Cairoli was spotted testing this secret air shock two weeks ago, but now it is in America. The WP designed shock, with a little nod to George Jobe’s air shock from a 12 years ago, will make its Supercross debut on Saturday night on Ryan Dungey’s KTM 450SXF (if all goes well during practice). As an added bonus, the WP air shock is so light that Dungey's KTM 450SXF could be the lightest bike on the track...even with electric start.
This is Dungey's shock at Anaheim press day. To overcome the inherent pressure build-up of air shocks, WP has designed a compensating piston that regulates the pressure to keep it within a known quantity.
As with all air shocks, the shaft size is jumbo.
Air shocks are nothing new. Georges Jobe was working with KTM on an air fork and air shock system in 2001. MXA actually tested Jobe's suspension and was very impressed with it. Jobe would later make a mountain bike version, but his motocross suspension never went into production. The FN Jobe air forks and air shock knocked 12 pounds off the KTM 520SX test mule that MXA tested.
Perhaps the best known air shock system was the Fox Airshox. It was used by virtually every rider in 1977...including factory teams. It had two air chambers. A low-pressure chamber for small bumps and a secondary high-pressure chamber for big hits. Word on the street is that WP has found a way to compensate for the air pressure gain caused by heat buildup with some type of compensating valve that changes volume as air pressure rises.
The only production bike to come with air shocks was the 1975 CZ Falta Replica (although Yamaha put air forks on their bikes in 1976).
Ryan Dungey has been testing the shock all winter and believes that it absorbs whoops better and is less likely to kick. It is obvious that Team KTM is taking a major step in giving up tried-and-true coil springs for air pressure. But, if Dungey believes in it, it works better than what they had before and it saves several pounds–they are compelled to try it.
The Fox Airshox and the CZ Falta shock were introduced 36 and 38 years ago respectively.
THE 2001 FN JOBE AIR SUSPENSION REVISITED
This is the FN Jobe air shock from 2001 as tested by MXA.
When George Jobe brought his radical air suspension to MXA back in 2001, he said, "I know the negatives, but I believe that at FN Jobe we have solved most of the problems. Air forks do not get as hot as an air shock, since they are not driven through the bumps, so the pressure buildup in forks is not as much of a problem.
“On the shock, I have included a series of pressure-relief valves and regulators that maintain a constant air pressure inside the shock. Our regulator system keeps the air pressure constant all the time, from the beginning to the end. We have developed a system that doesn’t require us to adjust the shock after every ride. We use both an air spring for compression and a negative air spring to control rebound.”
In essence the Jobe system was designed with a series of blow-off valves that released excess air pressure, while a regulator controlled the optimum pressure setting. There was a dial that allows the rider or mechanic to change the base air pressure setting with a bicycle pump. Even when MXA over inflated the shock on the stand, it would gasp out air when we exceeded the regulator setting. And that is what it does on the race track. As the air pressure increased with heat buildup, the shock bled off the excess pressure.
HOW DID IT WORK?
MXA tested with Georges Jobe in SoCal and he graciously let us spend time testing the settings, but we also raced the bike. We had two identical KTM 520SX four-strokes–one with stock WP suspension and one with FN Jobe forks and shock.
Weight: Our stock 520SX weighed 239 pounds, the Jobe-equipped 520 weighed 227 pounds.
Forks: Today, with both Honda and Kawasaki specing their 450s with air forks, people seem amazed that they work as well as they do. It is no surprise to the MXA gang because Georges air forks worked great 12 years ago. Georges said, “The front fork is the most important part of a race bike. If you have a good fork you can ride harder to make up for a slow engine, bad tires or bad shock, but with a bad fork it doesn’t matter how good your tires, engine or handling are."
Shock: The MXA test riders with Fox Airshox experience expected the Jobe-equipped KTM to sit higher in the rear because of the static pressure common in air suspension. Not so. We also worried about stiction caused by the large swept area of the seal (much larger than on a typical 18mm shock shaft). Jobe had handled both problems with careful valving and a special fluid, not really an oil, that lubricated the sealing surfaces. The performance was very good with virtually none of the attributes of previous air shocks (which if you weren't around during the heyday of the Fox Airshox you wouldn't know about).
Overall: In MXA’s opinion (back in 2001), the Jobe suspension was a step in the right direction. It offered a unique feel and was better than 90 percent of the suspension on the track at the time. Plus, the 12-pound weight savings was immense. Sadly, Georges was unable to convince any motorcycle manufacturers to use his suspension–although he did build mountain bike version.
In a sad note: Georges succumbed to cancer two weeks ago. But, he left a enduring legacy of excellence behind – as a racer, team manager and inventor. To what extent KTM's new air shock is built on the work of Georges Jobe will probably be argued, but just as Jobe built on what Bob Fox had developed, it is undeniable that WP has been pushed along in their air shock development by the thought processes of Bob and Georges.
KTM Motorcycle tests