Update (13nov11): Finally managed to get this revision out on snow. See the very end for the results..
First, I would like to thank Jay (tainted meat) and Andrew (Andrew L) and Mike (MD2020) for donating NTN parts for this experiment. It saved me from destroying my own working bindings as the prototypes were made and remodified as problems developed and were dealt with along the way… Thanks guys!
Theory: The theory I have is that NTN has significant resistance in tour mode that can be “detensioned” and improve tour mode greatly.
Analysis: The throw lever extends the plastic tensioning parts to engage the power tubes. Modifying those parts to have less extension could, in theory, leave the boot captured by the claw, but not under tension.
In Practice: You place the modified tensioner in the new de-tensioned mode position. You put your skins on your skis and climb in the modified free pivot mode. When you reach the top of your climb and remove your skins, you also reposition the mid part tensioner in the normal position and your binding is back to normal power tube tensioning for the ski down.
The modifications: I am not going to go through the evolution of discarded prototype modifications that led to the current version – just show the current prototype as it now stands. Here we go…. (To see any image enlarged, click on it.)
The tensioning mid part was the prime candidate for modification to relieve powertube tension. I thought that if I could modify it to have a quick release mechanism, I could drill another hole in the chrome throw lever and have a “detensioned” position for the cable tensioning parts to be in when the tour lever was lifted. The spring loaded “tits” on the tensioning midpart collapse like hammerhead adjusters to allow the midpart to be quickly switched to either position without the need of any tools.
Once I had the quick release part completed, I needed to compute how far backward to drill the new holes on the chrome lever to unload the tension on the power tubes, but still have the claw in position to capture the boot. The power tube settings affect this distance, but there is some leeway because the claw has 2 tiny springs that hold the second heel of the boot laterally.
One of the surprising things I found was how much resistance the center spring causes in tour mode. As the flex plate rotates when a skier strides, the cables are put under pressure to lengthen which engages the powertubes. De-tensioning the powertubes relieves about half that tension in free pivot mode, but as the cables shorten they must compress the center spring also which is felt as resistance in tour mode. I wanted to eliminate this resistance from the standard tour mode also.
If the center spring is removed completely, the binding doesn’t throw itself open to allow the boot to step into it, but is 100% free pivoting in tour mode if the de-tensioning holes are drilled correctly. Rather than eliminate the spring completely, I decided to try a few different replacement springs to allow the claw to spring open (with much less force now) when the chrome lever is up, yet still have a nearly free pivot tour mode in the new de-tensioned position when the chrome lever is down. (And the tour lever is up)
One of the slick things about NTN’s design is that the tensioning midpart has a little “shoe” on the bottom of it that engages the binding frame when the chrome lever is down so it takes the powertube cable tension off the arms of the tensioning midpart and rests it on the binding frame. It’s a pretty cool design. A second slot has to be precisely morticed in the frame to receive this “shoe” in the new position of the midpart or the throw lever won’t depress completely.
I was working with Version 1 bindings. They are nice because the center pivot is removeable and it allowed me to repair the v1 toe stops. I had 3 extra v1 stops that I filled with solid white oak and applied glass resin to the ends of to keep water out. The modified toe stops are not going to break.
So far, I have made 2 pair of these modified bindings and haven’t got them out on the snow yet. I am working on my house and my shop,.. and actual paying jobs (Hurray!), but I have a few local friends who also ski NTN who are the designated guinnea pigs. I hope they will give the modified binding a try and provide some feedback on the modification’s performance. One skier is Marcus, who has the TTS system, so his review will be critically awaited. Mike (MD2020) has also been extended the offer and is another local NTN skier I am friends with. Lastly is Randy, who is also a friend who skis NTN, who will be offered the chance to test the new tour mode too, if he promises not to huck them. Randy also has NTbulldogs, so his review will also be a valuable comparison of those two binding’s tour modes.
Really there’s only one more thing to do to this incarnation of NTN, and that’s to skeletonize it on the drill press to remove weight. I plan on taking one of these pairs and removing at least ¾ lb. for the pair, so the pair will weigh under 4 lbs. I think I will be able to do this easily. I am also thinking of replacing the “snow catcher” NTN heel piece with one of the more common, lightweight, streamlined 2 wire heel pieces.
Here’s the completed modified NTN with all the modifications I’ve done to it as noted.
The final modified binding has steel threaded inserts for the set screws, reinforced toe stops, the frame is cut in 2 pieces and relinked with a bicycle master link, the center spring is replaced, and the tour mode is modified to be free pivoting. I call it the “bulletproof NTN” since it addresses and corrects all the warrantied defects of NTN since it’s debut.
**** There are 2 significant things to mention:
1) These modifications will void your warranty with Rottefella
2) The changed center spring may effect the release function when returning the binding to normal position ski mode (thanks bambi for pointing that out).
FINALLY: On Snow Testing
What can I say — it worked flawlessly. It took me a total of 10 seconds per ski to switch each ski back from the modified tour mode to the normal ski mode. I didn’t climb a very steep hill, but the modified tour mode felt 100% free pivoting to me. It’s a vast improvement over the standard NTN tour mode. It’s not an easy modification to make to the binding, and I don’t see myself doing it for people who have already spent $300+ dollars on a binding when it would void their manufacturer’s warranty, but it does show that there’s more room for improvement in the NTN system, and hopefully the system will get lighter and more free pivoting straight from the factory while retaining all of it’s present features, and also skiing as well as it undeniably does.