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Discussion Starter · #1 · (Edited)
Ok. Once and for all I would like some help on suspension terminology and what it means.

Progressive means what?
Linear means what?
Coils are - linear or progressive?
Air is - linear or progressive?

Can someone give me examples of what kind of forks are linear or progressive.

Can someone tell me what kind of terrain or trail riding warrants either a linear or progressive fork.

Can someone explain to me why someone needs adjustable compression damping? ie; what kind of terrain or trail riding needs compression damping.

Can someone explain to me what kind of trail conditions or styles of riding each of the TST settings on an AM1 fork are good for?

I have been doing some reading on mtbr and now I am all confused.

EDIT: I am particularly interested in FORK technology and terminology.
EDIT again: I did not post this in the shox forum because people usually don't reply over there.
EDIT AGAIN: I am AGAIN looking at forks for the 5 spot.
 

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Linear refers to a "rate" (which is short for "rate of change"). If something has a constant rate, or no change in rate (rate of change is zero), it is said to linear. Think of a coil with a rate of 500# per inch (a typical shock spring). It takes 500# of force to compress the spring one inch. It then takes ANOTHER 500# of force to compress it another inch. Since it took the same amount of force to compress the second inch as the first, the rate of change is zero (no change in the rate), so it is "linear."

An air spring is different. It takes more force to compress the air spring the second inch than it does the first inch (say 500# for the first and 600# for the second). The rate (the rate of change) is increasing, so it is said to be "progressive."

I do not know of a spring which is falling rate.

Bike suspensions are also said to be linear, rising (progressive), or falling rate. This tells you how the bike behaves assuming it has a linear spring attached to it. This is an important point. A linear suspension (with the linear spring attached) acts just like the linear spring: it takes the same amount of force to compress the first inch of the travel as each additional inch. A progressive linkage suspension will get harder to compress as you go through the travel despite the fact that you have a linear spring mounted (remember, when talking about suspension types, it is always assumed you are defining it using a linear spring). A falling rate will take less additional force for the later travel than the earlier.

See how you have two things working here? You have springs AND linkages. Both of them can have either constant or changing rates. How you mix and match them has a big effect on the bike's behavior.

Now if you put a progressive air spring on a linear linkage bike, you will end up with the same effect as putting a linear spring on a progressive bike. Someone else can field what's a good or bad combo...
 

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Discussion Starter · #3 ·
so lets talk forks. An air fork like the Duc 32 is going to become more progressive as it nears its end of travel? But, a coil fork will stay the same towards the end of travel? Do all forks "ramp up" near the end of travel?
 

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A fork which is progressiv will ramp up. ie. makes it harder to bottom.

I like my fork to be linear while sitting on a fast singletrack, using lots of travel to take up all the bumps. I like my fork to be progressive when going downhill, to prevent it from bottoming on the small stuff, and so be able to take all the big stuff :) Tough job to be a fork.


This is also where slow and fast compression adjustment comes in, if I am not mistaking :)
 

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FleshwoundGravityResearch
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SMOKEY said:
so lets talk forks. An air fork like the Duc 32 is going to become more progressive as it nears its end of travel? But, a coil fork will stay the same towards the end of travel? Do all forks "ramp up" near the end of travel?
So what's up? You aren't liking the Z1FR?

As far as the progressivity of air forks, some are supposed to act more linear with the option of adjustable progressive travel. ie. The high end Manitou forks like the minute 2 and 3 and the top nixon have the option of increasing the spring's progression by turning the SPV nut into the fork. Supposedly the fork is near linear with the SPV nut all the way out. I believe this to be true because with the nut all the way out and the air pressure at the recommended setting, I get the fork to blow through its travel with only brake dive.
I am sure there are others that claim this ability to have a near linear air spring rate, but I am not sure which ones. (Float, DUC, Marathon...?)
 

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SMOKEY said:
Can someone give me examples of what kind of forks are linear or progressive.

Can someone tell me what kind of terrain or trail riding warrants either a linear or progressive fork.

Can someone explain to me why someone needs adjustable compression damping? ie; what kind of terrain or trail riding needs compression damping.
Smokey - as a GENERAL rule of thumb air forks will be progressive and coils will be linear. Air forks will ramp up at the end of the stroke to resist bottoming forces, but will loose "plushness" the farther you go into the stroke - classic examples of progressive shock are Manitous, Minutes, Mars, air Blacks, RockShox Rebas, Zoke Marathons. Air forks can be more sensitive to hits early in the stroke (rapid stutter bumps, smaller trail obstacles) but lose some performance when the fork hits get bigger. Coils by comparison will have a smoother overall rate of compression and give more consistent feel through the travel range but may be more prone to bottoming out, and may not be as cushy on the small stuff if the coil is heavy enough to resist bottoming on big hits - RS Psylos, Zoke Bombers, Manitou coils. Air shocks tend to be significantly lighter and more easily tuneable- coils are heavier, not quite as adjustable, but less prone to failure (no leaking air seals). A lot depends on the design of course but as general guides that's the difference. I think most riders of trail, FR and bigger hit bikes prefer coils, lighter XC rigs, racers and less aggro trail riders might prefer air.

Compression damping is just a method of tuning the fork to react to trail impacts. An XC racer typically will tune the compression to be quite firm on the theory that not having a plush fork conserves and better uses the rider's energy for speed. The price you pay for that efficiency is a harsher ride. Less compression will make the fork more reactive to hits but also introduces the potential for brake dive, unintended compression in high speed cornering, wallowing and funky steering and control. Compression and rebound are compromises based on the rider's preference. Example - I use an air Reba. On extended climbs I'll increase the compression damping to a point where I'll still get some front end compression, but not too much so I still have the ability to muscle ledge hops, techy manuevers, and climbing while standing without alot of bob. On the descent, I'll open up the compression to allow for full sensitivity going down the stuff I climbed while carrying more speed and energy.

Again, as a GENERAL rule, smooth single track, tough climbs, techy slow-mo trials type riding calls for a higher compression rate to enhance handling precision. More dh oriented riding, drops, hits, high speed descents and rolls would warrant less compression damping. So much of this is personal preference, rider weight, technique and style that it's impossible to set a hard and fast rule, but that's my .02
 

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SMOKEY said:
Ok.
Can someone explain to me what kind of trail conditions or styles of riding each of the TST settings on an AM1 fork are good for?
Here is my take on the 5 TST settings:

CS - almost completely locked out - has about 30mm of travel. Good for smooth climbing that is not steep enough to require ETA

Intermediate - Very stiff but not locked out. Good for not so smooth climbing that is not steep enough to require ETA

AM - Perfect for trail riding in most situations IMO

Intermediate - A Little more plush, better for rougher trails with not so much climbing.

DS - Z1 Plushness for DH days, baby!
 

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SMOKEY said:
so lets talk forks. An air fork like the Duc 32 is going to become more progressive as it nears its end of travel? But, a coil fork will stay the same towards the end of travel? Do all forks "ramp up" near the end of travel?
Well Sorta.

All air forks intrinsinctly ramp up by the fundamental nature that you are trying to make an air cylinder smaller and you get a ramp up near the end. However, if air volume is huge compared to the amount of volume compressed, the fork can act linear over the region the fork compresses. It does still have a ramp, but maybe not noticable.

Springs are almost always completely linear until they bottom out (the coils touch) and then suddenly they are highly non-linear (A hard stop)

In theory, I would think an sprung curve would be what you would want, Supple for small stuff, and it would never bottom out when designed right. However, in practice, the feel of a linear spring is better and it's mainly due to that when an air shock is really non-linear, there is too much sag in the beginning and then it's too harsh as it goes deep into travel.
 

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Old turners v. New turners

I apologize in advance for highjacking your thread Smokey.

This is great information. I believe one of the main difference between the old turner and new turner is the design of the rockers [xce & burner (old) v. flux, 5spot, 6pack (new)]. Based on the difference in the design of the rockers, can someone discuss how the change in the rockers affect the design of the suspension.

Are the old (XCE & Buners) suspension design linear, progressive or falling rate?
Are the new (flux, 5, 6) suspension design linear, progressive or falling rate?

Thanks in advance!
 

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nykat said:
I apologize in advance for highjacking your thread Smokey.

This is great information. I believe one of the main difference between the old turner and new turner is the design of the rockers [xce & burner (old) v. flux, 5spot, 6pack (new)]. Based on the difference in the design of the rockers, can someone discuss how the change in the rockers affect the design of the suspension.

Are the old (XCE & Buners) suspension design linear, progressive or falling rate?
Are the new (flux, 5, 6) suspension design linear, progressive or falling rate?

Thanks in advance!
Rising rate linkages on all of them - check out his thread for more details:
http://forums.mtbr.com/showthread.php?t=74798&highlight=geometry+curves
 

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Cutthroat makes some meaningful points about compression damping....and especially relevant to me because I've been debating the Fox Vanilla RL against its brother, the Vanilla RLC. I've been reading that Fox finally got the compression settings to work with their '05 forks. So I've been wondering if the "C" designation would be useful for me, and I'm slowly coming to the conclusion that it will. Especially in the area of brake dive.

The only problem is, this is not something you can adjust without stopping and spinning the compression dial. Maybe it's not necessary as an on-the-fly adjustment.

No way I'm buying a Reba. Not to discredit you guys that have, but I'm reading bad things about them already, and the nightmares of my old Judy are hard to overcome. RS will have to pull a BIG rabbit out of the hat to get me back. Geez, they were so promising with the Mag 21 too.....but I digress.
 

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FleshwoundGravityResearch
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lidarman said:
Well Sorta.

All air forks intrinsinctly ramp up by the fundamental nature that you are trying to make an air cylinder smaller and you get a ramp up near the end. However, if air volume is huge compared to the amount of volume compressed, the fork can act linear over the region the fork compresses. It does still have a ramp, but maybe not noticable.
Springs are almost always completely linear until they bottom out (the coils touch) and then suddenly they are highly non-linear (A hard stop)

In theory, I would think an sprung curve would be what you would want, Supple for small stuff, and it would never bottom out when designed right. However, in practice, the feel of a linear spring is better and it's mainly due to that when an air shock is really non-linear, there is too much sag in the beginning and then it's too harsh as it goes deep into travel.
This is exactly what I was talking about regarding the high end Manitou forks' claim to a MORE linear spring rate. I was not claiming that air sprung forks were not progressive. Compare a low end air fork now or any old air sprung fork and the progression through the travel ramps up exponentially. If you back out the SPV nut (which is the compression damping) you cannot tell there is any rise in the spring rate.
For what it is worth, I would think a combination air/coil would be ideal in theory. I have not tried what is out there right now, though. They all seem to be heavy forks for my use and weight. (ie, firefly, AM1)

EDIT: Here is Fox's claim to having a MORE linear air spring.

  • Proprietary Linear Air Spring system works "..." to provide air-spring weight with coil-spring feel.

Fox Shox Linear Air-Spring
 

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Roostalee said:
So I've been wondering if the "C" designation would be useful for me, and I'm slowly coming to the conclusion that it will. Especially in the area of brake dive.
What you really might want is a "pushed" fork or a fox with an intertial valve (or the inertial valve inserts you can by aftermarket). The inertial valve concept is sweet in it senses the direction of the force acting on the wheel. Thus a downward force like brake dive and pedaling is locked out and the bump forces upward from rocks, etc, are damped out.
 

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SMOKEY said:
Ok. Once and for all I would like some help on suspension terminology and what it means.

Progressive means what?
Linear means what?
Coils are - linear or progressive?
Air is - linear or progressive?

Can someone give me examples of what kind of forks are linear or progressive.

Can someone tell me what kind of terrain or trail riding warrants either a linear or progressive fork.

Can someone explain to me why someone needs adjustable compression damping? ie; what kind of terrain or trail riding needs compression damping.

Can someone explain to me what kind of trail conditions or styles of riding each of the TST settings on an AM1 fork are good for?

I have been doing some reading on mtbr and now I am all confused.

EDIT: I am particularly interested in FORK technology and terminology.
EDIT again: I did not post this in the shox forum because people usually don't reply over there.
EDIT AGAIN: I am AGAIN looking at forks for the 5 spot.
Your single speed with the rigid fork will be extremely progressive in nature
 

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FleshwoundGravityResearch
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lidarman said:
What you really might want is a "pushed" fork or a fox with an intertial valve (or the inertial valve inserts you can by aftermarket). The inertial valve concept is sweet in it senses the direction of the force acting on the wheel. Thus a downward force like brake dive and pedaling is locked out and the bump forces upward from rocks, etc, are damped out.
This seems a bit off to me. Brake dive/pedaling forces and bump forces would be seen by the inertia valve as going in the same direction, right? They are both still compressing the fork.
I thought the inertia valve worked by tuning out low frequency movements like pedaling/dive and still allowing the higher frequency bump forces through....No?
 

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As mtn hack mentioned, many coil forks end up being a blend of the two spring types, because they do have air trapped in them. The notable exception to this is the Pike coil, where the leg which houses the spring has so little oil volume in it that the air does not get sufficiently compressed to play a role like it does in Fox and Zoke coils. That is what I really did not like about the Pike Team coil: just waaaay too linear in spring rate and travel. Even with very little sag, it just went down like the Titanic on smallish drops and over braking bumps. The Pike Air, which has the exact same damping system (set up the same as on the coil), same sag (the way I aired it up), is still very supple around sag but has a smooth progression to it and the end of stroke ramp-up is so natural and subtle, yet effective, that it gives you that "bottomless" feel. (There was no missing the "bottom" on the coil version. ;) )
 
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