along with Brent Foes and Charlie Curnutt
What's up with the Fox RC4?
- Thread starter SthFRider
- Start date
Seems to me that if it were that big a deal, more bikes would concentrate on a lower ratio in their designs. Might point out that the v10 does pretty well too with a fairly high ratio.
Maybe its one of those things that applies more on paper? Just askin.
Socket, fill me in.
Maybe its one of those things that applies more on paper? Just askin.
Socket, fill me in.
there are a lot of bikes with lower ratios. the V10 is just one example that isnt.
lighter spring rate, higher shaft velocities, tunning makes a bigger difference...
I wouldn't say alot of current Downhill bikes are going totally with the lower leverage ratio fad. Example Trek Session 7, Specialized Demo 8, Giant Glory... Using 8.75 X 2.75 shock for 8 inches of rear travel = 2.99 Leverage Ratios.
I see no reason using the smaller stroke shocks (unless for weight purposes) but thats just retarded.
I see no reason using the smaller stroke shocks (unless for weight purposes) but thats just retarded.
Hmmmm, I could swear it 'feels' like it has lots of HSC even wound off. I perhaps don't know enough to really know what I'm feeling though. Ahhh I'm confused.
Uhh, no, there aren't. 2.5:1 is pretty common, plus or minus a bit, but definitely not 2:1. Yeah, there are a few lower leverage bikes out there, they are the exception, and my experience with foes is that their shocks work like crap, but that's probably not the leverage ratio, just the SPV valve.
2:1 is also a bit ridiculous because you then need to have smaller incriments with the spring to get the right spring weight, except that spring tolerances are only so good. You'd need something like 15 or 25lb incriments at most, and that causes issues because spring tolerances are simply not that great. There's a much higher chance of not getting the right spring. As long as you have enough fluid displacement and damping, I've never felt that a low-leverage bike works any better than a higher-leverage design, and I've owned a few low-leverage ones. Proper shock tune and damping adjustments are way more important, and there are negatives to running a 2:1 shock, like a huge and heavy frickin shock, the spring issue, etc.
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Curious why you think a leverage ratio of ~2:1 is the "most efficient ratio" for the damper? Most efficient in what way? There isn't any mathematical reason why it should really matter what the linkage ratio is, is it something to do with heat dissipation or what?
I think the low leverage thing is a bit of a hype magnet - the main advantage that I can see is that you have a bigger shock with more oil and more surface area to dissipate heat. However it still has to dissipate the same amount of energy as any other damper that's giving the same rate at the wheel, so it doesn't actually generate less thermal energy as such, it just has a bigger sink to get rid of it with. Lower leverage ratios also amplify seal drag and gas charge forces (unless you alter the gas charge pressure to match the leverage ratio, which nobody I'm aware of does except for the position-sensitive shocks) at the wheel. It might make it slightly easier for suspension tuners to work with trickier two-stage stacks and whatnot if the shaft speeds are higher and the valving is lighter, because those kinds of multi-stage stacks rely on the face shims deflecting far enough that they contact other shims in a second "stack" behind them. However I'd be pretty surprised if that was the actual reason people do it.Seems to me that if it were that big a deal, more bikes would concentrate on a lower ratio in their designs. Might point out that the v10 does pretty well too with a fairly high ratio.
Maybe its one of those things that applies more on paper? Just askin.
Socket, fill me in.
You also end up with a bigger, heavier shock and spring. Lighter spring rates = so what? Spring rate only matters when you measure it at the wheel. You can get any spring rate and any damping rate you'd reasonably want, when measured at the wheel, with pretty well any leverage ratio you're ever likely to come across in the real world, from 1:1 to 5:1.
I think a large part of the reason people started going to lower leverage rates was because years ago shocks such as the Fox RC just couldn't handle high leverage ratios - they didn't have enough compression damping, the shaft diameters were quite small and required huge internal pressures to get any significant amount of damping, and the seals didn't cope with it well. Running lower leverage ratios (anyone remember the 4:1 RM6s and RM9s that used to blow shocks to pieces on a weekly basis?) definitely made sense when it came to longevity and reducing shock fade on those things. However now we have shocks with 1/2"+ shafts, much bigger bodies, much bigger reservoirs and usable compression dampers. Maybe designers are still in the mindset of "well lower leverage ratios have made things better so far, so if we make it even lower it'll be even better!".
It might be that what you're feeling is the progression of the shock as it ramps up towards the end of the travel (both from the air spring effect and the progressive nature of the compression damping) moreso than strong HSC in the early/midstroke. Or you might have it on a bike with a significantly different leverage ratio to mine whereby it does actually have a lot of HSC when measured at the wheel.
Don't have any dyno data on me, but IIRC with a DHX5.0, the LSC damping ratio was roughly 0.35 the way I had mine set up, and the rebound (which was very linear unlike the compression) was actually close to 1.0 (quite close to being "critically" damped). You can't easily use the damping ratio as a particularly useful measurement on a bicycle though, the rider is nowhere near rigid and the nonlinearity of the damping curves means that in the HS region, the damping ratio itself is effectively speed-sensitive as even if the HS curve is dead linear, extrapolating it won't intersect with the origin. In other words, it's not a constant in the usual sense even in one direction - and the damping rates are always significantly different between compression and rebound; rebound damping rates can be anywhere from 2-4x as high as the compression.
I had never considered the impact that linkage rate has damping ratio, you have opened my eyes. I'm curious, what ranges of damping ratio are typical?
Theoretical idealism of damping rates being linear, critically damped etc as "optimum" are a long way off the mark in my opinion. There are SAE studies out there on bilinear damper modelling for cars (ie one damping coefficient in compression, one in rebound) that proved fairly effective in setting up racecar suspension to a base level, but on a DH bike those simplifications are way too extreme.
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2:1 vs. anything higher ends up demanding a higher shaft speed out of the shock. Don't really see how that is more efficient without significantly increasing the size of the shock to accommodate higher shaft speeds without spiking.
Also, any kind of shock drag is felt much more in a lower leverage system.
V10's are a great example of both of these things. Very rarely do they feel "spikey" or feel like they get overwhelmed by super high speed events. Wallowy, sure, but spiking/kicking, rarely. Their shock rate is is just lower (inverse relationship with leverage ratio). They also still feel very smooth even with clapped out and dry bushings and bearings. Sundays? Foes? Not so much...
Also, any kind of shock drag is felt much more in a lower leverage system.
V10's are a great example of both of these things. Very rarely do they feel "spikey" or feel like they get overwhelmed by super high speed events. Wallowy, sure, but spiking/kicking, rarely. Their shock rate is is just lower (inverse relationship with leverage ratio). They also still feel very smooth even with clapped out and dry bushings and bearings. Sundays? Foes? Not so much...
I don't like contributing observations as hard fact, but I've definitely seen more DHXs blow on V10 than any other frame. I'm not a fan on high leverage designs, but also not a fan of ultra low leverage designs either. I think the 9.5 x 3.0" shock dimension lends itself perfectly to the majority of 8" - 9" travel frame designs.
In the real world, I think a reasonable amount of leverage is a good thing. Shocks seem to be good enough to deal with higher leverage these days, and it just translates to a lighter shock, easier/cheaper spring rate choice (especially for lighter riders) and less seal stiction in the shock action. Plus it means you don't have to deal with obtainium's overpricing and crappy service to get your 275/325/375 spring.
Yeah ditto. I don't think there's any tangible advantage to running a leverage ratio much lower (or higher) than that on a DH bike. Maybe with air shocks it'd make more difference, where dissipating heat is more critical, but really, running a 4.5" stroke shock to get 10" of travel is a bit of an exercise in because-we-can type thinking IMO.
Thanks
I definitely agree. Critical damping across the board is only ideal if you are talking about an idealized situation, which is FAR from what we have. I was just curious to get a general idea of the realm in which our suspension operates (to try to relate it to my general, but somewhat useless, knowledge of vibrations). The butt dyno is deceiving. I definitely wouldn't have expected rebound and compression damping to be so different.
In the automotive world, rebound damping is generally about 3x as high as compression damping, because the primary concern is comfort. In racing vehicles, the compression levels are usually bumped up significantly to provide better handling at the expense of driver comfort. It's pretty rare for compression damping to ever exceed rebound damping though (if it does happen, something's probably a bit messed up, or you have a very strange/specific requirement from your vehicle) - it simply can't really, rebound dampers only have to deal with the spring force so the shaft speed is limited, whereas you can hit something harder and harder in compression, there is no real ceiling to the possible shaft speeds in compression.Thanks
I definitely agree. Critical damping across the board is only ideal if you are talking about an idealized situation, which is FAR from what we have. I was just curious to get a general idea of the realm in which our suspension operates (to try to relate it to my general, but somewhat useless, knowledge of vibrations). The butt dyno is deceiving. I definitely wouldn't have expected rebound and compression damping to be so different.