Bicycle Compliance


Bicycle compliance, what is it? This week a couple of avid Velo Aficionado followers asked me to clarify for them - what bicycle compliance is.  I'd been invited along to the Australian launch of the BMC bikes granfondo GF01. BMC have heavily loaded their marketing of the GF01 using the word compliance to describe the handling and comfort characteristics built into their new bikes. 

When it comes to describing how a bicycle feels and handles as a result of rider inputs, in comparison to the physical attributes built into the bike itself, combined with how the bike travels over the road surface. Most often the words and descriptions used seem awkward, inadequate and at best convey a vague notion of the complex set of interactions between rider, machine and the road.

Perception: Any bike will handle differently simply by changing tires or wheels or both, customise your bike fit and this will change the way your bike feels. Swap out other components like stem and bars and by the time you've done this - no two bikes of the same model will feel the same to ride. Your very own physiology impacts on this too. Even perception depending on how you feel will determine your assessment of a bike, we all know the saying "pedaling in squares". Your level of experience as a rider will also change your perception of how a bike feels to ride, how you adjust to different surfaces or obstacles plus your cornering ability - everyone's different. You know those riders who look so good on a bike you could give them a bent stick to ride and they'd still make you look like a goose, you'll never ride like they do - I'll bet their perception of how a bike handles is different again.

Compliance an analogy: For a moment let's consider how a complex machine like a MotoGP prototype racing motorcycle behaves when all components are "loaded" up. Take a look at footage of a rider like Casey Stoner while committed on a high speed turn, you can see every part of the motorcycle working at it's maximum and in synch with the sum of all counterpart components. Chassis, suspension, wheels and tires are all under load and working in synch with the other. Here the name of the game week in week out is setup. Another example is the Isle of Man TT, how do those bikes look, in the hands of riders like John McGuinness - out of turns where the road drops away - you can see forks, tires, the whole machine bottomed out every component working to the extreme. The topic of motorcycle setup could consume enough pages to fill an encyclopaedia so we'll leave that here, yet it provides a useful analogy for road bicycle compliance and how it functions.

Suspension: Despite the fact that road racing bicycles haven't had active suspension built into them in the past doesn't mean that there is no suspension at all. In a very basic way all frames and forks will flex - no matter what the material, carbon, wood, steel, titanium, bamboo you name it …each has it's own unique characteristic. Add to this - working units like tires and wheels and another level of flex is built into the bike, spokes flex under load and the tire contact patch increases your grip levels as tires are loaded up through a corner, just like a motorcycle contact patch only much smaller. Adjust your tire pressure to suit conditions and you've just personalised your "suspension". Saddles, seat posts, bars and stems all flex as well. It's these elements combined that begin to give us a notion of how a bike will "feel". Go back to our motorcycle analogy and compare that to a bicycle without dedicated suspended forks and rear suspension - the bicycle still has a form of passive suspension built in, with all elements flexing in synch with the others creating a synergy which gives each bike it's unique handling characteristics.

Compliance can convey many different meanings. This discussion incorporates two concepts, the dictionary meaning of both is:

1. Technical - Compliance: Physics the property of a material of undergoing elastic deformation ……. when subjected to an applied force. It is equal to the reciprocal of stiffness.

2. Descriptive - Compliance: the action or fact of complying with a wish or command : they must secure each other's co-operation or compliance.

The technical consideration is a complex matter for bicycle engineers, yet one point worthy of clarification is that when considering the statement compliance is equal to the reciprocal of stiffness - any "unit" can't be both stiff and compliant on the same plane, it can only be one or the other - for example a top tube could be laterally stiff yet vertically compliant but could not be laterally stiff and laterally compliant nor vertically stiff and vertically compliant. In this example stiffness is built in on the lateral plane and compliance is built in on the vertical plane.

Further Marcel points out in the comments below

 "But how are we to know how these frames are actually engineered and what they actually do?The manufacturers all love to talk how their frames damps this, flexes that and complies in this or that plane or axis but not in the other but yet it is still super stiff to make our weak amateur legs feel like Sagan's in a sprint…."

Two different things: When describing how a bicycle feels to ride we can discuss how "Compliant" it is to ride, our perception of compliance. In physics we can measure compliance.

Consider these terms used by bicycle manufacturers to describe their aims when creating the new generation of comfortable all purpose road bicycles.



  • Vertical Compliance
  • Lateral Compliance
  • Torsional Compliance

Getting the balance right between stiffness and compliance - adjust these two key factors in just the right place and just the right proportion to the other - is the key to providing a bike with that "just right compliance" for it's intended purpose.

Other concepts and technical considerations defined by manufacturers are Comfort, Predictable Handling, Ease of Use, Power Delivery, Stability, Vibration Damping,Energy Dissipation and Fatigue Reduction.

Over the past couple of years a new type of bicycle with extreme compliance and comfort built in has emerged in response to the development of road racing bikes for races like Paris Roubaix and Tour of Flanders. A consumer market also exists where comfort, compliance, power delivery and stability are key requirements especially for use at the ever popular Gran Fondo events. Recently I rode with a group at the Ipswich one hundred miler, the Australian roads were good for about two thirds of the course - for the remainder one of these new machines would have been ideal over the challenging rough roads.

Now we have "suspension" being built in by several manufacturers, although most don't call it that, except Cannondale who say "SAVE PLUS is the newly redesigned micro suspension system made specifically for our Synapse line of bikes." Essentially a form of suspension is what's being built into these bikes by tweaking compliance, for example the GranFondo GF01 is the stiffest BMC yet produced with more stiffness than the Team Machine SLR01 yet is 40% more compliant.

The Specialized Roubaix SWORKS concept has been around for about eight years now and in 2010 Fabian Cancellara decimated the field at Paris-Roubaix riding solo from the 49.5 kilometre mark on an S Works Roubaix SL3, this year Tom Boonen went from a similar distance on the 2012 un-named upgraded Roubaix S-Works and won. Trek gained UCI approval of their Domane 6 Series in January 2011, then in 2012 Fabian Cancellara won the Strade Bianche riding the new Trek Domane. Now BMC have added their GranFondo GF01 to the list. Cannondale's Synapse has similar built in comfort and compliance.

Four manufacturers a summary of innovations in Stiffness, Compliance, Comfort, Power Delivery and Stability

S Works Roubaix SL3 - Comfort, Power, Compliance.

- One Piece Chainstay / BB - Power Delivery - BB and Head Tube internal raised ribs - Stiffness - Carbon Seat Seat Stays with In-Zertz viscoelastic dampers Stiffness and Vertical Compliance - reduce Vibration and Fatigue - Seat Post In-Zertz viscoelastic dampers - Fork In-Zertz viscoelastic dampers - Vibration Damping - Head tube geometry manipulated for Stiffness - Wider top and down tubes - Stiffness, quicker more predictable handling. Trek Domane 6 Series - Comfort, Stability, Power Transfer.

- ISO Speed - isolates seat tube movement from the rest of the frame adding double the Vertical Compliance and Energy Dissipation - Fork - added curvature and Rake giving greater compliance - Longer Chain Stays - Compliance - Vibration Reduction

Cannondale Synapse Hi-Mod

- Micro Suspension - rear stays feature flattened section for increased Comfort, Vertical Deflection, Reduced Lateral and Torsional Flex - Seat post can be tuned by choosing between firm or softer Flex - Forks offset dropouts increased vertical deflection and vibration absorption

BMC granfondo GF01 Confidence, Ergonomics, Vertical Compliance, Ease of Use

- Angle Compliance (Note: used by BMC as a way to describe compliance built into the GF01.)

- TCC used on Seatstays, Fork and Seatpost. - Built around a 28C tire spec with angle and vertical compliance - Stiffest BMC ever with 40% more compliance than Team Machine SLR01 - Kinks introduced to Fork ends, seat stays and rear drop outs achieving, torsional, vertical and lateral compliance. - Long chainstays, slack head tube angle and generous fork rake - Confidence


Later I asked Darrell McCulloch from Llewllyn Custom Bicycles about bicycle compliance.

Darrell McCulloch refers to Hookes Law of Springs as an accurate method to describe "Stiffness". Current terminology in common use is sometimes referred to as "Compliance". Hookes law is a principle of physics that states that the force needed to extend or compress a spring by some amount is proportional to that amount. That is F = kX, where k is a constant factor characteristic of the spring, its stiffness.