ok, so there are probably hundreds of different types of full suspension designs out there but what design does what? what are the axles paths on each design? which have best small bump absorbsion? which are smothest? which have least pedal bob effect? which have least braking jerk or whatever its called? which are more like aggressive hardtails? which ones track the ground best? can anyone clear that sort of stuff up for me and any other information that might be relevent?

Off te top of my head i can think of: single pivot, VPP, FSR, four bar, faux bar, DW link, rocker actuated shock, iDrive, TARA, Maestro, Genesis. There must the hundreds more and probably some very obvious ones i’ve missed. but whats the difference between tham all?

Is the a comprehensive list and explanations anywhere on the WWW?

go boing.

everything else is just marketing….

Some stuff here:
http://en.wikipedia.org/wiki/Bicycle_suspension#Rear_suspension

james, thanks for that, it’s a great help.

So fari have learnt that:
Single pivot – simple, small bump sensitivity but suffers from brake jack and bobbing. If used with a linkage e.g. Commencal Meta 5 then it produces a more progressive spring rate.
Four bar/horst link/FSR – neutral under acceleration, relatively active suspension during braking.
Faux bar – not neutral under acceleration, similar axle path to single pivot, suffers some of the brake effect that a single pivot does
VPP – designed to aid pedalling without affecting the bump absorbtion properties negatively
dw-link – improves pedalling effeciency while also improving bump absorbsion capabilities.
Equilink – Felt’s attempt to simulate the dw-link.
ABP – active suspension including during braking and good small bump sensitivity.

This leads me to ask a few more questions:
What is brake jack?
Is a progressive spring rate one that gets harder or softer as it progresses through its travel?
In what way is a faux bar system not neutral under power? what does it feel like?
How does chain growth affect suspension?

Faux bar

is identical axle path to single pivot…

Brake jack geekery here.

http://forums.farkin.net/showthread.php?t=35572

Brake Jack is the tendency (maybe)* of hard braking on longer travel suspension systems to make it extend.

*most full-suss bikes will squat under braking, many people confuse this with jack, whether it actually exists, or is in fact a problem is a whole other debate

Is a progressive spring rate one that gets harder or softer as it progresses through its travel?

generally firmer

Hate to say it, but jam bo is correct here.

I have ridden two full suss bikes enough to draw a considered conclusion on. One single pivot (patriot) and one faux bar (so essentially a single pivot with a linkage (turner)).

Both very different riding bikes, even though the suspension design is superficially of the same type & similar travel. Each bike has it’s own strengths and weaknesses.

You really can’t generalise how a bike will ride based on the suspension design alone. You have to get out and ride them to know for sure.

FWIW, I also think brake jack is a myth – it’s just the rear end unweighting!

watch the video

brake jack

Brake Jack

Right, so locking the rear brake causes the suspension to partially compress – into the stiffer part of the travel where it behaves more like a HT – loss of traction and bounced around.

So anti-brake jack systems really needed when you’ve got to jam your rear brake on a lot i.e. AM riding?

Interesting demonstration, and obviously some effect given the specific circumstances demoed there.

HOWEVER, brake JACK is usually complained about as somehing which works to extend the rear suspension under braking, not compress it as shown in the clip. You could even argue the effect shown in that video is beneficial as it counteracts forward weight transfer during braking!

In addition I think if you apply what’s seen in the clip to a real-world riding scenario the effect would be minimal. What is demod in the clip is the instantaneous transfer of rotational inertia of the wheel (going at a fair lick!) into enough energy to raise the unsprung rear suspension assembly (what, 5kg?) up a few inches. If you added a spring & damper sufficient to hold up 100kg of rider & bike to the shock, then the effect would be nowt.

Also, you wouldn’t brake like that in the real world. Even if I took my bike out and did and locked the rear wheel into a big skid I don’t think I could detect any dropping away of the rear suspension. Might try it later though!

Bit of a rant that, sorry. Just got me thinking. And I still think it’s a myth

el_boufadour, you’ve just written what I was going to. That Vid is marketing bollards pretty much. “We’ll take the shock out to over emphasize the effect” ? i.e. with no rider weight, no damping from the shock, no ground, and really large braking forces, we can make this unweighted lightweight rear move about in a completely unrealistic manner.

Well done Kona.

“What is demod in the clip is the instantaneous transfer of rotational inertia of the wheel (going at a fair lick!) into enough energy to raise the unsprung rear suspension assembly….”

But it’s not is it? Because the wheel is symmetrical so the rotational inertia isn’t just transferred up, it’s transferred equally outwards in all directions i.e there IS something to do with the caliper placement that’s causing the brake force to compress the suspension.

What that is, I can’t really be assed to think about, and I do agree that the effect is exaggerated by lack of spring, but the effect is there none the less.

DrP

the merida 150 I rode the other day had a floating rear brake, bloody good it was.

Dr P,
Inertia is just a word for rotational momentum, I.e. kinetic energy.

When the brake is jammed on the wheel can no longer rotate about the axle, but given the suspension mechanism it can still rotate about the BB pivot. As such the inertia initially in the wheel rotates the whole assembly about this new axis. This moves the suspension assembly & wheel upwards, converting the kinetic energy (movement) to potential energy (height).

Quite a good review here, though he freely admits being 4-bar biased

http://www.titusti.com/fs_tech.html

el_bouf – again this is wrong!
Sure the wheel has inertia, but that inertia is equal in all directions. Thus there will be equal inertia up, down, back and forth. In the demonstration the bike isn’t moving, just the wheel. Just stopping the wheel wouldn’t move the swing arm up, but it’s to do with the placement of the brake caliper and the pivot points.

DrP

…and such, the different designs combat or emphasise the upward/squatting motion that sometimes occurs.

DrP

I don’t understand any of it.

I have nothing useful whatsoever to add.

But these little kittens are very cute, though!

brake jack only becomes noticeable on a bike with big travel, and even then it can be useful for cornering.

4 bar can sometimes be like riding a big mattress

one thing to note in all this, is that when your tyre is in contact with the ground under braking it will make the suspension move upwards regardless of linkage type, because the forces transferred by the tyres friction on the ground have to go somewhere, and they mostly go up.

When the brake caliper is free to rotate around the hub axle, the suspension is more compliant (able to follow the ground contours).
A four bar linkage bike will allow this to happen more freely than another (non Horst-link) bike.

All of this matters very little however, because sustained braking over rough ground is rare, and the loose surfaces on offroad conditions negates this effect as felt by the rider.

So, after having ridden nearly every type of linkage know to man/woman… i can conclude that the effect of brake/jack/squat/lock/etc: is negligable.

shock performance, and rider performance is massively more important than any of this nonsense.

So, dont worry be happy, and ride along.

Dr P,

Sorry, I’m not wrong.

The ‘direction’ of the energy is in the direction of rotation of the wheel (clockwise in the vid).

The brake Jams on and the direction of the energy is still the same, but about a different pivot (the chainstay BB end pivot, as opposed to the hub axle).

In the linkage frame in the vid, the dropout cannot rotate the chainstay in relation to the frame (due to the linkage creating a parralellogram), therefore any inertia is just transferred into heat by friction in the brake.

FFS. Nte to self: What a ghey thing for me to be posting at 11 pm on a sat night

Anyways:

1) Single pivot, some with link actuated shocks which includes fauxbar
2) virtual pivot, this includes 4-bar, DW, maestro, VPP

VPs have an axle path that makes an S shape to roll-back plushly over edges. SPs just do an arc so climb over edges which gives more “feel”. Cancellation of pedal forces and progressive spring rates is more to do with the positions/size of the links and/or the compression damping of the shock.

surely the answer to the OP is

“compensate for lack of skill” 😆

LOL! Funny, because it’s so true… 😉

My limited sperience of full-suss, is that it certainly does smooth out the mistakes. More comfy, though.

I don’t feel how there’s a huge difference between the different types, in the ‘real world’. Praps certain types are more suited for gnarly downhills, or XC climbing, but yer average mtber would be happy on most designs, let’s face it.

Biggest difference in suspension action is what gear you are in (combined with how hard you are pedalling)

The ‘direction’ of the energy is in the direction of rotation of the wheel (clockwise in the vid).

The brake Jams on and the direction of the energy is still the same, but about a different pivot (the chainstay BB end pivot, as opposed to the hub axle).

Aye, the direction of energy of the spinning wheel is in a clockwise direction, but because the wheel is symmetrical about it’s point of axis (the hub), when the wheel suddenly stops that force is equal up, down, forwards and backwards i.e. the wheel ‘tries to move’ outwards in all directions, not just up.
The reason the pivot jams upwards is to do with the position of the brake calliper – in this case the calliper is on a ‘different’ component than the axle/hub (different in the sense there is a pivot on the chainstay between them).

Take a single pivot bike and do the same thing. Because the calliper and axle are NOT separated by a pivot (i.e they are on the single chunk of metal – the swing-arm), simply jamming the brake on won’t make the wheel jump upwards like it did in the video.

Disclaimer – I’ve just done this test with my rigid road bike, and as the valve composes a considerable weight, it makes the wheel weight ASYMMETRICAL about the axle! Thus with correct timing i can make the rear force upwards and downwards – must fix that!

DrP

Of course all this talk is actually academic because, as someone pointed out, once the bike is actually rolling on the floor (in actual use!), once the brake is applied the force is that of friction against the floor pulling the rear wheel backwards, working against the force of the inertia of the bike/rider pulling forwards in the direction of travel. Thus the forces ‘try’ to separate the wheels, and depending on the pivot path will have different effects.

DrP

What I understand to be brake jack occurs when you brake hard at high speed over rough ground. For all I know this isnt actually brake jack but something else. At any rate a bike with a floating brake arm will perform better in this type of situation than one without in my experience. I would assume that trek’s active braking pivot has a similar effect.

“Disclaimer – I’ve just done this test with my rigid road bike, and as the valve composes a considerable weight, it makes the wheel weight ASYMMETRICAL about the axle! Thus with correct timing i can make the rear force upwards and downwards – must fix that!”

If you try the experiment on a rigid bike, so long as it is free to rotate (e.g. in a bike stand with a loose pivot) you will see that the bike will rotate in the same direction as the wheel when the brake is jammed on. This’ll work better the closer you can get the pivot to the back wheel (e.g. seat tube would be good).
In fact, this technique is used by dirt jumpers and MXers to bring the nose down during tricks.

If you bother to do this you’ll see I am correct.

yep, that’s true actually, my hardtails ‘jump’ in the workstand if i yank on the rear brake hard. try it with the front wheel and it trys to ‘drop’. Spin the front wheel backwards and it will ‘jump’.

basically, it always trys to rotate in the same direction as the wheels are rotating at the time.

Sorry DrP, I agree with the theory of el_boufador on this one. your’s might be more accurate to physics but i feel el_boufador’s is more accurate to this particular situation.

dr p: angular momentum in the wheel – it has to go somewhere when the wheel stops rotating, it’s transferred to the wheel/swing arm combined, causing it to rotate in the same direction that the wheel alone was turning

not very relevant to op, but pretty fundamental physics (read ‘important’, not ‘basic’)

“I have ridden two full suss bikes enough to draw a considered conclusion on”
Two single pivot bikes. One where the shock is linkage driven. How exactly do you have enough to go on to draw a considered conclusion on all suspension designs?

“sustained braking over rough ground is rare”
What about sustained braking bumps into a corner?

As sockpuppet said the key is angular momentum.

The reason it jumps is because of the rotation direction and switch from momentary pivot of the axle to being the swingarm pivot.

I will *attempt* to explain but obviously I may not be able to express myself well enough to get what i see in my head into words….

1. take the above video, remove all the ‘bike’ and visualise it as a simple bar (the lower swingarm) pivoting around the main frame pivot on the left.

ignoring the effects of gravity it is free to rotate up and down, but rests at a perfectly horizontal level.

2. now consider JUST the wheel. spinning around its hub (in either direction)

if it were to suddenly stop it will not travel up or down as direction of energy is equal in all directions.

3. now place the wheel axle at the right hand end of the pivoting bar from (1)

IGNORE SHOCK, CHAIN ETC.

4. rotate wheel CLOCKWISE and jam on brake and suddenly pivot swaps from hub to the left end of the swingarm (main frame pivot)

in this case the assembly will swing DOWN

5. rotate wheel COUNTERCLOCKWISE and jam on break and again suddenly pivot swaps from hub to the left end of the swingarm (main frame pivot)

in this case the assembly will swing UP

when the wheel is isolated it does not move but when it is attached to the swingarm you suddenly have a new pivot point. since the right hand side of the wheel is FURTHER away from the new pivot the turning effect of the energy at this point (which is straight up) is greater than that of the energy at the left edge of the wheel (which is straight down) and thus it jumps UP.

If you reverse the direction of rotation in that video and jam on the brake it would try to extend the shock and jump down.

however since we never travel at high speed backwards when breaking we never see that effect.

Matt

“Two single pivot bikes. One where the shock is linkage driven. How exactly do you have enough to go on to draw a considered conclusion on all suspension designs?”

James, the point I was making was that I have experience of two single pivot designs which ride very differently. As such you can’t generalise how a suspension bike will ride based soley on its suspension design. I only need experience of 2 bikes to be able to say this with certainty!

Thanks Swoosh, Sock Puppet & Amedias. Knew I wasn’t going mental in this pointless physics hijack. I did study this sort of stuff for 4 years many moons ago.

For an explanation of the Kona style of faux bar/four bar try here. It makes for interesting reading – expecially the comment on whether brake jack is bad or not.

A few notes of their magic link idea can be found here.

2. now consider JUST the wheel. spinning around its hub (in either direction)

if it were to suddenly stop it will not travel up or down as direction of energy is equal in all directions.

This is the point i was trying to make, but I feel I omitted the part about the angular momentum! I stand corrected!
I was thinking too hard about the outward inertia (which as it appears you all know is equal, well apart from my road bike), and not about the rotational aspect.

EL_bouf, you are indeed correct….

However, (and I’m not disagreeing here), what are the real life causes for brake jack then? Surely with spring tension, and the fact that in reality the rear wheel probably won’t be spinning at a mental pace then suddenly locking up, and the jack occurs at slow speed, surely it can’t all be due to wheel momentum, and must be due to caliper placement in relation to the axle etc?

DrP