Tuesday, June 9, 2009

Cycling Computers: Revisited

About three months ago I was looking at various options for replacing my bike's basic cyclocomputer with something more capable. Unfortunately, things got busy after that point and I never got a chance to do much more research. After getting back on the road for a while, however, the limitations that weren't so big of an issue on the trainer re-asserted themselves and brought this consideration back to the forefront. As such, over the last few weeks I've been doing a little more digging and re-examining my options.

Shortly after the last post, I was strongly gravitating towards the Polar CS600X but it wasn't available at the time. Thanks to some pro-active assistance from Chris at Polar USA, I was able to get confirmation that the CS600X with power is available in this country so it's just a matter of finding a retailer at this point. In the meantime, however, I've heard a lot of good things about the Garmin Edge 705 from local bike shops and riders that I've met out on the road so I'm reconsidering that option as well.

The other unit that I've heard good things about and didn't consider last time around is the Velocomp iBike series (specifically their Pro and Aero units). In addition to the basic cyclocomputer features, these units provide power readings using a relatively novel solution that measures opposing forces rather than measuring the drivetrain itself. Using an air speed sensor and a multi-axis accelerometer array within the head unit, it measures the various forces resisting movement (primarily aerodynamic drag and rolling resistance) and backsolves the amount of power necessary to maintain the speed the bike is traveling at.

Naturally, the power readings do make some assumptions that more direct measurements don't have to deal with. Primarily, when one changes positions during a ride their drag coefficient will change but the system has no way to know that this is happening. As such, when going down on the drops power will be overestimated and when sitting up to drink, power will be underestimated.

With that said, most people that I've talked to that have actually used the system appear to be impressed with it's accuracy. Part of that is likely down to the fact that one typically spends most of their time in one position so the impact of this is likely less significant than it would seem at first glance. Either way, Polar's measurement mechanism has significant sources of potential error as well and as the other power options aren't really realistic at this point this may be somewhat moot ;)

The one thing that has me intrigued by these devices, however, is their ability to record both the air and ground speeds of the bike. This provides a detailed log of the intensity of head and tailwinds, as well as a way to quantify the effects of drafting positions during group rides. This information can be extrapolated to an extent from heart rate and power data, but as other things can influence those values the air speed readings can be quite instructive (especially for a relatively new rider such as myself).

Further, their iAero head unit can actually provide estimates of your aerodynamic drag coefficient each time you coast (with the addition of an aftermarket ANT+ power meter, it can even provide a continuous readout). If accurate, this would allow me to experiment with different positions on the bike in order to determine exactly how efficient each of them are. At common cycling speeds, aerodynamic drag becomes the dominant force the rider is fighting against so the ability to fine tune one's position is potentially a huge feature.

The problem with the iBike products, however, is that their user interface is pretty crude compared to Polar and Garmin's products. Velocomp elected to use a simple three-line fixed element LCD, which is fine for the numeric information readouts but has severe limitations for the on-device menus. This is likely due to the fact that they appear to use the same hardware for their various models and differentiate based on firmware. As such, their design had to be profitable for their $199 Sport model and compromises had to be made to reach that price point. As a user, however, justifying paying $799 for this type of user experience is a bit frustrating. The biggest annoyance with their implementation, however, is that the user cannot select which pieces of telemetry are shown on each of their pages - one is stuck with the groupings that Velocomp offers.

Either way, I'll continue to do a bit more digging but wanted to get my thought process down here. Like anything, there are significant pros and cons for all three choices here and it's just a matter of figuring out which compromises are the least significant for my needs. Naturally, if anyone has any experience with these products I'd welcome any input on the topic!


  1. I have the RS800CX. Being a numbers person, there's nothing I can't get, the Polar ProTrainer 5 is excellent and has a lot of functionality. A little more setup required with the Polar, and it may be a little more complicated than the Garmin 305.

    The one thing that I dislike about the Polar however, is that the GPS is a separate unit, takes AA batteries, and I had bad luck using rechargeables, so depending on your use (I suspect quite a bit... lol) it can get a little pricy replacing these batteries all the time. Good luck with your choice! Chris @ Polar was a big help for me too, also proactive through my blog! I bought mine off ebay, a store out in London, Ont. I believe. If you want the info, lemme know, and I'll find the receipt that I got with it. Good luck with your choice!

  2. The RS800CX would have likely been my first choice if starting from scratch, however I currently use the older version of it (RS800sd). Unfortunately, the main thing that they added to the CX was the ability to work with cycling sensors (the sd only works with the S3 footpod or G3 GPS) :oP I could sell my current RS800sd and get the new version, but that'd get me close to the cost of the CS600X anyway (which has the advantage of the stem mount and the ability to work with their power meter).

    The Garmin certainly has some very interesting features (the on-board maps/navigation system could potentially be hugely useful for long rides), but with the talk of bugs and stability issues combined with the rock solid experience I've had with the RS800 it's a good argument for the Polar option. Either way, it's good to hear that Polar's cycling bits work just as well as their running ones ;)

    Thanks for the feedback!