Gear: March 2009 Archives


March 15, 2009

I've had my Roclite 295s for a bit over two months now, so I've got enough experience for long-term comments. First, they're still really comfortable. You quickly get used to the low heel and the impact it has on your stride, and they're great in the mud, which we've had a lot of with all the recent rain.

My only real complaint is that the inner part of the heel wears incredibly fast. I've got about 200 miles on the shoe and I've pretty much completely worn through the both layers of the lining and through the foam on the right shoe, which means now I blister on each heel unless I tape up before every run. This happens to all my shoes eventually and even with a shoe with a tough liner like my hiking boots, I tend to blister in the same spot, so I suspect that there's something about my foot shape and my stride that creates a lot of friction at the heel. That said, 200 miles is pretty fast; I don't want to have to buy new shoes every 2 months or so. I went by Zombie Runnner to buy a new pair and asked if there was anything I could do and they suggested Engo patches, which are designed to go on the inside of the shoe and reduce friction. I slapped some on today and while it looks like I need to do some trimming to the right size, so far so good:

Good thing, too, since my new pair is on back-order. Hopefully, if I slap the patches on as soon as I get them, I can extend the lifetime of the shoe towards something more like other shoes I have used.


March 11, 2009

OK, so the new iPod Shuffle looks incredibly sweet, except for the tiny little detail that there are no buttons on the unit. Instead, they're in the headphones, which, as Pogue obserevs, locks you into the Apple headphones which don't sound very good and I, at least, find hideously uncomfortable. The nice new feature, however, is synthesized voice prompts, which (if they work, which is a big if) remedy the major drawback of the old shuffle: you can't tell what's going on because there's no display. Pogue claims that you'll still be able to get the old shuffle, so maybe they'll add the voice feature to that as well at some point. Until then, I think I'll stick with a nano.

March 9, 2009

I'm planning on doing some more ultras this year and I thought it might be a good idea if I actually trained for them. Triathlon experience indicates you should train the way you plan to race, so I'm trying some new stuff this time:

Hydration pack: support in tris and road races is pretty good, but with trail ultras, the distance between aid stations is a lot longer, both in time and distance. Road races typically have aid stations at between 1-3 miles apart; for trail races it's more like every 5 miles, and because there's a lot more climbing, that's something like every 30-60 minutes apart, so you need to carry fluid. You've basically got four options: (1) carry bottles (2) wear a bottle in a waist pack (3) wear a fuel belt, and (4) wear a hydration pack. I don't like to carry stuff in my hands, and all the bottle on belt schemes seem to max out at about 30-40 ounces, which isn't really enough and you also have to fumble with the bottles, which is a pain. I thought this time I'd try a hydration pack, and after reading a bunch of reviews I settled on the Patagonia Houdini (no longer available it seems).

So far, I'm pretty pleased. It takes a bit of getting used to initially, since the weight on your shoulders is different and it seems like it's going to rub on your neck or clavicle. The natural thing for a backpacker to do is to try to take the weight off with the hip belt, but it actually wants to ride higher up on your waist, which is initially a bit odd, but not uncomfortable, really. I only have two small complaints: the drinking tube (I went with a Platypus) tends to slip down a bit and I had to keep readjusting it back into the pack. I think I can fix this with a little adjustment inside the pack. The other problem is that it tends to pull your shirt/jersey up a bit, so I'll want something a bit longer in the future.

PowerGel (new): I used to race with Powergel exclusively, but then Powerfood reformulated it with 300% more sodium and it just seemed too salty, at least the chocolate version [*]. Two weeks ago, though, I was out running and really noticed I wanted more salt, so laast weekend I gave it another try with the raspberry cream and strawberry-banana flavors. It's still too salty, but not quite as disgusting somehow and with the hydration pack you can wash it down quickly. I think I'll be using it more on long runs.

Running with music: Last few races I did I noticed a lot more people wearing headsets. This seemed kind of odd to me—don't you want to focus on the race?—but after reading this post by Scott Dunlap, I thought I'd give it a shot. I have an old iPod nano with a broken display, but it's almost unnoticeable in the pocket of my Race Readys. The only problem I had was that the headphone cord kept pulling out, until I turned it the other way up so that the cord exits at the bottomw, at which point everything was fine. It's hard to evaluate whether music actually makes a difference in your performance, but it certainly decreases the boredom level, which starts to get significant after 2 hours. It's probably worth spending some time tuning the music to the right inspiring level, but that seems like it should be easy enough.


March 2, 2009

As I mentioned, I have a Garmin Forerunner 305 (BTW, the 405 is now out and looks really sweet). Anyway, it's not bad for giving you a record of your workout, but like all GPS-devices, the vertical accuracy is pretty bad (see here for an overview of why.) The problem isn't just that the receivers are wrong, it's that they drift a lot over a short period of time. As an example, I just turned on my 305 and over the past 5 minutes, I've seen it record anything from 5 to 57 feet. While this isn't a real problem when you're using it as a straight altimeter, since you don't need to be accurate to within more than a few tens of feet. But when you're trying to measure how many feet you've climbed or descended, it's a different story. For example, here's yesterday's workout:

For those of you who live in the area, this is Rancho San Antonio: PG&E Trail + Upper Wildcat Trail (Rancho Runner code 1bEF3MNLKR654V2D1aEF3UTS6RKLNM3FEb1) and is nominally 16.58 miles/2515 ft of climb. By contrast, the GPS thinks it's 5200 feet of climbing. Now, the maps that Rancho Runner is based on could be a little inaccurate, but they're not off by nearly 3,000 feet. To get a feel for what's going on, look at the last major downhill, starting at around 12.75 and descending to around 13.75. This is more or less a continuous downhill with no significant uphills, but as you can see, the graph shows a nontrivial amount of climbing. I suspect that the error in aggregate ascent is basically due to this sort of error. Since the nominal altitude varies a bit around the true altitude it looks like you're constantly climbing and descending, even when you're not, so you get very inaccurate ascent and descent readings.

Obviously, what you really want is to correct the GPS readings with a barometric altimeter, of course, and you can get watch-sized altimeters. For instance, I have a Polar 625 SX. That said, the Polar isn't small and the Forerunner isn't small either, and I think it's fair to assume that if you stick them together, it's not going to get any smaller. So, it's interesting ask whether you can correct the errors via software-only fixes.

Obviously, if you're willing to stand in one place long enough, you can average out the error, but that's not very useful if you're running, since you actually may be changing your altitude: the system needs to discriminate between actual altitude changes and GPS error. This isn't to say you can't average out, though: one possibility is to assume that there's some maximum slope to the trail and fit some sort of smoothing curve (e.g., a Kalman filter, a spline, FFT to remove high frequency components, etc.) to the data points and then use that to remove some of the error. Unfortunately, this only works to the extent to which the GPS drifts faster than the slope of the hill, and I'm not sure that's true. I'm seeing fairly high levels of drift (3-5 fps) with the unit sitting on my couch, but I have lousy reception here and it might be better outside. A moderately steep trail can easily drop 1-2 fps, so we're right on the edge of this working here.

Another idea, suggested by Kevin Dick, is to simply try to estimate the aggregate level of drift of the system against some natural reference (e.g., when the horizontal position is more or less fixed) and then try to use that to produce an overall correction factor. It's hard to predict how well this work, too, since it depends on the vertical error rate being approximately constant. I'm not sure that's actually true, though, since it's dependent on how many satellites are in view, their elevations, etc. If the vertical drift isn't relatively constant, though, then your correction factor will be completely out of whack, and you'll still get bogus results.

UPDATE: Cleaned up the discussion of filtering a bit.