CYCLO CROSS and power meters (Pt 1)

There is endless content available across the internet and in various books on the subject of training with power. In these articles, I am not intending on describing the benefits of training to power vs training to heart rate – others have done a great job of that already. 

Much of what I’ve read describes different types of blocks of training, various training sessions and has some kind of link back to FTP, fitness, form or CTL graphs in a software program such as TrainingPeaks, GoldenCheetah, Strava or TrainerRoad.

It took me quite a while to figure out what works for me because there are so many opinions, so much science and so many types of intervals to consider.

After much research, trial & error and mistakes, I’d like to share what I’ve figured out. This is not intended as a manual or product review, more of a point in the right direction. 

1. Power meters

There are many types of power meters for bikes. I’ve used Powertap hub, 4iiii single sided crank arm, Computrainer and SRM power meters so far. 

Computrainer is the original smart trainer, with long-term reliable power readings it can be used to calibrate other meters, and its bomb proof design means it will probably be working in 2030! 

The Powertap was a very reliable powermeter, its power and cadence readings were consistent but being a hub, was limited to that wheelset, which meant a lot of changing between road and CX tyres. It was also inconvenient when it had to be sent away to have its bearings replaced.

The 4iiii, like other single sided crank arm meters, adds very little weight. In use, its cadence readings were good on road, but off-road were up to 20% different to a magnet cadence sensor… Power meters use cadence in their algorithm so it didn’t take long for that to be sold on. 

The SRM doesn’t miss a beat. It provides solid, reliable data. Having been through several CX winters, it has been jet washed countless times. It is an expensive investment at the outset and the battery isn’t user serviceable so needs to be sent away every 2 ½ years. But for proper training with power it is by far the best I’ve used, and carries a long warranty too. 

Single sided crank meters

Single sided meters such as Stages/4iiii offer a relatively low-cost entry to training with power, but are often described as “random number generators”.
This partly comes from the fact that the meter is simply doubling one leg to calculate the power. In practice, this isn't a big issue because most people are fairly closely balanced between legs. 
However, a friend of mine has had more than one single sided meter which records 50% extra cadence and +2400w for several seconds when riding in the woods (we think it could be pedal strikes).
A few seconds super high readings a few times in a ride might not bother many people but can play havoc with power training software – more on that in part 2. Quite a few CX bikes have clearance issues with the space between the meter on the back of the crank and the chainstay. 

Crank spider meters

Spider based power meters generally offer the best reliability. I’ve heard good reports from QUARQ users, the aluminium arms and GXP axle versions are heavy though. QUARQ uses accelerometers for cadence. After my 4iiii experience, I prefer the magnet system of the SRM...

I'm sure there are Power2Max, Rotor and InfoCrank users that are happy with them,  I just haven't chatted with any of them. 

Smart trainers

Many entry level smart trainers are regular turbo trainers which have been upgraded to smart with a Bluetooth module being added, these measure flywheel speed and use a programmed resistance curve to calculate, rather than measure, power. They tend to be pretty unreliable, especially when compared to a proper power meter – not ideal for Zwift.

Fully integrated models with an ERG mode (electronically controlled resistance) seem to be much more reliable, but (obviously) can’t be used outside. They are expensive though, and given that you'll need add a power meter to use outside too, are a limited choice.

I chose do my indoor sessions on a standard dumb turbo and use the power transmitted from the SRM.

Other power meters

Pedal based power meters aren’t developed yet for off-road, so there are no real options.

Kickstart companies like AVIO and ZWATT offer much lower initial cost than the recognised brands, but should be bought with caution. There are many reports of people feeling like they are being used as beta testers to help iron out software/firmware issues. 

There is even a power meter which measures air speed....R.N.G!

Independent advice

DC RAINMAKER's reviews of power meter related products are probably the best source for independent, and thorough power meter reviews. His site is well worth a read before investing in any power meter products. 

Buying used

Power meters are probably the most sensitive and complicated component on a bike. Best advice is to buy your power meter new. The warranty and support will come in handy to prevent you having a useless box of electronics when (more likely than if) it goes wrong.

That said, I’d be very confident buying a used SRM, assuming good used purchasing practice is followed - pay by PayPal goods and services, advert says in good condition etc - their customer service is excellent and all parts are carried. Used QUARQ and InfoCranks are less risky than most of the others too. 

Power meter best practice 

There are a few things you should do to keep your power meter data recordings accurate. 

  • Changes in temperature effect the readings of many power meters, doing a quick zero offset or calibration before each ride keeps things accurate.
  • If your Garmin or bike computer has an auto calibration setting, set it to off, it is better to do it manually without your weight on the bike.
  • Set your Garmin or bike computer to record the zeros, this way the Average Power will be accurate to compare to the Normalised Power - this is important when looking at off-road power files.
  • Set your Garmin or bike computer to display a 2 or 3 second averaged power, otherwise the number jumps around a lot – especially off road! 

"A person with a watch knows what time it is. A person with two watches is never sure."

It is worth remembering that two power meters, even of the same model, will give somewhat different readings. Also, comparing other people’s power data is futile (even if you know their weight). It is far more important that your power meter gives consistent readings that you can calibrate your training to.

It is tempting to geek out at other people’s power data though! 

If you choose to record from a smart trainer indoors and a power meter outdoors, it would be worth spending some time to investigate how similar/different they are. Some meters, such the 4iiii, allow you to easily adjust the power transmitted via their app. This way, you can calibrate the 4iiii to the smart trainer to keep their numbers similar. 

In part 2, we'll look at what you can do with your power data and how you can use it to get faster. 

Useful links


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