BanzaiRider said:
Wasn't sure where to post this, it's more linkage related than shock but I guess the experts all lurk here so... I currently have a Devinci Banzai, it's a "horst link/ICT" type frame with 5.75" of rear suspension and a 7.875x2.00 shock.
I've read all sorts of things about compression ratio, rising, falling rate, length of the rocker, axle path, etc. Unfortunately my technical knowledge and capacity to understand the technical stuff is quite limited, I guess my IQ is not that great or I'm too old! Hahaha
From what I understand, my frame has a relatively medium to low compression ratio. The main pivot on my bike is right above the crank like Turner's and Ellsworth's but I have a short rocker link compared to Ellsworth's bikes.
Now, you are probably asking, what the heck does he want.
Well, I've been thru 3 different air shocks on this bike, the latest being a Push'd RP3 custom for me which is supposed to be one of the best. I'm still unsatisfied with the performance of my rear suspension when going downhill, especially on small bumps but a bit also on medium to large stuff. Basically I have no experience with bikes aside from my old Giant NRS and my friend's Giant VT. We can skip immediately the NRS but as far as the VT is concerned, it's the version with the Swinger 4way and it is really quite a bit nicer then mine when going downhill. It feels much plusher, especially on small bumps.
So I am trying to understand my suspension design to see if it could be the culprit or if it is the shock, or even the geometry. It's definitely not my bearings; those are awesome needle bearings that feel like running on butter when I take off the shock. Also my suspension action is awesome for going uphill, no bobbing at all but it absorbs everything, never looses traction.
Do you guys think that with a rocker link like mine, this could lead to a "stiffer" suspension movement then if it had been conceived with a long rocker link like Ellsworth's? Is it the geometry since the seat tube places me relatively over the crank compared to the VT so the weight transfer is not as much on the rear? Is it because that type of suspension would perform better with a non platform shock? Or is it just because that type of suspension will never provide the bump absorption smoothness you get from a single pivot linkage like the VT? Would a VPP design be plusher then horst link/ICT designs by nature?
Sorry if this is a long post. Hope some of you can share your thoughts or theories on how my suspension should in theory be performing.
Thanks much.
There's nothing that is going to make a VPP design plusher by nature, there is just no variable that will make it feel better.
Traditionally, low pivot bikes (FSRs and the "faux bar" bikes like ventanas) feel "plusher' than high pivot bikes like many cannondales and santa cruz bikes. This is due to the fact that when you are pedaling the high pivot bike, the torque from your pedaling fights the suspension, making it feel choppy and harsh (add the bad braking effects of a single pivot and it can feel even worse on certain terrain).
On the other hand, the higher pivot bikes tended to do a little better on bigger hits (when you're not pedaling) due to a more rearward axle path. This is not cut and dry though, as many of these single pivot bikes had falling rate designs and without a linkage to make them progressive, they may or may not have fared any better in this particular situation. These days the shock technology makes up for this a little bit, but it doesn't address the first paragraph at all, so you'll still get some "choppy" and harsh feel in the suspension on high pivot bikes, shocks can't help with this.
So what you are describing is almost to the opposite of the "general" rules, but these do not always apply on a case by case basis.
First of all, the rate of your bike could be to blame. There's a wide variety of shocks out right now, and out of all the ones that I've tried, the fox DHX-Air, DHX-Coil and RP3 are worth talking about. The different sizes of air chambers and other factors will make these shocks perform differently on different bikes. So a bike may have a suspension rate that is "tuned" to work with a pretty linear shock. In other words, the bike is progressive, and adding a small-volume air shock like an RP3 may be overkill for progressiveness, making the bike feel very harsh at speed. On the other hand, a bike designed for a progressive shock like the santa cruz bullit, will feel like crap if you put a linear coil shock on it. The original bullits had the fox RC shocks, and you had to run a very high spring weight to keep from bottoming the falling-rate design, and this caused the low speed performance to be crappy, and while the excessively high spring rate would keep it from botting, it simply caused it to ride like crap in all other areas.
So, if you have a bike that "can accept" a coil or air shock, it doesn't mean that both will work equally well, the "rate" of your bike may work better with a more progressive shock, or a less progressive one, and if you use the wrong one, it will feel like crap.
The reason why the rate and amount of progressiveness is important is that a progressive bike will be able to run more sag, get much better low speed performance, and still be able to resist the big hits due to the progressiveness. This kind of bike will usually ride more into it's travel, and that fact allows it to feel very plush on the small stuff, even at high speed. This can go both ways though, as I have described above. I've ridden them all, and I feel a good progressive design really leads to a compliant feeling bike, but you can get "fooled" by a falling rate design as long as you don't hit a big enough bump or jump it too high, because the falling rate really allows it to go into the travel and eat up medium sized bumps, so just because one bike feels better at slow speed may not tell the entire story.
I've tried 2 air shocks on my Turner 6pack. One was the RP3 and the other was the Fox DHX-Air. These shocks were extremely different, and on different ends of the spectrum. The RP3 was very harsh overall, in my opinion it is overdamped. This makes it pedal pretty well, because the damping resists motion, but it makes it ride harsh over all sorts of bumps, and the progressiveness of this air shock (a smaller air volume=more progressive) coupled with the progressiveness of my bike simply makes it ride like crap. It's too progressive, and there's too much damping. If you want a firm and "snappy" feeling bike, the RP3 does deliver on this, and it doesn't bob much, especially in the "more compression damping" settings. Good for race-type bikes, bad for my trail/freeride bike.
The DHX-Air on the other hand was on the other extreme, too linear IMO. The air chamber is bigger (which means less progressive) and the damping at certain times feels like it is too light. This causes the DHX-A to feel excessively "plush" on certain mid-sized bumps. It has a hint of harshness on extremely small bumps just because it is an air shock, but this effect is hardly noticable. I'm extremely picky about my suspension, and I believe that this should NOT be a factor to consider when thinking about this shock. The low speed performance of the DHX-A is excellent overall, so while I can detect the slightest amount of stiction, I do not believe it is a detriment here. The excessively low amount of damping though allows the shock to blow through the travel on medium sized bumps, and while it feels very plush at a certain speed, if I go faster it seems to blow through the travel too fast, and at the end of the travel it "ramps up", so going fast over medium-sized bumps makes it feel pretty crappy, because it's trying to use up too much travel on one bump, and there isn't enough travel left over for the next bump. I tried the DHX-A with the same settings and sag that I use with the DHX-C, and from there I tried different settings, but the key is that with the SAME settings, the DHX-A did not ride the same. If you don't ride extremely fast at mach9, the DHX-A might be for you, especially if you like a real plush low speed and medium speed feeling.
The DHX-C was just right, in between the above two shocks, but that doesn't mean it's perfect. At speed it seems to get a little harsh on some impacts, a little "spikey". Better than progressive/manitou SPV stuff, and better than the curnut that I ran on my foes. I think that it can be better though, I want to try the marzocchi Rocco and the Ohlins rear shock. I simply want my rear suspension to work as well as possible, and I don't give a damn how bad it pedals.
What I really think is to blame is the current focus on "pedaling platforms" and "compression damping" that acheives better pedaling. What we are basically talking about here is low speed compression damping. Sometimes with a blowoff, and sometimes with a "threshold" in the case of SPV. What low speed compression does though is that it KILLS the ability of the bike to absorb small ripples and bumps, and it just makes it ride like crap through this stuff. A lot of people are ok with sacrificing some of the suspension to get better pedaling, but make no mistake; An increase in the compression damping, or a "platform" WILL sacrifice some suspension ability. There is no way around it. Most bikes will bob with the amount of compression damping that is required for maximum suspension performance. The DHX-C/A do a very good job of providing a decent tradeoff, and more in the direction of compliant suspension IMO than the SPV type stuff, but it's not quite far enough for my likings (then again, I'm never really satisfied!). This craze may be finally blowing over with stuff like the new Marzocchi Rocco, which is supposed to have very minimal compression damping. Also keep in mind that air shocks (on the most part, except for the DHX-A) are intended for XC bikes, so the compression damping and platform can be generally higher or more extensive than with a coil shock that is intended for freeride/DH. So that's why the RP3 has way more compression damping than many coil shocks.
I'd advise you to try a decent coil shock, DHX-C, Marzocchi Rocco, Avalanche, not romic, not a progressive, not a manitou swinger. The last three have an exceptionally high amount of compression damping that may not improve your ride at all.
Another thing that is worth noting; If you get a "pushed" shock, it depends on what you tell them, as to what the outcome is going to be. If you tell them you want to improve the pedaling, they will increase the low speed compression, and they use some very good parts, pistons, blowoffs, etc, but in the end, better pedaling is more low speed compression, and you can get the "overdamped" effect still. The other way to go about this is to tell push that you want the plushest and most compliant suspension, and you don't give a damn about pedaling. They can set it up to have much more minimal compression damping, and increase the oil flow. When dealing with Push, these two different approaches will mean an extremely different riding shock.
Although it's hard to tell if the rate of your bike is conflicting with the shock, another thing that will make a bike feel like crap is misaligned suspension, either at the shock or somewhere else where something is binding. It's rare, but it happens.
