RIDING FAST OR SLOWING DOWN? FACTORS AFFECTING SPEED

RIDING FAST OR SLOWING DOWN? FACTORS AFFECTING SPEED

There are a few different answers to this question depending on what you are trying to achieve. Many riders want to go faster, but not all. If you are mostly interested in getting fit and being consistent with your riding, then speed would not be your focus.

Another category are cyclists who are interested in doing weekend charity rides, where they can combine riding for a good cause and at the same time accomplishing a goal of completing 50km and upwards in distance. This type of cyclist too, would not need to be concerned with speed. The focus would be riding consistently and riding safely. The great thing about charity rides is that cyclists are supported by the event organizers, who provide fluids and snacks at stops throughout the route. This allows a rider to be able to complete the distance, while being able to fuel and hydrate themselves adequately.

Other events like Gran Fondos attract many different cyclists, from those who are interested in riding fast, to those who just want to complete a specific distance. Most Gran Fondos allow both types of riders to participate in the same event, by offering many distances.

For those who are interested in riding faster there are a few factors that you need to consider about riding at a “particular” speed. Many cycling clubs try to accommodate different levels of cyclists by having 2 or 3 speed groups, depending on how large the club/group. The groups are usually divided into speed categories such as 22 – 25km/hr, 26 – 30km/hr and 30+km/hr. If you are interested in joining a cycling club, I recommend enquiring how many levels the club offers for their weekday and/or weekend rides. This will help you to decide which club best suits your goals.

If you are riding with a club at a specific speed level, then riding at that speed will matter and should be a focus. I have written many articles on “getting faster” in previous Ask a Pro newsletters, or you could contact me directly. If riding at a particular speed is your goal, there are a few factors that will impact your ability to maintain any specific speed. They are as follows:

1. Wind:

Wind resistance contributes to approximately 85% of the effort an average cyclist must expend in order to propel the bike forward. This is the number one factor that can drastically affect your speed. Expecting to complete a ride, event or race at a specific speed on a windy day is unreasonable. Your speed will drop by approximately 10% for every 10km/hr increase in wind, if the winds are moderate – in the 20-25km/hr range. For example, on a route that would normally take you 2.5hrs then that same route would take you 2.75 hrs. If the winds are heavy – in the 30km/hr+ range, your speed will drop by 15+%.

2. Road Surface:

Much of the remaining 15% of effort expended is due to rolling resistance from the type of road surface you are riding on. Expect a “tar and gravel” and roads with frequent splits and cracks to reduce your speed by around 1-2km/hr. verses a smooth, asphalt surface.

3. Rolling Resistance:

This simply means how much friction your tire is creating when it is travelling over the road. The higher the friction, the more rolling resistance it creates and therefore slows the bike down. In addition to the roughness of the road as mentioned above, rolling resistance is also impacted by our choice of tires, temperature, and tire inflation (psi). The selection of tires is many and varied, at one extreme are the knobby-treaded steel-beaded mountain bike tires, which create huge rolling resistance. At the other extreme the 22mm tubular slicks, which create minimal rolling resistance. Tires flex and rebound over every bump in the road. Cold tires, due to low temperatures are not very flexible, which means the ability to absorb bumps is diminished, therefore increasing the rolling resistance. Contrary to popular opinion, hard or overinflated tires (relative to the body weight of the rider) increases the rolling resistance. This is because you and the bike will spend more time bouncing up and down, than going forward. This is similar to a down hill skier who takes “too much air” going over moguls and slows themselves down as a result.

4. Relative Humidity in The Air:

Before I give you the details on this factor, consider the example of wind turbines in Palm Springs, California, which is a very dry and warm climate, to wind turbines in off-shore Lake Ontario, Canada. Because the air in Ontario, Canada is much denser and more humid, the wind turbines can generate around 25% more power for the same wind speed, compared to Palm Springs. As a cyclist in this example, you are the wind turbine. The wheels of the bike are like the fans of the turbine spinning through the air. You, the rider, are a fixed source of wind resistance. So, expect to expend around 25% more effort to travel the same speed, versus in a warm and dry climate. If you don’t expend that additional effort your speed will drop substantially. The rule of thumb for this is that for every 10% increase/decrease in power (effort) results in approximately a 6% increase/decrease in speed.

5. Temperature:

Temperature effects air density, tire rolling resistance (see above) and your body’s metabolic efficiency (the body’s ability to burn fuel efficiently). That’s why there is a “sweet spot” for temperature, which is around 15 – 23 degrees Celsius. This temperature range is where the air density has dropped, and our bicycle tires have become warmer and more flexible (see above) yet our body remains more efficient. Above these temperatures your body’s ability to cope with dissipation of heat becomes the more dominant factor. In a previous Ask a Pro article I wrote details about how body and limb length affect the body’s ability to dissipate heat. So, body size is also a contributing factor.

6. Weight of The Bike:

Bike weight primarily affects your ability to accelerate and the speed at which you climb. If you are concerned about climbing faster, aside from managing your own body weight, the next best thing is to shed unnecessary bike weight. However, aside from getting rid of the unnecessary add-ons to the bike, for example bike panniers, filled with clothing etc. It is much cheaper and easier to shed a kg of body weight.

7. Aerodynamics:

Riders are inclined to spend a lot of money on aerodynamic wheels and tear-drop bike frames. However, the position in which you ride the bike has a much bigger impact on your aerodynamics and speed than any modification or upgrade you can make to your bike. Just leaning forward a little more and keeping your head down and more level is the biggest single thing you can do to improve aerodynamics and speed. Loose and floppy clothing is the second biggest cause in reduced aerodynamics. So, get rid of the parachute windbreaker and buy yourself a close-fitting jacket, or vest.

8. Gradient:

For every 1% increase in grade, for a rider of average weight (approx. 125lbs/56kg), your speed will decrease by up to 4km/hr given the same amount of effort. (see chart below)

9. Bike Maintenance:

A poorly maintained bike, particularly unlubricated drive train (chain and gears) will reduce your bike’s efficiency by anywhere from 5 to 10%. If you are riding with a dirty and/or dry chain, expect your speed to drop by 1-2km/hr.

As you can see, many factors impact how fast you can ride. It’s not just limited to how conditioned you are as cyclist.

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