Which wheel should you use-aerodynamic or light-weight?

Watching a stage game, you will see that the depth of the driver’s wheels changes with the terrain. Usually, the deeper rims appear in the rapid flattening stage, while the shallower lightweight rims are bolted to the mountain.

It is the most efficient at this level and benefits more when riding alone or in smaller groups. A set of conspicuous deep rims can even indicate that the rider likes to rest.

In contrast, a set of slender rims means that the rider wants the main action of the day to happen on the landing gear. But most routes consist of flat sections and hilly sections. Which wheel is the most effective; aerodynamic or lightweight?

Marco Arkesteijn, a lecturer in sports and sports biomechanics at Aberystwyth University, said: “If a cyclist rides 10 kilometers on flat ground and then goes uphill for 10 kilometers, the uphill section obviously takes longer.”

"Now let us [arbitrarily] say that on flat, shallower rims, deep-section aerodynamic wheels increase your speed by 10%, but due to their extra weight, there is a similar reduction in speed when going uphill.

"It makes sense that you should choose shallow rims, because you will spend more time on the ascent, so you want to save time."

Ah, but it's not that simple. Kevin Quan, Engineering Director of Knight Wheels, said: "My former colleague at Cervélo did a lot of tests and calculations to answer this question.

"They found that for the average casual rider, the aerodynamic weight reduction is better at a slope of about 5% and a slope of 8% for professional riders."

Therefore, if you are Chris Froome challenging Col de la Ramaz in the Tour de France, with a slope of 13.9 kilometers and an average slope of 7.1%, then deep rims are your best choice. If you are accountant John Smith, try it in the same climb, it is best to go shallow.

For a slightly different view, let's change the measure of comparison to trustworthy watts.

"At 40kmh, the conversion from shallow rims to deep segments may be worth about 10W, which can save you 30 seconds in an hour," said Rob Kitching, founder of the performance modeling equipment Cycling Power Lab.

"Let us assume that the weight loss of using a deep-section pneumatic wheel is half a kilogram. Even at a 10% slope, the cost of carrying the extra weight during the climb may be less than 5W.

"A course must have a lot of difficult climbs, and there will be a lot of weight loss before giving up the aviation upgrade."

Life’s a drag

One of the key factors we need to consider is the resistance area (CdA), which is the product of the resistance of an object and the area of its front face. It has been found that the use of pneumatic wheels can reduce the CdA of the cyclist by 3-5%, so if you generate 350W of power, the use of pneumatic wheels can smoothly increase your speed from 44.6kmh to 45.4kmh, an increase of 1.63%.

At a slope of 2%, aerodynamics is still the way to go-deep wheels must be at least 2.8 kg heavier than shallow wheels because they are not a faster option. But with the slope of the road, this value drops sharply.

At 4%, pneumatic wheels weighing 940 grams will still be the faster choice. At 6%, it will drop to 390 grams, but when you reach 10%, it will only have 50 grams, because the aerodynamic advantage can beat the shallow wheel.

So let us bring it into the real world. Zipp's 202 Firecrest clamp is a light and light option of 1,450 grams, while its 808s is a super aerodynamic option of 1,885 grams with a weight loss of 435 grams.

Based on our data modeling, this means that they are still a better choice when the gradient is as high as 5%, which is consistent with Quan's previous statement.

But so far, all our calculations have effectively assumed that any slope is constant and the road is straight, when in fact neither of them.

A new variable must be introduced into the equation through changes in curve and speed: inertia, which is roughly a calculation of mass multiplied by the distance to the center of the wheel.

Wheel manufacturer Mavic studied the effect of inertia on the wheel and found that the higher the weight of the rim (a la aero wheel), the greater the inertia.

"This is important because inertia affects the reaction speed of the wheels," Mavic research engineer Maxime Brunard said. "If the speed changes a lot from one moment to the next, you need low inertia. If you ride at a constant speed, high inertia will do.

In short, if you encounter a short but powerful climb, go shallow. For longer slopes that require a speed, choose pneumatics.

Performance modelling

Well, we have gotten somewhere, but so far it has only involved data to test our theory, now it's time to go all out. Best Bike Split, which was acquired by TrainingPeaks in 2014, has developed a performance modeling engine that can absorb a large amount of data—the rider’s functional thresholds, weight, bike settings, and wheel selection—before predicting the bike split for a specific route .

For professional teams such as Trek-Segafredo, this is a sufficiently accurate model that can be used to choose. For example, when facing an uphill time trial, their drivers should use the TT Speed Concept or the Madone with a clip.

FLO Wheels is an American wheel company that uses Best Bike Split to model its wheels in numerous Ironman bike courses to understand how terrain affects wheel selection.

These include flat, rolling and steep routes, as well as extreme routes like the Alpe d’Huez triathlon, including the iconic climbs used in the Tour de France.

The company compared light auxiliary wheels (1,100g) and pneumatic wheels (1,624g) with heavier auxiliary wheels (2,259g). On the Florida Triathlon track, the climbing distance of only 180 kilometers was 300 meters, and the heavier wheels entered in 5 hours, 21 meters and 44 seconds.

The lighter wheels only saved 2 seconds, while the eros entered at a speed of 5 hours, 14 meters, and 10 seconds—a saving of 7 meters, 34 seconds. Even in the 13.2 km Alpe d'Huez climb, the lightweight wheels were only 23 seconds longer than the final aerodynamic combination.

"Our model shows that when choosing wheels, aerodynamics are more important than weight," concluded FLO co-founder Chris Thornham.

Therefore, according to Chris Hewings of Lightweight Wheels, for most real-world scenarios, aerodynamics seem to win, but this lightweight and streamlined debate does not capture the point.

"Based on experience, anecdotal evidence, and being a bit fat, I would be more worried about bending the wheels," he said. "Most of the lightest wheels are inherently more flexible for anyone, except for the very skinny racing snakes.

"Power transmission due to wheel stiffness is as important as light weight. This is where most climbing wheels are lost, especially for riders like me who weigh more than 80 kg."

Hewings puts forward a valid point. In addition to the weight issue, it is worth considering the following points: If your weight is 90 kg, your bicycle is 7 kg, and the wheel set is only 1.1 kg, then your hoop is only 98.1 kg. 1.12% of the total weight of the kilogram is set.

However, if you weigh about 60 kg like Quintana, and the weight of the frame and wheels are the same, then your wheel sets account for 1.61% of the total, which may only be 0.5% more overall, but in comparison, its proportion increases Up nearly 50% to the larger rider's wheel.

So shallow rims are suitable for lighter riders, while aerodynamics are suitable for heavier riders? We will give the final word to professional aerodynamicist Chris Yu: "Combined with the given weight difference, the question of which wheel to choose comes down to the slope and wind-especially the yaw angle, which actually depends on the rider's speed.

"But depending on the specific combination of aerodynamics and weight differences, the trade-off point for the gradient can vary from about 4% to nearly 10%." This is difficult to determine, but it is an answer... oh wait , And more: "This is before considering crosswinds and rider speed."

If you have your own ideas, please contact us(sales1@gofastbicycle.com) to discuss and provide you with customized services.