Site menu:


Site search

Sigma Rox 9.1 – Initial Review and Thoughts

The posts and reviews I’ve written about my experience using a Sigma Rox 9.0 have been very well received over the past year or so.  (Check those posts out here for some background.)  I noticed that Sigma has recently released the Sigma Rox 8.1 and the Sigma Rox 9.1–two new units in the Rox range. Since there seems to be some interest in these computers, and little discussion (at least in English,) I thought I’d take a quick look at the features of the new units and provide my thoughts.

Sigma Rox 9.1

Sigma Rox 9.1

Note that I don’t actually own one of the new units, and haven’t even handled one (test units appreciated!) but will evaluate them based on my experience with the Sigma Rox 9.0 and the feature set I have found on the web for the new units.

To start with, the Rox 9.1 and Rox 8.1 look very similar to the old 8.0 and 9.0. No major changes in form-factor or controls that I can tell. I assume the mounting hardware, cadence and speed transmitters, and heart rate strap are all the same, so not much to comment on there.

New Features:

Unlike Apple, Sigma decided to add new features to their new product! (I know, I know, low blow post-iPhone 4S announcement.) Here are some of the noteworthy upgrades, and my comments on each.

Power: You can’t put out a high-end cycling computer and be competitive in the current market without including power. Unfortunately, Sigma chose perhaps a poor approach to adding power; they didn’t make the Rox 9.1 ANT+ compatible. This means you can’t link the Rox 9.1 with your SRM or PowerTap, or multitude of other ‘open’ devices. Sigma didn’t even make it W.I.N.D. compatible like the Look Power Pedal, which talks to Polar head units via the proprietary, and likely doomed-to-fail-because-of-it W.I.N.D. standard. (On a side-note, why don’t we all just move to Bluetooth and get along?!?) No, Sigma chose to go a similar route as the iBike, calculating power from some magic formula, not from strain gauges or other ‘direct measurement’ approach. According to Sigma, this magic formula to calculate power takes into account:

Bike type and position, bike and rider weight, rider height, shoulder width, speed, incline and cadence.

Of course, these factors:

can be affected by external forces such as the ground conditions or wind.

it looks like some of this has been taken into account during the calculations, as Sigma claims that:

These factors are reduced during mountain ascents and considered in the calculation.

Great. However, without some way to know the wind speed, you are reducing an unknown by an unknown. And even if wind speed was measured, what about when drafting? What about on a gravel road? What about with a knobbier tire…? There are just too many factors to accurately take into account. These issues are why the iBike has never really caught on, despite having a much more attractive price-point than other power meters. It just simply doesn’t work as well.

Having said all of that, the real question is; just how accurate is the power number calculated by this magic formula? I’d love to see some head-to-head tests that show it is within 1 or 2% of an SRM or PowerTap, but even the iBike had trouble with that, despite measuring much more than the Sigma will (wind speed, etc.) Again, I’d love to be proven wrong here, as we need an inexpensive, relatively accurate power meter for the masses!

Expansion: Another new feature is the inclusion of “Expansion” as an on-screen option, and a value recorded in the logs. What the heck this means isn’t clear from the name (perhaps German speakers would understand the translation thought process a bit better?) Essentially, it appears to be a term for what we would call “gear inches” or “meters of development” – essentially, how far you travel in one pedal stroke. Interesting to know, but… how applicable this is in your on-the-bike riding, or post-ride analysis, I’m not sure. I suppose it would be good for new riders to show overlap between gears? I’m assuming it’s calculated by taking into account your current cadence and distance travelled. No magic there.

Ghost Race: Perhaps the neatest and most useful of all the new features is (in my opinion) what Sigma is calling “Ghost Race.’ It’s the same concept as Garmin’s “Virtual Partner” – where you can load in a previous workout on the same course and then ‘race’ your previous effort. This (aside from being fun) I can see as a great way to push yourself just that little bit more in a Time Trial or similar situation. I bet I could make good use of it in my 40km Project! :)

Existing Issues:

We all know new features are great, but did Sigma take care of the existing issues with the unit before adding new ‘bling’? Lets see! Here are some of the issues I commented on that bug me about the Sigma Rox 9.0. Have they been addressed in the 9.1?

Durability: If you recall, my 9.0 has issues with ‘scuffing’ and paint chipping. It’s hard to tell if the new units addresses this issue. I sure hope so; a scruffy looking computer on a nice shiny bike is not a good look, no matter how cool the computer is!

Battery Life: The Sigma website lists the battery life as one year. This matches my experience with the Rox 9.0, and leaves me … unimpressed. A rechargeable battery would be nice, but may bump up the price point.

Resetting Distance: Again, hard to say if this issue has been corrected. I suspect it is a software glitch to begin with, so probably independent of the unit itself.

Heart Rate Zones: There are still only three heart rate zones. It seems like such a trivial matter to add 5–why not? Pretty much every heart rate monitor I’ve ever seen has five zones…

Saving Cadence: It appears that the Rox 9.1 may save cadence to the log. Under “Data Center Functions,” the feature list shows “Graphic display of the cadence,” so it appears that the data may be saved to the logs.  However, under the “New Memory Values” section, it lists only “Average power, maximum power, average expansion, average expansion uphill” as additions- no cadence.  So the jury is out on this one. I hope it’s there!

Log Saving Interval: Still no 1-second saving option. Again, since this is user-selectable, why not? If I am going on a longer ride, or know I am low on memory, then I could set it to 5 or 10 seconds. But if I know I am going for a 2 hour ride, and will be downloading immediately after, why not give me an option to record every second? Silly.


Without seeing and using one of these units (again, test units appreciated!) for at least a year, it’s really hard to say just how good it is. However, it appears that Sigma have added a couple of arguably less-than-useful new features (Power, Expansion) and one neat, but not groundbreaking one (Ghost Race) to their existing unit. With the competition that’s currently out there, I’m not sure the Sigma has a real value-equation working for it. Unless, of course, they’ve magically figured out the power calculation and the results are good, in which case this is a huge winner. Am I holding my breath on that? No. And I doubt you should either.

Having said all of that… the best thing to do is check it out yourself on the Sigma Rox website, and see what you think! If you can get a hold of a unit, give it a thorough test–I’d love to hear any comments from you below!


Comment from Alan Walker
Time November 19, 2011 at 2:38 am

The power calculation on the 9.1 seems a good feature combined with the ghost rider. Have you tried the 9.0 version on an indoor trainer as the polar W.I.N.D speed sensor can transmit from rear seat stay to head unit as does the VDO Z series which also offers power calculation and uses ANT+. I am currently looking for a unit which offers a low cost way to measure power both indoors and out but cannot find any info on the Sigma site re the range of speed sensor. I am drawn to the 9.1 but cannot find any mention of this or the 9.0 being used to measure or record indoor sessions.

Comment from Claudio Pompili
Time November 28, 2011 at 4:13 pm

Hi Alan
I’ve had my ROX9.0 for about 2.5yrs. As per the review, I’m very fond of my ROX but it has some glaring shortfalls. I’m now looking at upgrading to the 9.1. I’ve been using my 9.0 on my bike trainer all along. I’ve done a lot of playing around but the speed sensor transmission distance/angles to the head unit are critical. I have a rear wheel magnet installed on the spokes and temporarily attach my second head unit mounting bracket to the top tube, about 1/3 of the way towards the seat. The speed sensor on my Malvern Star Oppy C5 I mount to the under-side of the seat stay near the brakes. It’s not ideal but functional while I’m training. If I sit upright when resting, the HR monitor drops out because of angle. Otherwise, works OK. I too would have liked to see ANT+ compatible to attach power meters etc but no luck with 9.1. And really keeping my finges crossed that cadence is included in logs. I notice too a backup internal chip and up to 90hrs logging. It would have been great if there had been a miniSD card so that I could log long distance Audax rides up to and beyond 90hrs at 5sec intervals but alas not

Comment from Robert Grant
Time December 14, 2011 at 10:47 am

Based on the Sigma pdf for Data Center 2.1, it appears that the ROX 9.1 will transfer to SDC 2.1 the new power function as well as the cadence function along with the other familiar values of speed, HR, etc., for a total of ten functions viewable in the Log graph. Expansion is not included in this group. This is only a ROX 9.1/SDC 2.1 combined feature. Coupled to a ROX 9.0, the 2.1 software does not allow logging of cadence.


Comment from darrencope
Time December 14, 2011 at 11:42 am

Robert; great, thanks for the information!

Comment from Robert Grant
Time December 19, 2011 at 10:52 pm

When messing with the Rox 9.1 demo feature on the Sigma web site, I noticed that cadence does not affect power. In fact, at zero cadence power is the same as 120 rpm! I suspect that the unit will only be accurate when climbing.

Pingback from DARREN COPE » 2011 – The Year in Review
Time February 21, 2012 at 9:44 pm

[…] Sigma Rox 9.1 – Initial Review and Thoughts […]

Comment from Zmago1
Time July 16, 2012 at 4:37 pm

Only speed and incline seems to have impact on power and supposely weight?! Cadence and heart rate are not taken into account,… I really wonder how wind is taken into account? On climbs below and including 7% wind is crusial factor!

Comment from Reeder
Time July 30, 2012 at 6:10 pm

Anyone having issues with the ROX 9.0 connection to the docking station?

Comment from darrencope
Time July 31, 2012 at 10:09 am

Hi Reeder; I haven’t had many issues, except when the Adobe Air version needed to be updated. I find it fails until I do the update, then it seems to work fine. Have you tried that?

Pingback from DARREN COPE » 2012 – The Year in Review
Time February 3, 2013 at 11:35 am

[…] Sigma Rox 9.1 – Initial Review and ThoughtsQGIS Topological Editing […]

Comment from Bobo2012
Time April 20, 2014 at 1:48 pm

I have had a Rox 9.1 for since January 2014. Initially on a Tarmac Pro now on a Orbea Orca Bronze Di2. I enjoy the features but I have found some serious glitches. First is the manual I replaced my BC2909 which had a great manual with the Rox 9.1 which the manual is much more difficult to follow and I still am having difficulty. The 3.2 data center is much better and graphs displaying the cadence, HR,speed and altitude at 5 sec intervals is great.
On 4/19 40 mile event the logging stopped at 20 miles because the memory was full. I found on the web site that memory can not be deleted????? I guess the work around is before a big ride that you want to record create 7 dummy rides which sounds less than ideal. I am not aware if there is a setting that tells you how full the memory is. I have a request into the factory to see if there is another resolution.

Comment from darrencope
Time April 21, 2014 at 7:17 am

I believe that Data Center will tell you how full the memory is, and downloading to the PC and then clicking “Delete” (inside Data Center) will free up the space on the unit for a long ride.

Comment from pavuk
Time June 22, 2014 at 9:15 am

Did anybody have problem with heart rate monitor? My disconnects very often (about 50% of ride time is off, but last values usually freeze so you never know if it is disconnected or you have steady HR). I have 4th battery in HRM and 2nd in computer during one year.

It had many other issues. Memory just for 7 rides is stupid, when you can log 15 hours of ride. Counting of power is just joke from advertising department. Refresh rate is slow, measurement of angle and temperature unaccurate.
Computer doesn’t work in low temperature too. Less then 6°C and it’s dead (10 °C if you turn on backlight).

I truly hate this piece of garbage. If it didn’t cost over $200, I would take hammer and repair it with few punches.

Comment from kelly
Time January 9, 2015 at 3:53 pm

hi. ive brought the 9.1 but it never switches off. is there a way to turn off please

Comment from darrencope
Time January 9, 2015 at 7:24 pm

Kelly; it likely will never turn off, just go to ‘sleep’ — don’t stress about it :)

Write a comment