Archive for December, 2008

Awesome Umstead Park map

Sunday, December 21st, 2008

Backwoods Orienteering Klub is selling full-size Umstead Park maps. This is the same map we are using for our orienteering events, except that ours are generally scale 1:10,000 printed on a letter-size paper, whereas this is 1:15,000 printed on a much larger sheet (events are usually happening in about a quarter of the mapped area).

The park-maintained trails are marked with red on top of the standard orienteering black.

The level of details is amazing (what you expect from orienteering maps). There is history behind the map too, apparently after one of the major hurricanes (Fran, 1997) the map was redone and somewhere close to 15,000 trees were _individually_ mapped. Also, at some point you could see the trail of a tornado taking down a huge number of trees (1989) – now only impassible areas of overgrown vegetation.

To quote from the map description:

… Utilizing orthophoto base materials, detailed field surveys were performed in various stages by eleven different individuals over twenty-six yers. It took an estimated one thousand one hundred man hours of labor to produce this map. Drafting was done on computer using OCAD software. This map is printed, using soy based inks, on PaperTyger, a paper plastic laminate, making it water and tear resistant.

If you are interested in one, check out one of the retailers, or let me know and I can try to pick one up for you when I get mine.

Posted in Orienteering | 1 Comment »

Gear ratios

Saturday, December 6th, 2008

I was curious how important having a bicycle with 24 speeds (vs. 21 gears vs. 6 gears) is. I have an Iron Horse mountain bike with 24 speeds (3 gears front, 8 gears back). My daughter has a smaller mountain bike with 6 speeds (only 6 gears in the back). Obviously the wheel size matters a lot, but how much does having 24 speeds help *me* in particular? I know my 26″ wheels make me go faster than my daughter’s 20″, but wheel size being equal, how do various gear/sprocket combinations compare?

Being a geek by nature, I wrote a (python, of course) program to sort the speeds. Here is the output:

Front: [(0, 24), (1, 34), (2, 42)]
Back:  [(0, 32), (1, 28), (2, 24), (3, 21), (4, 18), (5, 15), (6, 13), (7, 11)]
0 (0:0): 0.750
1 (0:1): 0.857
2 (0:2): 1.000
8 (1:0): 1.062
3 (0:3): 1.143
9 (1:1): 1.214
16 (2:0): 1.312
4 (0:4): 1.333
10 (1:2): 1.417
17 (2:1): 1.500
5 (0:5): 1.600
11 (1:3): 1.619
18 (2:2): 1.750
6 (0:6): 1.846
12 (1:4): 1.889
19 (2:3): 2.000
7 (0:7): 2.182
13 (1:5): 2.267
20 (2:4): 2.333
14 (1:6): 2.615
21 (2:5): 2.800
15 (1:7): 3.091
22 (2:6): 3.231
23 (2:7): 3.818

What does this show?

First, the number of teeth in each gear (sprocket) for the front and back. They are sorted in reverse order front/back, since you will have the highest speed with the large sprocket in the front and small sprocket in the back.
Then, the first column represents the speed number, counting with the smallest front sprocket and each back sprocket, then the next front sprocket and each back sprocket etc. The second column shows which sprocket combination it represents (front:back). Third column is the ratio front/back (number of teeth). The higher the ratio, the higher the speed (and the harder you work).

What does this show?

Something I knew all along: I only need one front sprocket (the largest). I don’t do a lot of trail, even then I generally do 2:3 or higher, and on streets I’m using 2:4, 2:6 or 2:7. Notice how 2:0 is pretty high in the list, with a 1.3 ratio – and I feel like I don’t make any progress when I try that! This means that probably the combination of 8 sprockets in the back with the largest sprocket in front is way more than enough for me.

Again, I don’t do hard-core mountain biking, maybe if I did I’d find a need for the other two front sprockets. Can someone enlighten me if the other two front sprockets are really useful?

Posted in Sports | 2 Comments »