Aero vs Lightweight Bike

THE SHOWDOWN

RIDE AERO, RIDE FAST

For most riders, on flat or gently rolling terrain, the aerodynamic properties of their bike are more telling than its weight. On the flat, a road rider will expend between 70% and 90% of the energy they put through the pedals overcoming aerodynamic drag. Anything a cyclist can do to cut through the air more cleanly will gain speed and save time.

Reducing weight will help you go faster, too, but the evidence shows aerodynamics makes a greater difference, certainly on the flat. One of the UK’s leading bike magazines, Cycling Weekly, found that an aero bike (weighing 7.25 kg) was 2.6 kph quicker than a lightweight non-aero bike (weighing 1 kg less), with the rider putting out 300 watts on the flat. At 200 watts (a figure which many typical roadies would be able to sustain), the aero bike was 1.7 kph quicker.

RIDING UPHILL

What about when the road heads upwards, surely lightweight bikes will be faster when gravity forms a bigger part of the equation?

Well, aerodynamics is still a very important consideration, but when the gradient steepens, the benefit of low weight will eventually outweigh the gains of a slippery aerodynamic machine. One bicycle manufacturer crunched the numbers for its aero and non-aero bikes and found that for a rider putting out 250 watts, the aero bike was quicker going uphill until the gradient reached 5%, but from then on the lighter bike was faster. For a professional-standard rider generating 400 watts, the lightweight bike became faster on gradients of 8% or steeper.

Cycling Weekly repeated its aero vs lightweight comparison and found that on a 2.5 km climb with a 5% average gradient the lightweight bike was seven seconds quicker when the rider put out 300 watts. Dropping the power output to 200 watts increased the lightweight bike’s advantage to 18 seconds.

Of course, if different bikes from different brands had been chosen, the results may have varied, but the steeper the hill and the slower the pace the more it pays to be on a light bike rather than an aero one. But of course, other than in a hill climb, any race or sportive will have a mix of uphills, descents and flat sections. The ideal for mixed terrain riding is a bike that’s both aerodynamic and light.

AERODYNAMICS AND COMPROMISE

So, an aero bike is fast, but that doesn’t necessarily make it the perfect machine for all riders in all situations. We’ve seen that a lightweight bike is likely to be quicker if the road is steep enough, but that’s not the only reason to think carefullybefore choosing an aero road bike.

Compromise is an inherit part of bike design, but building an aerodynamic bike means balancing even more competing demands. A tube shape designed to slip easily through the air isn’t necessarily ideal for the tube’s engineering function. So, an aero bike may not be as stiff and responsive as a more conventional machine, and conversely it may ride harshly over rough roads. Bike designers are getting better at making aerodynamic bikes feel lively and comfortable, but it’s definitely a challenge.

Some aerodynamic features make maintenance more difficult. Integrated brakes (which are shaped to sit within the frame and fork) are notoriously difficult to set up, and may not perform as well as conventional callipers. Rear brakes positioned under the bottom bracket may offer a slight aero benefit, but adjustment is fiddly and in bad weather they’re soon covered in dirt and grime.

Are the marginal gains these features offer worth the extra hassle? For many riders, even those who compete, the answer is ‘no.’

HOW TO GO AERO AND LIGHT

Riding a more aerodynamic bike doesn’t have to mean ditching your conventional frame for an aerodynamic one, or putting up with poor brakes and difficult maintenance.

A pair of deep section wheels will make a conventional bike slip through the air more easily with very little downside, apart from the dent they put in your wallet. Wheels with a rim depth of around 40-50 mm strike a good compromise between weight, aerodynamics and handling in cross winds.

Remember that most of the drag on a bike (around 80%) comes from the rider, not from the frame, wheels or components. A jersey and shorts which fit snugly without any excess material flapping in the wind are inexpensive aero upgrades, and a good aero helmet costs a lot less than a new frame and fork. Think about your position, too. If you want to ride faster, get down on the drops, or ride with your hands on the hoods but with your forearms flat and level.

Just as most aerodynamic drag comes from the rider, so most of the weight you have to get moving is yours not the bikes. Upgrading components can shave a few hundred grams, but unless you have the build of a professional racer, the chances are you could lose a lot more weight yourself with a balanced diet and a bit more time in the saddle.

Being more aerodynamic and lighter may make you quicker, but think about upgrading the rider as well as the bike.

One thought on “Aero vs Lightweight Bike

  1. Mark says:

    I have to stir …
    Can we (and that includes Cycling Weekly) …. be a little less disingenuous please?
    The aero BIKE was not 2.6 kph quicker …… After all, your own facts state the rider accounts for over 80% of total drag. With rotating wheels, handlebar, drivetrain etc accounting for a significant percentage of the remaining 20% total drag, a bike frame alone will comprise typically between 3% and 5% of total frontal drag.
    Factor in limitations in proper setup, wind yaw and the rest and you can do the math on whether light is better than aero. IMO a facile argument when any serious rider knows comfort trumps all.

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