From daily performance to long-term impact on your joint health, the geometries of your road bike are an oft-overlooked but incredibly important aspect of cycling, and one that you will definitely not want to neglect.
The shape of the frame, its angles, and the overall size of your bicycle can all affect whether or not a bike is right for you, and your intended usage and current fitness level are all factors that will play a further role in your final decision.
There are so many variables involved when it comes to choosing the right road bike with the best geometries for your needs, but it doesn’t have to be an overly difficult or complicated affair.
This article will help you to develop a clear understanding of road bike geometries, including what they are and why they are so important to consider before you purchase your next bicycle.
An important determining factor of how steering works on a road bike is the trail.
The simplest way of understanding the trail is to think of it as the amount that the contact patch of your front tire rails behind the head tube in a straight line towards the ground.
The distance of trail is therefore obviously determined by head angle, with the average figure sitting around 60 – 70mm.
There are other things that can affect trail such as fork offset, wheelbase, weight distribution, and so on, but for the purpose of this section it isn’t necessary for us to go into such an in-depth analysis of these factors.
Generally speaking, the higher the trail figure, the sturdier your steering will be, but you may find it to be less responsive when compared to a smaller trail that offers faster, albeit slightly jerkier steering.
If you are unsure of the trail of a bike and can’t find it listed anywhere then you might find this calculator useful as a starting point.
Head Tube Angles
The head and seat tube angles of a bike can play an important role in its overall handling and responsiveness.
Road bike head tube angle declination typically ranges in the low to mid-seventies, with angles above 75 degrees being somewhat less common.
There are plenty of other factors that come into play but in general a sharper head tube angle will lend itself to looser, more response steering, while a lower angle will make it easier for you to travel in a straight line. The latter can be particularly useful when you are traversing unfriendly terrain but you might prefer the former if you are looking for something a little more agile.
The differences between the head angles of road bikes and, say, triathlon bikes are far more significant than you are likely to notice in most road bikes, so while it is a figure you’ll want to pay attention to it shouldn’t affect your riding as significantly as some of the other geometries in this article.
As a general rule of thumb you will want to make sure that just less than half of your combined weight with your bike is on the front wheel as this will help to improve your ability to maneuver effectively at high velocities.
The difference should be subtle, however, because if excessive weight is distributed to the back then you will find inclines incredibly difficult.
One factor that will affect your weight distribution is the length of your wheelbase, a figure that is also affected by the head tube angle.
Longer wheelbases will improve your high speed handling but again you will want to avoid extremes in this department because quick or precise maneuvering can become very tricky if your wheelbase is too long.
To summarize, the longer your wheelbase, the more weight will be distributed to the front, so it is best to experiment and gain both an intellectual and intuitive understanding of how subtle differences will affect your handling.
Seat Tube Angles
Turning our attention to seat tube angles we see that they tend to fall in that same range of around 70 – 75 degrees, with the lower end of the spectrum causing the saddle to be further back on the bike.
Steeper seat tube angles are generally preferable for high speed events such as races and time trials because they enable you to lean forward at a more acute angle to give your body a smaller silhouette and thus decrease your aerodynamic drag. It is for this reason that you must have a Triathlon / TT Bike for these events, which I covered in further detail in the article: "Triathlons: Why You Must Have A Triathlon Bike".
If you are more concerned with riding comfortably rather than going for all out maximum speed then you will probably be better off with a shallower seat angle, but of course most bikes allow you to adjust the position of your saddle slightly so be sure to experiment until you find the perfect angle for your posture.
As we have seen, there can be a lot of variables to consider when it comes to choosing a road bike with the road geometries.
The best advice we can give to you, regardless of your level of experience, is to always try out a few different models so that you can feel the difference that different angles can make.
We all know that there are a whole array of opinionated individuals both online and in print who will say that this or that angle is best for whatever purpose, so it is best to conduct your own research on the basis of what you want a road bike for so that you can ride safely and comfortably.
Form your own conclusions based on your observations and experiences; you might not get the perfect bike first time around but as you learn about your own proportions, posture, and cycling technique you will be better equipped to make the right decision for future purchases.
Of course this doesn’t mean that you can’t use your own due diligence to get yourself a top road bike from the offset, so reread this article if it will help you better understand the terms and you’ll be sure not to falter!
Let me know your thoughts in the comments below. I'm keen to hear about your experience in finding the right frame and geometry for yourself.