Aero versus lightweight. Which is faster?

A lightweight road bike or an aerodynamic one, which is right for you?

For decades the most important debate in road cycling (apart from the Shimano versus Campagnolo argument) was weight, and how to achieve the lightest possible bike.

Reducing bike weight was the biggest concern occupying bike designers and keen cyclists for many years. Advances in frame materials and better-designed components helped in the battle against weight, and the weight of complete bikes gradually dropped over the years. Thankfully we're a long way past the scary period in the 90s when it wasn't unusual for weight weenies to drill holes in components to trim the grams!

In 2000 the UCI introduced the 6.8kg weight limit because the governing body was worried manufacturers were pushing new materials and manufacturing processes beyond their limits, and worried about the safety of race bikes intended the weight limit to act as a sort of safety net.

But it wasn't long before bike manufacturers were able to produce race-ready bikes that needed lead weights adding to bring them up to the weight limit. Having managed to produce lightweight bikes and with no sign of the UCI lowering the weight limit, this effectively slowed down the development of lightweight bikes. It's possible to actually buy a bike that is lighter than those the pros race.

With the weight limit effectively putting the brakes on the pursuit of lighter bikes, bike designers turned their attention to aerodynamics. It was a natural progression. Decades of producing ever lighter bikes were resulting in ever smaller gains, the limits were being reached in frame and component weight.

It was time trial bikes that kicked off the aerodynamic arms race. Greg LeMond famously won the 1989 Tour de France with the first use of low profile extensions, and the aero floodgates well and truly opened. Rapid development aimed at reducing aero drag followed with time trial bikes transforming into the futuristic looking bikes.

Then, in 2002, Cervelo launched arguably the first aero road bike, the Soloist, and it opened the floodgates for the aero road bike. Aero road bikes have developed a long way in a short space of time. Most bike brands now have an aero road bike in their range, and many are in their second generation. Even bikes previously intended to be all-round lightweight models received aero makeovers, like the Trek Madone.

The availability of aero components also increased, with the widespread adoption of deep section wheels, aero handlebars and even aero clothing and helmets - given the rider causes 80% of the overall aero drag minimising baggy clothing provides some serious performance gains.

To go aero or lightweight?

So aero or lightweight? What's more important and where should you spend your money, a super light bike or one that maximises aerodynamics? Clearly both would be ideal, but currently most aerodynamic products, whether frames, wheels or handlebars, carry a weight penalty compared to products that are solely focused on weight and not the concerns of airflow.

Which you choose isn't an easy decision, but where you live and the nature of the roads you regularly ride can help inform your decision. If you predominantly ride flat roads your biggest hurdle is wind resistance, so an aero setup is going to provide a better return on your investment than a super lightweight bike. On a flat road at speeds of about 20mph up to 90% of your energy is consumed with pushing through the invisible barrier that is air resistance.

If you live in a very hilly area or only ride up big mountains (lucky you), then aero concerns will be replaced by weight, as air resistance is replaced by gravity as the biggest hurdle you face. For this type of terrain, a lightweight setup is going to be preferable and help you get up the climb more quickly. But the gradient can decide at which point you're better off with an aero or lightweight setup.

According to an engineering paper by Cervelo, ride a gradient under 5% and you're better off with an aero setup because you're travelling fast enough for wind resistance to still be a factor. A steeper gradient, however, sees the tide turn in favour of a lightweight setting, as you're not going fast enough for aero drag to be your biggest concern. The more power you can put out and the faster you can climb will influence the gradient at which the balance tips from aero to weight.

For riding on mixed and rolling terrain with flat roads and some climbs, the decision gets a little more tricky, but you can use the gradient rule of thumb above to decide which setup is going to benefit you the most. Whether you ride alone or in groups will also be a factor in the bike you choose. If you prefer to attack the climbs then you might be better served by a lightweight bike, but if you prefer solo breakaways on the flat, an aero road bike is probably going to serve you best.

Next: We look at different aero and lightweight bikes, components and accessories