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Old 10-21-19, 09:37 PM
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Originally Posted by FinkFloyd View Post
My questions are therefore as follows:

1. I see that SRM offer two basic iterations: wired, for use with the PCV system, and wireless (each can come with SRM cranks or Rotor cranks). Is there an advantage to the wired system? If I've understood correctly, it has to do with instantaneous data transfer; is there a different benefit that I'm missing?

2. Using the wired system obviously ties me into the PCV head unit. Does this do everything a more modern head unit does (e.g. syncing wirelessly, etc), and is it really worth the expense of buying a new head unit (I gather the wireless SRM will sync with ANT+) compared with sticking to my Wahoo unit?

3. Is the Power2Max system appreciably inferior in any important respect to the SRM? I note that the Power2Max system comes with a rechargeable battery, which seems to me better than the SRM sealed unit solution.

Thanks in advance for any help.
I used the wired SRM (non-track - Cannondale SI models, two of them, and one regular SRM crank) for about 8? years. I upgraded one then the other to wireless (my standard is still wired).

For wired, the disadvantages:
1. You have to use the SRM harness. I found that after a year of use the harness needs to be replaced. Knocking the bike around, moving the pickups just a bit to adjust for different wheels, the odd chain off, etc, will affect the harness.

2. The PCV has very little memory. It's a lot for most purposes, meaning like a crit or even a full day on the track, but it's limited to something like 6 or 8 hours at the finest granularity. I regularly downloaded data after running out of memory in races, which are honestly the only thing I really want to analyze.

3. Brings me to the download - it's a proprietary cable, USB on one end, fine, but the other end is a very hard-to-plug-in plug. I think it's meant to be almost waterproof, but it's hard enough to plug in, and delicate (it sticks out at a 90 deg angle). I've broken a couple download cables.

4. Battery is really easy to replace in a PCV, much easier than the crank/spider. The readily available battery is a bit lower capacity than the stock one, but if you leave it plugged in most of the time it's okay. Battery replacement in the spider is tricky to get right but possible. I send my crank back to SRM now because it's easier, and I have two SRMs partially because of this (I also have two almost identical bikes, both could be "primary bike", so that I don't miss anything due to a weird failure on one bike.

5. I used the (wired) BB pick up for the spider, much better than the chain stay mounted one. The latter can get knocked off kilter pretty easily, wire is fragile. The BB one is tougher, wire is easier to secure, and it's less likely to get knocked askew.


I upgraded mine about 2 years ago. I have the PC7, not the latest PC8. It doesn't hold as much data , there's some other stuff, but I was working within a budget and the PC7 seems good enough. My main goal was Ant+ compatibility so I could use my SRM to feed power data to Zwift, instead of using ZPower for "public" and SRM power "for real". I was being handicapped about 50w at lower power (200w SRM would register 150w ZPower) and 100+w at sprint power (1100w would register as 950-1000w Zpower).

1. Pickups - there's a magnet by the BB, but no wire so there is very little to move the magnet (no snagging the wire by accident). I use an Ant+ wheel speed pick up (don't use external Ant+ cadence, you must get cadence off the BB pick up else power doesn't get calculated - I didn't send my "broken" crank and PC7 back to Colorado to learn this, really, I didn't). Much simpler, no wires.

2. Memory. I read somewhere you could do the whole Tour before downloading data off the PC7. I haven't done the Tour but I've done 30 or 40 hours of riding before downloading data, and the memory is nowhere near full (1/3 full?). It's quite refreshing coming off of the "download 2x a week" PCV.

3. Download is very easy. Regular USB cable, both ends, it's the regular small USB end that goes into the PC7, not the microUSB. It takes longer to download than the PC5 but you're downloading a month or two of data. Data transfer speed is obviously limited (I think the PC8 is faster?).

4. PC7 battery is so good that I plug in maybe 2x a year? 3x a year? I plug in to download, leave it plugged in until next ride, then I'm good for months.


If you have a wired SRM, the nice folks in Colorado will upgrade you to a wireless for some very reasonable amount. One Cannondale SI was upgradeable (I think they replaced the circuitboard?), I think it was $450?, and $200 for a refurb PC7. Great investment. The second one I happen to send in around Black Friday, I simply bought a new Cannondale SI spider outright for about $600?, plus another refurb PC7.

Hm, maybe it's time to send in the regular SRM to get that upgraded. Well, I'd rather get some other stuff so maybe that'll wait.
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