Two Wheel Blogs

There is plenty of good conversation going on today over on the wattage list about choosing one's ATL Time Constant (ATL TC). I'm certain I do not have the answer for determining the right ATL TC, but that's only because I don't think there is a single right answer to that question. I do think there is a method you can use to get close enough though.

Like it or not, setting one's ATL TC is one of those things you ultimately realize as an inexact science. Stay on the task of finding the "right" answer and you'll see there is a range of numbers that seems to work fairly well. If you really try to analyze it you'll find at TC that works very well for some data but not as well as other values for another range of dates. After a time you eventually give up because you just can't find "the" right number. That's what happened to me.

Performance Manager was born as a spreadsheet. Having all that data just staring at you makes you want to perform all manner of statistical analyses in the quest to solve the mystery of the ATL TC. What I found was just what I stated above, at some times a shorter Time Constant worked well and at others a longer one was better. Worse, try as I might I could not find a correlation. There was nothing to indicate why the shorter TC worked better here and the longer TC worked better there.

The answer probably lies in the "other" category, the stuff we can't quantify and factor in. Can you really know whether you got the right dose of sleep last night? How about in total over the last week? Last month? Can you quantify the effects of temperature on your recovery ability? How about pollen, car exhaust or some other pollutant? What viruses did you fight off last week? Do you even know you had a virus?

See how hard this is?

I believe the ATL TC that's right for you is really a range of TCs. The trick is finding that range of ATL TC values that works fairly well. You'll know it when you're there because your performances will tend to line up with TSB regardless of your perceived effort, but most important, your performances will trend in the direction of TSB. When TSB is rising from negative through zero and into the positive you should start to have those good sensations. Let it go high enough and you'll be trash talking guys half your age who can make twice your watts. When you're pushing TSB down through zero it should feel like you're asking a lot of yourself. At first you'll deliver and come back for more. As TSB falls you'll get on the receiving end of the trash talk. (Just not from the ones you really want to hear it from, eh?)

See the rhythm? Rising TSB - you're riding closer to, and ultimately off, the front. Falling TSB - you're further and further back, off the back. Your ATL TC determines how fast TSB rises and falls. Find the range that meshes well with your performance trends. When you have that rhythm going on in your Performance Manager chart it's time to stop thinking about your ATL Time Constant. You're close enough.