"Why would anyone put a Power Meter on their Mountain Bike?" Some might ask.
Whether you believe this or have been considering powering up your , here are the thoughts of a Mountain Biker that has trained and race with a power meter for years.
Did I loose you already? If not let's get in to it.
I had trained and raced for years first using an HR monitor (mostly threshold, because that was where my HR stayed for most of the race! Boy was this not the case! I will explain later) and first used PMs in their stationary form (Computrainer) and switched to mobile PMs once they moved out of the upper stratosphere price wise.
I was convince about training with power, because I would come out of the off season on the Compoutrainer in great shape, but the threshold power I worked so hard for in the winter would slowly slip away as the season unfolded, as I could not get myself to hit the Computrainer in season, when I could do real riding. I did not realize it at first, but I was slowly de-training over the course of the season.
Enter the portable on bike PM and you could accurately work your energy systems in the real world. At first I had one of the original Power Tap hubs on my mountain bike (I only had a MTB for some time). This was prior to disc brakes and the bearings on the drive side were crap and the seals left a lot to be desired, especially for off road. But is was a start and my experience grew from there. Now there are other choices, while not inexpensive, are with the realm of possibility for many riders. Pedal and crank systems are probably best suited for road bikes, as you can't entirely eliminate pedal strikes off road. If you have a Mountain and road bike and can only afford one PM, it may make sense to get one for the road bike as it is usually easier to find suitable terrain to work the different energy system intervals and you don't have to change tires to put it on the trainer.
While I have PMs on my MTBs and race with them, it is not that popular yet and most riders are surprised when they see it. Partly to due to the fact for those early terrible durability issues, weight and then no disc brakes. Saris bought Power Tap and those issues began to be addressed. First they completely redesigned the hub putting cartridge bearings in the freehub body and shaving some grams, then going wireless with ANT then ANT+ and eventually got a disc brake version with some upgrades to the electronics and shaving some more weight. The road version became barely heavier than some performance racing hubs. I still have one of the first wireless hubs on my road bike, that I use manly for training, although I did a few road races with it. Having a bike with a smooth tire and a PM made the Computrainer redundant, if you have a decent indoor trainer. I used a trainer mostly in the winter, when light was short or the roads were not suitable for the energy system I was training that day. I have coached riders that would, on occasion, hit the trainer in the summer due to bad weather or scheduling issues. Many find indoor trainers frightfully boring, but for efficient use of the time you spend on one, a PM will get your session over as quickly as possible, knowing that you accomplished your training goals for the day.
Now this fine and dandy, but "Why would anyone put a Power Meter on their Mountain Bike?"
If you only own a MTB and want to train with power.
Probably the most important reason is keeping track of your Training Load.
The folks at TrainingPeaks coined the phrase Training Stress Score or TSS.
Why should you care? Wouldn't you like to know how much training is too much or how much is too little, allowing you find the Goldie Locks zone of your best performance?
The original low tech way to do this is to just multiply your Perceived Exertion times the duration of your workout. This is better than nothing, but is very subjective and really does not take your bodies actual output into account. But you can use a very simple spreadsheet or even just log it on paper
A step up is using heart rate instead of Perceived Exertion, TRIMP is and example of this. It is easiest to use HR Training software to accomplish the math. The trouble is that HR is a response to the effort you put out. Power is actually the measure of what you put out, just like Horse Power ratings of a race car engine. Just like strength training is measured by how many reps you do of a particular load (usually weight), PMs will show what you are able to do and if you are improving or just wasting your time!
The math gets even more complicated and unless you are a real math geek like me, you should use Power training software to track your TSS. Even Stava has it's own version of training stress measurement, although different from TrainingPeaks.
Tracking your training load, can get tricky, but with a PM a simple test and some training software, such as TrainingPeaks (on line) or WKO+ (desktop) you can track your fitness and your freshness and with WKO+ you can see you where your peak efforts are in relation to your training load.
Now fitness most people understand, but if you are tired from to much training you are will not be fresh when you want to be, that big race, event or that MTB trip to Sedona! Then add to that you can see your 10 top intervals in any duration that you want to monitor, to help you know when you are fit, peaking and the training loads and tapers that got you there.
In conclusion, a Power Meter will help you build your engine by targeting the energy pathway, read interval lengths that work best for your discipline, but most importantly, accurately track your training load!