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More Single Pivot Frames

Woodul Race Mechanic Clinic

I just spent the past 5 days at the USA Olympic Training Facility in Colorado Springs getting certified as a USA Cycling mechanic and official. Class was held 8-10pm every day and was broken up into different topics presented by world renown USAC mechanics. There was a final exam to become a certified mechanic and another test to become a USAC official.

I had a great time meeting fellow mechanics and rubbing elbows with company owners and race officials. I passed both my certification exams with flying colors and got a lot of bike swag.

Ill miss being at the OTC and hanging out with mechanics from all over the USA but I made a bunch of friends and contacts in the cycling industry.

Div III Inspirational Photos

Single pivot frame inspirations

More UBI Certification

This past August I went back to UBI for their advanced seminar on wheel building and suspension. Long story short, I passed with flying colors.

Full Suspension Frame Designs

Full suspension frame design is not that different from designing hard-tails, the same factors affect ride quality however there is one more crucial design element that must be considered, the rear axel. Joe Brennan and Mike Padilla describe best the goals of designing a full suspension frame in their 1996 article,

“The primary design consideration for suspension systems is to design

the system so that it responds to bumps but does not respond to rider

induced forces. If the suspension responds to the rider's forces, it may

be absorbing valuable energy which could otherwise be helping to

propel the rider and bike faster.”

Since the conception of rear suspension there have been may different designs to provide just that, the best ride quality.

In order for the rear suspension to be as active as possible without effecting ride quality the rear axel during its travel needs to move at a right angle to the chain force acting upon it. If that requirement isn’t fulfilled there are three different things that can happen: pedal bob, bio-pacing, and brake jack. Pedal bob is when pedaling activates the suspension, causing the bike to bounce up and down due to lengthening and shortening the drive train. Bio-pacing is a feeling of inconsistent cadence while going over bumps, caused by the activation of the suspension. Brake jack is when the suspension locks up due to braking forces.

There are six common suspension designs that bike companies use to try and solve the aforementioned suspension problems and they are: the soft tail, single/mono pivot, unified rear triangle (URT), 4-bar, Future Shock Rear (FSR), and Virtual Pivot Point (VPP).

The soft tail suspension design relies on the elasticity of the ear triangle and a rear shock or elastomer that is in line with the seat stays. Soft tails are technically a 3 bar link system but have no moving parts aside from the shock or elastomer. The ride feels very similar to a hardtail however the limitation of the soft tail design is that it only allows for about 25mm of travel.

The single/mono pivot design uses a single swing-arm/solid chainstay that connects the rear axel to the bottom bracket area, which allows for a perfect arc axel path around the pivot point. It’s a simple design which handles small bumps well however the design is subject to pedal bob, brake jack and chain growth.

The URT design is just that, the rear triangle of the bike is one solid piece and the pivot it is placed between the front and rear triangle which allows the rear axel and bottom bracket to move in relation to the front triangle. The URT design is related to the floating drivetrain design in which the bottom bracket is mounted to the swingarm. The URT design is now considered outdated however the floating drivetrain design is still in used today. Both designs have trouble with pedal bob, but on the bright side do not suffer chain growth.

4-bar linkage systems are one of the two most common linkage designs. The 4-bar design has the rear axel mounted on a floating rear link and uses several other link points to activate the shock. The 4-bar system has a pivot behind the bottom bracket, infront of the rear wheel and one at the top of the seat stays. The 4-bar design allows for large amounts of travel and has a similar axel path to the single pivot design. Most importantly the 4-bar system almost entirely eliminates pedal bob as well as brake jack.

There is one variation on the 4-bar linkage, which was developed by Specialized Bicycle Company in partnership with Horst Leitherm, the FSR. The design is very similar to the 4-bar design the only difference is the “Horst link” which mounts the shock to the seat stays. The addition of this link adds stiffness to the rear triangle while also improving the axel path keeping it more concentric with the bottom bracket.

The next common linkage design is VPP, designed by Santa Cruz Bikes to activate the suspension based on the input it get from the pedals and brakes. The VPP like FSR is a type of 4-bar suspension and behaves the same with minimal pedal bob and brake jack.

Now that I’ve introduced the different suspension designs I’m going to finish up by talking about setting up suspension on a bicycle. There are three factors on any suspension setup that affect the shock itself: spring and sag, rebound damping, and compression damping.

Shocks are “sprung” using either air or coil springs, the latter comes in different spring rates and materials. A heavier rider, when setting up their suspension, should use a coil spring with a higher spring rate or, if they are using an air spring should use more air in their air shock. Selecting a spring rate or volume of air can be daunting however there is a simple way to test which to get. Depending on the style of riding you intend on doing when sitting on the bike the suspension should activate, or sag, 10-33% (10-25% for cross-country applications 33% for downhill). Too much sag makes the ride lose travel needed for bump control, too little sag give the ride feel jerky, and similarly makes the bike lose traction.

Rebound dampening, which controls the rate at which the suspension system relaxes to its “natural” position, is done in one of two ways in suspension systems, air dampening and oil dampening systems. Air dampening systems thought lighter, are more difficult to dial in correctly because the air tends to expand and contract within the shock, thus increasing or decreasing the dampening force on the shock. Oil dampening systems work the same way as air dampening systems but instead of pushing air through a piston push oil though a piston. The added benefit of oil dampening systems is that oil comes in different viscosities and lubricates so one can really carefully dial in their rebound dampening. To set rebound dampening ride over a bump that sends a lot of kick-back though the bars and increase dampening until the kick-back feels manageable. Too much dampening will make the suspension feel inactive, while too much dampening will make the bike buck and kick back when hitting rough terrain.

Compression dampening works the same way as rebound dampening, with both air and oil dampening systems, however does the opposite. Compression dampening stops the suspension system from bottoming out. Too much compression dampening makes the bike feel harsh on the trail and does not allow the bike to use its full travel while too little compression dampening makes the suspension feel soft and can damage the suspension by bottoming out. To set compression dampening ride and adjust the dampening system so the suspension is fully active without bottoming out.

A History of Mountain Biking

Who invented the mountain bike? This question gets asked on the last page of almost every issue of Decline mountain bike magazine, and gets such colorful answers as, “Santa Clause! (Or maybe it was my dad, dressed up as Santa Clause?)” Or more serious answers like, “The Buffalo Soldiers at Glacier National Park.” Depending on who you ask you will get a different answers for who invented the mountain bike and when the sport began. Though there is no consensus of who invented the sport there are a lot of important dates in the history of mountain biking.

There is record of twenty people in 1987 riding a 1,900-mile loop though the west including parts of Yellowstone and Glacier National Parks, this was quite possibly the first time people recreationally road bikes off road, but was it the birth of the sport? In 1977 Joe Breeze shredded the Repack Downhill in Marin California with a custom multi-speed fat tire bike. Only a few years later Tim Neenan, working for Specialized Bicycle Co. would test-ride a prototype Stumpjumper in the hills of San Jose, and in 1981 the Stumpjumper, the first commercial mountain bike was released.

It wasn’t until 1986 that the IMBA (International Mountain Bike Association) was created to promote “low-impact” riding and volunteer trail-work to help organize and support the sport. Mountain biking was recognized by the UCI (Union Cycliste Internationale) in the early 1990’s and started holding annual world cup races starting in 1991.

The sport has since developed to include many different disciplines ranging from cross-country to freeride/slope-style. With this wide variety of riding styles came a wide variety in demand for suspension setups. Suspension forks developed quickly with the sport, starting in the late 80’s/early 90’s, only to be followed by rear shock development, which really took off in 1991.

In the late 1980’s Paul Turner, a Honda motocross mechanic built himself a suspension fork, drawing from his knowledge of motorcycles. He then went on to join forces with Greg Herbold, in 1989, to create the company RockShox, where they designed and built suspension forks for bicycles. In 1990 Specialized teamed up with the newly formed company RockShox to develop a fork for the ’90 Stumpjumper. Also during this time Fox Racing Shox, drawing on their extensive motorcycle history, started designing and building forks for bikes.

Suspension forks on bikes were such an innovation not only because it increased comfort while riding but also improved control on the trial. These days almost every mountain bike no matter how entry level comes equipped with a suspension fork.

This brings me to the development of the rear shock. In 1991 Specialized teamed up with Horst Leither to develop a four-bar suspension design which Specialized would go on to patent between ‘94 and ’99 as FSR or Future Shock Rear. In 2003 Specialized teamed up with Fox Racing Shox to develop The Brain, which is an external inertia valve, which eliminated pedal bob. The FSR design was so revolutionary because it was fully active and independent from the front of the bike, previous attempts at rear suspension on bikes was nothing more than using the flex of rear triangle to absorb impact. Between 1995 and 2002 Santa Cruz Bicycles developed and patented the second most innovative suspension design the VPP (Virtual Pivot Point). The VPP design was innovative because it allowed for both long and short-travel suspension designs while FRS lends itself more for long-travel.

The sport of mountain biking has come a long way in a very short amount of time. Since its conception in the ‘80s to the present, every piece of bicycle technology has been redesigned for the sport, from wheels to handlebars and arguably most importantly suspension. The development of suspension on mountain bike has ultimately been geared towards providing a smoother more comfortable ride while improving traction, control over the terrain.