This article was originally published on Kurt Kinetic's website. I have republished it here.
Kurt Manufacturing's fluid resistance unit is engineered not to leak and to replicate the feel of an outdoor ride. Here is how we do it. The roller, driven by your bike's tire, is connected to the impeller inside the sealed fluid chamber by a magnetic coupler. Twelve neodymiumrare earth magnets, 6 per side, create a virtual drive shaft to spin the impeller inside the sealed fluid chamber. Although the drive shaft has two parts, the magnetic coupler links the two parts and it spins as a single unit. The magnetic field is so strong; it can withstand the torque of suddenly accelerating the roller from 0 to 50 MPH with an electric motor. These magnets are not used for resistance, but only to couple motion across the leak-free barrier. Because there is no moving or rotating part penetrating the sealed fluid chamber, it just won't leak. Unlike competitive units, which are only warranted for manufacturer defects, Kurt provide a rock solid warranty for a lifetime of use.
All other fluid based trainers including those made by Cycle-Ops, Trek, Blackburn and Elite use a drive shaft and rubber seals to spin the impeller in the fluid chamber. This is simply a bad design doomed for failure. It is not a mater of "IF" the resistance unit will leak, but "WHEN" the resistance unit will leak. The more you use the trainer, the faster it will break. A Cycle-Ops is pictured below. As you can see, a drive shaft spins the impeller in the fluid chamber. Under extreme load, this drive shaft spins at 8,000 RPMs and the core temperature can reach 400 degrees F. A simple rubber " O- ring" with a backer spring is the only thing that keeps the fluid from leaking out of the resistance unit.
Using Crank Armstrong, Kurt Engineers can break a competitive trainer within several hours. Feedback from bike dealers confirmed that leaking fluid units are a major issue with " other" trainers. Below is a picture of Crank Armstrong, the newest member of the Kurt Testing Team. Crank is powered by a Dayton 3 HP electric motor, driving through a Boston 10 to 1 gear reducer, and connected to the non-chaining side of the bicycle bottom bracket. In this photo, Crank has a 207-pound"rider" and running at 25 MPH, adding mileage to the test resistance unit and checking the durability of our custom feet. After 96 hours of continuous riding (2297 miles), neither unit showed any signs of wear.
Bicycling Magazine, in their trainer review article, described one fluid unit as getting "blazingly hot". Kurt engineers designed our cast aluminum housing with over 80 cooling fins to dissipate the heat and keep the housing cooler, even at high wattage rates.In addition, we use specially selected thermodynamically neutral silicone fluid for resistance. At all temperatures, the liquid silicone will keep the same viscosity or resistance to flow. This means your resistance at the beginning of your workout will feel the same as resistance at the end of a workout. The Kinetic does not get easier as the fluid heats up. This is one reason the Kinetic Trainer maintains such a consistent ride and delivers the proper amount of resistance.
Kurt Quality Specialists used a Power-Tap hub to help calibrate the Kinetic trainer. Our goal was to exactly replicate the power required when riding outdoors under standardized conditions.On an outdoor ride, resistance grows exponentially with speed. When you double your speed, the resistance from wind is cubed. [Note: Drag is proportional to speed (v) squared; therefore with speed doubling, drag increases by a factor of 4.]
The Kinetic Trainer delivers the same resistance on your indoor rides. When you increase cadence or shift to a higher gear, pedaling gets more difficult. The Kurt Kinetic has a functional range from 20 watts(5MPH) to over 3,000 watts (50 MPH). The power chart below compares the speed and power requirements for an outdoor rider with those for an indoor rider on a Kinetic trainer.
If you add your average speed to this equation, you can calculate your average power.
[5.24482 x (Ave. Speed in MPH)] + [0.0191676 x (Ave. Speed in MPH)³]= Average Power
Kurt Manufacturing is the most innovative trainer maker in the industry. Kurt was the first bike trainer to accommodate a wide range of bike types and wheel sizes: Road, track, mountain, BMX, kid, and recumbents with wheels from 29" down to 16" OD. The standard Kinetic fits rear wheels 22" thru 29". Our patented small wheel adapter extends the range to cover 16" to 22".
The Kinetic trainer's folding legs also adjust for three wheel sizes, road, mountain and BMX. Settings of the legs allow raising or lowering the axle mount height and keep most wheels within 1.5 inches from the floor. This results in a more natural "level" riding position without front wheel riser block. A Kinetic Trainer is shown below with the Small Wheel Adapter installed and legs in third position for 20" wheels.
The Kinetic frame is robotically welded to be perfectly level. Unfortunately,most floors are not perfectly level. Our custom designed non-marring PVC feet absorb the irregularities in a typical floor. The Kinetic's trapezoidal footprint is the largest in the industry and maintains stability of rider and bicycle even in a "stand-up sprint". A quick release lock enables the user to quickly attach or remove the bike from the trainer. The frame's large OD steel tube frame is powder coated for extreme durability. It also folds in half for easy off-season storage.
The Kinetic Trainer has custom cone cup kits to accommodate for track bikes with double nutted axles, high end Ti bikes with breezer dropout and SRAM Dual Drive hubs with internal shifters.
Kinetic Manufacturing continue to perform destructive testing on the Kinetic trainer.Running at average of 25MPH, one resistance unit has logged over40,000 miles at up to 50 MPH with no leaks or breakdowns. The engineers believe it would run over 100,000 miles without a problem.