Sigma Rox Bike Computer

Unboxing: The Sigma Rox wireless bike package offers a lot of details to discover, which in turn require a lot of know-how in the installation of radio technology


Originally, I just wanted to move my wired sigma bike computer BC 8.12 forward with a stem butler to get a better view of the data.
However, it became a real bicycle craft project. It started with that old speedometer not in the Stem mount 2450 fit. So she first disappeared half a year in the drawer with my other bike parts. However, the stem bracket fit for the older Sigma Rox series 5.0 to 9.0 and last winter there was then an irresistible special offer: A technically dusty Sigma Rox 5.0 bike computer with all imaginable accessories for unbeatable 64, - EUR - Brand New!

These included a cadence counter, a heart rate counter with strap, a holder for the handlebar and a wrist for jogging and all, necessary attachments for various types of bicycles. Although I'm actually more against the installation of computer junk, Perma GPS and cyclist Tamagotchies, which you have to take care of like little kids all the time, I persuaded my inner bastard without much effort to buy.

Why do I have to buy a wireless bike computer after years of wireless abstinence on the bike?


  • The already purchased handlebar mount would fit and allow me a much better cockpit ergonomics than before
  • Sigma speedos are known for easy-to-use cycle computers with good value for money
  • Heart rate, performance areas and calorie consumption would be extremely interesting as values ​​after years of training
  • A slightly increased, deliberately trained cadence would make me feel better in the mountains in the future
  • I would not have to wire the whole Messkram, but he would only temporarily attach to the bike
  • The old speedometer with the cable could initially remain mounted as security
  • Wireless computer networks and the Internet have also proven their worth in everyday life
  • If the bike computer is not good for the road bike, I simply mount it to my commuter wheel
  • At the price, I can resell the Sigma complete box also needed

All killer arguments. Nevertheless, I somehow did not feel really good about buying my first wireless bike computer including four coin cells. And that should be confirmed.

The radio transmission of bicycle computers is still causing everyday physical problems

Sigma Rox 5 compared with Sigma BC 8.12

Both speedos show exactly the same values

After unpacking and clipping all parts of the Rox 5.0 for the first test ride in the freezing spring 2018, disillusionment and fascination set in simultaneously. The computer was easy to read, showed exactly the same results as the still-installed, wired Sigma BC 8.12. Unfortunately, the transmission of the cadence did not work. Not even if I fixed the transmitter very close to the magnet of the pedal crank. In addition, the system required a total of 4 button cells.

Sigma Rox stem mount / butler conversion

Conversion of the Rox stem mount

After I noticed that the transmission of the tacho signal occasionally turned out to be short, I decided to reconnect the speed signal, which was absolutely important to me, with a cable. Although there is a matching base plate from Sigma with a classic wired pulse generator, but unfortunately does not fit on the stem extension. Incidentally, I noticed later that the failed speed signal often occurred when driving under high voltage pylons. Unfortunately, I had hardly won anything over my old computer.

Conversion Sigma speedometer bracket

Only 4 holes need to be drilled in the bracket

So I optimized the whole bike computer system a little to my expectations. In order to connect the instrument boom to the sigma cable base plate, in addition to some carving with the cutter, only four small 1 mm holes had to be drilled. With feeling, the slightly warmed-up sigma plastic boom can then be bent around the road handlebar without disassembling the bicycle brake handle or handlebar tape and fixed with a single screw. Fits exactly and holds the sigma computer vibration-free on the handlebar.

Tag Sigma Computer Mount Rox outrigger

Where planing is done, ... any slightly fuzzy screw of the instrument carrier will be immediately negative. You will surely rust later!

Above the ready-modified instrument carrier with the wired base plate. Only the black screws reveal the do-it-yourself measure when the speedometer is removed, otherwise it looks like it was bought at the store. If you set the upper contact bolt in the socket underneath, this defines the corresponding bicycle name wheel 1 or wheel 2. The beauty of this wired bike computer system is:

The rebuilt Sigma Rox mount

All Tachogeberfunktionen funz even when cycling in the crowd with multiple radio tachos absolutely worry-free - even on e-bikes and when driving through strong sources of interference. I save the replacement of a button cell of the encoder with a special tool. However, I have honestly built this with bracket on my commuter wheel. So I can also test the calorie consumption here if necessary. The good, old bike computer remains permanently attached to this bike.

Sigma Rox with wired transmitter and stem extension

Sigma Rox with boom fully assembled

The speedometer is now finally centered centered on the road handlebar. The approximately 12 cm long instrument boom makes the view of the bike computer immensely easier. You can easily read the values ​​without head distortions and keep the road halfway in view. The big numbers of the Rox 5.0 are very easy to read. In addition, they can be lit at night. In freezing weather, they are a bit sluggish, but everything works reliably. Even a suitable thermometer is installed. The heart rate transmitter on the chest belt works without failures. In very few cases, it was necessary to once approach the bike computer with the folded transmitter belt to a few centimeters to trigger an initial synchronization. Fortunately, this happily worked automatically the first time the heart rate sensor was flipped, even though the bike was still parked.
However, the sigma cadence transmitter did not work properly until the end of all reconstruction work. Probably the transmitter's wireless path to the bike computer is just too long. Also, from some experiments with closer installed speedo, I was not smart at first, more on that later.

Sigma Rox with stem mount and cable harness in the shrink tube on the handlebar

Stem holder with wired computer

Without the feather-light Liteecco LED headlights unfortunately you can still see the remains of the ample cable, which is also suitable for mounting on extremely high bicycle handlebars. I have not cut it first, to eliminate sources of error. To visually clear up the cable tangle, it was simply plugged into a thick shrink tube and this heated slightly. The small headlamp visually obscures everything - at least from above.

LED battery light disturbs Sigma Rox bicycle speedometer

LED lamps and radio tachos are often incompatible

A known source of error in wireless bike computers is the lack of compatibility with LED lights. Often the receiving frequencies of the bicycle computer with those of the LEDs are superimposed and interfere with the receipt of the tacho signal. The phenomenon is under the keyword "Electromagnetic compatibility" short EMV explained. Something similar happens with electric and small motorcycles or motorcycles, because of the resulting electrosmog on motorized two-wheeler. Here I would always prefer a wired bike computer.

To avoid EMC problems on the bike, there are four possible solutions:


  1. Mount bicycle computer and LED headlamps as far apart as possible, or simply replace the position as a test, eg mount the headlamp on the right instead of to the left of the speedometer.
  2. Additionally shielding the LED light: There are folding ferrites that are subsequently clamped around the cables in the battery lights, but usually there is not enough space. A lining of the lamp housing with aluminum foil may possibly help in individual cases, if one manages to accomplish this without short circuit. Simulate the aluminum shield from the outside.
  3. Buy a compatible set of bike computers and headlights or try them out at the bike shop. With the newer Sigma Rox computers the EMC problem occurs according to forums only rarely.
  4. Immediately use a wired bike computer

Sigma Rox standard bracket

The included Sigma standard mount is ok, but you can not expect ergonomic high performance

Above, the Sigma Rox 5.0 computer with the original mount wirelessly mounted to my commuter wheel. The wireless tachometer signal transmitter I now had for a second bike over. The heart rate transmitter remains on the body and I renounce the cadence on this bike. The transmission of data is automatically as a "second bike" by the speed sensor is simply switched to the second-wheel mode. Both data pools remain cleanly separated from each other in just one bike computer, but can also be displayed as an aggregate: total kilometers, total calories, total time, and so on.

Cadence counter Sigma Rox 5.0 on chain side

Sigma cadence counter on the chain side

At first I mounted the Sigma-Rox cadence transmitter on the chain side, hanging downwards. There he was less noticeable. Unfortunately he did not work there at all. Only after I have a bigger and ultra-strong 10 mm neodymium magnets Instead of attaching the magnet to the pedal axle, the cadence counter started to work. Unfortunately, on the chain side, this meant that the (iron) chain was no longer running smoothly due to the magnet's strong magnetic attraction. The rotating magnetic force on the crank actually changed the chain escape.

Cadence transmitter Sigma Rox and and magnet on the crank

"Magnet-Tuning" on the cadence transmitter

So I installed the transmitter standing on the left rear strut. So the radio path to the bike computer was a bit shorter and now works reasonably reliable. It is important that the distance of the ultra-strong pulse magnet is as close as possible to the transmitter. If I turn on the LED light on the road handlebar, the cadence is unfortunately no longer displayed. But I can live with that, because the other channels all work. Only the cadence is no longer recorded in the dark or in the winter.

Battery replacement of the bike computer will preserve the data

The Sigma Rox computer receives the data when changing the battery

The first lithium battery type CR2450 of the Sigma-Rox-5.0 bicycle computer has only lasted five months with me. Probably it was already at the purchase no longer dewy, since it already in the package (since 2013?) Was activated. How long the box has been in the store before buying in standby mode, I do not know. Maybe a few years, because the model Rox 5.0 is already a bit old. Meanwhile, there is the Rox 12.0 with map GPS for just 500, - EUR ... Changing the battery is very comfortable with the Rox: All data is retained except for the time. It is the first cycle computer in my life that does not forget the data immediately after a short interruption of the power supply! After all, here are the values ​​stored by two bicycles. And there are a lot of them. The loss is very annoying in everyday cycling. Speaking of which: By the way, there is also a USB docking station for very little money for this older model, with which you can put the data in the free Sigma Datacenter on a PC, Mac or tablet. The synchronization has not worked for me after several trips in a row (good). It was always synchronized only the last bike ride. The Datacenter itself I find for Ottonormalradler in everyday life a bit oversized and above all confusing, but I'm not a cycling coach and can not allow me a judgment.

All in all, with a lot of tinkering, I rebuilt my sigma cycling computer dream package to work very well for my needs on two bicycles. Only the shielding of the LED lighting for a smooth cadence with the light on would be worth a try.

Wireless wireless bike computer tips and tricks

Conclusion: What should be considered when buying and installing wireless bike computers?

Obviously 2018 also a lot ...


  • Originally, I just wanted to install my simple bike computer as far forward on my handlebar stem. Regardless of the make and the question of whether wireless or wired, I can now make a statement with certainty: A far forward-facing bike computer boom is ergonomically worth every bike handlebar gold.
  • Wireless cycle computers are usually not (yet) suitable for electric bikes, e-bikes, pedelecs and two-wheelers with combustion engines.
  • The wireless radio technology on the bike is constantly being improved, but there are still EMC problems with the simple combination of a wireless bicycle tachometer with activated LED battery headlights. Typical scenario: "All I want is battery light and a reliable bicycle speedometer!" Oh a gap in the market?
  • Also problematic with wireless bike computers are cycling tours with several cyclists / inside at the same time in the group (peloton) when the radio frequencies overlap.
  • LED headlamps and wireless bike computers should be mounted as far away from each other as possible
  • Total mileage, daily mileage, current speed and time should always work under adverse circumstances.
  • Every cleanly laid cable on the bike is therefore still better today than a fault-prone radio link
  • Weak, externally mounted radio transmitters, such as the cadence transmitter, which receive a not sufficiently strong magnetic pulse, can function reliably with stronger neodymium magnets.
  • The Sigma Rox 5.0 was 2013 safe at the height of its time. He had a good price-performance ratio, but now the technology is outdated. The ability to connect all the important tachometer functions with a permanently installed encoder cable, however, still makes the appeal today. It works - under all circumstances!
  • An expensive bike computer can often be used for two bicycles that are not operated in parallel.
  • Wireless cycle computers consume many lithium button cell batteries even in low power standby mode. Therefore, pay attention to as few as possible, equally and easily available battery types and to a possibility of changing the batteries without complete loss of data. Button cells cost the Internet by mail often only a fraction of the supermarket price!
  • Smartphones are much more advanced: they can fully replace a cycle computer including state-of-the-art GPS navigation. Unfortunately, they are very sensitive, extremely energy hungry and light stolen goods. I was on a bike ride times my bike with a smartphone on the handlebars in a sudden gust of wind overturned. For an iPhone, that would have been at least 500, - Euro.
  • In the blazing sun smartphones, especially in bags with transparent display window extremely hot and then often fail permanently. Even with a light drizzle, they also quickly refuse service without a waterproof bag. But even so, an old smartphone with a few, but useful, handlebar-based bike apps is probably the best performance GPS compromise you can make when you want to spend as little money as possible. A paired Bluetooth heart rate monitor or a simple smartwatch measures the pulse and calculates the calories without cadence. That's the way it goes, of course.
  • Modern smartwatches are constantly being developed and certainly optimized for cyclists individually. So far, I've never met anyone who is absolutely convinced of the clocks when cycling. But it is still worth keeping a watchful eye on the market development here. Anyone who has already gained experience with a good smartwatch on a bicycle can write to me.

Supplement February 2019:

EMC shielding of a bicycle lamp with metal foil

EMC shielding of a bicycle lamp with metal foil

Self-built inner shield of a LED bicycle headlamp with copper foil to protect sensitive tachometers and treadmill and heart rate sensors against EMC problems. Metal foil in housings increases the electromagnetic compatibility. Whether the cadence sensor now works with the light on, I still have to test. The idea and the implementation with the copper foil as an experiment comes directly from the manufacturer Litecco, The lid is not available for purchase.

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