Vorsprung-Suspension profile

Unfortunately pretty well everything you just said that I said is simply flat out wrong. It's essentially a 2D planar free body diagram (missing force vectors at the wheels, to be fair, so not a true FBD of the whole vehicle, only the rider). The rider pivots around the BB unless there's chain tension to prevent it, and the load on your hands is what balances the moment generated by the horizontal delta between your centre of mass and your BB. You've made multiple incorrect assumptions here, including the notion we're analysing it at rest - steady state planar acceleration in the Z direction (ie being leaned into a corner during steady-state conditions) is where this is relevant. If the resultant resolved force vectors from the tyres aren't in plane with the rider, the bike/rider mass rolls one way or the other, but that isn't the point of the explanation, so the 2D analysis is entirely reasonable. You also didn't pay attention to the video whatsoever, to be frank, and clearly didn't watch the previous one, since it's been made very clear that if your CoM is directly above the BB, the weight on the front wheel is not zero as you say was claimed, but apportioned directly by the front centre and rear centre ratios. IE if your front centre and your rear centre were the same length and you were balanced over the BB with your hands off the bars, 50% of your weight would be on the front wheels. There are numerous valid critiques that could be made of this 15 minute concept explanation, that was not one of them.

How tall are you AJ, 6'5" or so? I agree that proper fitment trumps pretty well everything else really - having a bike you're comfortable on physically has a huge impact on how it feels to ride. 

Also worth noting that this comparison was only relevant when cornering (and maybe off camber straights). Generally though, in a straightish line, the longer FCs should be less tiring not more (unless for some reason you're struggling for grip on the front tyre, like it's off camber), we went into straight line performance a bit in the part 1 video.

Entirely possible - hopefully we'll find out once Leo signs him to Pole next year! :)

In all seriousness though it's hard to know. The super long/slack bikes are still mostly coming from relatively small manufacturers who aren't really able to afford to put the guys who are winning races on them. Mondraker is obviously the historical exception to that (although compared to Pole/Mondraker, the geometry is not as extreme), and they have pulled a few wins on the DH bike under several different riders (Barel, Hart and Brook IIRC?). Interestingly though, the Summum's FC:RC ratio @50% travel is about 1.61 in size large (if their figure of 1250mm WB is correct at the longest chainstay setting of 460mm?) which is actually quite low compared to many bikes.

I'd agree with you there, and that was largely based around the endo/looping angles discussed in part 1 of this video. Link here if you haven't seen it - https://youtu.be/P18SutYYL5I

Bigger wheelbases (not specifically FC/RC ratios as such) allow more rider motion, but they also require it. One thing I have discussed with a few others is how longer wheelbases effectively increase the resolution of your movements, ie if you have a 1000mm WB, a CoM motion of 30mm constitutes 3% of the WB that you've moved. If that WB was 1500mm, that 30mm CoM shift is only 2% of the WB - so coarser motions give you finer control. That's good for precision and stability, but in turn also means you need to move further to achieve any given CPL shift desired. However, even the difference between the medium Mega and the large Machine is only 12% in wheelbase, more like 10% in the same size, so the rider has to be 10% more precise (10mm motion becomes 9mm motion) in order to accurately weight the wheels as he wants to. That's not an insignificant percentage, but we (or I at least) don't have any data to show how precise the rider can actually be. Like if you have to be accurate to within +/-5mm of CoM position to get the load on the front tyre within the necessary range, and that becomes +/-4.5mm instead, but the rider's sense of balance allows him to be easily precise within +/-2mm then it's a bit of a moot point there. Or maybe we're already the wrong side of that and most riders can only be precise within +/-20mm to begin with and they need to be within +/-10mm? I don't know the answer to that.

The rider is obviously the dominant factor by far. Hill is going to smash most of us even if he's on a hardtail with a 100mm fork, but do you think he'd be winning WC DH races or EWS races on that? I think we'd all agree that that seems unlikely, so then the question becomes "how much of a bike handicap would he need to have before he's unable to win"? IE at the top level, between say Hill/Maes/Rude/Bailly etc, is it plausible that a better/worse bike could be the difference between winning and 2nd or 3rd place when the gap is 3 seconds after an hour of racing?

Hi Kyle - the stock rebound tunes are surprisingly versatile, and generally work well for riders between 60-110kg, though if you are above or below that then we'd recommend revalving the rebound as well. The way the rebound adjuster is designed is quite clever insofar as allowing such a wide range, but it also has some limitations in that it's hard to valve the rebound much heavier or lighter than stock and still retain useful adjustments for most people. In an ideal world the rebound bleed would be a bit smaller and we'd be able to run the valving a little softer, but to do that properly would require so many parts to be changed that it'd be approaching the cost of constructing a new cartridge.

It replaces the entire compression assembly, yes - this means you have a new compression shim stack that we valve for your specific requirements, new HS and LS compression pistons, new topcap, new adjusters, as well as a full service with seals.
- Steve @ Vorsprung

We did develop an upgrade kit for the Evolution series damper as well, but by the time we'd sorted everything we felt needed attention (compression damping, air/oil separation, volume compensation, shimmed rebound piston, proper sealing) we had replaced almost everything in the whole cartridge - it wasn't financially worth doing unfortunately, as it would have ended up being a $400+ upgrade.
-Steve @ Vorsprung

Thanks for the mention Dave! One other factor to consider is that running a 26″ wheel in a 27.5″ fork means you'll have more axle offset. In theory, this is a bad thing because it means you have less trail. Trail is essentially the amount of self-aligning leverage that your steering has; it's the distance between the tyre's contact patch and the steering axis (if you were to draw an imaginary line out from the headtube all the way to the ground), and bigger wheels require more fork offset to keep the same amount of trail. This means you'll end up with slightly less planted steering, but on the plus side your front wheel will be a little further out ahead of you on steep stuff (which is similar to the effect a slightly slacker head angle will have). While it'll feel a bit weird at first, it's not an unreasonable or unrealistic setup to run.

• Steve
  Vorsprung Suspension

Hey guys, Steve here - appreciate the coverage and the discussion. We're stoked about the reception the Corset has had, to say the least!

We've had so many questions about "will this work on my particular frame" that it seemed more efficient to write a small novel on how the Corset interacts with the various linkage types out there than to try to answer each question individually. It's a big, in-depth tech post that's arguably a touch large to reproduce here, but if you're interested in reading it the link is here - How Will The Corset Work With My Frame?

Any other questions, please feel free to hit me up on steve at vorsprungsuspension dot com.

I should clarify - we can check fitment if you're actually interested in buying one. If it fits, we charge you for the TLA system, if it doesn't, free service. Punky is first in line as it stands.

Is it available for a 34 Talas RLC K 29,

We actually haven't checked fitment with the RLC damper (since they were quite uncommon), however if you're interested in finding out, you can send us your fork and we'll check. If it doesn't fit, you just landed yourself a free fork service :)

Looks goofy to me with the top being open. I would go for the Push kit it looks cleaner and you don't need Allen keys to adjust it.

We did have a good look at this during the design stage, originally intending to use a fully-covering topcap like most forks do. However, in order to have two separate LSC adjusters, the "open top" is necessary unless you want to use a system like Fox use in the RLC or CTD Trail Adjust dampers, where there is a LSC knob with machined ramps that push a needle down. The reason we avoided that system is that due to the tight tolerances required coupled with the tolerance stacking involved, it's both highly ineffective and inconsistent between units (as proven on the dyno) as well as expensive to make. Expensive + inconsistent + ineffective = not a good choice. We recessed the topcap too because the alternatives were either a higher stack height (which interfered with some frames when you turned the bars 90 degrees) or insufficient purchase of the lever on the adjustment post mechanism (basically making the lever feel cheap and wobbly). This does mean that dirt can settle in the recess, however all adjusters are properly sealed and won't give you any issues - it was our opinion that having a system like Fox's that stayed cleaner was not as valuable as having precise adjustment. This may not sit well with everyone, however from a design point of view we saw it as a better compromise than the alternatives. Is it perfect? No - nothing is.

As far as allen key adjustment - while it isn't a big issue either way really, we are a fan of tooled adjustments because they force you to actually put some consideration into your adjustments, rather than just twiddling knobs trailside without much thought. You can see the effects of this with the CCDB, whereby people take their tools with them in order to focus on setting the damper up, then once it's done properly, they put the tools away and don't need to bother with it again. While it sounds good in theory to have completely tool free adjustments, our experience is that forcing people to actually concentrate on setup means that they do a better job of it. Plus, if you ride with allen keys, it's not too hard to pull them out to make adjustments :)

Hopefully this explains why we've done some of the things we've done. I have no doubt that not everyone will agree with our methodology, and that's fine, but at least you'll see that there's reasoning behind the decisions we've made :)

I've heard good things about the Vorsprung kit, but it is pricey for what it is for sure.

Update:

Rear shock is being replaced with a Rockshox Monarch Plus RC3, should be a huge improvement.
As for the fork, I'm going to run it until I can scrimp and save the cash for a Marzocchi 350CR. I don't think it's smart to put money into the 34 when it's always just going to be a sub-par fork with a weird steerer size. Something like polishing a turd…

To the best of my knowledge (ie unless some of the alternatives have come down in price recently), the TLA Compression System is actually the least expensive upgrade on the market for the 34. When you consider that you also get a full fork rebuild, new seals etc included in the price, a whole new compression assembly which is literally half the damper, as well as true custom valving (we have more than 15 valving configurations for this kit already, and will continue to generate more for other riders as required) rather than simply soft/medium/firm, it really is about as inexpensive as such a system can be.

As for the performance of the 34, don't take my word for it when I say the TLA completely transforms the fork - ask anybody else who rides one. The stock damper is really the only substantially sub-par aspect of the 34, and with that sorted, it rips.

It's most likely the check valve that allows air to move from the negative to the positive chamber - if this isn't sealing properly, air can vent from positive to negative sides of the piston, particularly when there's not much load on the bike. Feel free to shoot me an email if you'd like us to have a look at it, steve at vorsprungsuspension dot com. We guarantee our work - no fix, no charge. But having seen and fixed this issue before, it shouldn't be a problem.

Rodie - I should mention that I just noticed you're looking to extend your i2i rather than shorten it? This is not a good idea - the forces acting on your shock bolts are trying to compress the shock virtually all the time (the only time the opposite happens is when your suspension tops out as your wheel leaves the ground), and are likely to rotate the reducers within your eyelets, such that you actually end up shortening the eye to eye below stock. If you have frame interference issues, this will make it worse rather than better.

@Vorsprung Suspension

thank you for your continuing replies to my questions

another question.

since suspension appears to be a lot more complex than many layman (or laywomen) may assume, does the shock tune / setup actually play a larger role in the overall experience of riding a full suspension bike, than the suspension design itself does?

in other words, would a simple single pivot design with a dialled setup ride "better" than a short-link virtual pivot design with a bad tune or incorrect setup.

Or does some inherent advantage in the second example, overcome or mask to some degree a bad tune or setup?

The short answer is that both of them matter a lot. If one is good, shortcomings of the other can be reduced somewhat, but really both play fairly equal parts in making your suspension work well.

@Vorsprung Suspension

thanks for taking the time to answer my question, I certainly learnt a good deal from your information

from own experiences working as a wrench, I've found a good number of customer have gotten confused with their DB shock setup, due to the wide range of adjustment and number of adjusters on that shock

Is a simpler shock with a good tune, correct spring rate and only perhaps rebound adjustment, more suitable for many riders?

From your experience do many bikes come with specific tunes for the suspension design? (this is something many manufacturers will claim).

Or do many bikes come with a generic tune, and the rider would benefit from a specific tune?

one last question, some years back one of the German MTB mags did quite an in depth suspension test where they took something like a dozen Fox piggyback coil shocks, dyno tested them and found wildly varying results even though each shock had the same specification.

Have you seen this during your experience with different shocks?

I wouldn't say removal of the adjusters entirely (so that you only have say a rebound adjuster) is a good thing. What is a good thing is a smaller but more usable range for your adjusters - like what Ohlins are trying to do with their shocks, and like BOS have always done (the adjustment range on those is really quite small).

What Fox claim as say a "Medium" tune can vary quite a bit, esp from year to year. Unless those guys actually pulled the things apart and verified that the valving was the same, I would say they've simply missed that. From running them on the dyno, Fox stuff is typically very consistent between one shock and another. Where Fox shocks in the past have not been so consistent is with heat - because the Boost Valve is dependent on the air/nitrogen pressure in the shock, when the oil heats that air/nitrogen up it increases the pressure, all the while the oil is getting thinner as the temperature increases (although the stock Fox oil is one of the most thermally stable oils on the market FYI). As a result you end up with increased end-stroke compression damping, and decreased low-speed rebound damping. This is one of the legitimate drawbacks of position-sensitive damping.

Great information here!! What's your opinion (if any) on BOS shocks?… I have a Kirk on my AM bike and I think its flipping brilliant, although I am not a technical suspension geek. I also have a CCDB Air on my DH bike which I really like as well.

Hard to have an opinion on a whole brand or line of products, but for the most part I like their stuff. It's all very well made stuff, with very low friction, although the spring and damping curves work extremely well for some people on certain frames, and not so well for others. Again though, pretty solid stuff and typically good if not great.

But if you already own one, you know exactly what it's like, so no need to ask my opinion :)

How does a shock with no reservoir (like an old fox vanilla) deal with shaft displacement during compression?

They have an IFP inside the barrel that separates the damping oil from a nitrogen/air charge.