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October 28th, 2008
01:50 pm

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since some people gotta be doubters and i was bored...
some people have been disputing my youtube video of me going 39.6mph in 40x16 gearing on a fixed gear. i don't like to make false claims, and when someone calls me on it, i am a humble enough person to doubt myself.

i was bored, so i thought i'd double check the facts.



here is a google earth display of the hill i went down, showing my path from where i turned onto the pavement at 2:44 in my video, to where the brush along the small creek starts just before the uphill runout at 3:00 in the video.





i copied/pasted the path's xml coordinates into the path distance calculator at
http://www.emaltd.net/google/gec/utilities/index.asp?l=en

the results were:

Total: 289.1172 meter

1 of 1: Untitled Path (Path)
Total: 289.1172 meter
1 (of 8).Segment: 66.4454 meter
2 (of 8).Segment: 34.9489 meter
3 (of 8).Segment: 25.1322 meter
4 (of 8).Segment: 24.0846 meter
5 (of 8).Segment: 42.6433 meter
6 (of 8).Segment: 48.0340 meter
7 (of 8).Segment: 28.9769 meter
8 (of 8).Segment: 18.8520 meter

in 16 seconds (between 2:44 and 3:00), i traveled 289.1172 meters

solve for miles per hour:

289.1172 m / 16 sec = x meters / 3600 sec

x = 65051.37 meters / hour

65 km/hour = 40.3891275 miles/hour

...and that would be an estimated average speed. depending on the accuracy of my cyclecomputer, which i hadn't done a proper roll out test on, the 39.6 was my estimated maximum instantaneous speed.

according to the late sheldon brown's gear calculator website, my speed at 100 crank RPM in 40x16 gearing with 27" tires would be 20.1mph, meaning i was pushing near 200 rpms.

i suppose there is no real way to actually prove it was 40x16 gearing (or even that i was on a fixed gear and not coasting), but i can assure you that the original double chainring cranks have a 40t ring that i was using and the 16t cog was jb welded and lockringed permanently onto the stripped out hub. i'm sure there are pictures of the bike in this setup somwhere in my blog for anybody who cares to dig for them.

looks like i'll have to try to break 45, next time.

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[User Picture]
From:robotar
Date:October 29th, 2008 02:28 am (UTC)
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awesome.
[User Picture]
From:unixd0rk
Date:October 29th, 2008 06:15 am (UTC)
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well, it 's "inconclusive" to the latest to the latest hater. that means a lot.

i'm going to go 45 down that hill this weekend if i can find time, and i'm going to have it documented.

in the video i was pushing down that hill until i got past spinout, then i just let go. i'll take my 45x15 700c bike down that and probably hit 45 with just as much effort. the only limiting factor besides crank input after 30mph is the wind resistance (and how).

this next time, i'll count the gears on cam and show the tire size stamp before i blast down the hill without cutting the video so that i don't have to be annoyed by youtube notices from idiots who can't believe that 200 rpm over a 5-8 second span is possible.


Edited at 2008-10-29 06:19 am (UTC)
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