Do you need the ability to ride with power on the road or will trainer only do for now?
Is your trainer compatible with Trainer Road (i.e. does TR have power curve data for the trainer)?
You don't need any trainer connectivity if you have an ANT+ or BT speed sensor like a Garmin one and if TR has power curves for the trainer you use. You can have "virtual power" at no cost for use on the trainer. I have a good but dumb trainer, a Kurt Kinetic Road Machine, and I use it with Zwift to train with power all the time. I use the same tyre, with the same tyre pressure and same roller deflection every time and the results are very consistent. My trainer has very good accuracy, some are not so good, but it will still get you started if you're really on a budget.

Awesome info.

There are a number of options you have available to you, and if you are willing to go used you can get a very nice power meter for a much more reasonable price than $1000.

Basically for your situation you want a power meter in the pedals, crank arm, or crank spider. Of those I think a crank spider like a Power2Max or Quarq (What I previously used before my new bike was incompatible) is the best bet. Followed by pedals like the Powertap P1 or Garmin Vectors. Right now I use the Powertap P1 but that will be hard to find in your budget.

Lastly you can go crank arm like Stages. They aren't my favorite for various reasons but they do work. One-sided power is not ideal, and they have connectivity issues with 920s.

Another option is to look at the one-sided PowerTap P1S. Again not exactly ideal being one-sided but it will do the job.

I think your best bet, however is to try to find a used Quarq.

As mentioned, you can get a very good taste for training with power using virtual power on TrainerRoad starting tonight with a minimal investment. All you need is a trainer, a laptop or computer, an Ant+ speed sensor (your Garmin will work) and an Ant+ dongle for your computer. You probably already have all that but for the dongle and those are only $20-$50 depending on how hard you shop.

After several years of using virtual power on TrainerRoad, I ended up with the low end Quarq and got it with a discount coupon for less than $700. It has been flawless. If you are looking at crank based power meters, one thing that is confusing is you have to know something about bottom brackets to make sure you get one that fits your bike, or you get the appropriate new bottom bracket to make it fit. They also take a bit of assembly since you need to install your chain rings. You definitely can do all that yourself but this is something that if you are not kind of a wrench, it may be worth working with a bike shop on.

One of the advantages to a power tap wheel is those are 100% DIY for even the most unwrenchy cyclist. But, as you mention, you are then limited to one wheel (but I think you can rent race wheels with Power Tap hubs so you might want to look into that if you want a Power Tap).

The crank arm and pedal PM's are easy to install and swap between bikes. The pedals in particular are pretty much compatible with any bike out there. A beef against the crank arm ones are only measure on one side. That freaks some people out but my friends who have them seem happy. The pedals are nice but they are more expensive then the low end crank based models.

You can always go Powertap hub and get a cover for the wheel. They are basically just as fast as a regular disc wheel, but at like 10% the cost. You could then spend the extra $$ on a race front wheel.

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Strava

I have had a number of Powertap wheels, and I must say I am truly impressed with the consistency, ease of use and if ever needed the support. They are rock solid, so I would nudge you that way. Carbon wheels now are so durable that it is no longer an issue of training on one set and racing another. As some have said, add a wheel cover and you have power in a disk for not a ton of cash. I will say that you will find that for Ironman distance, power will be one of your best friends. Monitor power and HR response to give you so much information as to how your day is panning out. It will stop you from having your ego dictate how you ride and lure you into some big mistakes that will surface later. I think the longer the distance, the more the value of having power numbers in front of you.

I highly recommend Quarq. I've had a Riken past 3 years and it's been bullet proof.

I also had a powertap, but passed it to the wife once I invested in race wheels and was swapping wheels around. But it's also been bullet proof.

I think you can get Quarqs now for the $700 range. If you're OK going used you can get even less. I think warranty transfers to new owners (but not 100%). Then that saves $$$ for entry fees or other bike bling.

I'd highly suggest the P1 pedals! Work every time & easy to remove and install, I have a roadie and my speed concept and now I can have power on both bikes with easy!

These can be had used for 800ish give or take on how low in cash the seller is!

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Speed kills unless you have speed skills!!!

This

For triathletes, a PT hub built into a solid training wheel with a disc cover for racing is the most practical solution that allows you to train and race with power, and also have a very fast and cheap rear wheel for racing.

I went with a Quarq only because I have more focus on road racing, and I need more rear wheel options than just a training rear wheel or a covered wheel. When I was previously only focused on tri and TTs...the PT training wheel and cover was a great solution for me.

For around $500, cheaper if you can get codes for the site you buy it from, you can get a powerbeat (need hollow aluminum cranks), they are supposed to be pretty good. I do really like my P1 pedals.

I forgot you don't get a dongle with all Garmin devices. I had one already for uploading activities from my 910XT but now I think about it there was none with the 920XT since it's WiFi enabled like most of the current devices. So yeah, you may need to buy an ANT+ dongle.

I was planning to get some cleat based power measurement via Brimm Brothers Zone DPM but then after several years of development and a couple of postponements on launch they folded last year without going to full production due to accuracy problems. :(
I ride my road bike and tri bike about equally and really don't want to be swapping components back and forth. Pedals or a wheel would be pretty easy but I use Speedplays and don't want to change and the wheel option limits you to a single wheel. The cleats system would have been perfect as it leaves the bike out of the equation completely. Oh well! I might settle for a powertap hub at some point, but not for now. To be honest I'm okay with power on the trainer only. I do like my data but if I had power on the bike for outdoor rides I might be inclined to pay too much attention to it and enjoy my easier rides less. Sometimes it's nice not to have too much data and be able to blame the terrain or wind for a slow pace!

Quarq or P2max or powertap C1 would do it.
Powertap Hub with wheel cover would do it.

Good luck

If you want to use your 920, do not get a Stages. I have nothing bad to say about one sided power meters if you are on a budget, but the Stages PM will simply not connect with any regularity with your 920. I ignored this advice and wasted money. Anyone using anything other than a 920, Stages are fine I guess but that combo is awful.

Thanks for all the info. Much appreciated.

Probably go with virtual power for now. First race isn't until Texas. Maybe I can hide something more permanent in the Christmas bills 😀....it's for the kids....

Just so you know, the "only on the trainer" thing can work but in reality, once you train with power you are going to want it all the time ;-) But starting out with TrainerRoad is a great way to go. You can learn a ton about who structured training works by running through their training plans. Over time you will start to see how the whole interval training to target thing works as the structure plays out over time. The real key to power is not simply knowing at any given moment how much effort you are putting out but using that to structure your training over time, and tracking your data to manage your training. Using power to pacing a race is a nice feature too but really just a secondary benefit.


As someone mentioned above a wheel cover is for all intents and purposes just as good as a full disc wheel and they only cost $100 http://www.wheelbuilder.com/aero-disc-covers.html A decent set of wheels you can train and race on with a power tap plus a wheel cover will get you what you want.

I've been using it on the trainer only for about 10 months now. I'm happy to keep going this way for the time being.
As I said, if there was a suitable pedal or cleat PM available I'd consider it but for now I want it on both bikes or neither and I don't want to buy 2 PMs. Amongst other things I'd prefer the data to be exactly equivalent but value is a bigger concern. I'm not splashing out that money on something I only use 1/4 of the time.

^This.

I started with virtual power on my Kirt Kinetic and it is awesome. It is pretty accurate and consistent. But, after about six months, I got the strong Jones to have power all of the time. So, I got P1 pedals to have power all the time that I could swap between bikes. I absolutely love them. They are not cheap, but they deliver a ton of value.

Here is the quick decision tree to guide you to a choice, when you get there. Prioritize the list, and then pick the ...

• Lower cost (PT hub, single-sided crank, single-sided pedals, chain rings, some spiders)
• Total power (spiders, hub, dual-sided pedals, dual-sided crank arms)
• Dual-sided power (dual-sided cranks, dual-sided pedals)
• Move between bikes (pedals, hub, maybe cranks if compatible)