Finally decided to take some screen capture of some of my CompuTrainer sessions with 3 different set ups and report on the results.
I have been riding Rotor cranks for about 6 years and only recently switched my crankset with Dura-Ace 7900 while doing my Shimano Di2 Group Set evaluation and article. (appearing in the Triathlon Club of San Diego April Newsletter)
Here are some of my Lab result and comments. Shown are Computrainer’s Polar and Bar Graphs (click to enlarge)
Shimamo 7900 cranks/Standard Chainrings
The Good: Allows for perfect shifting, no chain rub or cross ever, able to use every gear.
The Bad: Excessive muscle fatigue (more lactic acid build up), elevated HR, reduced endurance, requires more caloric intake. If you don’t know about Rotor products you will not know there better options out there.
SpinScan: 75 /74 — ATA: 100/101 — Power balance: pretty even — HR: not accurate
Rider feedback: To maintain this SpinScan value a lot of effort and concentration on pedal stroke technique is required. Muscles are working hard, I would not be able to keep this effort (180 to 190 watts) up for a long time. Muscles would tire, and heart rate will be elevated.
Stronglight cranks w/Rotor Q Rings (mountain bike)
The Good: Removes most of the “dead spot”. Requires less concentration on pedal stroke to maintain efficient pedal stroke values. Reduced heart rate, reduced lactic acid build up.
The Bad: Set up of front derailleur is crucial an sometimes tough to get right. If not set up correctly, chain ring may rub on derailleur and/or excessive chain cross over.
SpinScan: 71 /76 — ATA: 103/98 — Power balance: Even — HR: 110
Rider feedback: Muscles are much more relaxed, would be able to keep this effort (150 to 180 watts) up for a long time. Heart rate seems lower due to less muscle strain. Body and legs feel better than Standard Chain Rings. Notice the more even transition from one color bar to the other… smoother than standard chainrings, also notice oblong circle; less pinch in the middle. that means more torque/power on the back side of the pedal stroke being applied (faster).
Rotor RS4X Cranks
The Good: OMG! my legs few so good – no dead spot! Pedaling is so smooth and effortless. My run will be much easier and better.
The Bad: I do not have full use of gears. I get chain rub when my I use small chainring and last 2 cassette gears. WIth the Di2, the auto trimming does great. It is the design of the back side of Rotor’s large chainring that is not truly compatible.
SpinScan: 77 /81 — ATA: 95/94 — Power balance: Pretty even — HR: 103
Note the almost perfect circle, no pinching in center) meaning very efficient pedal stroke (muscle usage/torque very well balance all around the pedal stroke), and an even smoother transitions from color bar to bar, ATA very close to 90 degrees (which is perfect).
Rider feedback: No strain on muscles, would be able to keep this effort (150 to 180 watts) up even longer. Heart rate even lower due to less muscle strain. Do not have to think about pedal stroke and these are my results. I can get SpinScan up to 92 but extra effort is require but not worth the extra strain on muscles and HR. Of the 3 set up my legs feel best with this set up. Less muscle strain on bike means easier and faster run… muscles last longer!