Vorsprung Suspension Corset Fox Air Shock Upgrade

Rhys_

Likes Bikes and Dirt
Missed my point, they are not using the same sag point, assume the sag point is 25% then the shock displacement should be the same for either shock at that point. Once you adjust for that the curves beyond the sag point are pretty much exactly the same. The way it is presented is not an apples and apples comparison.

Thinking about it more the thing that interests me is the graph, Vorsprung say "However, a particular standard Fox air spring curve has a spring rate that drops by more than 90% from the beginning of the stroke..."

So is it just one model or all models that exhibits this behavior? One example or all examples? Or one cycle or thousands of cycles on a shock dyno? If it is just one cycle that is a very different thing compared to use where the shock is constantly moving. Is it a stiction thing? Does it occur if you start the stroke from the sag point instead of zero? I am too cynical to believe one graph without questioning...




I'm not arguing suspension systems (I have both DW and VPP bikes), I agree that a falling rate at the start of travel is counter intuitive but I also find the falling rate of an Ironhorse Sunday over the last 40% of its travel counter intuitive :noidea: but hey they are a great bike and ride well and at the end of the day that is what counts.

I don't get the 'high initial spring rate of an air shock' I reckon that is BS. Air shocks increase in pressure as they compress as a result of the volume reducing and as a result the spring rate increases, the Vorsprung graph makes no sense to me with the really high spring rate at the begining (hence my previous question - if it a single cycle then stiction would play a big part in the readings). The graph below shows DB air with different air cans and the effect they have on spring rate, I know there are no numbers but it makes more sense.

View attachment 308863
These are probably questions for Steve. No harm in being a cynic, I usually am as well. However, I have a friend who is very close to Steve, and knowing how incredibly switched on he is about this stuff I'm happy to take his graphs and testing on face value.
 

placebo

Likes Dirt
Thinking about it more the thing that interests me is the graph, Vorsprung say "However, a particular standard Fox air spring curve has a spring rate that drops by more than 90% from the beginning of the stroke..."

So is it just one model or all models that exhibits this behavior? One example or all examples? Or one cycle or thousands of cycles on a shock dyno? If it is just one cycle that is a very different thing compared to use where the shock is constantly moving. Is it a stiction thing? Does it occur if you start the stroke from the sag point instead of zero? I am too cynical to believe one graph without questioning...

I'm not arguing suspension systems (I have both DW and VPP bikes), I agree that a falling rate at the start of travel is counter intuitive but I also find the falling rate of an Ironhorse Sunday over the last 40% of its travel counter intuitive :noidea: but hey they are a great bike and ride well and at the end of the day that is what counts.

I don't get the 'high initial spring rate of an air shock' I reckon that is BS.
The air shock initial rate might seem to be counter-inuitive to your assumption, but vorsprung say they've measured it, and produced a retrofit modification to reduce it which seems to be similar to efforts by fox and rockshox on new and upcoming models.

Additionally, I've got an old sunday, so I've read the ridemonkey thread a fair bit over the years, and Dave Weagle always said the linkage data and plot of the sunday was wrong, the rate didn't fall away to the same degree as in linkage. The vorsprung plot tends to support DW's assertion, and everyone's seat of the pants experience with the sunday:



Vorsprung sometimes seem to go against some widely held suspension beliefs, but don't seem to have ever done so without actually measuring what it is they're working or commenting on, so I'm looking forward to trying the corset mod on my float-x. You can never tell until you ride it though. Those two earlier plots were from the blog which I should've linked to. He does some older stuff as well, and it's interesting to go back and see why some old designs I rode sucked so badly. People used to blame early shocks, but the falling rates on some of those old bikes never gave the shocks and suspension fasteners a chance, and the anti-squat plots show why others pedalled so badly with 150mm or less of travel.
 

teK--

Eats Squid
I look forward to the real world results but...

I may be missing something (or I am just too old and cynical) but if I look at that graph, the vertical lines I assume reflect compression of the shock, each vertical line is 20%.

So the big benefit of the Corset is mostly in the first 5% of travel and its pretty much all over by 10-15%, beyond that it runs parallel with the standard Fox shock...otherwise known as slightly different air pressure

So better break away when you first sit on the bike and all over by the time bike settles into its sag at 25ish%...:whoo: not one of my criteria but hey :noidea:
I hear what you saying in terms of no bike ever really starting from 0 travel once the rider is on the bike. But that is in a static situation.

What about in a dynamic, riding position, when the wheel drops lower than the sagged position. Such as when the bike passes over a depression in the trail. The wheel would tend to extend towards 0 travel. Essentially this is what sag is for, so the suspension can compress and extend from the sagged position.

Perhaps this is when the reduced initial springrate will help, once the wheel comes back into contact with the level ground.
 

udi

swiss cheese
I've got a couple of these on the way for testing, so hopefully I'll be able to provide commentary on their function in both DW and VPP frames in a thorough review.

For those that think their DB airs are great, they actually have a particularly poor air spring curve (very high initial rate due to low negative chamber volume); don't let the damper confuse you. The Vorsprung product will make the Float substantially better as an air spring than both the stock Fox item, and anything Cane Creek currently produces. I believe they are working on CC cans as we speak to provide the same benefits there. The debonair can on the other hand produces similar improvements for RS shocks (i.e. does what it claims) but then you're stuck with an RS shock...

MARKL -
Both Rhys and placebo are correct on all counts from my skim of their posts. To keep it brief:
a) The leverage curves on most top link driven VPP bikes are (to put it bluntly) fairly flawed, there is no valid physics-backed reasoning that supports their use, and essentially they are the opposite of ideal. A digressive to progressive curve doesn't really belong on any MTB, but is particularly bad on those that use air shocks because it exacerbates all three of the key negative behaviours that typical air springs display in comparison to linear springs - the high initial spring force, the fall off in mid travel, and increase again at end of travel. A better designed frame for an air shock will apply greater leverage during high spring force travel regions to counteract the negative behaviour to some extent.
b) Acceleration losses in MTB stem primarily from the effects of squat due to load transfer, thus the correct solution involves an appropriate anti-squat curve to counteract squat behaviour. Using the leverage curve to solve acceleration issues just shows a lack of knowledge on the designer's part, and results in unnecessary compromise.
c) The initial large spike in spring force is the main reason air springs suffer poor performance in relation to coil springs. In actual riding scenarios, the wheel is constantly in the 0-15% travel bracket, assuming only sagged travel matters is completely unrealistic (as teK alludes to correctly) - in fact, the purpose of sag is to provide this important negative travel zone. Gapping over trail obstacles, jumping, or riding over ruts/holes/depressions amongst many other things will cause wheel extension into this region of travel. Reduction of traction and excess transfer of force to vehicle and rider occurs in all these scenarios (and others) due to spring force being far greater than ideal in this travel region.
d) Sunday EOS is not really digressive, especially not for anywhere near 40% of the travel. The last 15-20% has slight digression but once you consider the numerical variation it's pretty flat. Measured my own frame on a purpose-built jig, as below:

Ah, one of my mspaint masterpieces.
I omitted the numbers at the time (this is directly from my copy of linkage), but rest assured the leverage ratio values near the end fall within the range DW claims (roughly between 2.55:1 and 2.60:1 - i.e. the end travel leverage ratio of the Sunday is essentially flat). It is however worth noting that most modern bikes have a decreasing leverage ratio in this region, so the Sunday is a little different, just not as much as many would think.

If you've got an air shock that performs like a coil, why suffer the weight and the difficult tuning process of a coil over?
Weight.
The performance of most air shocks is currently distinctly inferior to a coil, and as John U points out, even with the spring curve made substantially more linear, there is still a reasonable increase in stiction that is unavoidable. However the weight difference (even with Ti spring) is also quite substantial, so if an air spring can realistically (rather than just in marketing) come closer to a linear spring force curve, then it's going to be pretty useful for a lot of bikes out there - particularly those that have to go up as well as down.

I don't get the 'high initial spring rate of an air shock' I reckon that is BS.
It's not.
The Vorsprung graph is an accurate representation of air spring behaviour in rear shocks, and understanding why requires a good working knowledge of the effects of negative/positive volume deltas dynamically. The primary issue is that the static negative chamber volume on most air rear shocks is far too small, and thus its volume differential dynamically (as percentage of original volume) is huge even with only small changes in travel position. Unfortunately this also means a huge pressure variation in this chamber (drops to 0psi and continues into vacuum far earlier in the travel than desirable), and this is responsible for the huge force spike which is depicted accurately in the graph.
 
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udi

swiss cheese
Would the corset's increased spring rate in the midstroke help with the higher leverage ratio of the 575 to remove the blow through?
The Corset will have similar effects on your frame (assuming the graph for it is accurate) to a VPP bike as you correctly note. In particular, bump absorption and sensitivity will be improved noticeably, there will be a modest improvement in midstroke support (should be enough to notice, provided you do apply the pressure increase as recommended), and the downside will be that there will also be a mild increase in end of stroke resistance - which may make it slightly more difficult to use full travel. I think the benefits outweigh the negatives but it's good to be aware of both.

As an aside, for frames like these (VPP etc), I think the best setup will be something like a Corset along with the removal of any volume spacers (if present). If this is something you can do, it'll alleviate potential concerns of limiting travel use beyond what these frames already have a tedency to do (this is caused by their decreasing leverage near end of stroke combining with or "doubling up" on the increasing air spring force towards end of travel). Another small suggestion I'd give is to use sparing amounts of float fluid during assembly (to lubricate seals only), as excess will take up can volume (fluid is essentially incompressible, so it can act as a spacer would) - I know for a fact that many Fox authorised service centers only use a very small portion of the pillow pack in services for this reason.

If you're currently running 250psi I think you should be okay with 300psi on the new sleeve, and I highly doubt running the full ~312psi suggested in your scenario would breach any reasonable safety margin (~3% over recommended maximum) but I'd re-send your email with regard to this particular issue if you want to be on the safe side.
Hope that helps.
 

merc-blue

Likes Bikes and Dirt
I have been following the Corset for a while and find peoples understanding bike/shock relationship amusing, you must consider a great deal of thing when looking at suspension,

The only extra I would note at this stage (UDI has you covered pretty well) is a Air sleeve wont cover up bad tuning or bad servicing, if you have a shock that is more than 12 months since its last service spending $150 on a Airsleeve is stupid considering your damper almost certainly doesn't function as it should you probably dropped a significant amount of the IFP charge into the damping oil.
Also if you have a giant with one of the L/L/150 shocks it doesn't matter what you do with the air sleeve as you essentially have no compression damping.

This is a great product that will make significant on trail improvement to your Float shock BUT I would be inclined to get a service and/or a tune to ensure your shock is a complete package.
 

jrewing

Likes Bikes and Dirt
What model shock was that initial graph depicted off?

In saying that would initial pressure be lower in high end larger volume shocks?
 

udi

swiss cheese
What model shock was that initial graph depicted off?
A Float, but since a few people have asked, a Float X / DB Air / DB Inline / Vivid Air is really no better in this respect. See below for details.

In saying that would initial pressure be lower in high end larger volume shocks?
Assuming you mean initial spring force, the answer is no - and the reason is because the high volume cans that have been advertised as linearising typical air spring curves for years now (Fox HV, CC X-Vol, DRCV) only really target the issues with excessive progression towards the end of stroke. This isn't even the big issue with air spring curves as the graph dictates, and having a larger positive air volume in the can in various shapes and forms does absolutely nothing to fix the real issue with air springs.

The Vorsprung (and Debonair) cans do something new that high end and/or large volume shocks (including DH-pegged items such as the DB Air, DHX Air, Vivid Air etc) haven't done in the past, by increasing negative volume substantially and tuning/modifying the equalisation point simultaneously with the intention of attacking the high initial spring force issue directly.

This is actually not hugely different to the methodology used in forks like the current air-sprung Boxxer / Pike, these feel substantially better than earlier generations of the same forks because of a targetted change in negative chamber design.
 

teK--

Eats Squid
Thanks for the info udi and Merc.

What are your thoughts on the size of the negative spring on the CC DB Inline?

It is not clear from what you said if Vorsprung are working on a Corset for the DB Air or the DB Inline. I was always of belief the DB Inline has a comparatively large negative spring which is helped by the diaphragm/bladder design, which leads me to presume they are working on a Corset for the DB Air?
 

blacksp20

Likes Bikes and Dirt
The Corset will have similar effects on your frame (assuming the graph for it is accurate) to a VPP bike as you correctly note. In particular, bump absorption and sensitivity will be improved noticeably, there will be a modest improvement in midstroke support (should be enough to notice, provided you do apply the pressure increase as recommended), and the downside will be that there will also be a mild increase in end of stroke resistance - which may make it slightly more difficult to use full travel. I think the benefits outweigh the negatives but it's good to be aware of both.

As an aside, for frames like these (VPP etc), I think the best setup will be something like a Corset along with the removal of any volume spacers (if present). If this is something you can do, it'll alleviate potential concerns of limiting travel use beyond what these frames already have a tedency to do (this is caused by their decreasing leverage near end of stroke combining with or "doubling up" on the increasing air spring force towards end of travel). Another small suggestion I'd give is to use sparing amounts of float fluid during assembly (to lubricate seals only), as excess will take up can volume (fluid is essentially incompressible, so it can act as a spacer would) - I know for a fact that many Fox authorised service centers only use a very small portion of the pillow pack in services for this reason.

If you're currently running 250psi I think you should be okay with 300psi on the new sleeve, and I highly doubt running the full ~312psi suggested in your scenario would breach any reasonable safety margin (~3% over recommended maximum) but I'd re-send your email with regard to this particular issue if you want to be on the safe side.
Hope that helps.
Thanks UDI, this is the kind of info I was after from Vorsprung and Tekin. I understand they have been very busy with inquiries about the corset over the last week, but neither of them even gave an inkling as to whether the corset would be suitable for the leverage curve of my frame, and I posted the exact same graphs to both of them.

Vorsprung stated that I may exceed 300psi but they have no idea if it's the seals or something else internal that Fox rate to a max of 300psi. They state the corset is good for 350 and beyond. I don't think I'll get any further info from them if I hassle them on that issue. Better leave their time for answering the questions of others.

As someone else stated, servicing is probably a bigger issue and I am planning to send my shock off to Avalanche in the USA later in the year for some mods and a rebuild as my shock is suffering from a lack of LSC at the moment. If I add a corset now, I'll be wallowing all over the place under pedal loads so I'll probably order a corset around that time and throw it on for a whirl. If it doesn't work well for me, someone on here will benefit from a cheap lightly used corset.

Thanks for the super useful and personal reply
 

Nautonier

Eats Squid
Some really useful information in this thread, I can't wait until we get the first ride report. I've emailed Tekin to see about availability and also ask if it will work with Specialized's 'autosag' valve. I suspect that it will have to lose the autosag, which is no great loss. Does anyone know if the 2014 Spesh Enduro is running what is considered a large or a small 'eyelet size' in the Fox CTD? It's kinda hard to tell from the diagrams as it doesn't really look like any of the 3 pictured.
 

udi

swiss cheese
Just got my hands on them, will write something up once I get a chance to test them on a few frames.


What are your thoughts on the size of the negative spring on the CC DB Inline?
See my comments in post #49, they apply to the DBI as well. The Inline is more about compressing a better damper into a non-piggyback shock (which it does successfully), I don't think they've really addressed issues with air springs in general. On the other hand I do think RS have done a better job at trying to address this than the other brands (Cane Creek and Fox), as I said though unfortunately it means you're stuck riding an RS shock which never seem to be particularly reliable. To answer the question directly, I do think both the DBA and DBI would benefit from the Vorsprung sleeve and they should be on the cards at some point in the future.
 

S.

ex offender
Thanks UDI, this is the kind of info I was after from Vorsprung and Tekin. I understand they have been very busy with inquiries about the corset over the last week, but neither of them even gave an inkling as to whether the corset would be suitable for the leverage curve of my frame, and I posted the exact same graphs to both of them.

Vorsprung stated that I may exceed 300psi but they have no idea if it's the seals or something else internal that Fox rate to a max of 300psi. They state the corset is good for 350 and beyond. I don't think I'll get any further info from them if I hassle them on that issue. Better leave their time for answering the questions of others.

As someone else stated, servicing is probably a bigger issue and I am planning to send my shock off to Avalanche in the USA later in the year for some mods and a rebuild as my shock is suffering from a lack of LSC at the moment. If I add a corset now, I'll be wallowing all over the place under pedal loads so I'll probably order a corset around that time and throw it on for a whirl. If it doesn't work well for me, someone on here will benefit from a cheap lightly used corset.

Thanks for the super useful and personal reply
Hey mate, Steve from Vorsprung here. Sorry for the slow reply to emails - trying to reply to hundreds of them within a few days!

So let's discuss the effect of different leverage rates, and how the stock sleeve and the Corset each work with them. Let's consider that there are basically four main variants of leverage rate curve that exist on modern bikes:

LEVERAGE RATE CURVE TYPES:
1. Linear - no substantial change in leverage ratio throughout the travel. Example - Yeti SB66C.
2. Progressive only - leverage ratio drops throughout the travel. Example - Rocky Mountain Altitude; lots of DH bikes.
3. Progressive to linear/digressive - leverage ratio drops throughout the first 2/3 of the travel, then either flattens out or increases again towards the end of the travel. This is THE MOST COMMON leverage rate found on bikes designed around air springs. Example - Specialized Stumpy/Enduro, Banshee Rune, Pivot Mach 6, Ibis Mojo HD.
4. Digressive-linear-progressive - leverage ratio INCREASES (this is known as a falling rate because the spring rate at the wheel falls, not because the leverage rate falls), flattens out (linear) then drops again (progressive). Examples - pretty much all VPP bikes where the shock is driven off the top link; Nomad/Tracer/Bronson/Carbine/Blur/etc.

Let's also consider the characteristics of an air spring in general: they are Digressive (starts stiff, gets softer) to Linear (stays soft) to Progressive (starts soft, gets stiff). That characteristic exists on all current air springs (DRCV being a semi-exception... long story for another day) to some degree. The Corset and the Debonair both have a far less extreme version of this than the stock Fox sleeves, but it's still there as you can see from the spring rate curve graph posted a few pages back.

Anyway, let's look at how each of the previously mentioned leverage rates works with each of the Fox and the Vorsprung spring curves:

1. LINEAR leverage rate aka constant leverage ratio (note that the words rate and ratio are not interchangeable; ratio is a number at a given point in the travel, rate refers to the shape of the curve).
Resultant wheel spring curve with Fox spring: same shape as the Fox spring curve, just multiplied by a constant number (scales it up/down) which is the leverage ratio. This means you end up with a falling rate (stiff but becoming soft) initial stroke, a low spring rate (soft) in the mid stroke, and an increasing spring rate (soft but becoming stiff) at the end of the stroke. Initial stroke is stiff, meaning low sag, which can be good for climbing geometry because it keeps the seat tube steeper and more weight on the front wheel. Mid stroke is soft, which usually means people want that to be stiffer for descending support, which in turn makes the initial stroke even stiffer and harsher. End stroke can be tuned by volume spacers to achieve whatever ramp you need to prevent frequent bottom out, but running suspension too soft and relying on sudden end stroke ramp creates harshness too because you end up just running into a wall of resistance.
Resultant wheel spring curve with Corset: same shape as the Corset spring curve. Compared to the Fox spring curve, far softer initially and firmer in the middle. Once again, end stroke can be tuned with volume spacers to achieve whatever ramp-up you need. This means you run more sag (can be bad if you already have a bike with a slack seat tube angle (eg SB66) and climb a lot of steep stuff (the kind of stuff where you're just about breaking your shifter trying to find an easier gear that doesn't exist... pretty well all the climbs in Whistler!) because the front wheel will try to lift up more. On most bikes the difference isn't anywhere near that much though, because despite running more sag, the mid stroke spring rate is quite a bit stiffer, so the settle point when your weight is shifted backwards is closer to what you'd get with the Fox sleeve. Descending, more sag gives more traction, firmer mid stroke means more support on bigger hits and compressions as well as a more predictable and lively feel.
Net result: Unquestionable improvement here, in my honest opinion.

2. PROGRESSIVE (only) leverage rate:
Resultant wheel spring curve with Fox sleeve: high initial leverage helps somewhat to overcome the stiff initial air spring feeling, but unless it's progressive enough, the mid-stroke is still very soft - and if it IS that progressive then it ends up ramping like crazy at the end of the travel. Cross multiply the progressive end stroke of the leverage rate with the progressive spring curve of the air shock, and you're either going to have something that sits at excessively high sag or makes it far too difficult to use full travel. Basically, progressive end strokes don't mix well with air shocks, it's very hard to get them sorted in such a way that the mid stroke is sufficiently supported without crazy end stroke ramp, although they do feel reasonably good off the top of the travel usually. That said, no frame I've ever examined has been anywhere near as progressive in the early stroke as a Fox air spring is DIGRESSIVE in the same travel - to do so you'd have to have the leverage ratio drop by at least a factor of five in the first 15mm of the travel, which would mean your leverage ratio probably starts at about 15:1... this is also very bad (gen 1 V10 had something almost like that) and it causes a lot of play at the start of the travel due to the immense leverage on both pivots and shock.
Resultant wheel spring curve with Corset: High initial leverage ratio combined with relatively linear spring curve provides very plush feel initially, mid-stroke support somewhat better, end stroke still over-supported and hard to use full travel - Corset can't fix that.
Net result of the Corset: Better small bump absorption, marginal improvements in mid-stroke, but can't fix the excessive end stroke ramp. Overall, relatively minor gain - you'd have to design an air spring specifically for this application in order to make it work well, but fortunately most bikes don't use this configuration unless they're intended for use with coil sprung shocks.

3. PROGRESSIVE-TO-LINEAR/DIGRESSIVE leverage rate:
Resultant wheel spring curve with Fox sleeve: high initial leverage helps somewhat to overcome the stiff initial air spring feeling, but unless it's progressive enough early enough, the mid-stroke is still relatively soft compared to the initial stroke. However, because the leverage rate flattens out (linear rate) or increases again (digressive rate) you do get better mid-stroke support with this, since you can run higher air pressures without causing crazy end-stroke ramp up. However, what we're really looking for overall, from start to finish, is an increase in wheel spring rate of about 55-65% overall (once shock spring rate curve has been multiplied through the leverage rate curve), which corresponds roughly to a coil-sprung bike with a leverage rate that starts 25-30% higher than it ends (progressive). This is slightly lower than what's been shown to work very well on both DH bikes and MX bikes, though most air-sprung bikes don't need quite that level of big-hit performance. In order for this to happen with existing Fox sleeves, we'd need to see frames with ~3-4x their existing initial progression, but only for the first 20mm or so of travel, before becoming comparatively linear throughout the rest of the stroke. This doesn't currently exist in anything I've seen.
Resultant wheel spring curve with Corset sleeve: much closer to the performance of a coil shock (on a bike that's well designed for a coil shock, not on the same frame!) because the leverage rate change can effectively cancel the slight falling initial rate of the Corset, the supportive mid-stroke of the leverage curve cuts the actual drop in spring rate at the wheel down to zero (or can even allow for a truly progressive spring rate in quite a controlled manner) without causing the excessive end stroke ramp. Once again, you can tune the end stroke with volume spacers.
Net result: Corset provides distinct improvements in bump absorption, support and liveliness. This combination is in my opinion the highest performance currently available from an air shock and linkage curve, on an only semi-related note.

4. DIGRESSIVE-LINEAR-PROGRESSIVE leverage rates:
Resultant spring curve with Fox sleeve: Low initial leverage (stiff) combined with high initial spring rate (stiff) = very stiff initial stroke. High mid-stroke leverage (soft) combined with low mid-stroke spring rate (soft) = very soft initial stroke. Low end-stroke leverage (stiff) combined with high end-stroke spring rate (stiff) = very stiff end stroke. As a result, you get a very stiff feel at the start of the stroke, like there's tons of preload on the suspension, followed by an unsupportive mid-stroke that is prone to feeling wallowy, which eventually runs into a fairly abrupt wall of progression at the end of the stroke. Good in that you don't bottom out easily, bad in that if you run higher air pressures for mid stroke support, the early and late stroke segments are just much too stiff.
Resultant spring curve with Corset: Comparatively low initial spring rate reduces the effects of the low (stiff) initial leverage rate and makes the early stroke much softer feeling. You can now run higher pressures for more mid-stroke support without making the early stroke feel too stiff. End stroke is still somewhat progressive - once again, no air spring system out there can really fix an excessively progressive ending stroke of the leverage rate curve - so achieving full travel can still be difficult.
Net result: much better overall in terms of support and bump compliance, but still the end stroke progression issues may remain - removal of any/all volume spacers in the shock is recommended in most cases.


I hope this has helped clear up how the Corset can work for you. Basically, the summary of all of the above is that the Corset is better in pretty well all scenarios, except the following:
1. Frames that already struggle with steep climbs due to slack seat tube angles and/or short chainstays will be worse at climbing. No ifs or buts, it's just harder if you have more sag. Frames that have steeper seat tube angles, longer chainstays etc (basically the frames that already climb well) won't be affected to the same degree... I have plenty of personal experience with this!
2. Frames with excessive ending stroke ramp up already will still have those issues - that wasn't something that we could really address without requiring pressures of 400+psi for the average rider. That's not to say that the Corset will be any worse, just that it won't fix that issue. As a general rule, it'll still perform better overall, but it's not perfect.
3. If your damper is improperly tuned for your frame (usually as a result of being switched out aftermarket, the ones that come with the bike are generally reasonable), in need of service/repair, this can't fix that. That'd be like changing your handlebars and hoping it somehow makes your tyres more grippy.

Is it the magic pill solution to every issue with every frame? Unfortunately nope. We've legitimately done our best to make this as good as it can be, and this is the ceiling of what we found to be possible. I can confidently say that on 99% of bikes it will make your suspension work distinctly better.
 

blacksp20

Likes Bikes and Dirt
S.

Thank you so much for taking time out of your already busy schedule to write that novel. It has been very informative and I have now made my mind up and will be purchasing a corset later in the year.
 

S.

ex offender
The mid stroke support in that graph is absolutely parallel - you would get the same thing by increasing the spring rate.



I agree that small bump compliance is an important trait but it is a trait that is either side of the sag point, not from 0 travel. Say, small bump compliance is 5-10% of travel either side of the sag point - so if we take a typical bike with 25% sag, small bump compliance happens between say 15% and 35% of travel, not between 0 and 10% of travel. And between 15-35% the performance is essentially the same
If you check out the spring rate vs displacement graph, you'll see that the spring rate of the Corset is sitting at about 300lbs/in in the middle of the stroke, whereas the Fox is running more like 200lbs/in. That's a 50% higher spring rate!

Missed my point, they are not using the same sag point, assume the sag point is 25% then the shock displacement should be the same for either shock at that point. Once you adjust for that the curves beyond the sag point are pretty much exactly the same. The way it is presented is not an apples and apples comparison.
Actually, it is a fair comparison - you do run more sag with a Corset. The sag rates typically run with current air shocks are a byproduct of the spring curve rather than the end goal. The curves aren't the same beyond the sag point, the Corset maintains a higher spring rate throughout the entirety of the middle of the travel. End stroke can be moved up or down by changing the internal volume on both the Fox and the Corset, so that part isn't so relevant.

Thinking about it more the thing that interests me is the graph, Vorsprung say "However, a particular standard Fox air spring curve has a spring rate that drops by more than 90% from the beginning of the stroke..."

So is it just one model or all models that exhibits this behavior? One example or all examples? Or one cycle or thousands of cycles on a shock dyno? If it is just one cycle that is a very different thing compared to use where the shock is constantly moving. Is it a stiction thing? Does it occur if you start the stroke from the sag point instead of zero? I am too cynical to believe one graph without questioning...
That graph is directly from the most common size of Float shock, the 7.875 x 2.00/2.25. All of them exhibit this behaviour; the 8.5 is not quite as bad as the others (only an eightfold drop in spring rate as opposed to tenfold) but the Corset still improves on that by a factor of about 4.... pretty substantial.


I'm not arguing suspension systems (I have both DW and VPP bikes), I agree that a falling rate at the start of travel is counter intuitive but I also find the falling rate of an Ironhorse Sunday over the last 40% of its travel counter intuitive :noidea: but hey they are a great bike and ride well and at the end of the day that is what counts.

I don't get the 'high initial spring rate of an air shock' I reckon that is BS. Air shocks increase in pressure as they compress as a result of the volume reducing and as a result the spring rate increases, the Vorsprung graph makes no sense to me with the really high spring rate at the begining (hence my previous question - if it a single cycle then stiction would play a big part in the readings). The graph below shows DB air with different air cans and the effect they have on spring rate, I know there are no numbers but it makes more sense.

View attachment 308863
It sounds like you're confusing spring force with spring rate. The spring rate curve is the derivative of the spring force curve, and is measuring the instantaneous rate of change in spring force vs displacement. A steep gradient on the spring FORCE curve means a high spring RATE at that point, even if the spring FORCE at that time is low. Spring force never actually decreases over the travel, and in actual fact the spring force graph itself is quite hard to directly extract useful information out of, but the spring rate graph is much more informative. Stiction is not part of the equation here; though to measure air spring curves accurately is more difficult than you'd think. The end result is that over 2 years we have developed an air spring rate calculator that matches our dyno measurements pretty well exactly, with more than 25 input parameters and more than 50 subsequent calculations for each movement increment, that has helped us understand air springs extremely thoroughly. I am reasonably sure that nobody else has the same degree of correlation between real world measurement and calculated spring rate that we do.

I have been following the Corset for a while and find peoples understanding bike/shock relationship amusing, you must consider a great deal of thing when looking at suspension,

The only extra I would note at this stage (UDI has you covered pretty well) is a Air sleeve wont cover up bad tuning or bad servicing, if you have a shock that is more than 12 months since its last service spending $150 on a Airsleeve is stupid considering your damper almost certainly doesn't function as it should you probably dropped a significant amount of the IFP charge into the damping oil.
Also if you have a giant with one of the L/L/150 shocks it doesn't matter what you do with the air sleeve as you essentially have no compression damping.

This is a great product that will make significant on trail improvement to your Float shock BUT I would be inclined to get a service and/or a tune to ensure your shock is a complete package.
You are right, the Corset won't fix a damper that's in poor condition. However it's worth noting that L/L tunes are correct for certain low leverage setups, especially if it's a Boost Valve shock in which case your compression damping is dictated primarily by the IFP charge pressure. As you mentioned, what really matters are the spring and damping rates when measured at the wheel - what's happening at the shock needs to be multiplied through the leverage rate curve to understand the wheel rates properly. A L/L tune won't work on a high leverage bike, nor will a F/F tune work on a low leverage bike.


Some really useful information in this thread, I can't wait until we get the first ride report. I've emailed Tekin to see about availability and also ask if it will work with Specialized's 'autosag' valve. I suspect that it will have to lose the autosag, which is no great loss. Does anyone know if the 2014 Spesh Enduro is running what is considered a large or a small 'eyelet size' in the Fox CTD? It's kinda hard to tell from the diagrams as it doesn't really look like any of the 3 pictured.
Check the photo at the bottom of the product page on our webshop (https://vorsprung-suspension.myshopify.com/products/vorsprung-corset-air-sleeve) to work out the eyelet size you need - I'm pretty sure it's a small volume eyelet. The Autosag feature will be gone.


For the record, the graphs shown are numerically accurate, and a fair representation of all models of Float shock currently out there.
 
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DeBloot

Likes Bikes and Dirt
Wow
Looking at the 'where are they now thread' and thinking, what happened to S.
I miss those long, in depth, informative and easy to understand technical posts of his
And then he pops up as Steve at Vorsprung based in Whistler

I was considering a corset for a Fox CTD that just never quite feels right
I was a bit sceptical, but I'm a sceptic no more
 

Geoff Gump

Likes Dirt
It's not.
The Vorsprung graph is an accurate representation of air spring behaviour in rear shocks, and understanding why requires a good working knowledge of the effects of negative/positive volume deltas dynamically. The primary issue is that the static negative chamber volume on most air rear shocks is far too small, and thus its volume differential dynamically (as percentage of original volume) is huge even with only small changes in travel position. Unfortunately this also means a huge pressure variation in this chamber (drops to 0psi and continues into vacuum far earlier in the travel than desirable), and this is responsible for the huge force spike which is depicted accurately in the graph.
If I am following you correctly does this mean that air forks do not have a huge force spike in the initial stroke because of the relatively large negative air chambers they allow (or negative coil sping in some cases)?
 

Nautonier

Eats Squid
Got my Corset today, but am a little confused by some of the steps in the installation instructions:

4. If desired, you may opt to perform an air sleeve service at this time as per Fox's service instructions. This will require a Fox air sleeve seal kit (not included with the Corset). If not, proceed from step 5 onwards.

5. Install the backup rings and air seal into the end of the Corset's inner sleeve. Once properly seated, install the dust wiper.

6. Wipe all seals (piston seal, air seal, and dust wiper) with Float fluid. You don't need much - enough to make the white PTFE backup rings visibly blue-tinged is enough. More than this hurts performance.

7. Install the air sleeve onto the shock body, and screw it into the eyelet by hand. Do it up firmly by hand - tools are not necessary.



I don't want to perform an air sleeve service or replace any seals, does this mean that I have to remove the old seals, backup rings and dust wiper from the old Fox sleeve and insert them into the Corset?? Or is the Corset a complete unit that simply screws into the shock body, sliding up over the shaft? I really wish the instructions had diagrams... Tekin said that it should be a 5 minute job, which suggests that's it's a lot simpler than what the (Vorsprung) instructions imply re the seal installation part.

Also, the Corset appears to already have the white PTFE rings and possibly the piston seal and dust wiper in it...
 
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blacksp20

Likes Bikes and Dirt
I would think that if you take off the standard Fox can and compare it to the Corset, you will be able to tell if the Corset comes with all the required seals.

Seems odd that it wouldn't come with new seals and be ready to install.
 
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