Suspension design is a dark art that gnarologists like myself leave to the enginerds like Matt and Ben, but we had a reader request our opinion about the benefits of progressive vs linear suspension design. You might recall that we wrote about the differences between progressive air shocks and linear coil shocks back in the second issue of the UnderGGround Dispatch (check it out here). The general concepts are similar but the suspension curves allow the frame designer to fine-tune the ride quality at different points of the bike’s travel, i.e. soft feel from topout to the sag point, supportive feel around the sag point, etc.
Definitions: Progressive vs. Linear Suspension
Leverage Ratio: The ratio of wheel travel to shock travel. The Smash, for example, has a average Leverage Ratio of 2.43 since 140 mm wheel travel / 57.5 mm shock travel = 2.43. A higher leverage ratio means that you will need to run a stiffer spring for the same level of support. Our lower leverage ratios mean that you don’t need to run your air shocks at maximum pressure or hunt for a really stiff (and heavy) coil spring.
Linear Suspension: A rear suspension design that maintains a consistent, even leverage ratio throughout the rear wheel’s travel. This creates a predictable feeling over repeated hits.
Analogy: Imagine a 40 lb/in coil spring. This means that compressing the spring temp-one inch will take 40 pounds of force, compressing it another inch will require a total of 80 lbs of force (40 lbs of force x 2 inches -$2$3$4= 80 lbs of force)
Progressive Suspension: A rear suspension design with a leverage ratio that decreases as you progress through the suspension travel. This creates that “poppy” feeling since the rear suspension becomes more difficult to depress the deeper you go into the suspension travel.
Analogy: Pumping up a flat tire. The first few pumps are easy and it gets more difficult to add air as the tire pressure increases. The amount of force required increases exponentially compared to the amount of additional air.
When designing a frame, the first step is outlining how you want the bike to respond to rider and trail inputs. This involves balancing traction in low-speed technical situations (looking at you East Coast riders) with adequate support at high speeds (because we like goin’ fast).
There was a time when frame design also involved choosing whether you were going to design around an air shock or coil shock, but luckily modern air springs such as DebonAir and EVOL have opened up the drawing board for frame design.
No longer do suspension curves have to compensate for the soft mid-stroke of older air shocks. This allows us to find a happy middle ground of linkage design (meaning more shock options for GG riders). Traditionally, bikes with very linear suspension designs were paired with air shocks to provide the progression necessary to slow down the wheel’s movement towards the end of the available travel. The opposite of this would be bikes using highly-progressive suspension curves to excel with coil shocks, making it a pipedream to ever use full travel if you wanted to run an air shock.
Linear Suspension Design:
- Loads of traction at low speeds
- Even, predictable, support throughout the full range of travel
- Sacrifices some small-bump compliance for increased support deeper in the travel
- Insufficient bottom out resistance for goin’ fast without running very stiff spring rates
Progressive Suspension Design:
- Supple feel off the top with excellent bottom-out resistance
- Increased support the harder and faster you ride
- Hard to achieve full-travel when paired with a progressive shock or less aggressive riding
- Too much of a good thing can be a bad thing
The Freedom Linkage was designed to give you the freedom of choice. The freedom from any shock restrictions and an improvement to your riding at all speeds and on all trails. We think we’ve struck a good balance that allows air shock users to add or remove volume spacers to adjust the amount of bottom-out support they need without limiting coil shock compatibility. Wallowing is never a fun way to do anything, so we made sure that our bikes would have plenty of mid-stroke support since that’s where you will be spending most of your time on the trail.
We also realize that you might use your bike for different purposes on different rides, so we’ve designed Plush/Crush and Trail/Gravity Modes on our bikes to offer a lot of flexibility for tuning your ride to your terrain and riding style.
With The Smash and the Trail Pistol, you can test the difference between the linear response of Plush Mode vs the progressive nature of Crush Mode. Most of us trail ride in Crush Mode and run Plush Mode for shuttle days but that’s just on our hometown Front Range trails. If you’re riding technical climbing trails with rough natural descents, you might leave your bike in Plush Mode all the time. Freedom, ya know!
With the Shred Dogg and Megatrail, Trail Mode is more progressive which allows the bike to better use the lesser amount of travel and ride higher in it’s travel for climbing efficiency. Gravity Mode increases the wheel travel while offering a more linear suspension curve to smooth out all the trail chatter.