The PowerTap SL 2.4 Disc Brake Hub System is now available. The product has been tested extensively by our Engineering team as well as several pro athletes like Jeremiah Bishop, Julian Absalon, Conrad Stoltz, Melanie McQuaid, Wendy Simms, Manual Prado, Danny Pate and Rocky Reifenstuhl.

What went into bringing this product to market? We got the inside scoop from PowerTap Product Manager Jesse Bartholomew and one of CycleOps Power's engineers who worked extensively on the project, Jordan Roessingh.

Why did CycleOps Power decide to create a disc brake PowerTap hub?

JESSE: CycleOps Power has the benefit of having very passionate customers that aren't afraid to let us know what they want. We do our best to develop products that meet those needs, and the SL 2.4 Disc is a result of that. In addition, the benefits of using a PowerTap only increase with the more data you collect, so it only makes sense to allow our customers do so in any discipline of cycling they choose.

What were some of the design challenges that you had to take into consideration with the PowerTap SL 2.4 Disc Brake Hub?

JORDAN: The three major design challenges were durability, wireless signal strength, and the rotor attachment.

Anytime you take a product off-road, the strength requirements go up significantly vs. on the road. We went through several design iterations of the rotor assembly to optimize the design for strength-to-weight ratio. In the end, the hub/rotor assembly passed all of our strength tests without failure, showing that this hub can take the abuse of everyday MTB riding.

The PowerTap wireless technology was not originally designed with a disc brake application in mind. Therefore, we had to be careful not to impede the transmission with a metal barrier like the disc rotor assembly. Further, as with all of our wireless hubs, each hub is measured for wireless signal strength prior to heading out the door to further ensure a robust connection from handlebar to hub on every system we ship.

The rotor also had a unique set of design requirements since we wanted to use our existing PowerTap Technology that has some geometric constraints that are crucial to the unit’s accuracy. This meant we weren't able to incorporate a standard 6-bolt or centerlock attachment mechanism. Instead, we added the rotor bosses directly to the non-drive flange of the hub shell and increased the flange diameter to accommodate the higher loads that that flange was now seeing.

This larger flange diameter also had the added benefit of allowing for equal spoke length between the drive and non-drive side, making wheel building that much easier.

The rotor is proprietary. Why is that?

JORDAN: Because we wanted to use our existing PowerTap technology in the Disc Brake Hub, we had to develop a unique attachment design. The 8-bolt, 72mm bolt circle diameter mates the rotor directly to the non-drive side hub flange. The use of 8 x M5 bolts may seem excessive given the effectiveness of the standard 6-bolt pattern, but it was required to better distribute the braking loads to the already heavily loaded hub flange.

Further, because of the requirement to use a proprietary rotor, we conducted extensive testing to ensure a proper rotor design that would be universally compatible with all major disc calipers on the market.

Why is the rotor 160mm?

JORDAN: 160mm is by far the most common rotor size used for cross-country applications. Because we're only offering one rotor size, 160 was the best option to accomodate the majority of the mountain bikes on the market.

Describe the testing process before the product is released to the market.

JORDAN: The PowerTap SL 2.4 Disc Brake Hub went through rigorous testing to ensure the product would hit the market as a robust product. From extensive ride testing to moisture, wireless signal strength, durability, and compatibility tests, the MTB Disc PowerTap was tested for every scenario a mountain biker could throw at it.

Did you collaborate with any athletes to test the hub (if yes, who)?

JESSE: Part of our product development philosophy at CycleOps Power is to introduce our products as soon as possible to professional athletes since they're able to put products through a massive amount of stress in short order. With the PowerTap SL 2.4 Disc Brake Hub, we had the opportunity to work with some new athletes that focus on mountain biking, including Melanie McQuaid and Jeremiah Bishop, but we also learned that many of the riders from Slipstream were extremely interested in the product because of the time they spend training off-road during the winter.

JORDAN: In addition to sponsored riders, we also had our own internal athletes put the hubs through their paces. Neil Swanson, a design engineer and expert category XC mountain biker, spent a good deal of the past 6 months racing and training aboard the PowerTap SL 2.4 Disc Brake Hub. He even surprised himself upon downloading his data with his power numbers from races. BJ Bass, another engineer at Saris Cycling Group, and a notorious bike-breaker, has ridden over 1500 miles aboard his hub on a rigid 29'er and is slated to compete in the Trans-Iowa (a 300+ mile non-stop race through the gravel farm roads in Iowa) this april with his hub.

What kind of feedback have you been hearing from the testers who are riding the PowerTap SL 2.4 Disc Brake Hub?

JESSE: The feedback has all been very positive. We've been testing prototypes since summer, and there have been no issues in the field.

JORDAN: The feedback has been overwhelming good. After months of ride testing by our internal testers at Saris and sponsored pros, we've only received positive feedback throughout the testing cycle. From braking performance to moisture resistance and ease of installation, the PowerTap SL 2.4 Disc Brake Hub has been a hit with all of our riders.

Do you feel this product will benefit mountain bikers the same say it has benefitted road cyclists?

JESSE: I do believe there will be a tremendous benefit for mountain bikers using the PowerTap. Perhaps even more than for a road cyclist because there is so much more research and data collected the training theories are a little further developed. This isn't the case on the mountain side.

Given the relative intensity and on-off nature of mountain biking, it will be interesting to see training methods develop as more data is collected. I think many athletes and coaches assume that because of that pattern of power output on the mountain side, the data is not as valuable, but it's just because previous methods of measurement (heart rate and RPE) don't allow for any meaningful analysis unless the intensity is fairly constant. With the PowerTap, the pattern of power can be characterized and quantified for a meaningful analysis, just like a road race or criterium can be on the road.

The PowerTap SL 2.4 Disc Brake Hub System is available as a hub-only system (computer, chest strap etc.) in 32 spoke configuration for an MSRP of $1599.99 each.