it's always dangerous for the manufacturer to get involved in these conversations...
... but, since I've been posting on MTBR for close to 10 years, wtf...
Anyway, let's clear up some common misconceptions first:
Suspension designs: If the rear wheel is located on a swing arm with one pivot between it and the front triangle, then it is considered to be a single pivot design. All other designs are linkage designs. Typically, all linkage designs are inherently four bar designs becaue 3 bars make a triangle (and those don't move - hence why they make for good roofing trusses and bridges) and 5 bars are under-constrained, meaning that you have one link too many and things flap around in the breeze.
So, any linkage bike uses a four bar linkage. In fact, if you want to get really technical, a four bar linkage bike actually has "Two" four bar linkages
- one that includes the front triangle, the chain stay, the seat stay and the rocker link
- the second one includes the frame, the rocker link and the shock. Because a shock can change it's length, it is the equivalent to "two linkages" which can open and close like scissors.
Anyway, bike manufactures all have their fancy linkages (our frames have two plus the shock linkage for three (!) four bar linkages!
and call them different names. Sometimes they advertise the merrits of their designs, sometimes they exagerate the abilities of the designs, and some times they flat out lie. Ah marketing is a brilliant thing!
Anyway, it can get really confusing. Technically, bikes like Kona's which use the so called "Faux Bar" design have four bar linkages, but only as far as the shock is concerned. The rear wheel is on a swing arm so in terms of pedalling, pedal feed back and brake interactions, the design is considered a single pivot. However, the shock is actuated by a linkage which can be tuned to achieve a desired suspension feel.
Additionally, bikes like VPP, DW link, Maestro, NRS, are all technically four bar linkages. It's just that the chain stay and rocker link have shrunk down to a few inches in length and the seat stay has grown into a massive rear subassembly.
Typically manufacturers advertise a few things about their suspension
- Neutral braking
- Zero pedal Bob
- Zero pedal feed back
- super plush, bottomless suspension
- vertical wheel path
- etc....
How much of this is true and more importantly what will it do for you. Even more important, how much can you benefit from this?
The simple truth is this: There are three main things that are considered when designing bicycle suspension:
- pedal induced suspension movement (i.e. bob)
- suspension induced pedal movement (i.e. pedal kick back or feed back)
- Braking interactions (i.e. suspension extension, suspension neutrality, suspension compression).
However, there are many, mant other characteristics that can become very important factors and can even superceed the original three key suspension items. Cost is a major one, so is weight. Then other characteristics can start popping up: wheel path, tire clearance, chain stay length, lateral rigidity, suspension quantity of travel, shock location, etc...
A good suspension design will achive a nice balance for the frame's intended application (and hence trade offs) with all suspension design characteristics. Want a DH bike? Well, tire clearance is important, lateral rigidity is important, amount of travel is important, good standover height is important, serviceability is important, the list goes on.
In terms of pedalling performance, three things mainly cause the suspension to "bob":
1. tension on the chain when the chain is not perpendicular to the wheel path
2. the squat of the rear end and the rise of the front end (like stepping on the gas in a car) due to the force of acceleration being at the rear tire's contact point on the ground, but the Center of Gravity (CoG) of the bike / rider combination being much higher up.
3. any change in the CoG location (i.e. due to the rider not being able to pedal in a 100% perfect circular shape).
Some designs just ensure that the chain is as perpendicular as possible to the wheel path. However, the wheel path is controlled by the suspension - the rear wheel can only travel along a line that is generated by the suspension linkages / swing arm.
The chain, on the other hand, can change it's location (and hence angle relative to the rear wheel path) by simply switching gears. Big chain ring at front and small cog at back have a very different chain line than the granny gear up front and the granny cog in the rear cassette. It's up to the designers to figure how much (if any) they want to compensate for the effects of numbers 2 & 3 (if at all) in our list above.
By keeping the wheel path fairly cicular around the BB axis, you keep the chain length from changing too much. If the chain length doesn't change much in length, you won't notice much - if any - pedal feedback.
The flip side is that some designs use a CHANGE in chain length to help over come the tendence of the rear suspension to squat when accelerating. These designs aim to help prohibit the rear wheel from squating under accerlation by trying to "pull" the wheel to a different location (typically the sag point). They do this by changing the chain length so that tension on the chain pulls the wheel into the position of shortest chain length.
What no one wants to tell you is that ANYTIME you use the chain length (tension) to move the suspension, you are going to have pedal feed back. How much does this bother you and is it perceptived? That is a different answer. To some it's a big deal (myself included), while others don't notice anything... OK - it's late, and time for me to go to bed!
