The Great Weight vs. Aero Debate - a Mathematical Approach
How do you make a bike go faster? It’s a question we ask ourselves every day. Our best answers result in our latest wheels and components. We then go back to the drawing board – sometimes literally a white board or even a pad of paper – to come up with even better answers.
It’s all part of bike science. Speed on a bike comes down to a battle between two things, propulsion and losses. Propulsion comes from one thing – the rear tire on the road, powered by your legs.
Losses are all the things that slow you down. The biggest are:
Which of these components of loss can we combat the most effectively? At Zipp, we’ve found that in most situations, aerodynamics has a bigger influence on speed than weight. We’ve reached this conclusion over decades of testing on the road, in the wind tunnel, as well as real-world experience working with some of the world’s best cyclists and triathletes during races and in training.
What follows are basic steady-state comparison examples based on some simple physics and wind-tunnel data. This force-balance technique is a glimpse into how we can cross-check CFD, wind tunnel, and field test results. Our examples below use the following assumptions:
In this scenario, that 3 pound weight reduction results in a power savings of 4.31 watts.
What about improved aerodynamic efficiency? Imagine installing a pair of deep-rimmed carbon wheels instead of wheels with shallow aluminum rims. Looks fast, right? We’ll begin here with our same rider traveling 40km an hour, but this time the rider achieves a 4 percent drag reduction by adding a pair of Zipp 808 NSW Carbon Clinchers, which are 82mm deep carbon wheels.
In this scenario, that 4 percent reduction in drag results in a savings of 17.49 watts.
Another issue to consider is the weight of the wheelset. Deep-rimmed wheels often are a bit heavier than more shallow wheels. For our example, a very high end set of aluminum clinchers comes in around 1,520g. A set of 808 NSW Carbon Clinchers weighs 1,810g.
That 290g difference results in a 0.92 watt advantage for the aluminum wheel due to weight in our scenario. Even after that adjustment, the 808 NSW provides a decisive wattage advantage.
Wattage-saving calculations such as the one presented here provide cyclists of all types and abilities with information for making decisions when it comes to wheel choice. Zipp provides a full range of rim depths for every terrain and rider type with our NSW and Firecrest and lineups:
- 202 Tubular (32mm depth)
When it comes to wheel choice, look at terrain, personal goals, and your discipline. But in most riding conditions aerodynamics plays a more important role to your speed than does weight.