I emailed Kinetic and asked them how many "turns" they used on the tensioning dial/knob when they set up their formula for calibrating the Cycle-ops trainers speed/power. Below is their answer, and they throw in tons of other great stuff too that all trainer riders should know!
Carl went way out of his way here and I appreciate it. Yes indeed Kurt is know for their great customer service!
Sorry in advance for the long answer. I am guessing you believe the amount of "turns" changes the resistance.
The amount of pressure between the tire and roller needs to be at 100% friction to eliminate slipping. If the tire slips at thigh speeds, the force curve is invalid. On most trainers, there is less than 10 watts of resistance difference between the 2 complete turns and the 5 complete turns of the tensioning knob. So once you achieve 100% friction, adding additional pressure between the tire and roller has no impact on the resistance level. At extreme levels of pressure like 15 turns the tire / roller pressure can have a impact on the force curve,
The amount of friction between the tire and roller is also affected by the tire width, tire pressure and tread pattern with a slick being the best.
With regard to the "turns" for the Cycle-Ops during the calibration, we used the same for every trainer. Since we were evaluating the trainers at higher speeds, the tensions was between 3 to 5 turns.
The wild card in the calibration is your Cycle-Ops Trainer. Please read the information pasted below. Armed with this information, you will need to select a course of action that best meets you training needs.
Here are the facts.
First, your Cycle-Ops Fluid 2 is a hybrid trainer with wind (from the cooling fan) and fluid both providing significant resistance. This requires multiple formulas to predict the force curve. For the record, there is no perfect method yet established to absolutely measure power of a rider on a bike. The SRM and Power-Tap are estimating the power output of a rider with an error of approximately + / - 3% . Other power measurement tool are off by up to 30%. Frankly, with all the variables involved, 6% variation is pretty good, but it is not a perfect science and has room for improvement.
Second, Saris / Graber, the manufacturer of the Cycle-Ops Trainers has been removing fluid from the unit to minimize leaking and fine tune the force curve. This is why the maximum resistance has changed and is now listed at only 725 watts. When a manufacturer changes their design specifications, and does not inform the public , we have no way to update our tools. Ask Cycle-Ops to provide you with the force curve and ride / rider specification that they are based upon. They will not provide Kurt with this information. For the record, the Kinetic fluid line of trainers has a force curve based upon a universal rider who weighs 165 pounds with a 23 pound bike, with 0.7 square meter frontal area, at sea level, going up an average of 1% grade on rough asphalt road, neutral or zero wind, 170 mm cranks and several other variables which are not really significant.
Third, the fluid in your Cycle-Ops is not thermodynamically neutral. The fluid gets thinner as it gets warmer and even thinner when hot. This further reduces the resistance and sets multiple force curves, based upon temperature. In short, your Cycle-Ops fluid 2 trainer has a temperature variation in the force curve. We can not mathematically reproduce a force curve with a variable that is not measured. Therefore, the formula created for the Kinetic PC for the Cycle-Ops fluid 2 is a best guess estimate based upon fluid temperature warmed up fro 10 minutes at 20 mph. Kurt's Kinetic line of fluid trainers use thermodynamically neutral liquid silicon to provide the resistance. the fluid maintains the same thickness or resistance to flow at all temperatures. The temperature of the trainer is also effected by the design of the fluid housing. Kurt's fluid trainers have 80 cooling fins and an low velocity internal air channeling system that effectively cool the unit to maintain safe operating temperatures. The Road Machine after 20 minutes at 20 mph will have a temperature of 125 degrees. All other fluid trainer run hotter.
Forth, the Kinetic PC, like all bike computers made, only measure wheel rotation. If a user accurately measures there wheel circumference, it will accurately calculate the ride data like distance. Combining the distance data with a clock / stop watch function, the bike computer can calculate average, current and maximum speed. Ride time is a clock function and odometer is a distance function. Kinetic Trainers have measurable and repeatable workload, so we can graph the force curve and generate a formula that for the Kinetic PC to display power output in watts. With other trainer brands, we do our best to estimate the power based upon the limitations of their products.
If this estimate of the power output on a Cycle-Ops Trainer meets you training needs, keep the computer. If it does not, replace your trainer with a Kinetic.
http://www.kurtkinetic.com/computer_tech.php?osCsid=b6025ebb43483b1eab82b8775848d4b4
http://www.kurtkinetic.com/calibration_chart.php
http://www.kurtkinetic.com/powercurve.php
I am interested in your response to the above information and look forward to your call or reply. I would be interested to know what support you get from Saris / Graber / cycle-Ops. My contact information is listed below. Feel free to call later at night for I take calls until midnight CST.
Thanks Carl
Carl Gulbronson
Kurt Manufacturing
Carl went way out of his way here and I appreciate it. Yes indeed Kurt is know for their great customer service!
Sorry in advance for the long answer. I am guessing you believe the amount of "turns" changes the resistance.
The amount of pressure between the tire and roller needs to be at 100% friction to eliminate slipping. If the tire slips at thigh speeds, the force curve is invalid. On most trainers, there is less than 10 watts of resistance difference between the 2 complete turns and the 5 complete turns of the tensioning knob. So once you achieve 100% friction, adding additional pressure between the tire and roller has no impact on the resistance level. At extreme levels of pressure like 15 turns the tire / roller pressure can have a impact on the force curve,
The amount of friction between the tire and roller is also affected by the tire width, tire pressure and tread pattern with a slick being the best.
With regard to the "turns" for the Cycle-Ops during the calibration, we used the same for every trainer. Since we were evaluating the trainers at higher speeds, the tensions was between 3 to 5 turns.
The wild card in the calibration is your Cycle-Ops Trainer. Please read the information pasted below. Armed with this information, you will need to select a course of action that best meets you training needs.
Here are the facts.
First, your Cycle-Ops Fluid 2 is a hybrid trainer with wind (from the cooling fan) and fluid both providing significant resistance. This requires multiple formulas to predict the force curve. For the record, there is no perfect method yet established to absolutely measure power of a rider on a bike. The SRM and Power-Tap are estimating the power output of a rider with an error of approximately + / - 3% . Other power measurement tool are off by up to 30%. Frankly, with all the variables involved, 6% variation is pretty good, but it is not a perfect science and has room for improvement.
Second, Saris / Graber, the manufacturer of the Cycle-Ops Trainers has been removing fluid from the unit to minimize leaking and fine tune the force curve. This is why the maximum resistance has changed and is now listed at only 725 watts. When a manufacturer changes their design specifications, and does not inform the public , we have no way to update our tools. Ask Cycle-Ops to provide you with the force curve and ride / rider specification that they are based upon. They will not provide Kurt with this information. For the record, the Kinetic fluid line of trainers has a force curve based upon a universal rider who weighs 165 pounds with a 23 pound bike, with 0.7 square meter frontal area, at sea level, going up an average of 1% grade on rough asphalt road, neutral or zero wind, 170 mm cranks and several other variables which are not really significant.
Third, the fluid in your Cycle-Ops is not thermodynamically neutral. The fluid gets thinner as it gets warmer and even thinner when hot. This further reduces the resistance and sets multiple force curves, based upon temperature. In short, your Cycle-Ops fluid 2 trainer has a temperature variation in the force curve. We can not mathematically reproduce a force curve with a variable that is not measured. Therefore, the formula created for the Kinetic PC for the Cycle-Ops fluid 2 is a best guess estimate based upon fluid temperature warmed up fro 10 minutes at 20 mph. Kurt's Kinetic line of fluid trainers use thermodynamically neutral liquid silicon to provide the resistance. the fluid maintains the same thickness or resistance to flow at all temperatures. The temperature of the trainer is also effected by the design of the fluid housing. Kurt's fluid trainers have 80 cooling fins and an low velocity internal air channeling system that effectively cool the unit to maintain safe operating temperatures. The Road Machine after 20 minutes at 20 mph will have a temperature of 125 degrees. All other fluid trainer run hotter.
Forth, the Kinetic PC, like all bike computers made, only measure wheel rotation. If a user accurately measures there wheel circumference, it will accurately calculate the ride data like distance. Combining the distance data with a clock / stop watch function, the bike computer can calculate average, current and maximum speed. Ride time is a clock function and odometer is a distance function. Kinetic Trainers have measurable and repeatable workload, so we can graph the force curve and generate a formula that for the Kinetic PC to display power output in watts. With other trainer brands, we do our best to estimate the power based upon the limitations of their products.
If this estimate of the power output on a Cycle-Ops Trainer meets you training needs, keep the computer. If it does not, replace your trainer with a Kinetic.
http://www.kurtkinetic.com/computer_tech.php?osCsid=b6025ebb43483b1eab82b8775848d4b4
http://www.kurtkinetic.com/calibration_chart.php
http://www.kurtkinetic.com/powercurve.php
I am interested in your response to the above information and look forward to your call or reply. I would be interested to know what support you get from Saris / Graber / cycle-Ops. My contact information is listed below. Feel free to call later at night for I take calls until midnight CST.
Thanks Carl
Carl Gulbronson
Kurt Manufacturing
