...you know, something that expalins the different designs and advantages and disadvantages of each.....
looking for good full suspension reference
- Thread starter MtnBikerChk
- Start date
There isn't really one out there. The best I know of is a site by an engineering student in NZ, Dougal. Dougal's World
But I actually don't agree with him completely on some of his assessments.
If you really want to get into, I just recieved the new addition of Motorcycle Chassis Design: The Art and the Science, by Tony Foale, which is more accurate and comprehensive than anything you'll find on bikes. You can borrow it next time you make it up to Boston.
FS MTBs are just SO young that a lot of the people designing them, and most of the people reviewing them have no clue HOW they actually work, just that they do. A good example is Ellsworth, who has managed to accidentally design great bikes
.
The other thing is, suspension design is finally refined enough, that any of the remaining styles can be designed really well, so that fit and proper shock setup makes as much, if not more of a difference in the suspension feel and performance.
But I actually don't agree with him completely on some of his assessments.
If you really want to get into, I just recieved the new addition of Motorcycle Chassis Design: The Art and the Science, by Tony Foale, which is more accurate and comprehensive than anything you'll find on bikes. You can borrow it next time you make it up to Boston.
FS MTBs are just SO young that a lot of the people designing them, and most of the people reviewing them have no clue HOW they actually work, just that they do. A good example is Ellsworth, who has managed to accidentally design great bikes
.The other thing is, suspension design is finally refined enough, that any of the remaining styles can be designed really well, so that fit and proper shock setup makes as much, if not more of a difference in the suspension feel and performance.
okay MBC, you asked for it. Here's a quick primer for current MTB suspension designs.
Notes - for all of these explanations I am assuming a middle chainring/middle cog (e.g.32t/20t). I am generalizing, so I'm not going to bother with minute details unless they make a BIG difference in the suspension performance. I also might not explain why each one does what it does fully for the sake of simplicity. If you want to know why, I'm either going to charge an hourly rate or page konadude and DW.
1. Chain induced interactions
A. Single Pivots
- High and forward pivot point: Pedalling will stiffen the suspension.
The higher it is the more the chain effects it
e.g. SC Heckler, Orange Patriot, Mountain Cycle, Cheeta Prowler
- Pivots slightly above and/or behind the BB:
Pedalling will have little/no effect on the suspension performance
Many people complain these bikes "bob". This is due to an unsmooth pedalling stroke, NOT the chain compressing the suspension.
A pivot too low and back CAN experience suspension compression if pedalled well into it's travel.
e.g. Locomoto, Ventana, Kona, Foes
B. 4-bar linkage
The same rules apply as to single pivots, except these bikes have an effective pivot point determined by their axle path. For FSR style bikes that point is almost always an arc around a point above and slightly behind the BB. This means they pedal like a Locomoto, or a Kona. If they feel different it's due to other factors, such as suspension rate, bike stiffness, and geometry. Don't believe the marketing.
The only non-FSR 4-bar I'll discuss is the "VPP" because there's too many variations possible (Karpiel, Canfield, DW) for me to cover. The VPP has an S shaped axle path. This means for the first part of it's travel the chain tension tries to pull it into a point in it's sag. If it is extended beyong that, the chain compresses it. If it is compressed beyond that, the chain extands it. Deep into it's travel, the chain stops effecting it, because you won't be pedalling then anyway. In theory it's an excellent idea. I haven't ridden one yet though.
2. Braking interaction.
The braking interactions are more complicated.
A. Single pivots- ALL single pivots experience brake induced compression (brake-squat). ALL of them. However,
-The lower and more forward the pivot, the less brake-squat. This is why the Locomoto and Turner DHR brake very well. This is why the Bullit can skip and stutter under rough braking.
Except in the parking lot you will not feel brake ssquat as the rear end actually squating. You will feel it as the rear end skipping as the brakes catch->suspension compresses->tire breaks loose-> suspension extends -> brakes catch, and so on...
B. 4-bars can either cause brake squat or brake jack, and some can do both at different points in their travel. Most brake squat very slightly, and will brake better than a single pivot. All of this is dependent on the brake caliper being mounted on the seatstay. If the caliper is on the chainstay, it is a single pivot.
C. Floating brake mounts- these eliminate ALL braking interactions, assuming they are designed properly.
3. Suspension rate - this is the most ignored but probably most important distinction between similar suspension designs. In general all MTBikes either use a straight rate or a rising rate. A straight rate, means that it requires the same ADDITIONAL amount of force to compress the suspension through a given amount of travel. e.g. 100lbs = 1in, 200lb = 2in, 300lbs - 3in, 400lbs = 4in, and so on. This results in a very consistent, and predictable feel, but can bottom out on hard hits and drops. A rising rate gates consistently harder to compress as you move further through the travel. e.g. 50lbs = 1 in, 150lbs = 2 in, 300lbs = 3 in, 500lbs = 4 in. This is very soft in the initial travel, which can enhance any pedalling problems but makes the suspension very supple. It can feel too soft or a little dead, but it won't bottom out as easily on big hits. Rising rates can also be overdone. Too much and the travel feels like mush until the end when it stiffens like a rock.
Most bikes without linkages have straight rates, e.g. Bullit, Locomoto. These benefit from shocks that have an inherent rising rate ("progressive shocks"), like air shocks, stratos helix, or 5th element. Bikes with linkages can have straight rates, rising rates, or both. A bike with a signicant rising rate linkage benefits from a straight-rate shock (most coil-overs) and will usually not feel good with a progressive shock. Usually (but not always) the smaller the linkage actuating the shock, the more rising the rate. Beyond that will take up too much space to explain.
So there you go. Feel free to dissent, flame, disagree, or whatnot. If you have any questions, I can try to answer them.
Notes - for all of these explanations I am assuming a middle chainring/middle cog (e.g.32t/20t). I am generalizing, so I'm not going to bother with minute details unless they make a BIG difference in the suspension performance. I also might not explain why each one does what it does fully for the sake of simplicity. If you want to know why, I'm either going to charge an hourly rate or page konadude and DW.
1. Chain induced interactions
A. Single Pivots
- High and forward pivot point: Pedalling will stiffen the suspension.
The higher it is the more the chain effects it
e.g. SC Heckler, Orange Patriot, Mountain Cycle, Cheeta Prowler
- Pivots slightly above and/or behind the BB:
Pedalling will have little/no effect on the suspension performance
Many people complain these bikes "bob". This is due to an unsmooth pedalling stroke, NOT the chain compressing the suspension.
A pivot too low and back CAN experience suspension compression if pedalled well into it's travel.
e.g. Locomoto, Ventana, Kona, Foes
B. 4-bar linkage
The same rules apply as to single pivots, except these bikes have an effective pivot point determined by their axle path. For FSR style bikes that point is almost always an arc around a point above and slightly behind the BB. This means they pedal like a Locomoto, or a Kona. If they feel different it's due to other factors, such as suspension rate, bike stiffness, and geometry. Don't believe the marketing.
The only non-FSR 4-bar I'll discuss is the "VPP" because there's too many variations possible (Karpiel, Canfield, DW) for me to cover. The VPP has an S shaped axle path. This means for the first part of it's travel the chain tension tries to pull it into a point in it's sag. If it is extended beyong that, the chain compresses it. If it is compressed beyond that, the chain extands it. Deep into it's travel, the chain stops effecting it, because you won't be pedalling then anyway. In theory it's an excellent idea. I haven't ridden one yet though.
2. Braking interaction.
The braking interactions are more complicated.
A. Single pivots- ALL single pivots experience brake induced compression (brake-squat). ALL of them. However,
-The lower and more forward the pivot, the less brake-squat. This is why the Locomoto and Turner DHR brake very well. This is why the Bullit can skip and stutter under rough braking.
Except in the parking lot you will not feel brake ssquat as the rear end actually squating. You will feel it as the rear end skipping as the brakes catch->suspension compresses->tire breaks loose-> suspension extends -> brakes catch, and so on...
B. 4-bars can either cause brake squat or brake jack, and some can do both at different points in their travel. Most brake squat very slightly, and will brake better than a single pivot. All of this is dependent on the brake caliper being mounted on the seatstay. If the caliper is on the chainstay, it is a single pivot.
C. Floating brake mounts- these eliminate ALL braking interactions, assuming they are designed properly.
3. Suspension rate - this is the most ignored but probably most important distinction between similar suspension designs. In general all MTBikes either use a straight rate or a rising rate. A straight rate, means that it requires the same ADDITIONAL amount of force to compress the suspension through a given amount of travel. e.g. 100lbs = 1in, 200lb = 2in, 300lbs - 3in, 400lbs = 4in, and so on. This results in a very consistent, and predictable feel, but can bottom out on hard hits and drops. A rising rate gates consistently harder to compress as you move further through the travel. e.g. 50lbs = 1 in, 150lbs = 2 in, 300lbs = 3 in, 500lbs = 4 in. This is very soft in the initial travel, which can enhance any pedalling problems but makes the suspension very supple. It can feel too soft or a little dead, but it won't bottom out as easily on big hits. Rising rates can also be overdone. Too much and the travel feels like mush until the end when it stiffens like a rock.
Most bikes without linkages have straight rates, e.g. Bullit, Locomoto. These benefit from shocks that have an inherent rising rate ("progressive shocks"), like air shocks, stratos helix, or 5th element. Bikes with linkages can have straight rates, rising rates, or both. A bike with a signicant rising rate linkage benefits from a straight-rate shock (most coil-overs) and will usually not feel good with a progressive shock. Usually (but not always) the smaller the linkage actuating the shock, the more rising the rate. Beyond that will take up too much space to explain.
So there you go. Feel free to dissent, flame, disagree, or whatnot. If you have any questions, I can try to answer them.
there is something on the web where you can d/l files and it explains path analysis pretty well (i haven't really chugged through it much).
try doing a web search for this:
Path Analysis.
A Bicycle Rear Suspension Analysis Method.
by Ken Sasaki.
try doing a web search for this:
Path Analysis.
A Bicycle Rear Suspension Analysis Method.
by Ken Sasaki.
have a buttload of information:
if you sit on my full squishy, it will be a good reference point
Narlus, any more info on the "Path Analysis" stuff?
I've tried doing web searches but to no avail.
Anyone else help?
I've tried doing web searches but to no avail.
Anyone else help?
Well, that's a pretty good answer. I don't think anybody can argue those, unless they misunderstand the intricacies of what you wrote (ie "means that it requires the same ADDITIONAL amount of force to compress the suspension through a given amount of travel").
As far as Ellsworth accidentally designing great bikes, that's something dhdescender and I were talking about quite awhile ago actually. We said the exact same thing!
G
gravity
Guest
Ellsworth never actually designed the "ICT" bikes. he originally had a pretty standard Turner linkage but with exotic framework (you know, all the super-lightweight stuff, no expense spared. not a new design in other words). a guy from one of the Japanese car companies (Nissan i believe) called him one time and said "I know why that linkage works so well, and how you can make it even better."
so the other guy basically redesigned the suspension geometry so that it worked so well, and Ellsworth tried (and failed) to understand and explain it.
there's an interview with him in one of the recent editions of Australian Mountain Bike, where he mentions it.
so it was no accident that they're good bikes, it's just Ellsworth taking credit for something that he doesn't understand and never designed anyway. Even he admits that he is "not as skilled as a trained engineer".