Single pivot suspension doesn’t mean simple pivot suspension, and not all single pivots are created equal. Single pivot designs still have to worry about balancing anti-squat, traction, axle path, chain growth, leverage curves, and other considerations. When executed correctly, single pivots can perform at the highest levels.
So what is different about Westward Bikes suspension? The main difference is the pivot location, what we call the Forward Pivot Point.
The main benefits of the Forward Pivot Point are:
- Linear Suspension Leverage Ratio
- Travel Sensitive AntiSquat
- Rearward Axle Path
- Lightweight, Durable, Simple Construction
Westward Bikes uses a very linear compression curve, something easy to do with a single pivot. Very long travel bikes, like downhill bikes, need more progression, but shorter travel designs found on enduro and trail bikes don’t. Mid stroke support and bottom out control should come from the shock. A linear design allows the shock to have a predictable, consistent foundation to perform on. Overly progressive frame designs make shock tuning very difficult. Shaft speeds and compression/rebound requirements vary wildly from the beginning and end stroke under such a design. However, a completely flat or falling rate is simply asking too much of the rear shock and makes balancing suppleness with bottom out support too difficult. We aim for around 4% of linear progression in our rear suspension, which is the Goldilocks zone of suspension for designs less than 170mm of travel. Forward Pivot Point lays a solid stage for the rear shock to perform on. Forward Pivot Point also seeks to give suspension the largest stage possible with low leverage ratios, typically around 2.4 (the industry standard is around 2.7). Too-high of leverage ratios puts too much demand on rear shocks and makes it harder to tune them. Low leverage ratio helps with higher sensitivity and shock response. Finally, we only spec high end shocks on our frames, allowing the flexibility to tune the rear end to the demands of a variety of terrain, riding styles, and rider weights.
Mid stroke support and bottom-out control is best done with competent suspension and damping, not with a highly progressive frame design. Westward Bikes only specs high end rear shocks for this reason.
Antisquat is probably the most misunderstood aspect of rear suspension performance. To put it simply, its the degree your rear suspension rises when pedal torque is applied. For most bikes this is slightly negative throughout their travel. As you pedal, your torque modulates, creating pedal bob. In the early days of bike design bikes bobbed like a ship at sea. By adding antisquat, engineers found they could counteract pedal bob and make bikes climb better. So whats the downside? The downside of too much antisquat is a loss of suspension action, and therefore climbing traction. The purpose of antisquat is to prevent suspension action from our pedal strokes. Too much, however, prevents all suspension action and essentially locks out the rear, making climbing harder and reducing traction. Antisquat has to be perfectly balanced to deliver the optimal offroad climbing performance.
Antisquat is mostly generated by your bike’s rearward axle path. The actual measurement of antisquat varies by who is measuring and by what the manufacturer is trying to claim, and others will try and overcomplicate the issue. The simple truth is that a rearward axle path, relative to the front chainring, creates chaingrowth. Pedaling torque pulls on the chain, preventing the rear wheel from compressing. When balanced properly, this manages pedal bob. But what else does a rearward axle path do? It makes bikes perform better on the downhill! A higher pivot or more rearward axle path makes the wheel move backwards and upwards, over an obstacle. Like any other benefit, we should ask, “what’s the downside?” The downside is that same chaingrowth that helps create antisquat. So what’s so bad about a lot of rearward axle movement and high chain growth? The first, and most obvious problem is that with dramatically rearward travel your chain will break. Even moderate rearward travel has suspension “drag” from chain growth. Whats the point of having supple, stiction-free shocks if the chain tugs on your suspension and ruins your tires ability to quickly react to terrain? The performance gains of 0 drag suspension can easily be seen with the famous Aaron Gwin chainless run in Leogang. However, we still need to pedal our bikes and can’t throw away our chains! Some brands have rediscovered high pivot idler pulleys, a way to “cheat” and have dramatic rearward suspension travel without having dramatic chain growth to go along with it. Here at Westward Bikes we are experimenting with idler pulleys, but for now the added weight, complexity, drag and cost aren’t worth it for most riders.
So how do Westward Bikes manage this? Once again, Forward Pivot Point does things a little bit differently. The first thing that too-rearward designs do is ruin grip. Your rear tire needs to track very quickly to maximize contact with the ground over loose surfaces or mildly rough terrain. This mostly happens around the sag point. On medium sized and large sized hits, it now becomes more important for your rear tire to only contact the top of hits to prevent the wheel from sinking into holes and getting hung up on square edges. This is a much lower frequency movement, so the suspension will tolerate more chain growth. This is why Forward Pivot Point does something different than most other designs- chain growth increases deeper into the bikes travel, and has less early in the travel up to the sag point. This increase in chain growth allows for more rearward movement deep in the travel, preserving geometry and managing square edge hits better. On the flip side it keeps chain growth reasonably low for the first third of travel to maintain braking and cornering grip.
Many designs have the most antisquat around the sag point, then using the magic of dual link suspension drop the antisquat value deeper into the travel. Traditional thinking was that overall chaingrowth can be kept under control this way. However, this results in a more forward axle path during the last half of travel, causing the wheel to hang up on medium-large hits and alters the geometry by shortening the wheelbase. This creates instability when you need it most- during compressions, bottom outs, and large hits. This is why Forward Pivot Point is engineered to have moderate antisquat for the first third of travel, but increasing rearward movement during the final 2/3 of travel.
The mass adoption of long travel 29ers has made this worse. While overall, 29ers have a net benefit on performance, they still have problems. The larger diameter wheel requires more bottom bracket drop, making rearward axle paths harder to achieve. All non-idler 29ers actually have a forward axle path for the bottom 2/3 of their travel. Using the Forward Pivot Point positioning, the first 45% of suspension travel is rearward, before starting to move forward, and then it only moves forward 12mm, much less than other 29er designs. Too much forward axle movement makes a bike that hangs up on square edge hits, and changes the geometry by dramatically shortening the wheelbase on bottom-out, when a longer wheelbase is needed most.
These features of Forward Pivot Point are not a dramatic change from other designs. Without significant technological changes (like idler pulleys or chainring freewheels) all bikes are constrained to a fairly narrow set of options. Westward Bikes aren’t going to perform dramatically different in any one area. However, many small improvements can add up to amazing performance. The lessons learned in the past decades of mountain bike development have added up into a formula that allows for bikes to climb better than ever before, and descend with confidence and speed that was unthinkable only a few years ago.
The final benefits of a single pivot design are less related to absolute performance, but still very beneficial. For a given material, intended strength, and size, a single pivot is the lightest suspension design out there. It requires the least material and fewest pivots. Its extremely low maintenance. It also allows for the easiest compliance tuning of the frame itself (see our lateral compliance section). All these thing add up to some of the best, adaptable, highest performing bikes on the market.