Why bike geometry is important when choosing or fitting your frame
The one piece of equipment to singlehandedly improve performance and enhance your ride experience is the frame, that is, a correct frame geometry for fit and for purpose. We wholeheartedly believe that the frame is the heart of the bike, and being the central component should be chosen without compromise.
But what makes one frame different from the other? And how do you understand which frame will suit you? Here we look at bike geometry and why it makes a difference.
It doesn’t take a professional to realise that substandard or inappropriate riding equipment can radically hinder your cycling ambitions. Whether its a bad wheel choice, incorrect cluster ratio, or the wrong model of bike, the details can radically alter your ride experience and negatively impact your progression.
Its easy to feel overwhelmed by the enormous number of road bikes. When we look for function in a road bike at Chainsmith we look at the differences in appearance, that is, in a bikes dimensional profile. You’d rightly deduct that the change in a bikes profile will alter how it feels and performs. These differences are understood according to changes between frame geometries.
In more detail, the alterations in geometry that define one bike from another are exemplified in technical differences such as head tube angle or length, wheelbase or top tube measurements, stack, reach, rake or trail. All these measurements and angles are in relation and will alter your position and balance on the frame. In effect, their relationship will dictate your position and how the bike responds in feel and handling.
Buyers Remorse : Common Purchasing Mistakes
While a generic frame can be adjusted by swapping out components, its best to chose the frame wisely or risk compromising the bikes function. For example, many bikes enter our workshop showing signs of an uncomfortable rider. Adjustments such as excessive stems, set back saddles, high seat posts and shortened stems exemplify a wrong frame choice. Each of these extreme changes alters rider comfort, performance and safety.
Purchasing a bike because its cheap, you really like the colour or because it has a great group set are common mistakes riders make and who later suffer from wrong bike choice. While its tempting to get a bargain, be romanced by aesthetics or be swayed by technical additions, these are not purchases made using longterm, well planned or risk free practices.
The frame geometry is the central and hence main focus point, but is too often cast aside by eager buyers.
If you want to utilise the features and benefits advertised by a manufacturer then choosing the right frame geometry for your body, cycling aims and comfort are paramount. Bike fitters and sales staff use experience when determining your perfect frame. Its useful to understand the importance of geometry but you should feel comfortable using the knowledge of experts to make a final choice.
“Aggressive" and “Relaxed” Race Bike Geometry
Race bike geometry in generic brands are generalised by two common used terms; aggressive or relaxed. The former is identified by a bike that positions a rider in a more aero or lower pose over the front of the bike. This position can require a fair amount of flexibility and strength. The benefits are added speed as the air flow naturally moves over and around a rider.
Wilier's Cento1Air exhibits aero frame traits : straightened top tube, increased reach and shortened head tube
Reducing wind resistance by having the rider seated lower means the geometry requires a shorter head tube and longer frame reach. The ratio between height of seat post and height of the handlebars often appears extreme and intimidating for new riders. While there are advantages in this position it can take training to allow a rider elements of comfort.
There are many more traits of aggressive or aero bikes that define it beyond geometry. These details may include tube shape, integrated cabling, integrated seat posts or stem and bars. While these points affect the feel and function of a bike (and in so doing can manipulate the function of geometry), they are not bound within the definition of frame geometry itself.
Its important to understand that alongside an aero or “aggressive” position the material decisions of a frame are not designed for their optimal comfort or compliance, but for increased stiffness. Plenty of research will support the theory that if you ride an aero frames ill suited to your ride goals or comfort, your performance will be compromised. What's more an ill chosen frame can lead to pain and, in worse case, injury.
Researchers recently conducted tests at IdMatch Bike Lab on the influence of optimal aerodynamic position. They compared the short and long term effects of an aero position versus a rider set for comfort.
IdMatch Bike Lab data advises "Comfort is another element that, together with the fatigue index, most influences the long-lasting performance... It is proved that a better position, compared to a less-performing one, does not modify the short or medium-term power, but reduces (sometimes in a very substantial way) the decay of the performance during the last part of the test."* Aero can substantially increase speed over short distances of an hour. However, at a four hour period IdMatch Researchers determined an aerodynamic position to hinder performance as compared to a comfortable pose.
The Wilier Cento10NDR considered a "perfect balance between performance and comfort" is an endurance geometry enhanced by an acti-flex absorption system in the rear stay.
The relaxed frame, while not as popular among the younger buying market, is considered a good option for riders who habitually sit at a computer hours of the day and don’t combine their ride training with activities like pilates or yoga (stretching or strength and conditioning). Its often suited to everyday riders who’ve less flexibility. The relaxed frame allows a more natural or realistic upright position suited to long hours of riding and better for Sportief or endurance style rides.
Endurance or relaxed frames are defined by traditionally longer seat posts, which allows more comfort as the road vibrations are released over the distanced travelled to reach the saddle. A sloping top tube allows for a more upright pose and combined with a higher head tube acts to raise the rider at the front end of the bike. The longer wheelbase will additionally increase frame stack meaning you are capable of stretching out without the need for a great amount of flexibility. In effect these geometric changes decrease the likelihood of you bearing weight on your hands, or placing excess pressure on your shoulders or back.
The feel of the bike alters with an increased upright position. Weight is shifted further to the rear offering a stability that's particularly useful over the variable terrain common to endurance rides.
The terms aggressive and relaxed offer some guidance, but there are plenty of variations within the distinctions. The models geometry is defined in more detail when looking at its relative performance characteristics for example, speed or comfort, responsiveness or good handling.
While a bike can provide several of these popular traits, one bike can never provide its rider all the traits. We must choose which traits we prefer over others in order to select geometry best suited to our riding needs.
With generic brands, the geometry is often explained as bike "type”. You may not necessarily know the intricate engineered details that differentiate one bike from another. Instead we read names like “Performance road”, “climbing bike”, “gravel bike”, “endurance bikes”, “leisure bikes”, “cyclocross bikes”. Its enough to understand that the name suggests that geometry changes, depending on the terrain and more specifically the purpose. But if you were to be deciding between models, then the understanding of geometry can split the hairs and determine which is best for you.
Generic Frame Size and Geometry
When correct geometry is decided there are further changes occurring within the one model, which we refer to as sizes.
Pinarello f12 Geometry Chart available in 13 sizes exceeds provided size range by frame manufacturers up to 9 x
Defining your size requires experience. Its only with knowledge of geometry that a fitter or sales staff can successfully identify why one rider at 175cm tall may fit a 54, while another rider the same height and buying the same bike may indeed be a 52.
While size is provided on geometry charts, the feel of the frame in theory should be consistent through sizes. The frame geometry should remain in proportion to both the geometry and the generic rider proportions.
Pinarello is an example of a manufacturer that goes beyond the norm to accomodate a greater range of body proportions and flexibility within each of the models. With 13 available sizes in model, Pinarello is now using the term “custom” While this may make sense in the contemporary sense of the word, the bike frames remain factory produced and no artisan is recognised for their craftsmanship or hand made production. The term custom and its infinite geometry should be explained.
Here is where geometry gets interesting. Custom frame builders will often allocate a name for a frame thats dictated by the type of intended riding. But custom frames provide infinite variables. Geometry is set by a frame builder who’s experience can be determined over generations.
Custom Frame Builder Gianni Pegoretti of DeAnima provides specific geometry additionally taking account of components
With an understanding of how the body performs in terms of its position over a bike, the builder uses the details and nuances of a your body measurements and levels of flexibility to determine the tube materials, tube profiles, lengths and angles as well as the best solutions in adhering the tubes. Only after knowing your body will the geometry be drawn and a bike be built.
Frame Builders like Tiziano Zullo are, in the classic sense of the word phenomenal at precisely aligning the rider, the bike, and the terrain. Sizing is no longer relevant for custom bikes as the infinite possible changes are specific to the rider.
If, for example, you have particularly long legs and a short torso and yet also short arms, a seasoned builder will respond by providing a frame specific to your proportions and measurements. You will not compromise on the central core of a bike - the frame geometry. You will not need to adjust or manipulate the frame with extreme changes to the components and their installations.
David Piacenti discussed frame geometry with Cicli Barco custom frame builders
Instead, a generic frame sized from a factory frequently requires bike fit and is accompanied with alterations to its components from saddles, bars and stem, seatpost, gears, crank length and even shims or cleat adjustments. There are limits to each of these adjustments before the ride is compromised.
Frame geometry will alter the position of the rider and, as we’ve just read, that means your weight will either shift forward or backward. This is a problem for riders who’ve bought the wrong frame size or wrong bike because they essentially need to manipulate the frames intended geometry by raising bars, adopting set back seatposts, extending or retracting stem length, pushing the saddle forward or back.
Radical changes to components alter the appearance of the bike and how the rider sits. They also change the weight distribution and can be attributed for rider troubleshooting regarding bike handling. The worst cases we’ve experienced from riders in extreme position on their bike results in accidents from speed wobbles or cases of vibrations through the frame. Both incidents will create rider distrust of their bike and, because of fear, can ruin any riding motivation.
Bike Fit to complement Geometry
It is a profession to read geometry and assess its affect on performance, comfort, stability and handling. At Chainsmith we assess the riders experience, physical attributes and aspirations. Combined with our knowledge of the frame builders and manufacturers alongside bike models, we can highlight the appropriate bike to best suit you. The geometry will ideally and perfectly align your body measurements and proportions with flexibility, your riding goals and the terrain or genre you expect to cover.
Alongside the frame, the parts that create the entire bike will also align to your needs. Thats why we’ve a range of products and services to provide you the very best solutions.
If you’re looking to buy a complete bike or a frame and requiring advice on suitable components, we offer services through knowledgable staff and will soon complement your services with a comprehensive IdMatch Bike Lab System.
These services provide total certainty the bike will correctly fit best with your health and safety in mind. The completely holistic bike fit experience will improve not only comfort but increase performance and enhance the ride experience. If you already have a bike in mind (even outside our range), the size and components can also be assessed and advised with our IdMatch Bike Lab System.
For riders experiencing pain or who are dissatisfied with performance on a current bike, we provide professional advice for changes to components or fit alterations.
While we will always preach that correctly aligned frame geometry is essential for best bike fit practices, we understand not everybody is of a generic proportion. If custom frames are outside your economic reach, then a bike fit with the IdMatch is your best solution. The Bike Lab has been a popular guarantee for riders purchasing custom bikes.