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How many G's?


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At the 2010 SES I collected a bit of data on the lateral acceleration we achieve when carving. Since SES 2011 is right around the corner it is more than past time for a quick report.

I made most of the measurements with a 10 hz Performance Box GPS. I checked a few turns by measuring the radius of curvature of the track several places along the turn (With the GPS speed, this is another way to calculate acceleration). The GPS accelerations agreed with the acceleration calculated from the GPS track and the measurements of the real track. I did several comparisons between the G-Meter that Fin had and the GPS. The G-Meter averaged 30% lower than the GPS.

1) In harder turns most of us are getting about 1.4 g laterally.

2) For the most part, the more skilled riders went faster but had a similar lateral acceleration to the less skilled control (me). The speed difference in harder turns was 28-32 mph vs 21-23 mph.

3) Bill Sauer was turning harder turns than anyone else on the G-Meter. The highest reading I got for him was 1.67 g on the GPS (1.25 on the G meter). Trent was close at 1.65 g.


See 3/8/08 post for a more detailed post on what the GPS data looks like.


PS: I will not be at the SES this year so I won't be pestering anyone to carry my pack down the hill.

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The best software for such analysis is either GPSAR or GPS Results.

Both were developed for speedsurfing, but also allow you to analyze and graphically display acceleration etc.

Both are non-commercial, both have a trial period (60 days for GPSAR, don't know for GPSR). Afterwards you pay 30 euros.

Download both and see which one you like best. I use GPSAR, but GPSR is most straightforward IMO.

GPSAR: http://gpsactionreplay.free.fr/index.php?menu=2

GPSAR requires JAVA.

GPS Results: http://www.gps-speed.com/

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Sultan: Theory about the difference between the G meter and the Performance Box GPS: I can only speculate. Maybe they are using a longer data averaging time. I used 1/2 sec which corresponds to roughly 12-15 feet which is about as long as minimum radius part of many turns. Maybe the G meter is filtered or programmed in a way that gives a lower result.

Low Rider: Max Speeds: I did not pay much attention to that as it generally occurs in a long relatively straight run. <o></o>


Menno: GPS Action Replay and other analysis programs: I have used them for displaying sailboat tracks and they are great for that.The Performance Box comes with similar software. Unless the GPS is faster than 1 Hz (one measurement/sec) you typically only get a couple points in a turn. This is not enough to reasonably resolve the shape and size of the turn



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