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# High DIN binding question - Page 4

Quote:
Originally Posted by crgildart

The deal with GPS speed tracking is that the steeper the pitch, the more over the speed estimate will be because it measures your horizontal position change over time.  You are actually covering more ground than the horizontal change due to pitch, not very well accounted for by GPS platforms.  It does better in cars when comparing because you're not going down a 40* pitch in a car, more like a 5% pitch.

Your GPS is measuring Delta for b from above to calculate the speed where your actual ground distance is c.  Hence it will always say you are going considerably faster than you actually were. If you are making turns the speed estimate will be even more off because you are covering even more ground than was measured as b.  But if c>b then it must be overcompensating somehow or else it would show you going slower than actual rather than faster than actual.  Regardless, the slope messes with it.

..... now I'm confused, I thought GPS indicated speeds SLOWER than what you were actually travelling down a steep slope. Take your steep 30-60-90 triangle there - GPS tracks the horizontal speed (1), even though you covered the greater distance (2) during that time - which would have been at a higher speed. Distance (2)/hour would be faster than Distance (1)/per hour .... yes?
Quote:
Originally Posted by SkiersLeft

..... now I'm confused, I thought GPS indicated speeds SLOWER than what you were actually travelling down a steep slope. Take your steep 30-60-90 triangle there - GPS tracks the horizontal speed (1), even though you covered the greater distance (2) during that time - which would have been at a higher speed. Distance (2)/hour would be faster than Distance (1)/per hour .... yes?

Yes.  I wonder if it is calculating the distance referencing the closest road data points, which would likely be major switchbacks and a whole lot more ground than what the skier had actually covered?  That would explain the gross over calculation.  But who knows?

I think a radar gun would be OK as long as the person holding it was close to the skier and pointing it up at roughly the sale slope as the trail.  They'd have to in order to capture the skier in the reference area.

I believe the conclusion is to NEVER reference a GPS when setting your DIN

thinking about it, a speed-gun would require the following things to be "accurate" (and probably more):

1. the pitch of the ski slope does not change during the measuring - a few deg roll over will throw the gun off.

2. the gun is held at the same inclination as the slope.

3. the gun is on-slope, not in the flats below.

4. the gun is square at the skier's line of motion, not a little off to the side.

all these things are basically a non-issue for a traffic officer, since motion is horizontal, and they are in-line with the motion of traffic, but seem very hard to control on-snow.

even a couple % off on each point is going to get you a 10-15%+ high reading.

Quote:
Originally Posted by msolson

beyond - just for the record, while i have never used it professionally, i did graduate with degrees in both astrophysics and atmospheric physics ;)

and here was me about to say that this wasn't rocket science.......

Quote:
Originally Posted by msolson

thinking about it, a speed-gun would require the following things to be "accurate" (and probably more):

1. the pitch of the ski slope does not change during the measuring - a few deg roll over will throw the gun off.

2. the gun is held at the same inclination as the slope.

3. the gun is on-slope, not in the flats below.

4. the gun is square at the skier's line of motion, not a little off to the side.

all these things are basically a non-issue for a traffic officer, since motion is horizontal, and they are in-line with the motion of traffic, but seem very hard to control on-snow.

even a couple % off on each point is going to get you a 10-15%+ high reading.

The obvious  workaround is to mount the radar gun to the skier and to look for the highest relative speed solution within the FOV.

Quote:
Originally Posted by cantunamunch

The obvious  workaround is to mount the radar gun to the skier and to look for the highest relative speed solution within the FOV.

Or, they could just measure the dents, teethmarks, blood splatter and missing bark from the tree during the forensic investigation.

Edited by crgildart - 6/3/13 at 2:36pm
Quote:
Originally Posted by ScotsSkier

Quote:
Originally Posted by msolson

beyond - just for the record, while i have never used it professionally, i did graduate with degrees in both astrophysics and atmospheric physics ;)

and here was me about to say that this wasn't rocket science.......

A radar gun sends out a radio signal, which bounces off the approaching object (skier) and because of the relative motion of the gun and approaching object the reflected radio wave is percieved by the guns reciever to have different frequency than the wave sent out.  The change in frequency (known as the Doppler Shift) can be used to calculate the speed of approach of the object.

GPS use a combination of distance over time and Doppler shift of the radio signal recieved from the satellites.  On my GPS MAP 76 CS, the Trak Logs appear to store a speed that is equal to the distance between two adjacent points divided by the time.  The Max speed seems to be higher, and therefore I assume is using the doppler shift, which would reflect actual movement, see eample below:

501    13/01/2013 10:41:31 AM     1041 ft            57 ft    00:00:01    39 mph    40° true    N46 30.515 W80 57.536
502    13/01/2013 10:41:32 AM     1022 ft            56 ft    00:00:01    38 mph    25° true    N46 30.522 W80 57.528
503    13/01/2013 10:41:33 AM     1005 ft            60 ft    00:00:01    41 mph    15° true    N46 30.531 W80 57.522
504    13/01/2013 10:41:34 AM     986 ft            68 ft    00:00:01    46 mph    347° true    N46 30.540 W80 57.518
505    13/01/2013 10:41:35 AM     969 ft            76 ft    00:00:01    51 mph    344° true    N46 30.551 W80 57.522
506    13/01/2013 10:41:36 AM     950 ft            62 ft    00:00:01    43 mph    354° true    N46 30.563 W80 57.527
507    13/01/2013 10:41:37 AM     945 ft            55 ft    00:00:01    38 mph    330° true    N46 30.573 W80 57.529

http://gpsinformation.net/main/gpsspeed.htm

Track logs may not give you as much to brag about, but at least you can look at how the data is changing second by second and eliminate the false readings.  The above isn't an example of the following, but it's also interesting to see how much acceleration you can get when you land a lot of vertical on a sloped section of a run and convert a chunk of that vertical velocity (which doesn't show up in the track logs into horizontal velocity which does.

Quote:
Originally Posted by msolson
he brings a bushnell verified speed gun.  feel free to debate the margin of error on that gun, but if you think its error is on the order of 10% or more, then please provide links about how a bushnell verified speed gun is that far off.

Well, I just ran a quick search on radar gun accuracy in scholarly journals. Nothing came up. Lots of radar guns used in research on sports, conditioning, and biomechanics, but reliability is always assumed, couldn't even find references to another article. Then I Googled Bushnell Radar Gun Accuracy, and came up with dozens of typically bullsh*t discussions, chiefly related to baseball. One forum was solid that the Bushnell consistently underestimated the real speed by 7-8 mph, using a \$600 unit as a "gold standard." Another forum was equally assured that the Bushnell overestimated by 3-5 mph. All forums agreed that higher priced units like the Stalker were more accurate, and plastic units like the Mattel the least, although I could not find a single instance of anyone knowing this through more than anecdotal information. The only "research" I can find was offered by Bushnell in-house sources, so not precisely unbiased. Not surprisingly, they claim plus or minus 1 mph. But in all honesty, I'd believe an experienced baseball scout over you guys.

Apparently the problems with all guns include the "Cosine Effect," where the placement of the gun relative to the axis of motion will affect the estimate, as well as where in the objects' path the actual measurement is made (these are not average speeds but "snapshots."), and whether or not the gun itself is in motion, however slight. Some guns apparently measure balls as they are midway to the plate, the Bushnell was said to measure at the plate, and so on. Moreover, no gun can be positioned so it's exactly on the axis of the ball, even if the catcher wants to hold it, or there's no catcher, because the ball describes a curvilinear trajectory. Much disagreement about what a 90 mph fastball even means, in fact, as in when it leaves the pitcher's hand, when it crosses the plate, other? And finally, all guns need to be "tuned" with a special device everytime they're used, I discover. Apparently they have a lot of instrumental "wander" and can lose precision within a few usages.

I did not find any particular awe for law enforcement guns, and apparently courts routinely throw their findings out if the defendant bothers to contest it and get an attorney. So more of the "that's how it's done" than any reason why it's consider a standard. Lot of funny stories about sprinting palm trees and so on. A recent court case, in fact, was brought to argue that GPS is more accurate than police radar. Couldn't find outcome, although what courts know about science could be put in your back pocket with room to spare.

The takeway, for me, is that a) none of these devices approach anything like scientific reliability except under experimental lab conditions. And b) pointing a garden variety gun at a moving skier will be affected by the pitch and angles of the slope, when the reading is actually taken, whether the skier is accelerating or decelerating, how steady the hand of the user is, and where the gun is relative to the axis of skier motion when the actual measurement is taken. The further off the axis of motion, or the more the various motions change trajectories in space, the less accurate the reading. I don't find a lot here to suggest that this is a "gold standard" that can calibrate GPS.

So sadly, I still don't believe all these speeds I read about on Epic. Or more precisely, I don't know which ones to believe, since by chance some will be more accurate than others, and a couple will be very accurate. But the differences between them look fairly random, so impossible to predict which ones to believe. Except for my own speed estimates, which are dead on. Always.

Cosine effect will cause the gun to be inaccurate in that it will read a speed that underestimates the speed of the object.  Just say'n.

It's deja vu all over again

A couple of decades ago I got clocked doing 60 mph wearing jeans and a parka at the Jay Peak Citizen's run as a last minute entry.  I would have been faster but I opted to stand up out of my tuck on account of the fool standing in the middle of the course looking up hill to see if there was in fact a last minute entry on the way down.  I deliberately stood up straight as I wanted to kill a little speed so I would be able to safely negotiate my way around any and all obstacles and fools.  The run for the race, and the ensuing speed were much less inspiring than many other runs I had been on previously, not as steep for not as long and consequenlty a lot slower.

Go ahead, one more to go.

Quote:
Originally Posted by Ghost

To save time, here's a summary of those threads.

How fast do you ski?

a:I ski x miles per hour.CHECK

b:That's not possible, unless you are on a WC team, and wearing a speed suit. What makes you think you ski that fast?

a:I'm going by comparing it to speeds on my bicycle that has a speedometer, and how much eye protection I need to see, speeds on a motorcycle, etc..

b:That's not good enough, you need better measurements than that.

a:OK, I bought a \$750 handheld GPS unit that records every second and has a rated accuracy of plus or minus y mph, and it says consistently that I ski x miles per hour.  CHECK

b:GPS is highly inaccurate.  Unless you had a radar gun showing your speed, you were not going that fast.CHECK

c:I went to the TGR speed day, we had a radar gun, I skied x miles an hour,  another skier skied  x miles an hour switch in baggy clothes.

b:That radar must have been faulty.CHECK

a:A couple of decades ago, I went to the Jay Peak Citizen's race as a last minute entry and they used a calibrated radar gun to show my speed was x miles an hour wearing a parka and jeans, even though I had to stand up out of my tuck for several seconds to kill speed until some clown standing in the middle of the course looking uphill to see if there was another skier coming down got out of the way, and I know the speed was much lower than what I usually ski when going for speed.  CHECK (with this post!)

b:I don't believe it.  You can do it!

On the other hand, it is summer here and those threads are entertaining; go ahead and read 'em all.

"I was having a wicked fast run until" or sometimes "There I was, doing a buck ten, when suddenly" have always sufficed among my friends. But then they call it beer league for a reason.

Quote:
Originally Posted by Ghost

It's deja vu all over again

A couple of decades ago I got clocked doing 60 mph wearing jeans and a parka at the Jay Peak Citizen's run as a last minute entry.  I would have been faster but I opted to stand up out of my tuck on account of the fool standing in the middle of the course looking up hill to see if there was in fact a last minute entry on the way down.  I deliberately stood up straight as I wanted to kill a little speed so I would be able to safely negotiate my way around any and all obstacles and fools.  The run for the race, and the ensuing speed were much less inspiring than many other runs I had been on previously, not as steep for not as long and consequenlty a lot slower.

Go ahead, one more to go.

Excellent, and you forgot to check off several (b)'s also covered including: "That's not good enough..." and "What makes you think...?" I'd suggest a sticky, in fact, where we can just link to particular a/b sequences instead of posting them. Again.

OTOH, you are penalized one check, and do not pass go, because of egregious use of cliche humor ("It's deja vu all over again").

Quote:
Originally Posted by beyond

So sadly, I still don't believe all these speeds I read about on Epic. Or more precisely, I don't know which ones to believe, since by chance some will be more accurate than others, and a couple will be very accurate. But the differences between them look fairly random, so impossible to predict which ones to believe. Except for my own speed estimates, which are dead on. Always.

well, i guess its on you to believe or not believe if the iPhone gps (or speed gun) actually said whatever the person is claiming... but the question is what does that data actually mean?  is it meaningless?  or is there a approximate margin of error?   i would be interested to hear from atomicman if his son felt their 78mph gps reading was comparable to a 70mph speed trap reading?

anyhow, i personally really don't care.  i just run my GPS to count runs.  my point, that got everyone's panties in a bunch, was that straight lining a steep run devoid of other skiers can yield speeds as high or higher than average speed of GS race runs.  if the top speed is actually comparable to a JO or WC racer, is well beyond the point.  the point was that GS average speed over complex terrain is a different thing to consider than top speed on a single steep pitch.

atomicman's post, however, is interesting, in that he is using his son's experiential data to "disprove" the gps data, which is fair enough.  i don't doubt his son's understanding of speed, but at the same time, if you can accept experiential data to "disprove" GPS findings, can you not use experiential data to "support" them...?  its just a matter of opinion, and the reader is presented with a choice about which opinion might be "more valid", and generally on the internet, that will come down to which source is more inclined to boast about their background.

in the baseball analogy using a speed gun is used for relational data - measuring a pitcher's velocity thru a game, opposed to the absolute speed of a single pitch.

I only read the first page, but here it goes.

Bindings are designed to prevent bones breaking, not ligaments.
Soft tissue will break st MUCH lower forces than bones, so hoping to save an acl by setting your din at 9 instead of 11 doesn't make any sense.
Even a setting of 2 would not prevent acl breaking in a wrong fall.
Also, there is a lot if safety
Sorry, hard to post from a phone.
There is a lot of safety built into the din charts.

So Dan, nothing wrong with din11 or 12, if you have strong bones.

I run high DIN bindings for the housing, because they are better built. and not so much for the spring. I have no ego into what DIN I run.

Quote:
Originally Posted by Philpug

I run high DIN bindings for the housing, because they are better built. and not so much for the spring. I have no ego into what DIN I run.

Which is exactly why the FKS155 is my very favorite modern binding!

(DIN 5-15)

Quote:
Originally Posted by crgildart

The deal with GPS speed tracking is that the steeper the pitch, the more over the speed estimate will be because it measures your horizontal position change over time.  You are actually covering more ground than the horizontal change due to pitch, not very well accounted for by GPS platforms.  It does better in cars when comparing because you're not going down a 40* pitch in a car, more like a 5% pitch.

Your GPS is measuring Delta for b from above to calculate the speed where your actual ground distance is c.  Hence it will always say you are going considerably faster than you actually were. If you are making turns the speed estimate will be even more off because you are covering even more ground than was measured as b.  But if c>b then it must be overcompensating somehow or else it would show you going slower than actual rather than faster than actual.  Regardless, the slope messes with it.

crgildart, what you are describing is s more in line with taking vertical measurement with aerial photos. Several years back I was heavily involved in a project in determining vertical measurement of buildings and TOPO features for mapping.  This is exactly the problem.

Unfortunately you have forgotten that the GPS measures in 3 dimensions not 2 and therefore is accurate.  What does play into it is the sample rate and this causes speed errors.

As I mentioned in my earlier post the sample rate on the app is slow and therefore causes some variance of actual speed.

Other factors that vary speed  and accuracy on the GPS is the drift induced by the government intentionally on the public band.  This is as simple as slightly changing the clock rates.  The commercial and military GPS are significantly more accurate. respectively.  (The reason for this ability is to prevent unfriendlies from using your own system against you to launch an attack).

If you want to check this out take a know point and switch your GPS to UTM coordinates system and track the point it will drift through out the day. Knowing the drift you can compensate if you want (the differential GPS system is based on this).  Google this and you will find the related documents that provide the information.  I haven't looked into it recently to what the current variance standard is.

Other errors are caused by signal reflection/blockage and since you are in the mountains skiing there is a good chance that this can happen which will greatly vary the speed.

Quote:
Originally Posted by Rossi Smash

Which is exactly why the FKS155 is my very favorite modern binding!

(DIN 5-15)

Them along with full steel Salomon Drivers...Metal goodness with out an uber high DIN to enter the game.

Quote:
Originally Posted by Philpug

Them along with full steel Salomon Drivers...Metal goodness with out an uber high DIN to enter the game.

Let's toss in a plug for the binding that started this epic thread, shall we: Tyrolia FreeFlex+20

Oh, and here it is set on the DIN that didn't release in my cartwheeling ACL-tearing crash...

Yes, I am an idiot.  No, I have not enjoyed rehab.

Quote:
Originally Posted by Philpug

Them along with full steel Salomon Drivers...Metal goodness with out an uber high DIN to enter the game.

Quote:
Originally Posted by AlbuquerqueDan

Let's toss in a plug for the binding that started this epic thread, shall we: Tyrolia FreeFlex+20

1995 997E updated with the wide AFD from a new Sth16:

Quote:
Originally Posted by AlbuquerqueDan

Oh, and here it is set on the DIN that didn't release in my cartwheeling ACL-tearing crash...

Yes, I am an idiot.  No, I have not enjoyed rehab.

Wow. Yeah a 14 will probably release after most ACL's. Sorry. And rehab truly does suck. The good news is that after a few years there's a window where everything's good. Before it starts south again. God, we must really love this sport.

If I lose the 35 lbs that I should, I may be pushing the lower end of the DIN range at my age {59}. I picked up a couple of pairs of the Solly STH14's this spring, for the lower DIN range. My daughter's free skis are all mounted with either the Rossi FKS155's, or the Look P14. The green color works, BTW. My son still has a number of Head race skis, but his free skis are all Blizzard, and all are mounted with 916's. He spends most days coaching and skiing with his kids on a pair of Bonafides. The beat up SL skis that he uses when he's wearing coaching boots are always mounted with 916's, which work as well as anything for that purpose. The newer Solly's with the rollers in the toes may be an even better solution.

If you need to be in the DIN range of an all metal race binding, I think they are the way to go. Particularly if you could care less about older bindings on newer skis. I've also stockpiled a number of the Head/Tyrolia race plates, which are very versatile in terms of application. The wider my skis, the less use the lift, but here on the ice coast, I've found that plate to be a good one. Fairly easy to find at about \$100 a pair.

"All Metal Goodness." I love that term.

Quote:
Originally Posted by AlbuquerqueDan

Quote:
Originally Posted by Philpug

Them along with full steel Salomon Drivers...Metal goodness with out an uber high DIN to enter the game.

Let's toss in a plug for the binding that started this epic thread, shall we: Tyrolia FreeFlex+20

Where you free skiing them at 14 or racing?

Quote:
Originally Posted by jzamp

Where you free skiing them at 14 or racing?

I was free skiing on some cheater slalom skis with a bunch of gaper friends of mine after a long night of debauchery.  But I don't want to hear it; I learned my lesson.  I've already toned them down (all the bindings I'll free ski on are now set at 10.5/11).

i was just curious, not trying to lecture you ;)

One of the things that I see here  and  in another thread is that most (here) ski higher DIN bindings (and Race bindings) because of the construction and materials used and not so much so because of the higher DIN settings that are available in with these bindings (its not ego driven).  What else is interesting is that most would actually like bindings that places them in the middle of the DIN range of the binding with better materials and construction available, but if it comes down to a choice between one or the other they will opt for the better materials and construction over lower (and possibly more reasonable DIN settings, myself included).

To given an example here is the LOOK Binding (only because I know it better than the rest, so no offense intended on the LOOK's) in the PX14 vs PX15/PX18.  Given a choice, I'd take the higher series just because of the toe piece, even though it puts me below the bottom of the DIN scale at 3+ on the PX18's. Plastic just doesn't do it for me.

So maybe, manufacturers REP's listen up here,   there is a market for upscale bindings that are non-race (but built like race) and have a lower DIN range. Funny enough the market is telling you that and paying the money for it (by buying the race bindings and also looking for the protection at reasonable DIN settings).

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