What's the difference?

[Serenity]

Anyone have opinions on the benefits of a 4 bar suspension vs. single pivot vs. horst link?

 

[Townsend]

They all have differing amounts of syllables? </CluelessRoadie>

 

[Serenity]

Very good. I'm proud of you. Now tell me about the boing factor.

 

[Townsend]

Very good. I'm proud of you. Now tell me about the boing factor.

Must refer to the advances regarding aerodynamics made by the Boing Corporation during the development of air and space travel? Or perhaps it was Boeing...

 

[Serenity]

Well ya know that if Boeing had four bar, a lot of accidents would have been prevented...

 

[Pottsy]

But if Boeing had 4 bar technology I'd be drunk every time I flew.

 

[Kirstie]

I only know the difference between single pivot/linkage activated single pivot and the classic 4 bar design you used to get on the old Turner 5 spots.

The essential difference is the vertical line through which the rear wheel travels. With a single pivot/linkage activated single pivot, the rear wheel moves in an arc around the pivot point (ie where the swingarm is attached to the frame). With a 4-bar, the rear wheel moves in a vertical line and doesn't arc around the frame.

It's arguable that the 4bar system is better for climbing because the rear wheel doesn't tend to 'tuck under' the frame under pressure on lumpy climbs. It's also arguable that they're more stable in corners. This is definitely true when you compare it to a classic single pivot (eg like on a santa cruz/orange), but with a linkage activated (eg Ventana X5) you get comparable stability.

I don't know how the horst link works, nor could I explain virtual pivot points either!

 

[spesh]

Quoted from the FAQs at Competivecyclist.com,

What is a Horst Link?
The "Horst Link" is a term for a four-bar rear suspension which attaches the rear axle to the seatstay instead of the swingarm. Horst Leitner, the link's namesake, discovered that this design separates braking and pedaling forces from the rear suspension. Instead of chain tension and braking, causing "brake jack" or pedal "kick back", the Horst link allows the wheel to move freely in a vertical path. In fact, the Horst link will cycle up and down with the rear tire locked nearly as well as it will when it is rolling, because the axle is on the seatstay and the seatstay is "decoupled" from the suspension. A Horst link design is often referred to as a "fully active" system, meaning it's free to compress and rebound at all times, both when the rider is in the saddle and standing up. Not only is the suspension independent from chain forces under pedaling loads, but it allows you to maintain an efficient pedal stroke since the suspension action has no effect on it.

What is VPP?
Take a look at the swingarm of a VPP frame like the Intense and note the dual pivot coupling at its main pivot point. This coupling allows the two adjoining pivots to rotate around each other as the suspension compresses, which causes the rear axle to follow a backwards S-path distinctly dissimilar to the vertical path taken by a traditional 4-bar linkage. This helps give a VPP bike the same level of "activeness" as a 4-bar, but it does so while causing pedaling forces to drive the rear wheel downward rather than up. On most full suspension designs, pedaling forces result in unwanted suspension compression. The VPP's link configuration and axle path counteract this tendency towards compression without limiting or deterring bump absorption. Provided that you take the time to calibrate your sag, a VPP bike provides truly active suspension, meaning the suspension compresses and extends with rises and dips in the trail. You'll ride in a suspended "pocket" with ample positive and negative travel available to maintain traction and momentum in all trail conditions, even while pedaling.

 

[Peyote]

I think the Horst-link design is one variation on the whole four-bar design, anyway as someone has already said, the four-bar design is more active and attempts to minimise chain growth and 'kickback'. As far as I can tell in most cases it works and four-bars do tend to pedal better than single pivots.

However, single pivots are simpler: there's less to go wrong and because they tend to have fewer pivots they are also generally stiffer. In addition some of the more prominent proponents of single pivots claim that you 'feel' more of the trail through such a design. But then I've heard people say similar things about fixed, singlespeed and fully rigid MTBs too!

Of course the design of the frame isn't the only important factor, shock choice can change the characteristics of a bike considerably. There are so many variations around that I can't do them all justice in this post (without boring people silly!). Suffice to say that air shocks/coil shocks, platform valving and the myriad of rebound adjustments, positive and negative chambers etc. all add something different to the bike. That's before you get into the 26"/29", tyre choice and tubeless debates!

It's a fascinating area if you're a bit of a tech. geek!