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  1. #1
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    Explain "too linear" 2013 Fox forks to me.

    I'm trying to understand how Fox's 2013 fork offerings are "too linear", per multiple reviews.

    Recalling my intro physics class, coils are completely linear. The force to compress the coil is directly proportional the distance from the resting state. For the record, I've never ridden a coil fork regularly.

    Haven't we been trying to get air forks to "feel like coil" for years?

    What does "too linear" mean? I understand that this means that you may blow through the travel, but wouldn't this be a problem with coil forks as well?

    I have a 2013 Fox 160mm fork and do occasionally use all the travel. I feel that it is light-years beyond my older Fox fork that never got more that ~130mm of travel (even when going over the bars after big drops).

    Please explain.

  2. #2
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    An air fork has to support a wide range of weights, unlike a coil which uses different springs for different weights.

    This can cause an air fork to have the possibility of having too much initial spring force, or too little at the end of the travel. It is most likely to happen if the rider is very heavy or very light, but it also depends on the course. On a very smooth trail, an average rider-- right in the meat of what the fork was designed for-- may complain they don't use enough travel. On a trail with huge drops, that same rider may complain that they bottom harshly, unless the fork is so stiff as to be punishing on small bumps.

    This is why the air forks are often progressive. Fox heard people complaining that their forks were too progressive, and no doubt saw discussions on MTBR and elsewhere about people modifying their forks to be more linear.

    For me, I like the progressive rate of my bone-stock (so far ) 2012 Fox Float 32 RLC fork. It is plush on the trail, I have dialed in enough compression to strongly resist brake dive, and a combination of the air spring rate and compression damping ensures I don't bottom even when I catch 2' of air.

    However, I weigh 170 pounds geared up. I am neither overly light or heavy. The base fork works well for me and my riding conditions. And reading your post again, it sounds like your 2013 fork is working perfectly for you. So don't worry if another rider feels their 2013 is too linear.

  3. #3
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    Btw, you absolutely can have a progressive coil spring. It has different winding and/or thickness which results in a non-linear spring rate. This is very popular on passenger cars because it gives a nice ride on city streets, expansion joints, etc, but then the spring rate becomes higher to take a fast corner or absorb a big pothole.

  4. #4
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    Quote Originally Posted by ColinL View Post
    Btw, you absolutely can have a progressive coil spring. It has different winding and/or thickness which results in a non-linear spring rate. This is very popular on passenger cars because it gives a nice ride on city streets, expansion joints, etc, but then the spring rate becomes higher to take a fast corner or absorb a big pothole.
    Do the coils in contemporary coil forks have different windings or thicknesses in the same coil?

  5. #5
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    Quote Originally Posted by meph2 View Post
    Do the coils in contemporary coil forks have different windings or thicknesses in the same coil?
    No. Progressive coil springs for bicycle suspension do not exist. Although it would be a nice feature to have a slightly progressive coil for a fork. Instead, damping and bottom out bumpers are used.

  6. #6
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    A single progressive coil spring could probably be made for a bicycle at a high cost. The issue of mass producing them is that if you have too much sag or preload on a progressive spring, the softer section can be entirely collapsed, which then leaves you with a shorter main spring. You would gain no benefit from the softer section.

    To avoid that issue, you would need a greater number of progressive springs, each supporting a narrower range of rider weight, instead of 3-4 springs that cover 140 pounds to 260 pounds.

    It's also far easier to tune all aspects of your suspension if you have a linear spring, and many racers prefer linear because they want a consistent feel and are willing to give up plushness.

  7. #7
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    Quote Originally Posted by ColinL View Post
    A single progressive coil spring could probably be made for a bicycle at a high cost. The issue of mass producing them is that if you have too much sag or preload on a progressive spring, the softer section can be entirely collapsed, which then leaves you with a shorter main spring. You would gain no benefit from the softer section.

    To avoid that issue, you would need a greater number of progressive springs, each supporting a narrower range of rider weight, instead of 3-4 springs that cover 140 pounds to 260 pounds.

    It's also far easier to tune all aspects of your suspension if you have a linear spring, and many racers prefer linear because they want a consistent feel and are willing to give up plushness.
    Taking a stock spring and adding a little bit of tighter wind would not change over all spring, it would just at a little bit up ramp up at the end of the stroke. That said, the very few choices of coil springs for forks is a problem regardless of linear or progressive. its very easy to get caught between coils. I still ride coil forks because the mid stroke support and small bump compliance cant be matched by any air spring I have used.

  8. #8
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    Quote Originally Posted by mullen119 View Post
    No. Progressive coil springs for bicycle suspension do not exist. Although it would be a nice feature to have a slightly progressive coil for a fork. Instead, damping and bottom out bumpers are used.
    Years ago Stratos had progressive rear coil springs (still have one in my junk box). Marzocchi had progressive fork springs for their Monster T. For a given weight of 600lb the progressive Stratos spring felt a good 150lb lighter in tension than a straight rate 600lb coil. I believe the Monster T springs were also ranged for a lighter rider.

  9. #9
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    Quote Originally Posted by keen View Post
    Years ago Stratos had progressive rear coil springs (still have one in my junk box). Marzocchi had progressive fork springs for their Monster T. For a given weight of 600lb the progressive Stratos spring felt a good 150lb lighter in tension than a straight rate 600lb coil. I believe the Monster T springs were also ranged for a lighter rider.
    KTM motocross bikes had progressive coil springs for years trying to do away with linkage in the rear suspension. They eventually gave up and went with a linkage design because it works better. This makes me think that progressive springs for rear shocks are pointless because bike designed for coil rear shocks will incorporate a rising rate leverage ratio to combat bottoming. In forks on the other hand, I can see a market for a slightly progressive coil spring to help prevent harsh bottoming since only a handful of forks have a hydraulic bottoming circuit. I have always been somewhat surprised that they dont exist for modern forks.

    Anyway, we are hijacking the OP's thread with coil spring talk, Sorry about that OP.

  10. #10
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    I don't think that the "too linear" applies so much for forks greater than 120 mm of travel. But less than that, since you have so much less travel to start with, it becomes very difficult to get a fork that is not too firm without it blowing through travel.

  11. #11
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    Forks are usually not exactly linear, whether coil or air.

    Coil forks have a large "air chamber" within, and apart from that, usually either a charged space on top of a piston to prevent foaming, or air above oil on an "open bath" design. Both of these add progression as the fork progresses through travel and pressure is added to the oil column and onto the damping piston, usually resulting in more damping. This isn't a dramatic effect though, so often times a hydraulic cone is added to the bottom of the damping piston, as with some Fox designs and the Avalanche cartridges (not sure if marzocchi is doing this yet, but their newest cartridges are nearly a carbon-copy of the Avalanche stuff).

    The old "oil bath" system was easy to adjust the progressiveness via the oil height, allowing you to run a decent amount of sag and still ramp up to avoid bottom out.

    Most all-air forks have enough progression due to the air spring to get away without any of these additional systems or features, although sometimes they still inherently have some of them and in some cases can end up too progressive.

    Interestingly, it's usually the linear forks that feel over-sprung and too stiff when set up properly to avoid bottomout. They will run less sag when set up like this, and ride harsher. If it's a "linear fork" and it's truly "blowing through travel", you're going to be feeling it bottoming and you'll figure this out really fast and up the spring pressure or spring weight.

    The more progressive stuff can feel like it's "blowing through the travel" more, especially as long as it's not bottoming out. That real supple initial action can be nice, but must be supported with the right amount of damping. The faster an impact happens, the faster the oil is forced through the pistons and the more the fork is slowed down. This means the low-speed damping is usually lacking and where the fork falters a bit, but this is very subjective to the exact fork and damping system.
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

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  12. #12
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    Quote Originally Posted by mullen119 View Post
    No. Progressive coil springs for bicycle suspension do not exist. Although it would be a nice feature to have a slightly progressive coil for a fork. Instead, damping and bottom out bumpers are used.
    Marzocchi pro-wind springs existed, and I used them on several forks. Not really any improvement. Other forks used multi-stage coil springs of different rates as well, not sure if it was Risse, but it was one of those earlier small-production manufacturers. Heck, even the simpler manitou coil+elastomer stacks would qualify here (which were copied the next season by RS if I recall correctly). I had a few of these manitou forks, they were pretty terrible due to how sticky all of the parts were. I took my 97 FS and converted it to "mostly coil" like the FS Ti model, it was an improvement, but the chassi (lubrication) seriously held it back. It was hard to make any assessments of those based on the performance. The marzocchi forks obviously worked, but was there any benefit to using them in an open bath fork that could already be adjusted? No.
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

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  13. #13
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    Quote Originally Posted by mullen119 View Post
    KTM motocross bikes had progressive coil springs for years trying to do away with linkage in the rear suspension. They eventually gave up and went with a linkage design because it works better.
    Naw
    It's because their suspension components and design were crap. Their forks had the worst build quality bar none until a few years ago. It took them almost a decade to make their pds shock work near as good as the Ohlins version that they didn't want to pay to license. It's definitely not because of the spring that they went back to a linkage design.

  14. #14
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    Quote Originally Posted by kan3 View Post
    Naw
    It's because their suspension components and design were crap. Their forks had the worst build quality bar none until a few years ago. It took them almost a decade to make their pds shock work near as good as the Ohlins version that they didn't want to pay to license. It's definitely not because of the spring that they went back to a linkage design.
    Its not the spring itself, its the bad design of a linkageless rear suspension. There is no reason to use a progressive rear spring when you can use linkage to create the progressiveness. It was just a bad idea from the start to try to make a linkageless design.

  15. #15
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    So, why can't the new 2013 Fox air forks use the compression damping mentioned above to correct the "too linear" feeling.

    Isn't the Vanilla RC2 damper from last year the same as this year's Float damper?

  16. #16
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    Modern air forks really need adjustable air spring volume. Maybe even a staged air volume like the "DRCV".

  17. #17
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    Quote Originally Posted by meph2 View Post
    So, why can't the new 2013 Fox air forks use the compression damping mentioned above to correct the "too linear" feeling.

    Isn't the Vanilla RC2 damper from last year the same as this year's Float damper?
    Is the RC2 really progressive? I pulled the RC2 cartridge out of my 06' Vanilla RC2 and if you cycled the damper , by hand, it would have no resistance until the last 3/4" of travel then hit a hydraulic wall.

  18. #18
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    Quote Originally Posted by keen View Post
    Is the RC2 really progressive? I pulled the RC2 cartridge out of my 06' Vanilla RC2 and if you cycled the damper , by hand, it would have no resistance until the last 3/4" of travel then hit a hydraulic wall.
    I would think that it would stop hard bottoming. The reviews I've seen report hard bottoming even with the RC2 damper.

  19. #19
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    Quote Originally Posted by mullen119 View Post
    Its not the spring itself, its the bad design of a linkageless rear suspension. There is no reason to use a progressive rear spring when you can use linkage to create the progressiveness. It was just a bad idea from the start to try to make a linkageless design.
    Sure there is

    You shave around 3-4lbs off the bike and you lower maintenance time/costs for enduro bikes. I think the idea is great it was just a poor execution.

  20. #20
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    It is very easy to make the new forks more progressive. All you have to do is add oil to the air chamber. Should take all of 5 minutes.

    One of the reasons they made the fork more linear was to allow custom tuning of the spring rate.

  21. #21
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    Quote Originally Posted by ColinL View Post
    This is why the air forks are often progressive. Fox heard people complaining that their forks were too progressive, and no doubt saw discussions on MTBR and elsewhere about people modifying their forks to be more linear.

    For me, I like the progressive rate of my bone-stock (so far ) 2012 Fox Float 32 RLC fork. It is plush on the trail, I have dialed in enough compression to strongly resist brake dive, and a combination of the air spring rate and compression damping ensures I don't bottom even when I catch 2' of air.


    Correct me if I'm wrong, but all air forks are progressive based on the volume and well, they use air. It's a gas priciples basic property. Boyle's Gas Laws. Coils are not in this category. As already stated, they're linear.

    For me, a good coil, with a upper gas cushion to catch the big hits. Coils are often referred to as "buttery." Because they're linear.

    Adding oil makes the fork have a steeper "ramp" in the spring rate curve. If it's too steep the rebound damping control might not be able to control the higher rate as it was not tuned to this rate, or lower volume of air.

    Adding air to a coil makes it more progressive at teh top of the stroke. A desirable trait , imho.

    Been doing full sized suspension for years on off road race vehicles. Bypasses , gas springs and all disc valving. Progressive leveraging. The tenets are very similar.

    DR
    Last edited by dirtracer; 11-04-2012 at 11:24 AM.

  22. #22
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    Quote Originally Posted by dirtracer View Post
    Correct me if I'm wrong, but all air forks are progressive based on the volume and well, they use air. It's a gas priciples basic property. Boyle's Gas Laws. Coils are not in this category. As already stated, they're linear.

    For me, a good coil, with a upper gas cushion to catch the big hits. Coils are often referred to as "buttery." Because they're linear.

    Adding oil makes the fork have a steeper "ramp" in the spring rate curve. If it's too steep the rebound damping control might not be able to control the higher rate as it was not tuned to this rate, or lower volume of air.

    Adding air to a coil makes it more progressive at teh top of the stroke. A desirable trait , imho.

    Been doing full sized suspension for years on off road race vehicles. Bypasses , gas springs and all disc valving. Progressive leveraging. The tenets are very similar.

    DR
    Air springs can be engineered to be linear throughout the entire stroke. The reason coils are considered "buttery" is because they lack the initial stiffness that MOST air springs possess, and don't have the extra friction caused by more sliding surfaces.

    Coil springs alone are dead linear within their usable stroke, however without some form of ramp up (be that spring, damping or hydraulic lock anti-bottoming systems, or a leverage ratio that decreases to increase the effective spring/damping rates at the wheel), completely linear sprung suspension needs to be run at a level of stiffness most people would consider unacceptable in order to prevent harsh bottoming out on bikes that are ridden aggressively. The "plushest" feeling suspension (not necessarily the most stable or controlled) invariably comes from a system that has a soft spring rate (measured at the wheel) at the start of the travel and a stiffer rate at the end of the travel - in other words, a progressive system.

    Obviously, suspension that is TOO progressive lacks control in the early and mid stroke, and/or ramps up too savagely.
    VorsprungSuspension.com - fully engineered suspension retuning & servicing in Whistler, BC.

  23. #23
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    Quote Originally Posted by dirtracer View Post
    Correct me if I'm wrong, but all air forks are progressive based on the volume and well, they use air. It's a gas priciples basic property. Boyle's Gas Laws. Coils are not in this category. As already stated, they're linear.

    For me, a good coil, with a upper gas cushion to catch the big hits. Coils are often referred to as "buttery." Because they're linear.

    Adding oil makes the fork have a steeper "ramp" in the spring rate curve. If it's too steep the rebound damping control might not be able to control the higher rate as it was not tuned to this rate, or lower volume of air.

    Adding air to a coil makes it more progressive at teh top of the stroke. A desirable trait , imho.

    Been doing full sized suspension for years on off road race vehicles. Bypasses , gas springs and all disc valving. Progressive leveraging. The tenets are very similar.

    DR
    Still, can't you alter the progressive rate by changing rates of how much oil is allowed to pass through the shims by changing the diameter of the shims? It seems that not all coils are as linear as they seem, either. The property of a gas is progressive and the property of the coil is linear, but with augmentation to the overall system, these rules seem to have exceptions.

  24. #24
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    [QUOTE=ehigh;9842232]Still, can't you alter the progressive rate by changing rates of how much oil is allowed to pass through the shims by changing the diameter of the shims?

    Changing damper shims would alter lo/hi speed compression characteristics. Progression should be handled by the spring air chamber size. My Rockshox Pike coil bottomed out quite easily as the air volume filled the entire stanchion and no oil other than semi-bath was used (pop seals if you tried adding oil). I asked a Rockshox tech what would control bottomout for a properly sprung Pike ? He said the fork had bottomout cushions in the lowers. Ok so my fork is slamming the bumpers on 1' drops ? I was told to go up a spring rate. Ok now my fork has terrible small bump compliance - SOL.

  25. #25
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    Quote Originally Posted by Steve VS View Post
    Air springs can be engineered to be linear throughout the entire stroke. The reason coils are considered "buttery" is because they lack the initial stiffness that MOST air springs possess, and don't have the extra friction caused by more sliding surfaces.

    Coil springs alone are dead linear within their usable stroke, however without some form of ramp up (be that spring, damping or hydraulic lock anti-bottoming systems, or a leverage ratio that decreases to increase the effective spring/damping rates at the wheel), completely linear sprung suspension needs to be run at a level of stiffness most people would consider unacceptable in order to prevent harsh bottoming out on bikes that are ridden aggressively. The "plushest" feeling suspension (not necessarily the most stable or controlled) invariably comes from a system that has a soft spring rate (measured at the wheel) at the start of the travel and a stiffer rate at the end of the travel - in other words, a progressive system.

    Obviously, suspension that is TOO progressive lacks control in the early and mid stroke, and/or ramps up too savagely.
    Air springs are not linear. Period. The only way I can see that a air spring will become linear is if A) you bleed off air at certain points in the travel to create a linear spring rate or B) you have a rather large air chamber, and this will only make it less pregressive. High volume air cans for example.

    "Initial stiffness"? Please elaborate. I have seen air forks compress over the tiniest of rocks. Also, "more slidng surfaces"? Again, please elaborate.

    "completely linear sprung suspension needs to be run at a level of stiffness most people would consider unacceptable in order to prevent harsh bottoming out on bikes that are ridden aggressively" I have trouble believing this because motorcycle suspension doesn't use any air at all and has been working in off-road flawlessly for years.

    "The "plushest" feeling suspension (not necessarily the most stable or controlled) invariably comes from a system that has a soft spring rate (measured at the wheel) at the start of the travel and a stiffer rate at the end of the travel - in other words, a progressive system." Again, dirt bikes dont have progressive suspension and they seem to have the whole " two wheeled off-road thing" pretty dialed. Coil is the way to go. Plain and simple. The only drawback of coil in a pure performance situation would be weight. And titanium springs will fix that.

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