INTERVIEW
We chat to Ben Waite, a Senior Design Engineer at Zipp, to get the lowdown on the little innovation set to make a big difference to how you ride.
"Oh, easily five but up to eight or even ten," says Ben Waite, a Senior Design Engineer at Zipp, owner of a voice made for radio, a face for TV and the person responsible for shepherding Zipp's new AXS integral tire pressure system into the rim of the brand's newly released 353 NSW and 303 SW wheels. We're talking about PSI, of course. Specifically, how much your beloved at-home pump is leading you astray. "We have multiple pumps here", says Ben, waving his arms in the general direction of the wider HQ and factory in Indianapolis beyond his office. "And none of them are accurate. Back in the day, when we were all running 120 psi on the road, plus or minus 3 to 5 didn't matter much. But now we're running 50 with wider tires and hookless rims, 5 is 10%. That's a lot."
To a company like Zipp, that level of variation was metaphoric grit in the hub. A solution was needed. “We didn’t want to make a super accurate pump just to sell to people,” he says. “Plus, we’ve had the Quarq team part of the SRAM business since 2011, and together we have a huge amount of experience with their Tyrewiz pressure monitoring system.” So, according to Ben, Zipp decided to do something very difficult indeed: integrate a TyreWiz-like system inside the rim of the next iteration of its 353 NSW and 303 SW models.
If you’re wondering why integrating a pressure sensor within the rim of a bike wheel would be difficult, consider the sealant. The stuff we pour and pool in our tires, the elixir that equips us for the thorns, shards and sharp rocks that lie in wait, exists to find holes and close them. A pressure sensor is a small hole. And worse, it’s open almost all of the time (Zipp’s pressure sensor system takes a peek into your PSI every second). For Zipp to succeed, Ben and his team would need to find a way to stop the sealant from getting to the sensor and snuffing it out.
Before getting to Zipp’s elegant solution, I ask Ben when Zipp’s history with real-time tire pressure monitoring began. “It started with the first Tyrewiz in its original flag design from 2018,” he says. “The solution we have in the rim of the 353 NSW and 303 SW is very similar to that, most likely because we had the Quarq team working on the new integral sensor.” The Tyrewiz, says Ben, was perfect, albeit too apparent. “The feedback we had from our community was that an exterior tire pressure sensor was somewhat at odds with the clean aesthetic of the rest of the wheel. They wanted it hidden. So did we.”
However, integrating the sensor in the rim would require Zipp’s engineers to reassess everything about their approach. “We spend a lot of time making these rims as strong and as light as possible, and now you’re telling us we have to put a 50mm x 12mm hole in the rim to house the sensor!” he laughs. “And that’s with trying to shrink the unit as small as possible. But you still have to fit a coin cell battery that’s 20mm in diameter. So that was a huge challenge: can we make a slot in the rim with consistent dimensions so the sensor is always flush, and can we hit it at that slot with our impact tests and have it survive? Those hurdles alone were six months of the project.”
If you’re of a practical mind, you may already have reached the next hurdle: balance. Specifically, adding weight in one place in the rim would require a similar amount on the opposite side to counter it. “Even with a standard tire valve, a really attuned rider might be able to feel its offset on the wheel, and that’s like 5 grams,” he notes. “But our team did a great job of working on the plastics and electronics of the sensor to minimize everything, all of which helped us arrive at a weight of 14g for the complete unit, including the battery, which is pretty light.”
Still, some putty was called for. “We had some fun finding a road that we could use to test the wheel’s balance,” says Ben. “Long, smooth and slightly downhill was the ideal. For each run, we applied some putty to the opposing side of the wheel and added or removed it until the wheel felt balanced.” However, as Ben explains, his team didn’t need to offset the weight of the sensor completely. “It’s more about what you can feel than scientifically balanced,” he says. “And we learned a lot in the process. Like discovering that riding really fast downhill made testing impossible, as the wheel was simply going too fast for us to feel the difference of the sensor. The time window was too small.”
To add to the project’s complexity, Ben and his team had to ensure that when they tested the integrated sensor, they were feeling the wheel and not the imbalance of the tire. “Oh man, tires are a problem!” he laughs. “We learned a lot about tires and how hard it is to manufacture them precisely. So the location of the tire’s out-of-balance spot was important, otherwise we’d be tuning for the tires on our test setup, not the wheel itself.”
As tubeless-ready wheels, the new 353 NSW and 303 SW have removable valves. They’re an integral part of how Zipp’s pressure sensor functions. “The wheels use a special valve with a hole in it where the air is transmitted into the sensor,” says Ben. “Above and below the hole are two seals. When you push the valve in, it seals the sensor, and the air from the tire can get in, and that’s where it reads it. We also have TPU versions of it so that you can use a tube or a spare. Plus, if you have a flat and a different tube, you can still run a regular valve through it,” he says. “You just won’t get a pressure reading.”
BEN WAITE
To the elephant in the rim then: the sealant. “We leant heavily on the expertise of the Quarq team,” he admits. “Their above-the-rim pressure sensing solutions all have the valve going through the unit, which we realized was the big lever in preventing the sealant from fouling the sensor. They knew it worked, they just didn’t know why.”
Ben and his team realized Quarq had hit upon the Venturi effect: the reduction in pressure that results when a moving fluid flows from a larger pipe to a smaller one. “If you blow air through the valve, the higher the velocity, the more suction it puts on the path that goes to our sensor. So as you inflate or deflate your tire, if sealant starts to get towards the sensor, it gets sucked back out.” Ben calls this the belt of the system. But Zipp would also need some suspenders to ensure its trousers wouldn’t fall down. “We tried to complicate the path to the sensor as much as possible, to provide an additional defence against sealant fouling the system,” he explains, before going on to describe a very specific air path that collects any misplaced sealant for ejection the next time the tire pressure changes. “We have a whole room of 3d printers,” he says, “so we could iterate and test new and ever more complicated pathways. But while we could rely on 3d printing in development, the end product would be injection moulded, which meant we had to be able to machine a tool to make our design.” How many iterations did the air path go through? “Hundreds,” he says, “with different shapes, angles, diameters and so forth. And we even printed a clear material, so we could pressurize and put fluid into our fake unit, send air through a valve, and see the sealant get sucked out.”
If all of that sounds complicated, in use, the new AXS pressure sensor is simplicity itself. Those who ride tubeless can still use the pour-in method or top up their sealant via the valve. Zipp includes a special syringe with a smaller diameter aperture that goes through the valve, allowing sealant to pass through without worrying the sensor. The only visible change to the 353 and 303’s rims over previous iterations is the outline of the sensor unit, which sits perfectly flush on the rim, and an LED, which only flashes to report its status. Otherwise, it’s all below the fold and a rim like (and unlike) any other.
With any innovation, riders will wonder how reliable the system is. Will it ever foul? “As an engineer, you can never say bullet-proof,” says Ben. “But that’s the nature of what we do. No engineer worth their salt would want to be 100% because that probably means you overbuilt it.” To the rider at large, though, the system has proven to be absolutely reliable, with Zipp’s testing exceeding 100,000 kilometres across diverse terrain and conditions from dry and arid to humid and heavy rain without a single instance of sealant fouling the sensor. In short, it works.
Beyond the hardware itself, with the new sensor integrating with the AXS Echo system, Zipp has gone way beyond simple PSI reporting. “Some of the software and what we can do with it is pretty awesome,” says Ben. “Yes, the system can report your pressure to your head unit. But within the AXS Echo framework, when you get your bike and register everything, the system will know, ‘ok, this is a 353 with this serial number and a certain type of tire and size, so here’s a recommended pressure setting’ and so forth. There’s a nice cohesiveness to having your wheels become part of the wider data set around your bike and your drivetrain.”
Could Zipp take that further and even provide an element of real-time advice based on the terrain ahead? “For sure. There are so many ways we could use the data. It’s pretty exciting.”
We’re looking forward to what’s around the bend.
FEATURED PRODUCTS
A sensational new hub, less spokes yet more strength, integral tire pressure monitoring and an all-new cleaner graphics. Meet the new Zipp 353 NSW wheel.
