Goal: make an air sprung rear shock for World Cup downhill racing. Sounds easy, but no-one has done it with true success – yet. Enter RockShox's latest project, Vivid Air.
It might just be the downhill air shock that succeeds. After all, RockShox already make a successful air sprung downhill fork – the Boxxer World Cup.
Jeremiah Boobar, RockShox’s long-travel product manager, said the company were keen to re-establish themselves in the downhill shock market, which has been dominated by Fox in recent years.
“This is a solution that other companies have tried to get to and have not successfully made,” he said. "We wanted to go for the big one and prove that we can solve problems that no one else has been able to solve”.
RockShox's engineers based the new shock’s damper on the successful Vivid Coil. Originally, they stripped the damper and built a super-high-volume Dual Air style air spring around it. It worked well, but tuning it required putting more air in the negative chamber than in the positive – the opposite of all RockShox's other Dual Air products.
“We raced it at Sea Otter last year,” said Boobar of the Dual Air Vivid. “But simultaneously [during its development] the guys who work on the cross-country shocks had developed a new air spring system that was a new refined version of our Solo Air spring. It was so good we scrapped all the work we'd done on the Dual Air system for the new Solo Air system.”
The simplified Solo Air system uses a single air fill valve and bypass notches on its inner shaft to allow air to transfer between the positive and negative chambers, which set the negative spring automatically. Once RockShox had decided on this system for the new shock, there were still a few hurdles to clear.
RockShox's long-travel product manager, Jeremiah Boobar, with the new Vivid Air
Getting the feel right
There were a couple big challenges out there,” said Boobar. “One was making sure the shock feels the same at the top of the run as it does at the bottom. The other one is getting it to feel like a coil spring.” So, have they achieved both of these aims?
“The number one question people ask us is how it compares to a coil,” said Boobar. “Does it feel like a coil? No, it doesn’t. It reacts in a very favourable manner, but it feels different. Once you get up to speed and are hitting successive bumps it feels different. It doesn’t feel bad, it just reacts differently than a coil and that’s due to this speed sensitive nature of compressing a gas spring.”
When a gas is compressed, the molecules inside it collide creating friction and heat, which leads to a small increase in pressure. This causes the shock to ride higher in its shaft travel.
“Breaking the air shock stigma is going to be a big one,” said Tyler Morland, RockShox’s PR manager, who is also a pro-level downhill racer. “I don’t think we’re past that quite yet. Initially Vivid Air feels the same [as Vivid Coil], honestly, in terms of breakaway and everything, but at the performance end of things the air spring is different.”
Fade is also an issue that requires special attention in air sprung shocks, because they can potentially run at higher temperatures. “Our shock doesn’t have a huge percentage of fade in it, in general,” said Boobar. “But one of the things that we’ve done to combat the fade that does occur is we’ve taken the rebound adjuster rod, which is typically made out of aluminium, and put a plastic centre in it.”
This thermoplastic insert is designed to expand when heated to maintain the integrity of the damper’s beginning stroke rebound. End stroke rebound isn’t as affected by fade, because it relies on a poppet valve, which is more pressure sensitive and isn’t as affected by changes in oil viscosity.
Testing with real live World Cup downhillers
So what’s the benefit of Vivid Air? Thus far we haven’t mentioned weight, because it’s secondary to the performance story. Here's what SRAM’s BlackBox riders, some of the biggest names in downhill, came away from their test sessions with; it wasn’t a weight issue for them either.
“When we test with our BlackBox riders we try to give the shock a fair shake,” said Boobar. “We don’t just try and wow the guys with telling them that it’s the greatest thing ever and that they’re going to love it. For this project we showed up at each test session we did with [Greg] Minnaar, Peaty [Steve Peat], Sam [Hill], Mick Hannah and Brendan Fairclough, and had them do runs on their coil shocks and get totally dialled in, happy and comfortable at speed on the track, first.”
Only after the coils were working perfectly did the BlackBox staff put their stars on the air shock for testing. Then they took it away and put the coil back on. The point was to try to gain a proper comparison through use of the riders’ feedback and lap times, and back-to-back testing. “Consistently, the riders came back saying that, as they head into corners, they have a lot more to push off of,” said Boobar. “They also said that the faster and harder they push the shock, the better it feels.”
Boobar attributes this feeling to the speed sensitive characteristic of the air spring. “The nose of the air shock’s spring rate curve changes a little bit as you increase the shaft speed,” he said. “It’s really subtle, but basically the angle will change. When you do compress it at a very low speed the air spring will line up right on the coil spring’s rate. It’s extremely linear. Once you change the speed, that nose shows up.”
Now, let’s talk weight
“The racers have consistently said that they want to race the shock,” said Boobar. “They feel faster on this shock and that’s not based on the weight of the product.” Nonetheless, the shock is darn light. It’s claimed to weight more than 400g less than a Vivid that’s equipped with a steel spring.
“The BlackBox guys are on coil springs, so it’s a 200-something-gram difference, or about a half a pound,” he said. “But none of them is making the choice based on the weight; they’re making the choice based on the ride quality.”
Where should you ride it and when can you?
“This shock is going to be downhill capable, definitely for freeride,” said Boobar. “I think it would be silly not to put it on every freeride bike out there.” But Vivid Air isn’t for everyone. It’s a high-end shock that requires regular maintenance, like the Boxxer World Cup.
So, if you’re all you're doing is hammering out runs in a bike park, RockShox will tell you outright that you should be on coils front and rear. That way you don’t have to worry about maintaining the spring.
If you’re looking for performance, however, Vivid Air is at the top of the RockShox pile. Pair it with the Boxxer WC and you’re guaranteed to pull massive weight off of your bike. Vivid Air will hit shops in late summer. It should be available sooner on select manufacturers' 2011 bikes.