Stupid Question series! This week, we’re looking at how to setup a Dirt Jump Fork. We’re taking your questions to some of the most capable riders on the planet, from ex World Cup DH racers, to Red Bull Rampage riders, all of whom are pretty proficient in the art of getting air.
We’re asking them how they set up a specially designed Dirt Jump Fork, like the Marzocchi Bomber DJ or the Ohlins RXF36 EVO DJ… and, how they’d set up a fork on their enduro bike if they were taking it to hit some jumps! Your contributors are:
- Tyler McCaul, Pro Freerider and regular at Red Bull Rampage
- Innes Graham, ex-World Cup DH Racer, BMX Rider and Mountain Bike Coach at the Borders Academy for Sporting Excellence
- DJ Brandt, Slopestyle Rider, seen at Red Bull Rampage, Fest Series and Crankworx
- Matt Jones, Pro Dirt Jump Rider and Builder
- Marzocchi Sports Marketing Specialist, Ben Tapiz
How do you go about setting up a Dirt Jump fork?
Tyler McCaul: I run 115 PSI in my Bomber DJ. In comparison, I run 78 psi in the Bomber Z1 on my trail bike.
The main reason for this is that if a dirt jump fork is too soft you will lose a bit of your pumping speed in between transitions, and it also causes you to lose your ‘pop’ when you’re trying to get a lot of height on steep take offs. There is definitely a happy medium though, because I like to still have that bit of cushion for when I land.
Now, if I were taking my trail bike to a dirt jump park, I would most likely add some PSI and/or crank the compression knob a bit stiffer so that I’m not sinking too deep into all the transitions and losing speed and pop. Dirt jump parks don’t necessarily have a lot of bumps, so you want it set up pretty stiff for the same reason mentioned above.
In comparison to a lot of other serious dirt jumpers, I actually run my fork on the softer side. It’s common for riders to set their fork so stiff that it barely moves, so it’s only really there for big impacts (if they go too far or too short on a jump).
I have my compression knob turned to about 3 o’clock on the dial and rarely adjust it from there, but will occasionally turn it to about 5 o’clock if I’m riding a real tight pump track or something where I don’t necessarily need the fork to absorb any bumps. I run the rebound knob turned 2 clicks out from fully closed so that it has sufficient rebound and doesn’t come back too fast.
For reference, I weigh about 150 pounds and I’m riding a size Large GT La Bomba.
Innes Graham: If we think about how Dirt Jumps compare to your regular enduro trails, and what a rider’s motivation is while riding each, I’m sure we can agree the two disciplines are hugely contrasting!
A dirt jump park or “set of trails” as they are commonly referred to is generally a number of jumps set one after another progressively growing in size. Normally trails are built on a flat area of ground and packed down with shovels etc to be as smooth as possible. This means a dirt jump fork can get away with being generally no more than 100mm of travel and set fairly stiff compared to an enduro bike fork.
Seeing as a dirt jump rider would rarely ride in wet conditions and there are no rocks or roots to navigate you can get away with having a shorter travel fork set up much harder.
I personally don’t have my fork set completely rigid. I like the beginning of the travel to have a small amount of “give”. This aids grip and comfort and also allows the fork to help with “pop” when hitting larger, more steep take offs. The suspension on a DJ Bike is primarily there to take big impacts when landing flat. Rebound is also normally set to be somewhere in the middle of its range.
I like my fork to feel very progressive and my rebound is also on the slower side. So, when I do take a bigger impact and need to use the travel the fork doesn’t rebound back too quickly and you get kicked back in the face or chest. I find a slower rebound more predictable on jumps too.
I feel like less experienced riders think that a fast rebound will help you jump bigger and higher. I don’t agree with this statement as in my opinion 80/90% of a jump comes really through driving with your legs through a take off instead of pulling with your arms.
Matt Jones: I’ve always been a fan of running a super stiff jump bike and fork. I used to be happy with a fork that doesn’t even move and was permanently locked out. But, in recent years, I’ve found a balance where I run lots of volume spacers to ensure that the fork ramps up quickly and gives immediate support whilst riding steep take offs.
This means that I have minimal sag and movement to ensure that my bike can react quickly to small changes when popping off ramps or pulling for flips, etc. I run an Ohlins 36 boost fork that has been converted to 90mm travel for my dirt jump bike.
I then run plenty of compression and also fast rebound to again assist with popping off lips and keeping the bike feeling reactive. All of this isn’t conducive to a soft landing, but if you’re up for nice squishy suspension then dirt jumping isn’t for you (wink).
DJ Brandt: When I set up my DJ fork I run it stiff! So usually maxed out volume reducers, pretty close to maxed out PSI and moderate/slower rebound. I ride a Commencal Absolut size medium. I’m 6’2” and weigh 185 lbs.
Marzocchi: A DJ fork is set up to only compress under large impacts. They are not set up to absorb all of the small chattery bits. The rebound is much slower and the compression is more towards the closed side.
If I wanted to take my enduro bike to the DJ Park, how should I set up the fork differently to how I set it up for trail riding?
Innes Graham: Good question. I think firstly you should check the settings that are on your bike’s suspension already. Write everything down in your phone or on a note pad before you go changing anything. There’s nothing worse than messing with your suspension and then being unable to get it back to where you like it. So, note down the pressure in your fork and shock along with any compression and rebound settings you have. This depends on the brand and model of your suspension.
From there, I would recommend adding a little air to both the front and rear, if you have the option of doing so, just to allow your bike to carry a little more speed while pumping the transitions of jumps along with maybe adding a few clicks of compression and rebound (to stiffen and slow your suspension).
The key to most bike set ups is in my opinion is to find a happy middle ground. If you know how to set your sag, I’d say go down to around 15-20% front and rear compared to the 25-35% that is fairly standard on enduro bikes these days. Make sure your suspension remains balanced and both are working well together. There is no point locking your fork out and not doing anything to your rear suspension.
My last piece of advice would be, if you are a less experienced rider looking to join in a little at your local jump spot, is to not make any drastic adjustments. The last thing you want to do is add more variables that you are unfamiliar with when trying a new discipline. If you are comfortable on your bike, keep it that way. You will be at a much lower risk of crashing in that case.
Matt Jones: Riding enduro bikes at jumps parks can be super fun, but if your suspension is too soft and slow then it’ll feel impossible to get the bike off the ground because you’ll lose all your speed in the tight radius take offs and landings.
So, definitely wind on some clicks of high and low speed compression, and if you have a shock pump then add much more air than you’d typically run for an enduro bike. This will mean you lose less energy in the jumps, and that saved energy can mean you jump higher and further for sure.
Marzocchi: You will want to slow the rebound down and firm up the compression in order to maintain speed through a set and avoid any “bucking” sensations. You don’t want to lock out the suspension.
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