Spotted over at PinkBike, Specialized’s Jason Chamberlain has been working on a lightweight, dedicated pump track machine.
Dubbed StumpPumper and inspired by BMX bikes, it’s built specifically for the small jumps, rollers and berms of pump tracks. That means it has a lower center of gravity, no suspension and tight, twitchy handling meant for experienced riders. Beyond the geometry, the most interesting part is the offset crank installation. Rather than put them in perfectly opposite each other, they’re installed such that the rear one is angled down slightly, giving them about a 170° angle. This means you’ve gotta decide which leg will run in the front and commit to it, but if you’ve ever ridden a pump track, you’ll know pretty quickly which way you feel more comfortable. Even without offset pedals, it usually feels more natural one way or the other, but this bike’s set up does mean you won’t want to switch it up. The benefit? An effective BB height of just 10.9″ and a bike that comes in at 17.9lbs.
It’s not likely you’ll see the StumpPumper on a showroom floor, but if this gets you excited, check PB’s full post for spec list and details.
UPDATED! Pump on past the break for comments from Jason Chamberlain…
“The thing we might want to emphasize is that this is a one-off. It’s a “concept”. There are no plans, nor were there ever plans, to build a production version for sale. It is far too niche and far too expensive. It is just an experiment. If anything, some version of this bike will show up under our top athletes at some high profile pump track events.
“Why didn’t I build a custom frame too? There were not any more gains in the frame to be had. The P geo is perfect and 17 lbs is plenty light. The things I really wanted to explore was the slammed offset cranks, rigid but light wheels and rigid fork. There is a lot of skepticism over the fork, which I expected. On a smooth pump track, you really don’t need a suspension fork. Any small bumps can be handled with tire pressure and keep the fork rigid for better response and less energy lost when pumping. Damping in a fork is designed to deliberately absorb and dissipate the energy of bumps. This is good a good thing if you are riding in the rough, but it’s the opposite of what you want on a smooth pumptrack were all your speed in generated by pressing and pumping. Hence the BMX analogy – suspension forks scrub speed and energy in this application.
“However, a person will be fastest on what they are comfortable on. Even if they would be faster on paper and in theory with this setup, they may have mental reservations and that translates into reality. It’s not a bike for everyone, but it’s a bike I recommend trying if your goal is to go really fast on a pump track.”
