How to choose the ideal potentiometer
Choosing the ideal potentiometer that is most suitable for our needs is not easy, and in recent years it has become a very common accessory on our bikes and is no longer an exclusive complement for professionals. This has mainly contributed to the decrease in the cost of the same as well as a growth of the options in the market that in recent times has seen the birth of many varieties of potentiometers of different typologies and, especially, of very different prices.
But, among all these proposals, which one should you choose?
1. How do they work?
First, let’s take a step back and try to understand how a potentiometer works.
In short, power is the result of the force applied to the pedals multiplied by the pedalling rate. Most potentiometers use sensors (called tension gauges) that measure torque in Newton per meter. The data obtained is cross-referenced in real time with the angular velocity and provides the power value expressed in watts.
What makes one potentiometer better than another?
The accuracy of the measurement. Clearly, we have to rely on the data declared by the manufacturers who, on the basis of the tests and analyses carried out, declare tolerances between 1 and 2% (therefore very acceptable for non-professional cyclists).
2. Types of potentiometers
The substantial difference between a potentiometer depends on the bike component on which the power is measured. Basically, there are 4 main types:
- For the chainring or steering stem
- For the crank
- For the pedals
- For the rear hub
2.1 Steering stem potentiometer
Almost 30 years ago, the first potentiometer to appear in the cycling world was the famous SRM, and it measured the power at the steering stem of the crankset.
Although it has improved over time, this system has essentially maintained the same way of measuring. Depending on the brand you choose, you may only need to buy the steering stem to fit the chainring if it is compatible. It is usually a very accurate measurement and provides, among other data, the balance between the right and left leg.
The disadvantage of this model is the assembly: unless you are an expert, you will have to contact your trusted mechanic. Also, considering the many frame standards on the market, a chainring purchased for one bike model may not fit a new frame.
Still on the subject of measuring power at the crankset, another popular system is the measurement at both cranks. It weighs little, provides a lot of data, and gives the power ratio between the two legs.
Finally, within this set are the crankset power meters that work on the crankset axle itself. In this case they have advantages and disadvantages similar to those of the steering stem. As in all the cases we are analysing, the aesthetic impact is practically null.
2.2 Potentiometer on a single crank
The gauge in this case is usually placed on the left crank and weighs very little.
The advantages of this system are:
- Low cost
- Easy to assemble
- Possibility to add the potentiometer, changing only the left-hand crank
The disadvantage is that the measurement will be done on one leg only, and then duplicated to get the total result. We understand that if there is a difference in strength between the two legs, the data will not be reliable. To avoid this problem, there are some systems on the market that measure on both cranks, but the cost is higher, and they have been mentioned in the previous point where we talked about chainring potentiometers.
Caution: in this case it is very important that you read the compatibility tables carefully to make sure that the crank is compatible with your groupset. There may be problems with a limited number of rear derailleurs and with frames where the rear brake is located under the bottom bracket. The increase in the thickness of the connecting rod, due to the measuring system, could interfere with the passage of the connecting rod itself in correspondence with the brake.
2.3 Foot pedal potentiometer
Currently the most popular system is the meter on the pedals.
The main advantages are
- Ease of adjustment
- Possibility to change them from one bike to another
In addition to the power and balance values, other interesting data on pedalling dynamics can also be obtained. For example, you can see the time spent standing or in the saddle, the angle of thrust at which the most power is expressed, whether the thrust is in the central area of the pedal or in the lateral areas. All very useful information to improve your cycling performance.
Not to mention the price, in this case it is in line with most power meters.
2.4 Hub potentiometer
The system of power detection at the hub is nowadays partially challenged by the development of new systems, but it is still a valid solution.
The detection is carried out by sensors inserted inside the hub, which measure the torque generated.
Obviously, the biggest problem is the weight of the wheel.
In this case we do find a small aesthetic change as this type of bushings are much bulkier. However, it is the most suitable system if you have several bicycles (with the same groupset) on which to mount it, as it is already mounted by simply changing the wheel.
2.5 Other potentiometers
There are also some meters that calculate power indirectly by cross-referencing a wide range of variables that measure the forces opposing pedalling, such as wind, slope, rider and bike weight.
In this case, 3 sensors are used (accelerometer, air pressure meter and altimeter) and complex algorithms ensure accuracy similar to that of traditional potentiometers.
Very easy to assemble, disassemble and change from one bike to another, they have their disadvantage in the initial adjustment operations. You have to enter a lot of data and set up different profiles in case you use it on different bikes. For example, you will have to enter the weight, and you will understand that, just by changing the wheels or increasing/decreasing the body weight you can falsify the data: in these cases, you will have to constantly change the data in the setting.
3. Other important things to mention
It is important to know the data transmission protocol: Ant+ and Bluetooth systems are currently the most widespread and compatible with almost all cycle computers on the market.
4. In conclusion
What we advise you to assess is:
- Value for money
- Amount of information provided
- Ease of assembly
- Compatibility and easy portability (if you have more than one bike)