I'm looking for a light ANT+ compatible head unit that can record power data (besides speed/cadence/HR) such that it can be downloaded to a computer later on. Preferably it should also be able to not just display the current power, but also some average (e.g., 3s) to deal with something like PowerCal.

Some head units that I checked/have:
- CycleOps Joule 1.0: 43.5g
- Garmin Edge 500: 57.6g
- SRM PC 7: 69g

Unfortunately I'm having a lot of problems with the Joule: the battery lasts less than 15 hours of riding (a new firmware supposedly fixes that), it shows lots of bogus rides (e.g., from 2037 with -5371km, or 1 minute ride time but 300km; and it seems impossible to get rid of them) and right now it is completely "dead": no display activity at all - even with a new battery, so I'm looking for an alternative that is lighter than the Edge 500 (and reliable!). Any suggestions?

The Garmin is the industry standard.....save weight elsewhere.

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if you want long battery life, the srm is the one, bulletproof but pricey

for light weight there's the motoactv at 35g, not sure how good the display is for cycling, and as it has gps, the battery life is probably not great

The soon to be released Cateye Stealth 50 has a small form factor. Can't find any exact weight specs for it though.

For GPS-enabled The Leikr looks to be the upcoming lightest, but (1) it's still Kickstater, which has an exceptionally high vapor rate, (2) no handlebar mount yet, just wrist, (3) sampling rate is an open question, as it's now running focused, but that's just a software matter and the software may not be fully written.

Note the 55 gram weight includes a wrist strap. 55 is basically a tie with the Edge 500 (57 g) without its mount. So w/o its strap it's probably down int he 35-40 gram range. The Edge 510 is considerably heavier (75 g, more or less).



No GPS and Specialized Speedzone Expert is ANT+ enabled. I saw one on Ned Overend's bike @ the Diablo Hillclimb in 2011 after it was showed @ Interbike 2010, and it seems it's finally being publicly released. But a bike computer in that price range needs GPS these days because of Strava and its social media and competition aspects. People think phones will take over this role but I just don't see it: the phone will go into the bike computer rather than vice-versa. Phones just aren't well suited as cycling head units.

An example for why GPS is going to be needed is week 4 of my hillclimb series this year Sure, this isn't a race, but rather a fun competitive ride, but on this particular week I'm scoring people based on how they ride 6 climbs as I derive from their GPS data. There's errors in timing which result but I can do better than Strava with my own custom timing code since I use a different algorithm (interpolated line crossings versus uninterpolated point approaches). It's finally to the point where everyone either owns or can borrow GPS, either phone or otherwise, in this region. In any case, there's clearly going to be more of this sort of thing in the future.

On the Garmin/non-Garmin issue Garmin is first to the table with new ANT+ features, since they own Dynastream, which controls the ANT+ standard. So things like L-R power balance hit the Garmin units first. Next thing is probably some sort of "pedal stroke quality" index. They're also good about providing different types of power (instant, 3-second, interval avg, ride-avg). But if all you wants is watts, this may not be important to you.

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The Joule 2.0 is pretty good too. 20 hours of riding , nice big readable screen, waterproof, and pretty compact.

I just weighed one and its 76gr. I would not worry about a couple grams. You can save weight on other things.

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If you aren't running an SRM PowerMeter, you may have issues with the PC7. If you are running SRM, the PC7 is pretty hard to beat from the perspective of reliability, data storage and transmission and battery life.

^ +1 on that. I like my PC6 very much indeed, but as mentioned doesn't like to play with others.

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Thanks for the suggestions about light alternatives, I will look forward to seeing the CatEye, Specialized, etc to be released.

The main purpose of the head unit will be to record the "power" data from the PowerCal, which I intend to use in conjunction with my "light" bike; hence "saving weight elsewhere" doesn't make much sense for this. Currently only my training bike has a power meter and since I'm trying to be a bit more serious about "training with power" I also want at least some estimation of it when I ride a different bike.

I have no intention to use those "social" sites, so I don't really need GPS (however, it allows to not having a speed sensor, so there might be some overall weight saving).

My power meter itself (PowerTap) is exceptionally heavy, so when I do hillclimbs I use data from my Edge 500 in conjunction with a power-speed model I calibrate against other riders who did the same climb in the same conditions with power meters. It's quite a hassle, but even a few seconds in a climb can make a difference. But in doing this I lose pacing data: I still have the Garmin VAM number, but that's imprecise over small times. And I completely agree with you that it's important to save weight where you can. It's not a zero-sum question.

I'm disappointed no ANT+ Sport lightweight no-display recording devices have been released. Some friends of mine have built these from hobby kits with chips like this: http://www.ti.com/ww/en/mcu/ant/index.shtml . But it's not a practical solution for most people.

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Is there a PC7 with GPS planned ?

DJ, I've been following dcrainmaker's coverage of the 4iiii Viiiiva Heart Rate Monitor. It is a heart rate monitor that consolidates all Ant+ and Bluetooth 4.0 signals into one output. There is also an accelerometer and some storage. Further development may include the ability to record all the inputs in the HR strap itself. Not quite out yet, but check out the latest updpate from CES, if you're interested.

http://www.dcrainmaker.com/2013/01/ces- ... -week.html

Will solve some problems as devices transition away from Garmin's standard over to the open Bluetooth Smart stuff.

Thanks. But that's still going to be heavy. For racing, you're not going to be carrying your phone.

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No. That's my point. The device has the capability to record .fit files. Then wirelessly transfer after the event. No computer/phone/display needed. All you carry is the heart rate strap. And power meter, if desired.