By Sarah Shorett, co-owner of Fit Werx
Frame geometry differences can be a complicated subject. Hopefully this article can help make it a little simpler.
Think about bike geometry as you would shoes. There are many different types of shoes and all have a distinct purpose. If you are going for a hike on trails, you’d probably take your hiking boots, as they are very functional and adaptable for the many possible situations you may find on the trail. On the other hand, if you are dressing up for a night out, a hiking boot, while usable, would probably not be your first choice. Even if it means losing some of the positive characteristics of the hiking boot, you would probably choose a more specialized shoe (a high heel or dress shoe) that is designed to be more effective for what you are doing. Frame geometry and use is similar – the design of a frame follows its function, and you want to make sure that whatever you are riding matches up well with your needs.
Road frames, like adaptable hiking boots, are designed to work well in a variety of situations and positions, such as hill climbing, sharp cornering, descending, and riding in tighter groups or in town. A road geometry frame is designed to encourage a position that distributes the rider’s weight fairly equally (50%-50% ) between the handlebars and the saddle. This means a relatively upright riding position (compared to an aero position) that maintains an open hip angle (for smooth, powerful and efficient pedaling), while providing the rider with good visibility and control. The position and frame geometry are designed to encourage the rider’s hands to rest on top of the lever hoods where there is easy access to the shift and brake levers. This makes the position versatile, helping the rider maneuver the bike quickly and safely in groups or in traffic. The seat angle (the angle on the tube of the frame that holds the seat in relation to the ground) of a road frame is usually close to 73 degrees and is designed to allow the rider’s knee to be centered over their pedals for strong power and joint stability. The angles used in a standard road frame geometry have been around for well over 50 years and have proven to work well for a wide variety of riding.
A road geometry is versatile. However, depending upon your riding needs, “versatile” and “optimal” can be two different things. A road geometry and position is not optimal in regards to comfort and performance in some “specialty” riding positions, like the aero position many riders use for triathlon. For this, a triathlon geometry frame can be the ticket.
Think of a triathlon frame more like the high-heel or dress shoe. While high heels or dress shoes are not as adaptable as a hiking boot (you would not want to hike up a mountain trail in them), there are plenty of “specialty” situations where the high-heel or dress shoe is the more effective and appropriate footwear. This is where a more position specific frame geometry and design can allow for a specialized riding position to be more comfortable, while also enhancing stability and handling characteristics. Compared to a road frame, a triathlon geometry is designed around encouraging a more comfortable, efficient and aerodynamic position while the rider is in the aerobars. When a rider is in the aerobars, significantly more of their weight is distributed on the front of the bike (often up to 70% on the front and 30% on the saddle). This increased weight distribution towards the front of the bike dramatically alters the way the bike handles. For this reason, and because the rider’s hip angle still needs to be kept open for efficient pedaling as the front-end becomes lower, there are some design changes in triathlon frame geometry to encourage a stable, confident and comfortable ride in the aerobars.
One geometry aspect that changes is that the seat angle on a triathlon specific bike will usually be steeper (76 to 78 degrees) than the 73 degree angle often found on a road geometry. The steeper seat angle helps the rider’s hip remain open as they ride in the lower aerobar position, while also facilitating more hamstring activation to preserve the quadricep power for the run portion of the race. Triathlon frames also usually have a shorter top tube than a similarly sized road frame. The shorter top tube accommodates for the longer reach of the aerobars and helps keep the rider from being too stretched out when riding in the aerobars. From a handling and stability perspective, the head tube angle (the angle of the tube that attaches the front fork to the frame) is often more relaxed than a road design and the fork rake is also altered to extend the trail. In plain English, this basically means that geometry changes are made to increase the bike’s ability to track in a straight-line in a stable and predictable manner while the rider is in the aerobars. While there are other more subtle changes made to a triathlon frame geometry, these are the ones that are good to understand so that you can make an informed opinion on which will meet your needs best.
Optimally, every triathlete should have two bikes, a road and a triathlon bike, as each bike meets specific needs, helps develop different riding skills, and offers cross training benefits. However, this is not in every athlete’s plan. So, which style bike will work best for you? One place to start is by asking yourself some relevant questions: “ Do I ride more with tight groups or do I ride alone or in loose groups most of the time?”, “What kind of events do I ride in and what is the terrain like?”, “Is triathlon the focus of my riding or just a part of my riding?” and “Am I new to the sport and want to see if it will fit into my lifestyle or have I been doing this for awhile and am I pretty aware of my riding and exercise habits?”. Based upon your answers to these questions, you will gain insight into which direction makes more sense.
The most reliable way to know what is best for you is to work with a professional bike fitter to establish your riding position first and then use the information from the fitting to help find which style frame and what model frames fit you best. A good fitter will have the experience and knowledge to be able to make recommendations that will take the guess work out of the process and that you know will fit and work well for you – thus saving money and helping your bike work as it was designed. Also, remember that fit is dynamic and the position you were riding in two years ago when you first started riding may be different than what will work optimally now.
While road and tri frames are similar in their general use, they perform different functions. Each design came about as a result of a need and each one is most efficient and effective when used for the application it was designed for.