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BMX 98 chatter on hard snow. Potential tuning issue?

post #1 of 17
Thread Starter 

I just bought a pair of used Kastle BMX 98 from a fellow bear.  I took them out for a spin this past weekend at Massif du Sud, Québec. Over the course of the weekend, we experienced a variely of conditions.  On Saturday, the conditions were machine groomed hard pack, because of a mid week thaw and subsequent dip in temperatures.  No ice, but reasonably firm conditions. 

 

After a prayer to the snow gods, the skies opened up on Saturday night and over a foot of fresh fell overnight.  Thus, Sunday's surfaces were quite different, with powder and crud to be found everywhere.

 

I skied the BMX 98 in both conditions.  They were stellar in the powder, crud and windpacked snow, but much less so on groomed firm conditions.  As a matter of fact, on a hard surface, there was quite a bit of chatter. One thing that I noticed is that the edges appear to be dulled on the part of the sidecut that is in front of the early rise point.  (i.e. in front of the contact point, but behind the point of maximum width of the tip.  Otherwise, the edges are quite sharp.  Could that be the cause of the chatter.  Should I sharpen the entire length of the sidecut?


Edited by Pacobillie - 3/16/15 at 5:09pm
post #2 of 17

So you're saying they were detuned ?!?!   :rolleyes

post #3 of 17
Thread Starter 

Looks like they were detuned, indeed!

post #4 of 17
Quote:
Originally Posted by Pacobillie View Post
 

 One thing that I noticed is that the edges appear to be dulled on the part of the sidecut that is in front of the early rise point.  (i.e. in front of the contact point, but behind the point of maximum width of the tip.  Otherwise, the edges are quite sharp.  Could that be the cause of the chatter.  Should I sharpen the entire length of the sidecut?

The best thing to do is dull the area behind the early rise point. That'll fix'em (and cause a few bear's heads to explode).

post #5 of 17

Sounds like the skis do well on the conditions they are designed for.  You could reset the edge bevels tip to tail and sharpen them as much as possible, but a rockered 98 ski still isn't going to shred loops on hardpack the way a thinner, full cambered ski does. 

post #6 of 17

My guess is too much base bevel. This can happen just from wear or from over-tuning. The ski can still be sharp, but will feel vague from edge to edge and will chatter. Also, the ski has no metal, expect a bit more chatter than something with metal such as an MX series ski.

post #7 of 17
Thread Starter 
Quote:
Originally Posted by epic View Post
 

My guess is too much base bevel. This can happen just from wear or from over-tuning. The ski can still be sharp, but will feel vague from edge to edge and will chatter. 

Nope!  I just ran a true bar against the length of the ski and the base bevel appears to be normal, i.e. about one degree and it looks consistent from tip to tail.  Further, the ski does not feel vague when skiing.  Edge engagement is very positive, but when carving at medium to high speed, the ski starts chattering and it skids a bit.

post #8 of 17
Quote:
Originally Posted by Pacobillie View Post
 

Nope!  I just ran a true bar against the length of the ski and the base bevel appears to be normal, i.e. about one degree and it looks consistent from tip to tail.  Further, the ski does not feel vague when skiing.  Edge engagement is very positive, but when carving at medium to high speed, the ski starts chattering and it skids a bit.

Where is the chatter coming from?

 

.....or is it more tip flap?

post #9 of 17
Quote:
Originally Posted by Pacobillie View Post
 

Edge engagement is very positive, but when carving at medium to high speed, the ski starts chattering and it skids a bit.

 

It's a 98mm ski without metal.

post #10 of 17
Thread Starter 
Quote:
Originally Posted by Atomicman View Post
 

Where is the chatter coming from?

 

.....or is it more tip flap?

It does not feel like  tip flap to me.  More like the front part of the ski vibrating and losing and then regaining grip over the snow surface for successive fractions of a second.

post #11 of 17
Quote:
Originally Posted by Pacobillie View Post
 

It does not feel like  tip flap to me.  More like the front part of the ski vibrating and losing and then regaining grip over the snow surface for successive fractions of a second.

Since I have to been on that ski, hard to say. 

 

But I would put a 3 degree side edge on them and make them sharp contact point to contact point . BE sure to remove hanging burr after filing and diamond stoning. 

 

If they still do it, maybe the ski is to soft torsionally for hard snow.

post #12 of 17
Thread Starter 

Thanks for the feedback.  I think that I figured out what is wrong.  The rockered section has only been partly detuned.  When I press the skis together, the rocker starts between the "A" and the "S" of the "Kastle" mark, on the topskin.  Upon closer examination, the first two inches of the rockered section are still fairly sharp.  I have a hunch that what I interpreted as chatter is actually the edge of the rockered section grabbing and then letting go, and then grabbing again, etc...

 

Please let me know if that makes sense and I will just run a gummy stone over that section of the edge.  

post #13 of 17
Quote:
Originally Posted by Pacobillie View Post
 

Thanks for the feedback.  I think that I figured out what is wrong.  The rockered section has only been partly detuned.  When I press the skis together, the rocker starts between the "A" and the "S" of the "Kastle" mark, on the topskin.  Upon closer examination, the first two inches of the rockered section are still fairly sharp.  I have a hunch that what I interpreted as chatter is actually the edge of the rockered section grabbing and then letting go, and then grabbing again, etc...

 

Please let me know if that makes sense and I will just run a gummy stone over that section of the edge.  

It could, but you should sharpen the dull part not detune the sharp part. 

post #14 of 17
Thread Starter 
Quote:
Originally Posted by Atomicman View Post
 

It could, but you should sharpen the dull part not detune the sharp part. 

With all due respect, did you not  say the exact opposite earlier,i.e.:

 

Quote:
Originally Posted by Atomicman View Post
 

 

 

But I would (...) make them sharp contact point to contact point . 

Unless by "contact point" you mean the widest part of the ski, as opposed to the contact point when the ski is flat on the snow.  In other words, are you suggesting that the whole rockered section be tuned sharp?  

post #15 of 17
Quote:
Originally Posted by Pacobillie View Post
 

With all due respect, did you not  say the exact opposite earlier,i.e.:

 

Unless by "contact point" you mean the widest part of the ski, as opposed to the contact point when the ski is flat on the snow.  In other words, are you suggesting that the whole rockered section be tuned sharp?  

No, I was talking about the contact point when the ski is tipped up on edge. not flat. 

I

 

How often do you flat run skis on hardpack...almost never. At least I don't, I always tip them up some and ride an edge. As the ski is tipped, 

 

So, for hardsnow you have to look at the contact point with the skis tipped not flat and tune it sharp from that point back. 

 

This is in reference to YOUR ski

 

So what I was talking about before is detuning towards the tip from the contact point with the ski tipped up on edge. 

 

 

SHOVEL GEOMETRIC

HOOK FREE SHOVEL

Hook Free Shovel -

SIDECUT

DUAL RADIUS BIG MOUNTAIN

Dual Radius Big Mountain -

CAMBER

EARLY RISE LOW CAMBER

Early Rise Low Camber -
post #16 of 17
Thread Starter 
Quote:
Originally Posted by Atomicman View Post
 

No, I was talking about the contact point when the ski is tipped up on edge. not flat. 

I

 

How often do you flat run skis on hardpack...almost never. At least I don't, I always tip them up some and ride an edge. As the ski is tipped, 

 

So, for hardsnow you have to look at the contact point with the skis tipped not flat and tune it sharp from that point back. 

 

This is in reference to YOUR ski

 

So what I was talking about before is detuning towards the tip from the contact point with the ski tipped up on edge. 

 

 

SHOVEL GEOMETRIC

HOOK FREE SHOVEL

Hook Free Shovel -

SIDECUT

DUAL RADIUS BIG MOUNTAIN

Dual Radius Big Mountain -

CAMBER

EARLY RISE LOW CAMBER

Early Rise Low Camber -

BTW, the last picture in your diagram shows two "Auflagepunkt"  i.e. contact points (grey arrow), which are the contact points when the ski is laid flat.  But obviouly, that is not what you meant by "contact point."  You meant the point on the edge corresponding to the widest part of the tip.  

 

I can try that.  It was my first inclination, but I also read that this will make the skis overly hooky.

post #17 of 17
Quote:
Originally Posted by Pacobillie View Post
 

BTW, the last picture in your diagram shows two "Auflagepunkt"  i.e. contact points (grey arrow), which are the contact points when the ski is laid flat.  But obviouly, that is not what you meant by "contact point."  You meant the point on the edge corresponding to the widest part of the tip.  

 

I can try that.  It was my first inclination, but I also read that this will make the skis overly hooky.

I don't think so, as long is the base bevel is correct.  All my skis are sharp contact to contact point and I have an early rise Atomic Ritual, Have a 3 degree on them and they ski great!

 

The problem is if you detune the ski that much when you are on groomers the front of the ski will not hook up at all.

 

So I would sharpen all the way to the front contact point. If you find that too hooky slightly detune a little tiny bit at a time, until you find your comfort zone.


Edited by Atomicman - 3/18/15 at 6:25pm
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EpicSki › The Barking Bear Forums › On the Snow (Skiing Forums) › Tuning, Maintenance and Repairs › BMX 98 chatter on hard snow. Potential tuning issue?