Renoun Endurance 98 184, Look Pivots mounted to the recommended boot center.
Me: 5’ 10”, 175 lbs, PSIA 8 (on a good day).
Current daily driver: Head Rev 85 Pro 177, which I love. Past loves: Atomic Access 171, Head Worldup iSL 160.
Conditions: Bulletproof groomers early, changing to softening corn over hardpack and deep heavy mashed potatoes.
Short summary: Part of me was really hoping that I wouldn’t like them, because then I could send them back and get a pair of Rustler 10’s for less than half the price. But I don’t think that’s gonna happen.
There's a lot of headscratching about these, so first I want to talk about what I think I understand about the technology; I’m a mechanical engineer and during my one day on these skis I had so many seemingly contradictory impressions of them that I needed to do some research to try to make sense of it. Hopefully by the end I’ll be able to do that, and if I get anything terribly wrong I’d appreciate being corrected.
We talk a lot about stiffness and dampness, but I think it would be good to make sure those terms are carefully defined. Stiffness is the measure of how much a spring will deflect under a given load. Damping is the measure of how aggressively the energy of the motion is dissipated by the system.
Think about a mass hanging on a spring. If you pull it down and release it it’ll bounce up and down for a really long time because there’s very little damping; this condition is called underdamped. On the other hand, if you attach a really strong damper between it and the ceiling it’ll very slowly return to its normal position; this is called overdamped. Somewhere in between is an amount of damping that will allow it to settle to its final position in the least amount of time without any overshoot; this is called critically damped. If take a critically damped system and make the spring stiffer, you’ll find that it’s now underdamped. So this balancing act between mass, stiffness and damping is what you’re feeling when you experience how damp a ski feels.
HDT is Renoun’s name for what is more generally known as dilatent fluid damping. As you know from watching Renoun’s videos, dilatent fluids have a viscosity that increases with increasing strain rates (the speed at which its being deformed); silly putty and water/corn starch mixtures are common examples. If you google search the phrase “dilatent fluid damping” you’ll find a boatload of technical papers on it, one paper in particular being Smart Viscous Dampers utilizing Shear Thickening Fluids with Silica Nanoparticles (http://www.iitk.ac.in/nicee/wcee/article/WCEE2012_1639.pdf). I’m pretty sure that the material tested in that paper is similar to what Renoun uses (EDIT: I’ve since found out that it’s NOT the same material - see post #12 below). Pull the paper up and study Figure 4.2(a), and you'll see that the material it tests shows some very interesting behavior: if you hold the displacement of the material constant and increase the frequency at which you deform it, the amount of force it takes to do so increases. If you compare that with Figure 4.2(b) through (d), you’ll also see that if you hold the frequency constant and increase the displacement, the amount of force needed also increases.
So how might I expect these skis to feel? Think about a sharp-edged ski with this stuff in it on a hard-frozen groomer. When you tip the ski and get the edge to bite there won’t be a lot of compliance in the grip; the edge will either grab or it won’t. The leading point of contact will skip over surface irregularities (such as the peaks of the corduroy) at a very high frequency, which will cause the fluid viscosity to increase to a very high level. The ski will be highly overdamped; when you pressure the tips to try to bend the ski it will respond very slowly and give the impression of being very stiff (but remember, the dilatant fluid does not actually make the ski stiffer).
As the surface begins to soften it will begin to yield to the leading point of contact; there will be a transition from skipping over a hard surface to a steady peeling away of the snow under the edge. As that happens both the input frequency and the amplitude of deformation of the ski will drop, which means the fluid viscosity will drop, which means that the ski will bend more readily in response to pressuring and will thus feel softer. When conditions are very soft and you’re going slow you’ll have a very low deformation amplitude and frequency, and the ski will feel fully compliant. But then if you increase speed the amplitude and frequency of deformation will go back up, and the ski will feel less and less compliant again.
And guess what? - that’s EXACTLY what I had experienced. In the morning when I put them on edge on a bulletproof groomer I couldn’t get them to bend, they felt like 2x4s locked into a single turn radius that they liked and that was it. But as the hardpack softened up they started feeling more compliant. In deep cut-up piles of mank I was making these nice bouncy short radius turns, then bombed some wide GS that ended up going a LOT faster than I normally would have felt comfortable with in that stuff but these things were just smooooooth. At one point on a steep, firm (but not too firm) run with piles of corn all over the place, I realized at the last instant that I was about to carve over a nasty set of slalom-course gate ruts going completely the wrong way and my heart leapt into my throat. I KNEW I was going to get spread out all over the hill, but they just registered as a blip as I went over them. It was a total non-event, even though my GPS showed I was doing around 40 mph. And then I went dancing though a mogul field for a while, and that was good too.
I did end up concluding that the 186’s are too long for me, just a bit too much input was needed to get the turn shapes I wanted. But aside from that, I found that pretty much no matter what I wanted to do or where I wanted to go, whatever turn shape I tried, these things would go there at any speed that I had the nerve for without any excitement. At first they seemed boring because they’re so quiet, they don’t feel poppy and energetic and I like poppy and energetic so I missed that. But they’re compliant and responsive enough to be a lot of fun in bumps and at low speed, and then at high speed can go from hardpack to piles of mush and back in a single turn with minimal disturbance. As the day progressed I went from “meh” to “hey, that’s neat” to “wow, that’s really impressive” to “damn, these things are kickass!”.
So pending further evaluation, it looks like the biggest tradeoff I can find on these things is compliance while on a hard carve on boilerplate. Yeah, well, boilerplate isn’t what I’m getting a pair of 100-ish underfoot skis for. And there’s probably a lot you can do with the fluid properties in terms of strain-rate sensitivity and relaxation time to tailor the feel differently for a different style ski… I’d really like to drive the Z-77s sometime to see how it compares. I’m kicking myself that I didn’t think of this first, and I told Cyrus that I hope he makes a boatload of money on it.
And I’m really impressed by the customer service. I sent an email explaining why I thought I should get the 178s, and a couple of days later Cyrus sent me an email on Sunday evening. We had a brief back-and-forth, and the next morning I had a tracking number by 9:00 AM and the skis in hand by Tuesday evening (overnight from VT to MI was only $50). He didn’t even wait until I shipped the first pair back, told me to swap the bindings out and ship them back afterward! So I’ve got the 184s boxed up now for return, am waxing the 178s to take north this weekend, and have a trip to A-Basin tentatively planned for April 12-14.
Oh, yeah, one more thing: the talk about how this fluid doesn’t comply with Newton’s Third Law drives me crazy. EVERYTHING complies with Newton’s Third Law, these are non-Newtonian fluids but that refers to Newton’s Law of Viscosity which is a completely different thing. That really gets my inner nerdgeek-rainman going.
Anyway, back to putting base-prep heat cycles on these things!
Me: 5’ 10”, 175 lbs, PSIA 8 (on a good day).
Current daily driver: Head Rev 85 Pro 177, which I love. Past loves: Atomic Access 171, Head Worldup iSL 160.
Conditions: Bulletproof groomers early, changing to softening corn over hardpack and deep heavy mashed potatoes.
Short summary: Part of me was really hoping that I wouldn’t like them, because then I could send them back and get a pair of Rustler 10’s for less than half the price. But I don’t think that’s gonna happen.
There's a lot of headscratching about these, so first I want to talk about what I think I understand about the technology; I’m a mechanical engineer and during my one day on these skis I had so many seemingly contradictory impressions of them that I needed to do some research to try to make sense of it. Hopefully by the end I’ll be able to do that, and if I get anything terribly wrong I’d appreciate being corrected.
We talk a lot about stiffness and dampness, but I think it would be good to make sure those terms are carefully defined. Stiffness is the measure of how much a spring will deflect under a given load. Damping is the measure of how aggressively the energy of the motion is dissipated by the system.
Think about a mass hanging on a spring. If you pull it down and release it it’ll bounce up and down for a really long time because there’s very little damping; this condition is called underdamped. On the other hand, if you attach a really strong damper between it and the ceiling it’ll very slowly return to its normal position; this is called overdamped. Somewhere in between is an amount of damping that will allow it to settle to its final position in the least amount of time without any overshoot; this is called critically damped. If take a critically damped system and make the spring stiffer, you’ll find that it’s now underdamped. So this balancing act between mass, stiffness and damping is what you’re feeling when you experience how damp a ski feels.
HDT is Renoun’s name for what is more generally known as dilatent fluid damping. As you know from watching Renoun’s videos, dilatent fluids have a viscosity that increases with increasing strain rates (the speed at which its being deformed); silly putty and water/corn starch mixtures are common examples. If you google search the phrase “dilatent fluid damping” you’ll find a boatload of technical papers on it, one paper in particular being Smart Viscous Dampers utilizing Shear Thickening Fluids with Silica Nanoparticles (http://www.iitk.ac.in/nicee/wcee/article/WCEE2012_1639.pdf). I’m pretty sure that the material tested in that paper is similar to what Renoun uses (EDIT: I’ve since found out that it’s NOT the same material - see post #12 below). Pull the paper up and study Figure 4.2(a), and you'll see that the material it tests shows some very interesting behavior: if you hold the displacement of the material constant and increase the frequency at which you deform it, the amount of force it takes to do so increases. If you compare that with Figure 4.2(b) through (d), you’ll also see that if you hold the frequency constant and increase the displacement, the amount of force needed also increases.
So how might I expect these skis to feel? Think about a sharp-edged ski with this stuff in it on a hard-frozen groomer. When you tip the ski and get the edge to bite there won’t be a lot of compliance in the grip; the edge will either grab or it won’t. The leading point of contact will skip over surface irregularities (such as the peaks of the corduroy) at a very high frequency, which will cause the fluid viscosity to increase to a very high level. The ski will be highly overdamped; when you pressure the tips to try to bend the ski it will respond very slowly and give the impression of being very stiff (but remember, the dilatant fluid does not actually make the ski stiffer).
As the surface begins to soften it will begin to yield to the leading point of contact; there will be a transition from skipping over a hard surface to a steady peeling away of the snow under the edge. As that happens both the input frequency and the amplitude of deformation of the ski will drop, which means the fluid viscosity will drop, which means that the ski will bend more readily in response to pressuring and will thus feel softer. When conditions are very soft and you’re going slow you’ll have a very low deformation amplitude and frequency, and the ski will feel fully compliant. But then if you increase speed the amplitude and frequency of deformation will go back up, and the ski will feel less and less compliant again.
And guess what? - that’s EXACTLY what I had experienced. In the morning when I put them on edge on a bulletproof groomer I couldn’t get them to bend, they felt like 2x4s locked into a single turn radius that they liked and that was it. But as the hardpack softened up they started feeling more compliant. In deep cut-up piles of mank I was making these nice bouncy short radius turns, then bombed some wide GS that ended up going a LOT faster than I normally would have felt comfortable with in that stuff but these things were just smooooooth. At one point on a steep, firm (but not too firm) run with piles of corn all over the place, I realized at the last instant that I was about to carve over a nasty set of slalom-course gate ruts going completely the wrong way and my heart leapt into my throat. I KNEW I was going to get spread out all over the hill, but they just registered as a blip as I went over them. It was a total non-event, even though my GPS showed I was doing around 40 mph. And then I went dancing though a mogul field for a while, and that was good too.
I did end up concluding that the 186’s are too long for me, just a bit too much input was needed to get the turn shapes I wanted. But aside from that, I found that pretty much no matter what I wanted to do or where I wanted to go, whatever turn shape I tried, these things would go there at any speed that I had the nerve for without any excitement. At first they seemed boring because they’re so quiet, they don’t feel poppy and energetic and I like poppy and energetic so I missed that. But they’re compliant and responsive enough to be a lot of fun in bumps and at low speed, and then at high speed can go from hardpack to piles of mush and back in a single turn with minimal disturbance. As the day progressed I went from “meh” to “hey, that’s neat” to “wow, that’s really impressive” to “damn, these things are kickass!”.
So pending further evaluation, it looks like the biggest tradeoff I can find on these things is compliance while on a hard carve on boilerplate. Yeah, well, boilerplate isn’t what I’m getting a pair of 100-ish underfoot skis for. And there’s probably a lot you can do with the fluid properties in terms of strain-rate sensitivity and relaxation time to tailor the feel differently for a different style ski… I’d really like to drive the Z-77s sometime to see how it compares. I’m kicking myself that I didn’t think of this first, and I told Cyrus that I hope he makes a boatload of money on it.
And I’m really impressed by the customer service. I sent an email explaining why I thought I should get the 178s, and a couple of days later Cyrus sent me an email on Sunday evening. We had a brief back-and-forth, and the next morning I had a tracking number by 9:00 AM and the skis in hand by Tuesday evening (overnight from VT to MI was only $50). He didn’t even wait until I shipped the first pair back, told me to swap the bindings out and ship them back afterward! So I’ve got the 184s boxed up now for return, am waxing the 178s to take north this weekend, and have a trip to A-Basin tentatively planned for April 12-14.
Oh, yeah, one more thing: the talk about how this fluid doesn’t comply with Newton’s Third Law drives me crazy. EVERYTHING complies with Newton’s Third Law, these are non-Newtonian fluids but that refers to Newton’s Law of Viscosity which is a completely different thing. That really gets my inner nerdgeek-rainman going.
Anyway, back to putting base-prep heat cycles on these things!
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Ahh now I understand why I had such a hard time in bump camp at Mary Jane. I was on my Renoun's. Are they the best choice for mogul's? Probably not. Are they 2x4's? Probably not. 
