SRM vs. PowerTap

A while back I mentioned that the CFO (aka, my lovely wife), had recently authorized a new purchase. Several of you have guessed that I was getting a new bike. Others thought it was new wheels. You were all correct that it is bike related. After a few years of riding with a PowerTap power meter, and racing without one, I am the new proud owner of an SRM power meter!




Yes, it's used. I haven't ridden it enough yet to cause that much crank rub. But I have ridden with it enough to know that it is WELL worth the extra price over the PowerTap. And if you want to race with the PowerTap, those $850+ hubs for all of your race wheels will quickly add up to more than the cost of an SRM.

So far, there are several things I like better about the SRM:

1. I can finally race with power. Because PowerTap measures power from the rear hub, you have to either race on your training wheel, or buy new hubs for every wheel you race with. And as you know, from my latest marathon adventure, I am an idiot when it comes to pacing during a race. The SRM measures power in the cranks, so it doesn't matter what wheels you are riding on. Now, I can race with whatever wheels I want (including a disc), and still get instant feedback, which should keep me from going out too hard in an Ironman or even a 70.3 race.

2. The computer displays more information. The PowerTap only shows Power, Speed, and one other reading, so you have to toggle to see distance, time, cadence, work, and heart rate. This is very distracting when you're trying to do intervals and you need to see, for example, cadence and time. You can leave it on cadence, but then if you want to know how much more time is left in the interval, you have to push a button SEVEN TIMES to get back to time! That can actually be dangerous if you're working hard during the interval. The SRM computer, as you can see here:



displays power, heart rate, speed, and cadence all at the same time, while time and distance toggles back and forth on its own. Much better for those intervals! Speaking of intervals . . .

3. Interval times on the SRM start over from 0:00 so that the time you are looking at during the interval is the actual time you have been doing the interval. The PowerTap will record splits, but you can only look at the overall ride time, not the time you have been doing the interval. In other words, you have to do math and remember what time you started the interval! This is very annoying. Let's say you're doing 8 minute intervals with 6 minute recovery intervals. You warm up for 15 minutes, and start your interval. That means you have to remember that your first interval ends at 23 minutes, you start the next at 29, then it ends at 37, and so on. With the SRM, you start the interval at 15 minutes, and the time goes back to zero. When the interval is over, the time goes back to your total ride time. Again, MUCH better than the PowerTap.

Some people complain that because the SRM is in the cranks, you can only use it on one bike. NOT TRUE. If you add a sensor to your second bike, you can swap the cranks back and forth to whichever bike you are riding that day. This takes less than 10 minutes, and is perfectly safe if you know what you're doing.

I can't wait to do some shorter races and find out what kind of power I can push for a sprint or Olympic distance event! It's impossible to push yourself in training as hard as you can push in a race. Now we're going to know exactly how hard I can work under race conditions. But more importantly, I'm going to know early on in an Ironman bike leg, whether I'm working too hard, long before it's too late to do something about it.