Running length vs effective edge - conversion

[nate]

The conversion does not work for any snowboard out there.

I'm not sure why you say this. The math is exactly the same either way.

I am not shure if I understand the problem... effective edge is just another name for the length of the sidecut in a straight line, running length is the length of the camber. there is not necessarily any coherence.

If you have the circle that is the sidecut radius of the ski, the running length is a secant whose midpoint is x mm above the edge of the circle. [x is the sidecut of the ski. Ie in a symmetrical ski it's the width of the tip minus the width of the waist, divided by two. (as it turns out I neglected to divide by two in my previous calculations, so the effective edge is actually slightly less)] The effective edge is the length of the curve belong that secant.

I doubt that made this much clearer for you.

[Head Monkey]

Here you go: http://mathworld.wolfram.com/CircularSegment.html

I think that with a tiny bit of discussion you’ll find that you can get a reasonable group of people to agree what these two terms should mean. Unfortunately, that doesn’t mean anyone else in the industry agrees with you. You will continue to find EE and RL used interchangeably all over the place, or transposed, or just given as two measurements that appear to have zero mathematical relationship. Why? Two reasons I suspect: the first being that most of the people who design skis and boards aren’t engineers (or sticklers for detail) and the second being that it really just doesn’t matter all that much.

The most interesting thing here was articulated quite nicely by G-man back on page one…

[endre]

If you have the circle that is the sidecut radius of the ski, the running length is a secant whose midpoint is x mm above the edge of the circle. [x is the sidecut of the ski. Ie in a symmetrical ski it's the width of the tip minus the width of the waist, divided by two. (as it turns out I neglected to divide by two in my previous calculations, so the effective edge is actually slightly less)] The effective edge is the length of the curve belong that secant.

I doubt that made this much clearer for you.

the math is very clear to me nate, I just say there is no geometrical coherence between the running length and the effective edge of skis.

[knightsofnii]

check rome's boards,

every single one i checked, in every length, has an effective edge 5cm longer than the running length.

Still looking for their definitions. But to me that does not compute to Rome using any kind of arc length as their "effective edge" but I have no time to do that math.

I think they simply want the contact points 2.5cm out farther than where the tip bends start, to keep things from being catchy. They probably discovered this by trial and error and not anything mathmatical

[doughboyshredder]

you make me want to scream.

[doughboyshredder]

I think they simply want the contact points 2.5cm out farther than where the tip bends start, to keep things from being catchy. They probably discovered this by trial and error and not anything mathmatical

did you even read the thread??????????????????????????????

how much did you smoke?

They are tossing out a number for no reason other than it doesn't fracking matter.

They decided to add 5 to all their boards prolly because the actual variation is so minor that it doesn't matter.

running length is straight, effective edge is measured along the curve of the edge. so with a big sidecut add 3 with a small sidecut add 7, for literature, and ease SINCE IT DOESN'T MATTER add 5.

[CFO]

Knightsofnii, I am with you on this. Burton's decks seem to have effective edge 4 cm longer than running length. And now when you mentioned that it could be due to widest part of tip/tail being off the ground, it makes sense.

Doughboyshredder, I checked you post on "v" sidecut (the one with radii outside and straight lines in the middle). How does the board perform btw? Anyway, it made me wonder how to compare K2 geometry (snowboards) and say Burton. I emailed K2 to ask for conversion of RL to EE, and they could not tell me (I guess the reply came from a salesperson rather than from a tech guy, which does not help much).

So in the end I think Knightsofnii's explanation makes the most sense to me. Because according to the formula, there is no way a snowboard or a ski would have 5 cm extra effective edge when compared to RL. So I guess it all comes down to the definition.

Peace!

[doughboyshredder]

wow, you guys are dense.

[numpty]

I assume this discussion ended already and I may have missed the point but since the original question hung somewhat unanswered I thought I would explain my understanding just in case it helps a new builder.
Effective Edge is the length of the sidecut between the widest part of the tip and tail.
Running Length is the distance between the two points that a ski touches a flat surface when you sit it on its base.
They can differ and are not related. Where the tip and tail start to bend up is a matter of choice. It can be the widest part of the tip and tail making EE and RL the same but this may not be ideal, certainly at the tip. Starting the tip rising before the widest part can have many advantages in turn initiation.

[Alex13]

I'd tend to agree with Head Monkey - there's probably no real set definition. My own definition of it is pretty similar to numpty - running length is the linear distance between the tip and tail of the board that touches the snow, effective edge is, well, the effective edge... the length of the edge that has an effect on turning.

I wouldn't be surprised if some companies use effective edge as the linear distance between the two points, where some others include the extra distance taken up by the arc of the curve.

For my own input on Rome's designs though, Paul Maravetz (one of Rome's co-founders, and design engineer at Rome) is a qualified engineer. Engineers don't generally just throw out useless numbers, or "close enough" estimates. I would think that the 50mm difference has meaning somewhere, though I don't quite buy the "25mm extra either side fits all" explanation either. It's more plausible to me than "it means nothing" though.

Whether it matters or not is another story.

[numpty]

I think this issue really matters if you want to design & build skis or boards for groomed snow.
I have a pair of Fischer Cold Heat skis in front of me. These are really solid carving skis and they initiate and carve better than any ski I own.
The widest part of the tip is a full 3" in front of the point where the tip begins to turn up. This makes the effective edge 3" longer than the running length.
In snow boards the widest part is often 1" in front of the tip or tail bend giving a total of 2" (50mm)longer effective edge. I think this was found by testing various designs and it is not mathematical, it just works better.
Initiation and stability in a carve are not easy to design in without actual ski testing.
Anyone out there ever work for Fischer or one of the other trad ski companies that can speak to the effect of changing the effective edge?

[knightsofnii]

I think this issue really matters if you want to design & build skis or boards for groomed snow.
I have a pair of Fischer Cold Heat skis in front of me. These are really solid carving skis and they initiate and carve better than any ski I own.
The widest part of the tip is a full 3" in front of the point where the tip begins to turn up. This makes the effective edge 3" longer than the running length.
In snow boards the widest part is often 1" in front of the tip or tail bend giving a total of 2" (50mm)longer effective edge. I think this was found by testing various designs and it is not mathematical, it just works better.
Initiation and stability in a carve are not easy to design in without actual ski testing.
Anyone out there ever work for Fischer or one of the other trad ski companies that can speak to the effect of changing the effective edge?

what do you mean by "the widest part of the tip is a full 3" IN FRONT OF the point where the tip begins to turn up" ? Is the widest part in the rise of the tip bend, or is it in the flat part of the ski/board?

From my experience this part needs to be beyond the point where the bend starts, ie pulled away from the snow.

Now, I will go and read the rest of this, sorry doughboy no i did not read this entire thing, i saw secant this and that and it made my brain hurt.

I've come to my own defenition of effective edge and running length, and am figuring our their relationships basically by trial and error, but my own definition is probably not going to be in line with anyone elses. I'll talk more to that when i'm done reading, byebye.

[numpty]

In many modern twin tip skis (non-rocker) the point where the ski touches the snow when it sits flat is also the widest part of the ski. I have an Icelantic Pilgrim in my hand and it is this way.
In skis designed for carving the widest point of the tip is further forward (away from the center of the ski).
This makes the effective edge longer than the running length. It helps the performance of the ski, I am not sure why. Snowboards do the same.

I am curious why this is and would love to hear from anyone who has practical theories as to why this works. I am going to build a pair of skis identical to a pair I have with the EE = RL and increase the EE just see what happens. A huge investment but I am curious now.

[knightsofnii]

ok DB i now understand why you want to scream. You believe the running length is the length of the board in contact with the snow (when camber flattened) correct? And that the "effective edge" is this value except the arc length of the sidecut along this running length, thus being a pinch longer than the RL?



But it hasnt changed my own opinion of what these things are.
Maybe I drew my opinion on assumptions that were less educated till now...

Though I believe you're right.

And g man is right as well. Effective edge will change based on how the board is bent, what type of snow, where you weight the ski/board, etc.

And doughboy is probably also right that lots of times the numbers on the sites are completely fictional, as they will even take the exact same board as last year and somehow it's a different length... anyway.

My definition of "effective edge" which is wrong by nature, comes from the design stages. In a 2d shape of the board, the effective edge, for me, is the distance between the widest parts of the board. Why is it wrong? because when i bend the board, the REAL effective edge becomes just what doughboy says, or what g-man says. So maybe I'll call it "design effective edge", because the actual effective edge will change when I bend the board.

Anyway, I like my boards with a "designed effective edge" going beyond the points where the tips are bent. So my "running length" will end up shorter than my "designed effective edge". The actual effective edge will probably be somewhere between the two.

To put it in my perspective, make a mold with running length beyond the widest parts of the board, and go ride that board, or go try to ride it.

[Alex13]

Doug,

Are you talking about the linear (straight line) distance between the two points as effective edge, or the length along the curves (both sidecut and camber/tip/tail bends)?

If it's the linear distance, I see your point; if you're talking including the bends then it should stay the same regardless of bends, should it not? Assuming no stretch in the board during pressing of course.

My own definition is the same as yours, i.e. linear distance not the arc of the sidecut. Why? Essentially because determining the length along the sidecut arc is extra work for no real benefit, it's basically irrelevant if the arc diameter(s) itself is also specified.

BTW guys this is great insight in to the design itself of the boards for new people like myself, the "arguments" presented for each of your cases are giving me some good knowledge, so thanks.

*edit* - I'm not sure your definition is "wrong by nature" either - it's effective edge, not effective edge length. To me that leaves it open to interpretation.