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mounting twin tips behind centerline? why? how much?

post #1 of 23
Thread Starter 
On a thread about the Dynastar Troublemakers I believe someone mentioned they either mounted theirs 1 cm. behind centerline (or wished they had). I also saw something similar on some review online where someone said they wished they had thiers mounted 1-2 cm behind centerline (since they didn't do the park that much and used them more for mogul or tree skiing).

Can someone explain me the reasoning behind this, as well as what the recommendation would be (1cm? 2?). That last statement peaked my interest because I've been checking out the troublemakers and I am mostly a mogul/tree skier and if I hit the park, it'll only be to practice some basic old man jumps (no crazy stuff).
post #2 of 23
>...Can someone explain me the reasoning behind this, as well as what the recommendation would be (1cm? 2?)...

The assumption behind this suggestion is that the mfgrs' suggested mounting point is biased towards users who would prefer ease of spinning their skis for tricks in the park. As the mounting point is moved forward, the "swing weight" (polar moment of inertia) of the skis decreases.

As to "how far", it all depends on how far the mfgr moved the mounting point forward of the "normal" fore-aft position, and that is something only the mfgr knows. IMHO, 1 or 2 cm is a reasonable guess, but still is only a guess.

HTH,

Tom / PM
post #3 of 23
Besides inertia twins standard mounting points is moved forward also for switch landings and other fakie maneuvers in the park and espacially pipe. If you want to hit the park don't move the mounting point backwards.

For normal skiing use 3-4-cm back from that point usually works best - I got mine (1080 in 181 length) mounted 2 cm back which is somewhat of a compromize in between.

Hope that helps.
post #4 of 23
Thread Starter 
It helps. So what you are saying is the centerline on a twin tip is forward of the centerline of any other ski the same size (whether it's a carving ski, powder ski, or even a mogul ski).

I wouldn't be using the skis to do anything switch (at least not on purpose or if I do.. it'll be once in a very rare while if I am screwing around). I normally ski on bump skis and this would be my 'all mountain skis that do all right on the bumps' so I would be using them for; bumps and tree skiing, and just cruising around.. and if I hit the park it'll only be to do some jumping on the smaller jumps, but NOT riding in or landing switch and the types of jumps I would do would be stuff like spreads, twisters, daffys, cossak (my favorite), and I am going to learn the helicopter this year. I don't plan to hit the pipe or the rails.
post #5 of 23
What I did Mack, was to have the shop mount atomic 412's moved to the bindings forward position, and then mounted on the ski at the suggested ski mounting position. This gives the ability to ski the ski in three positions behind the skis normal mounting position. I ski them with the binding in it's normal center position, which is about 1 cm back. I haven't tried the farthest back position, nor have I tried the forward position. I think the total movement of the binding is about 2-2.5 cm. If you don't have a problem with atomic bindings this a very flexible arangement. Later, RicB.
post #6 of 23
Quote:
Originally Posted by Mack
It helps. So what you are saying is the centerline on a twin tip is forward of the centerline of any other ski the same size (whether it's a carving ski, powder ski, or even a mogul ski).
Correct.
If any, you can only compare (well - just a bit) the center positions relatively to the length of the running edge, meaning deducting most of the twin's rear tip.
post #7 of 23
Thread Starter 
I got some look bindings already bought for them so the Atomic binding is not an option. Although I'll say that's good thinking!
post #8 of 23
Go to a shop and take a look at the Rossi Scratch FS, they have two marks for bindings. Try contacting Dynastar, get their advice.
I think a person with bigger boots could move their center back more than
someone with smaller boots, and get their ball of foot on the center of running length.
On another subject, if you are thinking about foamed liners, why not look into Green Mountain Orthotic Labs as opposed to Surefoot? I don't know, Surefoot is OK--but the person foaming your boots might have been working in the sunglass store next door
a few weeks previous... GMOL does Conformable liners also. Finally, if you are a bumper, you might want to go with having the liners foamed "stiff", they'll hold up better to the pounding.
post #9 of 23
Thread Starter 
Thanks for the advice. If anyone else has any experience with the troublemakers or other twin tips and mounting them behind centerline (and how much or what it did to the ski).. I'm all ears.

JohnJ - yeah.. I might just go to GMOL.. I've been considering that. IF I go to surefoot, I'd only go to 'Ray' at Killington, who comes highly recommended and has been doing it for a long time.. Thanks for the advice on how stiff to get the foam, not all I got to decide is about how stiff of flex (forward flex) do I want on the boot for bumping.
post #10 of 23
Be careful on this one. The centerline on many twins is a compromise between better park performance and better slope performance but not always. One idea is to mount your ski via the method Peter Keelty and others recommend. They believe the ball of your foot should be mounted on the center of the ski. They remove their liner from their boot so they can determine where the ball of their foot is and mark it on their shell. They then put the ski flat on the floor and measure the running length then the place on the ski which is half the running length. They have the ski mounted up so the ball mark on their boot is on the running length center mark.
post #11 of 23
Yeah it definately depends on the ski.
post #12 of 23
Thread Starter 
Quote:
Originally Posted by Scalce
Yeah it definately depends on the ski.
That's kind of why I am hoping someone responds with some experience on the troublemaker. Otherwise, I'll probably just mount on the centerline, even if I don't really care about 'park performance' (just to play it on the safe side).

Rio - on regular (not twin tip) skis, is the marked centerline usually the same as that method you describe? or will that method provide something different than centerline even on a ski that is not a twin tip? Also.. do a lot of shops know of that method or would I have to measure it on my own and mark the ski and then tell the shop to mount it at the spot I marked?

Stupid question.. the marked centerline.. how are the bindings mounted relative to it?
post #13 of 23
look at your boots, there is a little arrow that shows the center of the boot. That arrow is typically lined up with the centerline on the ski and the binging is mounted to the ski to allow the boot to be in that position.

Now, I haven't seen the troublemakers, but do they have only one mark? A lot of twin tips are being marked for center and core center (usually like 7cm forward of center). Personally, I do not like the concept of mounting behind the standard mount position (hell even a lot of racers race with their bindings mounted +1 or 2 cm).

With Dynastar (and other major manufacturers) I would assume that the centerline is marked the same as a non-twin tip ski. When you start getting into the more "niche'd" twin tips (and smaller companies, i.e. Line, Armada, 4FRNT...) they may mark their center a little different (but they normally have multiple mount reference points).
post #14 of 23
There is a center of boot sole mark, that is lined up with mark on ski.
These marks seem to be all over the place, even skis by the same mfg.
I have a 177 724 Pro and a "180" Explosive(CMH). They are the same stand up
length. The Explosive mark is 71cm off tail (2.5 cm behind "regular" Exploders).
The Pro mark is 76.5cm off tail. Now, Volkl was touting a forward set to their
sidecuts on skis such as the Pro, so that accounts for some difference.
And CMH has their center mark further back than the regular, figuring
that customers are not necessarily in skiing shape......
post #15 of 23
Quote:
Originally Posted by Mack
It helps. So what you are saying is the centerline on a twin tip is forward of the centerline of any other ski the same size (whether it's a carving ski, powder ski, or even a mogul ski)...
No. Not only will the position of "the centerline" (sic, fore-aft center) of a ski vary within a group of skis of the same size, there are many fore-aft centers that must be considered for each ski. Below is some material I previously wrote on this topic:

"...using a binding and/or plate that is easy to adjust (fore-aft) is really the way to go. I’ve experimented with binding position in the past, and it is a very informative experience.

The problem with trying to do better than the mounting point recommended by the mfgr is that there are a lot of other nearby interesting mounting locations besides the center of the running surface. One can make valid arguments that:

1) Mounting the binding at the center of mass of the ski reduces the "swing weight" or polar moment of inertia. Such a position would be good for pivoting and aerial maneuvers;

2) Mounting it somewhere between the center of sidecut (ie, the waist of the ski) and the center of flex might be good for pure carved turns;

3) The center of area (which is very close to the center of upward pressure) would be good for softer snow;

4) A bit “forward” (ie, from something … what?) is better for lower level skiers to help initiate turns;

5) A bit “back” is better for powder to reduce tip dive. Volkl got burnt on this one in their early Explosivs.
6) The center of the chord length is easy for techs to measure and reproduce, etc. etc.

7) The center of contact length is a fore-aft location on the ski that is relatively easy to measure (albeit a bit more difficult to measure than the center of chord length), and may be an interesting "cener" for hard snow when you are on your edges much of the time. However, if this "center" is suggested for soft snow use, be aware that is only is an approximation of center of pressure, a location of much more significance for this application.

Mfgrs try to achieve a compromise between all of these "centers", biased/weighted by their perception of how the particular ski model will probably be used by the "average" buyer. On a pair of skis that you are not familiar with, you have absolutely no idea where their compromises caused them to place their mark, and hence, you generally don’t even know which is the correct direction to go from their mark for your own particular purposes (TT's being an exception). Go with an adjustable binding, particularly if you have never played with fore-aft adjustments before..."

The other posts in the quoted thread may also be of interest to you, as well as other similar threads, e.g.:

http://forums.epicski.com/showthread...5680#post15680
http://forums.epicski.com/showthread.php?t=4058
http://forums.epicski.com/showthread.php?t=3091
http://forums.epicski.com/showthread.php?t=3937

This topic comes up on EpicSki with clockwork regularity, usually in the fall. The above threads are from 2001, 2002, 2003, and 2004.

HTH,

Tom / PM
post #16 of 23
My Pistols have a "Core Centre" and "Mid Sole" marked on it.
The core centre is 7.5cm ahead of the mid sole. My bindings are mounted at Mid Sole + 1 (or, 6.5cm behind the core centre)
I wanted them set up purely for powder, not for the park.
post #17 of 23
Quote:
Originally Posted by Mack
Rio - on regular (not twin tip) skis, is the marked centerline usually the same as that method you describe? or will that method provide something different than centerline even on a ski that is not a twin tip? Also.. do a lot of shops know of that method or would I have to measure it on my own and mark the ski and then tell the shop to mount it at the spot I marked?
No, the midsole mark varies between skis. Volkls tend to be mounted further back than the average ski while Dynastar's & Salomon's tend to be mounted forward. That is why Peter Keelty prefers figuring it out himself. A lot of good shops have heard about this form of measuring but I don't know of anyone that provides any help. In Bozeman all the shops will mount the bindings to where you want since so many people request custom mounts. At the shop I usually get my skis mounted at the guy says the most popular request is to move the bindings forward on normal skis.

Here is a thread where we talked about it last season.

http://forums.epicski.com/showthread.php?t=1840
post #18 of 23
In a controled test done at snowbird by Nordica, the results were that every skier prefered a froward mounting, and the mean was 3.2 cm's. The results were then totaly ignored. Later, RicB.
post #19 of 23
Quote:
Originally Posted by PhysicsMan
>...Can someone explain me the reasoning behind this, as well as what the recommendation would be (1cm? 2?)...

The assumption behind this suggestion is that the mfgrs' suggested mounting point is biased towards users who would prefer ease of spinning their skis for tricks in the park. As the mounting point is moved forward, the "swing weight" (polar moment of inertia) of the skis decreases.

As to "how far", it all depends on how far the mfgr moved the mounting point forward of the "normal" fore-aft position, and that is something only the mfgr knows. IMHO, 1 or 2 cm is a reasonable guess, but still is only a guess.

HTH,

Tom / PM
I agree with Tom and would emphasize his point that the instruction is to ease spinning, INCLUDING flat spins a la 70s freedogger style.

be careful, as you could make engaging the shovels very difficult if you move the bindings rearward. my AT binders on my BD Havocs (twin tip) are mounted at the factory recommendation, which turns out to be in a spin-friendly position which makes switching front/back skiing easy, but makes engaging the tips for sweet carves almost crazy hard. I'm moving the binders forward this season.
post #20 of 23
Quote:
Originally Posted by PhysicsMan
4) A bit “forward” (ie, from something … what?) is better for lower level skiers to help initiate turns;
Really good stuff, I just had to take exception to this one.

I personally know of several sub 100 points (male, beefy dudes) racers that enjoy their skis mounted forward of manufacturer suggestion.

Most female racers should be mounted that way, though interestingly few manufacturers point this out.
-Garrett
post #21 of 23
Quote:
Originally Posted by skiingman
Really good stuff, I just had to take exception to this one.

I personally know of several sub 100 points (male, beefy dudes) racers that enjoy their skis mounted forward of manufacturer suggestion.

Most female racers should be mounted that way, though interestingly few manufacturers point this out. -Garrett
For reference, the quote from my previous post that is under discussion is:

"...One can make valide arguments that ... a bit forward is better for lower level skiers to help initiate turns..."

The above statement does not imply that mounting bindings a bit forward would *not* also be better for high level skiers. It simply makes no statement about high level skiers. It's just like saying, "good tires are important for a novice driver". That certainly does not imply that good tires are not important for an experienced driver - it makes no statement about the experienced driver.

I intentionally didn't make a statement about the preferences of experienced skiers because some like their bindings forward (as you pointed out), and some prefer their bindings mounted a bit back (at least for some applications).

Sorry for I wrote this particular sentence so tersely. I hope I didn't mislead anyone else, but the post of mine that you quoted from was already getting way too long, and I was trying to prevent it for getting even longer.

Cheers,

Tom / PM
post #22 of 23
Quote:
Originally Posted by PhysicsMan
Sorry for I wrote this particular sentence so tersely. I hope I didn't mislead anyone else, but the post of mine that you quoted from was already getting way too long, and I was trying to prevent it for getting even longer.

Cheers,

Tom / PM
]

I know that feeling. It was a really good post.
-Garrett
post #23 of 23
Actually have/ski the Tms. they do come with a 'long' tail - that is compared to my previous volkl twin tips, they are mounted further forward. However, after a few days of skiing them (and for that matter any other ski), YOU will adapt to them, and enjoy them in the conditions you speak of with out having to have the headache of adjusting the mount.

I ski mine both in the park and as my allround everyday ski - and have no problems with them as they are recommended to be mounted.
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