Testing grinds for cold temps
Tue, Dec 15, 2009 - By Mark Waechter
Tuesday is a ski testing day. A few new experimental structures were tested by feel and in a speed trap.
The test skis got a fresh grind - in this case there were 3 structure variations prepared, and two benchmark structures for comparison. With the current conditions and morning temperatures, the Ultratune S2 and XC02 were used as the benchmarks -- both are running well in the morning when temperatures are in the single digits (-15C approx).
The grinds were done on Monday afternoon, and all the skis were prepped the same - all getting the same wax (a good fluorinated race wax, but no powders or top-coats).
It is important to note that the test skis are factory matched pairs that were specially made as test skis. They've been tested to verify that they're very even skis (all tested with the same grind and same processes and waxing), so there are very few variables to botch the test data.
It is important to note that the test skis are factory matched pairs that were specially made as test skis. They've been tested to verify that they're very even skis (all tested with the same grind and same processes and waxing), so there are very few variables to botch the test data.
The speed trap was set up on a gradual, but somewhat fast, run. The begin and end points are 70 - 80 meters apart, and trap times were around 10 seconds. This gives average speeds of 25-28 km/hr, which is a bit faster than average race pace. Since conditions here right now are pretty fast, there is only a short gap from the start point to the beginning of the speed test zone - just enough to let gravity get a little motion going. (today times were around 10.2 seconds, and the trap was set around 80 meters)
Testing consisted of two sets of three runs per pair. Using two sets is a good compromise between switching skis after every single run (time consuming!), and doing a single set of data (which can yield systematic data errors if the tracks are getting faster or slower). Doing two sets is useful in showing offsets in times. Differences in times for different sets, for the same ski pairs, will show if the tracks are getting slower or faster.
Results are stored in the timing unit, and downloaded back at the house. I enter all the data in a notebook, and then into the computer where I use an excel spreadsheet to crunch the data for basic statistical results (medians, std-dev) and look for trends. It's common to see times improving as trap tests progress, as the tracks get skied-in. Sometimes they'll get slower.
Expectations vs. Results? Today I was looking at minor variations in well-documented grinds. I find that there are no big differences in the data; this is pretty much as expected. As much as anything, I'm getting the test processes dialed-in for the season... ...there's finally enough snow and enough time available to start the weekly ski testing program.