Cycleops PowerTap SL 2.4 Disc Hub

Heart rate monitors have evolved from a very expensive, exotic training tool available only to elite athletes like Greg LeMond in the 80's to a mundane cycling accessory often purchased alongside visor helmets, rear view mirrors and disturbingly large gel saddles. While it is relatively easy to measure now, the results aren't quite as informative as they were once thought to be. Heart rate is variable -- it's subject to outside factors like heat, time of day, nervousness, and accumulated training fatigue. Because of this, it's difficult to compare one day's workout to the next.

Unlike heart rate, power is a consistent, instantaneous and brutally honest measure of effort on the bike. As a result, power meters have created a revolution in the approach to training and racing for road cyclists over the past few years. Until now, a feasible option for mountain bikes has been unavailable. Enter the CycleOps PowerTap SL 2.4 Disc Hub, a new era in training for mountain bikers.

For those serious about training -- OCD numbers-lovers who salivate at the thought of spending hours analyzing ride data, and those brave enough to be humbled by comparing your watts per kilogram to the pros -- the CycleOps PowerTap SL 2.4 Disc seems like an ideal option. Needless to say, we fit the bill, and we were fired up when our care package arrived from CycleOps.

Physically the SL 2.4 Disc is a fully wireless power system that reads wattage, heart rate, speed and cadence all from the hub. No wires, no sensors, just lace the hub up in a wheel and mount the computer to the bar with a couple zip ties. This is accomplished by a 2.4 GHz transmission directly from the hub. There are batteries located in both the head and hub to power operation. From our experience with the road system, the computer head battery needs to be replaced every few months, and the hub batter probably once a year dependant on usage. You know it's time for a new battery when you notice the signal fading in and out.

The hub mimics its road counterpart in many ways, save for the proprietary 160mm rotor unit included when purchased. This very sharp looking, wavy stainless rotor is riveted to an alloy carrier that uses eight bolts to attach to the hub. We found the rotor to be not only extremely stiff, but offer excellent braking power. CycleOps included some small rotor shims that we used to properly space the rotor for use with our Formula disc brake caliper. This allowed us to match the spacing to our race wheel -- allowing us to swap wheels without caliper adjustment. The proprietary rotor can be purchased separately. But given its solid construction, we think the need for replacement will be unlikely. All said and done, the whole unit including the rotor weighed a mere 680 grams on our scale.

We laced our CycleOps PowerTap SL 2.4 Disc hub to a Stan's No Tubes Arch rim with DT Swiss Competition spokes -- identical to the wheel we've been riding save for the hub and rotor. We compared the weight of the two wheels to find just a 250 gram differential -- credit that to the DT Swiss 240s Disc hub and Formula rotor combination. So basically the CycleOps PowerTap SL 2.4 Disc adds a half-pound to your bike -- a pretty reasonable trade-off considering the training benefits.

We hammered the daylights out of our test wheel over the past few weeks, intentionally testing on the roughest sections of single track we have locally. While we did blow out a tire and flat spot the rim in the process, the signal continued to transmit consistently -- very impressive given our advance concerns. We experienced unusually heavy rainfall during our month of testing, and got caught in a few April showers. We had to forge through soupy trails and overflowing creek crossings. After each ride, we were happy and surprised to find the internals of the hub dry and tidy after removing the cap to check things out.

Uploading our data was a piece of cake. First, we downloaded the latest Power Agent 7.2 Software from the CycleOps website with ease. This took just a few minutes via our broadband connection. While it was downloading, we connected a USB cable to the PC and to the PowerTap head unit. When the download was complete, we opened the program, clicked on the "upload data" link and the upload process began. All said and done, the entire process took us about 15 minutes start to finish the first time through. Each upload thereafter took just a minute.

Power Agent 7.2 gave us multiple options for analyzing our ride data. With our sometimes macho, "How many watts you putting out?" tendencies, we especially liked having the ability to pinpoint our highest power output sections. We then related them to specific climbs and saved them with the interval function. While it was helpful for course strategy, this data will continue to be ideal as we compare our season-long progress, or for trying to impress our training buddies with our best efforts. We look forward to pre-riding a hot lap on race courses for which we're preparing and seeing in black-and-white what demands we need to train for -- 30 second bursts of power out of tight turns, longer 5-20 second threshold climbs, etc. Additionally the PowerTap data will allow us to track our progress as we prepare for these events, and check our race performance.

The CycleOps PowerTap SL 2.4 Disc hub lived up to our every expectation -- providing us the ultimate training tool for the dirt. We'll check back later in the year with regard to long-term durability, and how the data helped us to the state title.