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Lightweight v aero: which is best?

If you want to ride faster, should you go for a lighter bike or one with less drag?

When it comes to choosing a new bike or upgrading your components you’ll often face the same decision: whether to go for light weight or better aerodynamics. Which offers you the greatest advantage?

Look at the ranges of most of the major manufacturers and you’ll see the performance race bikes divided up in this way. Trek has its Emonda lightweight bike and its Madone aero bike, Giant has its TCR lightweight bike and its Propel aero bike, Merida has its Scultura lightweight bike and its Reacto aero bike… You get the picture.

Some lightweight bikes, like Specialized’s new Tarmac, blur the boundaries with aero features, and many aero bikes are pretty lightweight, but the point remains that you can’t have everything. So which should you go for, a lighter weight or better aerodynamics?

Find out about the new Specialized Tarmac here.

When Merida launched the second version of its Reacto aero road bike (it recently launched the third incarnation, pictured below) it employed some outside scientific consultants to analyse the stages of the previous year’s Tour de France, and they concluded that there wasn’t a single stage where the lightweight Scultura SL Team (which has since been updated) offered an advantage over the more aero Reacto.

Merida’s Head of Design, Jurgen Falke, said, “Bike weight is only relevant for acceleration and very steep mountains. The influence of the weight is the most overrated issue [in] road bikes.”

Merida Reacto 2018 - 2.jpg

Why? Perhaps because weight is so tangible. Pick up a bike and you can immediately tell if it’s lightweight or not. We all do it. These days we might have a vague idea of what an aero bike looks like but actually measuring aerodynamic efficiency is a lot more difficult. You need a wind tunnel and/or CFD (computational fluid dynamics) software. You can’t pick up your mate’s bike before a ride, whistle through your teeth and tell how aero it is.

Merida told us that if you were riding at 30km/h (18.6mph) on a flat road at a given power output, a 2kg reduction in weight would increase your speed by just 0.05km/h (0.03mph) – you’d go just 50 metres further in an hour of cycling. And 2kg is a big reduction in road bike terms.

To take Bianchi’s range as an example, the Specialissima lightweight road bike has a claimed frame weight of 780g and the fork is 340g, a total of 1,120g. The Oltre XR4 aero road bike has a claimed frame weight of 980g and a fork weight of 370g, a total of 1,350g. That means the difference between the two is 230g. Throw some aero wheels and an aero handlebar on the Oltre XR4 and the difference is still going to be a long way shy of 2kg. 

In other words, it’s very difficult to save enough weight on your bike to make a significant difference when you’re riding at a steady speed on the flat.

Most of us don’t ride on the flat the whole time; what about when the terrain is lumpy?

Swiss Side Wind Tunnel 25.jpg

Wheel brand Swiss Side www.swissside.com feeds aero and weight data into a model that crunches the numbers for different types of ride profile and length, and then spits out the likely speed and timing penalties based on a reference ride. 

One of Swiss Side’s programs is a 120km (74.6 mile) rolling ride with 1,200m (3,937ft) of height gain. Swiss Side’s theoretical ‘average’ rider completes this parcours at exactly 30km/h (18.6mph, 211.4W average power). 

What difference would adding 100g (from an 8kg bike to an 8.1kg bike, with a 75kg rider) do to the ride time?

It would add three seconds.

Making a 100g weight saving is obviously far more realistic than making a 2kg weight saving, but the benefit is small.

Aero gains are worth far more. On Swiss Side's rolling ride scenario, making an aero improvement of a given percentage will save you six times the amount of time you’ll get from a reduction in weight of that same percentage. On flat and rolling terrain it's worth going more aero and taking a hit in terms of weight.

Is there a tipping point where weight becomes more important than aerodynamics? Yes. According to Swiss Side, for an average rider weight gains will mean bigger time savings than aero ones if the ride has an average gradient of 4.5% or more. So if you’re racing a hillclimb, or you’re on a really hilly ride, then shaving off the grams becomes relevant. At other times, you’re better off focusing on aerodynamics.

“Ah,” you might say, “but I can sit in behind other riders when riding a non-aero bike on the flat and never get dropped. It’s on the hills where gaps most often appear so surely I want a bike that’s as light as possible to give me the biggest advantage at a time when I’m most vulnerable?”

6.8kg scales 2 - 1.jpg

Chris Yu, Director of Integrated Technologies at Specialized – who you might have seen on videos from the brand’s Win Tunnel – says, “Races are dynamic and the calculation of which bike attribute to favour (in this case it’s aero versus weight) depends as much on the course and environment profile as it does on the race dynamics. This is something that we needed to take into account when working with our teams on equipment selection simulations.

“If there is a Grand Tour stage that is primarily flat but has a finishing climb with a short but extremely steep section, a simplistic calculation would likely always point to the most aero setup as the fastest (almost regardless of weight penalty, within reason). However, we know that the selection and time gaps are likely created on that short and steep section, so it makes more sense to bias the results of the tradeoff calculation to that segment (or even only compare weight and aero in that section).”

Makes sense although those are very specific circumstances.

Swiss Side’s Jean-Paul Ballard says, “There are for sure arguments to be had here. However, this only plays out if it is a mountain finish stage. For hobby riders, the average gradient where weight is more important than aero is 4.5% or more [see above]. For pro riders who have a higher speed, it is around 7.5%. Once you are doing more than 15km/h (9.3mph), the aerodynamic drag is the biggest resistance for the rider. At 35km/h (21.7mph) it’s four times more potent than the effects of weight. 

Pedaled-Ventoux-022.jpg

“So, back to this question; normally people share the lead riding so one could say that the energy level is the same. Once they break, they are out on their own. If they remain on a climb to the finish and the average gradient is on or more than the figure(s) above, then they are better off with the lightweight setup. However, if the gradient is less after their break, and the speeds increase again, then they will benefit more from aerodynamics than weight to remain in the lead and not get caught.”

Can you be too slow for aerodynamics to be important?

You might have heard people say that they don’t ride fast enough for aerodynamics to be important. There’s definitely a view out there that it’s only something you need to think about if you’re habitually gunning it. Indeed, we’ve heard people put a figure on it: aerodynamics only matters when you’re riding at 25mph or faster. Why 25mph in particular, we couldn’t tell you.

When road.cc’s Dave Atkinson visited a wind tunnel with the aforementioned Swiss Side he found out that the slower you ride, the more you stand to gain from fitting aero wheels, up to a point.

Trek Madone 9 Series Project One - riding 1.jpg

The faster you go, the lower the range of relative wind angles you'll experience, Dave found out. Wind angles relative to the bike are usually referred to in terms of yaw. If you're cycling directly into a headwind the yaw angle is zero, and if you're at a standstill with a direct crosswind, it's 90°. When you're moving, the yaw is a combination of the wind speed, the wind direction and your speed. Straightforward stuff.

“Professional riders in normal conditions won't see anything over about 10°, whereas us sportive bashers and lower-category chuffers will see much higher yaw for the same wind, because we can't go as fast through it,” Dave explained. “It’s those higher yaw angles that see the biggest gains, up until about the 20° mark when the airflow detaches from the rim and you lose the aero advantage.”

It’s true that drag increases massively at high speeds but it doesn’t follow that faster riders will benefit most from aerodynamic improvements.

“Faster riders generate more drag because drag is proportional to the square of velocity,” Swiss Side’s Jean-Paul Ballard told us. “But faster riders are also on the course for less time, and experience a narrower range of yaw angles. Through our simulations, we see that slower riders actually save more absolute time. They’re out on the road for longer and can therefore benefit from the aero gains for longer."

Don’t believe him? Plug your figures into an online power/speed scenario calculator like CyclingPowerLab’s and see how much difference dropping 1kg, say, makes to your speed at a given wattage. As well as altering weight you can play around with the average gradient and wind speed, and also with CdA (coefficient of drag). You might well be surprised at just how little you’ll gain in most circumstances by dropping bike weight. 

Conclusion

So, that question we started with: will a lighter weight or improved aerodynamics offer you the greatest advantage? 

Well, in certain specific circumstances (see above) a lighter weight will help most… but, unlike the pros, the majority of us don’t have the luxury of different bikes for different ride profiles. When we buy, we have to choose between light weight and aero. We can’t afford both, so we have to plump for one or the other.

We’ll leave the final word to Swiss Side’s Jean-Paul Ballard.

“In general, I say that in more than 90% of cases (rides), you would choose the aero setup.” 

Mat has been in cycling media since 1996, on titles including BikeRadar, Total Bike, Total Mountain Bike, What Mountain Bike and Mountain Biking UK, and he has been editor of 220 Triathlon and Cycling Plus. Mat has been road.cc technical editor for over a decade, testing bikes, fettling the latest kit, and trying out the most up-to-the-minute clothing. We send him off around the world to get all the news from launches and shows too. He has won his category in Ironman UK 70.3 and finished on the podium in both marathons he has run. Mat is a Cambridge graduate who did a post-grad in magazine journalism, and he is a winner of the Cycling Media Award for Specialist Online Writer. Now over 50, he's riding road and gravel bikes most days for fun and fitness rather than training for competitions.

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47 comments

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Surreyrider | 1 year ago
1 like

This is a regurgitated 2018 story. I thought I'd get better by paying a monthly subscription. Seems not as this happens regularly. Come on Road CC - you need to up your game here. 

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jaymack replied to Surreyrider | 1 year ago
1 like

Old articles or new journalism, which is better? You decide...

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Nick T | 4 years ago
2 likes

You'd need a seriously fast frame to catch up with a comment posted 2 years ago

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FrankH | 4 years ago
0 likes

I'm getting on a bit (70) and I had an illness three years ago which left me borderline anaemic  so I don't have a lot of power to spare. I'm reasonably happy with my speed on the flat, it's the hills I struggle with so any help I can get is welcome. I'll take light weight over aero every time.

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mikewood | 4 years ago
0 likes

Surely the aerodynamics of the rider are much more important than the bike and that's largely defined by position. Lowering the bars on the bike you already have is likely to give the best bang per buck.

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Psi Squared | 4 years ago
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@handlebarcam

Yeah, there are almost no scientific studies that back up your claim. Yes, it is true that beyond a certain road grade (depending on bike/rider mass) less mass will trump aero.  Fortunately those are the minority of situations.  Most of the time, aero is going to trump less mass, including when you come back down that climb.

Note that reading the article and making informed comments is always better than pulling a comment out of your ass.

Why is it that internet commenters think they've found the situation wherein physics is wrong and doesn't apply to cycling?

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Psi Squared | 4 years ago
0 likes

@handlebarcam

Yeah, there are almost no scientific studies that back up your claim. Yes, it is true that beyond a certain road grade (depending on bike/rider mass) less mass will trump aero.  Fortunately those are the minority of situations.  Most of the time, aero is going to trump less mass, including when you come back down that climb.

Note that reading the article and making informed comments is always better than pulling a comment out of your ass.

Why is it that internet commenters think they've found the situation wherein physics is wrong and doesn't apply to cycling?

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andyspaceman | 4 years ago
0 likes

Neither are as important as comfort and stiffness (in the right places).

Aero bikes tend to have a long, low geometry. If you're not proportioned or flexible enough to fit one, then any advantages will be negated on longer rides as your body tires faster through poor positioning.

Likewise, if you are riding on poor surfaces then something too stiff through the rear end will beat you up and you'll tire faster. Many areo bikes are designed around bigger tyres now, which is helping there.

Lightweight bikes also often come with an aggressive geometry, but there is more choice and you're more likely to find one with the perfect fit. There's more likelihood of the rear end having a degree of comfort too.

Torsional stiffness for power transmission and good handling is easier to achive with teh rounder tube shapes of a lightweight bike. I have ridden aero bikes that have been astonishingly quick in a straight line but that have scared the life out of me on twisty descents with lateral frame flex.

If I had to choose only one road bike the order of priority would be fit and torsional stiffness paramount with aerodynamics and weight in 3rd and 4th place.

Cannondale Synapse with some 40mm aero wheels - perfect all-rounder for me.

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Bigfoz | 4 years ago
0 likes

I ride a steel bike. It's quite light for steel at 9Kg for a 57cm size, triple gearing. It's 2+Kg more than the average "Pro" Aero bike in weight. But it's still less than 10% of the equation when added to my weight... 

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ChrisB200SX | 6 years ago
2 likes

Weight improvement is more tangible to our perception than aero benefits. Aero benefits are much easier to achieve in like-for-like measurement value.

Yes, a lightweight bike feels faster, but it simply isn't compared to a more aero bike until you hit quite steep hills.

Decades of weight obsession has resulted in bikes being generally quite light, maybe a decade or two of obsessing over the aero will bring even better bikes. If we're all on lighter, aero bikes, we go faster and get to spend a bit more time in the coffee shop to compensate  1

Of course, making bikes lighter is good, but making them more aero is better, both is great  4

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HenHarrier | 6 years ago
2 likes

Aren't most modern 'reasonably priced' road bikes pretty much a mix of aero and lightweight anyway? Are any recognised manufacturers really putting out heavyweights with big blocky tubes that act like sails? I prefer the look of eg the R series Cervelo over the S series. Might be a bit slower perhaps but it's hardly a lump with the aerodynamics of a brick and personally I love the fact that we've such a huge choice of frames to choose from. Each to their own, just enjoy the ride eh.

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Canyon48 | 6 years ago
1 like

I still don't get the comments here - the engineers themselves who design these bikes know that aero is far more important, yet some people still refuse to believe it.

The article says it pretty well, aero is far far far more important in almost all situations.

Even when you consider a climb i.e. Cheddar Gorge... The average gradient is 4%, somewhere around 2.5 degrees. Up which, my PR is 13 and a bit mph(which isn't at all impressive).

So, in terms of actual force...

EDIT: Well this is awkward, when I first did the calculations I forgot to convert CdA values from imperial to metric (I couldn't see the units on the graph I used).

The force due to gravity acting on an inclined plane is about 32 Newtons (9.81 x 75 x Sin(2.5)). The force due to air resistance is about 18 Newtons (not taking into account the fact that drag increases exponentially with velocity - i.e. actual average drag is higher). [1/2 rho v^2 CdA].

Assumptions:

  • ISA
  • CdA = 0.8 m^2 (on hoods)
  • Mass of rider and bike is 75kg
  • Gravity is 8.81 ms^-2

So, initially I was wrong, weight IS more important on a pretty big hill when you're going slowly.  But as soon as you hit the flat, weight is *almost* irrelevant.

The other thing that is REALLY important to remember, no matter how fast you're going, the force due to gravity remains constant (assuming constant gradient) but the aerodynamic drag force increases exponentially.

The fitter you are, the more weight you lose anyway and the more important aerodynamics become.

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Dnnnnnn replied to Canyon48 | 6 years ago
4 likes

wellsprop wrote:

I still don't get the comments here - the engineers themselves who design these bikes know that aero is far more important, yet some people still refuse to believe it.

I think - for many of us - it's more about perceptions than scientific fact though. So much of leisure riding is about feeling and perception - and that's not the opposite of objective - we almost all do it because we like doing it and how it feels.

So even if we intellectually understand that they will save more time/energy through aero gains, the feeling isn't as visceral and obvious as a lighter bike that feels (and is) more responsive when you stomp on the pedals in a steep uphill sprint. Or the feeling when you (or your mates) pick it up. 

The vast majority of us aren't going to win any races. Or even try. And where we do try to be competive (even just against our mates), or exert ourselves, it's probably on the climbs. When I look at my times/rankings on Strava, it's the hill segments I check out. I give my (feeble) best there: on the longer, flatter sections, I'm usually cruising, chatting, looking at the scenery, draughting.

So on those criteria - as opposed to more scientific (but less fun) ones - weight could be argued to be more important for most of us.

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Canyon48 replied to Dnnnnnn | 6 years ago
4 likes

Duncann wrote:

wellsprop wrote:

I still don't get the comments here - the engineers themselves who design these bikes know that aero is far more important, yet some people still refuse to believe it.

I think - for many of us - it's more about perceptions than scientific fact though. So much of leisure riding is about feeling and perception - and that's not the opposite of objective - we almost all do it because we like doing it and how it feels.

So even if we intellectually understand that they will save more time/energy through aero gains, the feeling isn't as visceral and obvious as a lighter bike that feels (and is) more responsive when you stomp on the pedals in a steep uphill sprint. Or the feeling when you (or your mates) pick it up. 

The vast majority of us aren't going to win any races. Or even try. And where we do try to be competive (even just against our mates), or exert ourselves, it's probably on the climbs. When I look at my times/rankings on Strava, it's the hill segments I check out. I give my (feeble) best there: on the longer, flatter sections, I'm usually cruising, chatting, looking at the scenery, draughting.

So on those criteria - as opposed to more scientific (but less fun) ones - weight could be argued to be more important for most of us.

Good point, well made.

I've always noticed how much more sprightly my bikes feel if I'm riding without water bottles and tools (my two camelback podiums, plus my inner tube, tools, and pump, come to nearly 2 kg) - even though I know it has no significant effect on my ride time.

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OR_biker replied to Dnnnnnn | 6 years ago
2 likes

Duncann wrote:

wellsprop wrote:

I still don't get the comments here - the engineers themselves who design these bikes know that aero is far more important, yet some people still refuse to believe it.

I think - for many of us - it's more about perceptions than scientific fact though.

Yep.  Could really see this firsthand yesterday on my way home from work.  Finally got a deeper set of wheels a couple months ago, and though they're not the new super-aero U-shaped profile that's trendy right now I immediately noticed a benefit compared to my shallow wheels.  They're a bit heavier, though (Shimano RS81 C50's, so aluminum rim w/carbon fairing), but was still getting new PR's up some local climbs on my first few rides with them.

Since we're now fully into the rainy season I put the shallow wheels back on, and I could really feel the weight difference.  Each push of the pedals felt a bit easier, and the bike even felt livelier - and faster.  However, glancing down at the computer I could see I was going 1-1.5mph slower than usual, and my time over the 13-mile commute was several minutes slower than what I had been averaging with similar power #'s on calm days (wasn't even raining on the ride home either).  I guess it's like that idea of higher tire inflation feeling faster as you're getting bounced around but not actually going faster.

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Dnnnnnn replied to OR_biker | 6 years ago
3 likes

OR_biker wrote:

I guess it's like that idea of higher tire inflation feeling faster as you're getting bounced around but not actually going faster.

Or why people like classic cars. Objectively they're pretty shit but the classic little convertible I hired for a weekend around the Yorkshire Dales was thrilling, visceral, and occasionally terrifying  at anything above 20mph or 30mph on the tiny roads. A modern motor would have felt boring at twice the pace.

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Simon E replied to Canyon48 | 6 years ago
1 like

wellsprop wrote:

I still don't get the comments here - the engineers themselves who design these bikes know that aero is far more important, yet some people still refuse to believe it.

I agree, although what some are pointing out is that, all else being equal, the gain of an aero frame over a standard one is tiny. That's because the rider is by far the biggest factor in the drag coefficient.

It's why adapting to ride in a more aerodynamic position is the biggest gain you can make but lots of people prefer to buy stuff instead of do the work. That's not a criticism, it's human nature.

Thanks for describing the physics equations. Some of it went over my head a bit but it was good to see it explained. smiley

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Jimnm | 6 years ago
3 likes

It’s like saying what’s most important heart or lungs. I’d say both light weight and aerodynamics are part of cycling. Ultimately fitness is also a part of the whole cycling thing. Everything matters 

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hawkinspeter replied to Jimnm | 6 years ago
0 likes

Jimnm wrote:

It’s like saying what’s most important heart or lungs. I’d say both light weight and aerodynamics are part of cycling. Ultimately fitness is also a part of the whole cycling thing. Everything matters 

Heart is more important than lungs - that's why modern CPR teaches chest compressions over rescue breaths. (I'd still prefer to have both).

I reckon aero is better bang for your buck as light-weight only really helps whilst accelerating and going up inclines/hills. Aero helps going down hills and on the flat, so you get more benefit from aero.

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fenix | 6 years ago
1 like

Exactly. Look at the bike. Now look at yourself in the mirror. You're by far the least aero part of the equation.

I'd not fret if you haven't an aero bike

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davel | 6 years ago
2 likes

It's all part of the fun and entertaining battle to part cyclists from their hard-earned.

Bikes can get as light and aero as they like. It's just noise compared to the elephant on the bike, which really can't be arsed getting particularly light or aero.

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Canyon48 replied to davel | 6 years ago
2 likes

davel wrote:

It's all part of the fun and entertaining battle to part cyclists from their hard-earned. Bikes can get as light and aero as they like. It's just noise compared to the elephant on the bike, which really can't be arsed getting particularly light or aero.

Yep!

Does amuse me when I see an aero bike being ridden by someone who is quite clearly not aero...

Equally, amuses me when I come hear people I come across at cafe stops bragging about how light their pedals are when they are 100kg plus.

Don't get me wrong, I'm not saying they shouldn't be allowed to have those bikes, I just wonder if their money could have been better spent improving their fitness.

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I love my bike replied to Canyon48 | 6 years ago
0 likes

wellsprop wrote:

davel wrote:

It's all part of the fun and entertaining battle to part cyclists from their hard-earned. Bikes can get as light and aero as they like. It's just noise compared to the elephant on the bike, which really can't be arsed getting particularly light or aero.

Yep!

Does amuse me when I see an aero bike being ridden by someone who is quite clearly not aero...

Equally, amuses me when I come hear people I come across at cafe stops bragging about how light their pedals are when they are 100kg plus.

Don't get me wrong, I'm not saying they shouldn't be allowed to have those bikes, I just wonder if their money could have been better spent improving their fitness.

Or just not stop at the Cafe!

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alansmurphy | 6 years ago
1 like

Ohhhh go on then... Oill have a cup of tea.

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alansmurphy | 6 years ago
1 like

Oooh there's my last ride... Ventoux, why did you try and kill me.

I was looking at a Merida Reaction - aero alloy bike versus the chosen Cannondale Carbon lightweight bike. The Merida blurb said "when you're cruising along at 25mph".

Yep, that's not me...

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dottigirl | 6 years ago
0 likes

Sorry, but please can someone briefly summarise what shape profile I should be looking for, if I was wanting to be a little more aero?

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Jack Osbourne snr replied to dottigirl | 6 years ago
5 likes

dottigirl wrote:

Sorry, but please can someone briefly summarise what shape profile I should be looking for, if I was wanting to be a little more aero?

The temptation is sooooooooooooo strong right now.........

 

Must resist.

Must resist...

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dottigirl replied to Jack Osbourne snr | 6 years ago
2 likes

Jack Osbourne snr wrote:

dottigirl wrote:

Sorry, but please can someone briefly summarise what shape profile I should be looking for, if I was wanting to be a little more aero?

The temptation is sooooooooooooo strong right now.........

 

Must resist.

Must resist...

G'wan, g'wan. You may as well...

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simonmb | 6 years ago
4 likes

The answer lays within ourselves. Most cyclists can more than double the gains from an aero bike by simply riding in a properly aero position. Equally, most cyclists can afford to lose more weight than they'd save by buying a lightweight bike. 

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turnerjohn | 6 years ago
0 likes

and what do Swiss Side make?...oh yeh aero wheels...co-insidence then  3

aero def has its place but real time riding is totally different to what can be shown in a lab....just like car fuel economy....

echo above ...TdF riders seemed to use low section rims rather than super deep....even for sprint stages.......that says it all !

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