One viewer of the Hambini YouTube channel sent in a bike for service and a new bottom bracket. This bike was fitted with a Rotor power meter crankset. In the process of making a new BB for this bike, the rotor crankset was measured and checked. This post covers the engineering and a general opinion of the construction. If you want a review of the Power meter accuracy, this will not be covered in this guide.
A hot topic in many internet forums is which power meter to get. This situation is muddied because of the varying axle and bottom bracket combinations that exist.
Introduction: Rotor Bicycle Components
Rotor are a Spanish company that have long been associated with cranksets and more recently entire goupsets. Their offerings have not always gone well. Their UNO groupset came out when there was a paradigm shift from mechanical to electronic and finally wireless shifting. It was left languishing and very few have been spotted out in the field.
Mechanically, this crankset represents a complete overhaul of the Rotor crankset system. Large elements have been copied from Shimano’s Hollowtech 2 system. Here are some of the mechanical bits in brief:
- 30mm Aluminum axle
- 90-92mm DBCA (Distance Between Crank Arms)
- Axial preload adjuster integrated into the non drive side crank arm.
- Single pinch bolt system for the non drive side crank arm
- Lightened aluminum alloy crank arms
- Accepts standard 130BCD rings and Q Rings
- This particular unit has an integrated power meter
This crankset is a different animal. From the outset it is well engineered
Geometrical checks were carried out to establish the true quality of the manufacturing. The axle appears to be pre-machined before a final grinding process on the bearing landings.
The diagram below is an approximation of the measurements taken. A is the datum, P and Q are measures of roundness and indicate the bearing landings. X and Y are run outs and they indicate the amount of bend, strictly speaking the runout at X is the same as the out of roundness of P
For all practical purposes, the runouts and deviation were less than 0.01mm which can be considered to be zero and thus very good.
Improved Preloading system
A common theme across bike cranksets is poor preloading systems. The displacement type preloading systems such as those used by Shimano are the best. Wave washers are effective but adequate knowledge and use of shimming is required to obtain the best performance. This is often beyond the scope of expertise of most amateur mechanics and even some bike shops.
This rotor crankset has a preload system which is a larger version of that found on the Shimano Hollowtech cranks. A preload bolt on the end of the non drive side crank moves the crank arm in and out and provides displacement level preload adjustment. This is easy to use and mechanically effective.
Installation into a Cervelo Frame with a Hambini Bottom Bracket
This crankset was installed into a Cervelo bike frame with a Hambini Bottom bracket. The final fit and finish were very good. No shimming of the crankset was required
This is a well engineered product. Rotor have really made some vast improvements, the quality of the machining and geometrical accuracy are amongst the best out there. If you are in the market for a 30mm crankset, then this is recommended.