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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

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

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

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

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

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 worked for loads of bike magazines over 20+ years, and been editor of 220 Triathlon and Cycling Plus. He's been road.cc technical editor for eight years, 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 past winner of the Cycling Media Award for Specialist Online Writer.

37 comments

Avatar
handlebarcam [1064 posts] 4 months ago
1 like
Quote:

Lightweight v aero: which is best?

There's only one way to find out...

Seriously, it's lightness. Get on a brand new bike that is one kilo lighter than your old one, and ride up Mont Ventoux, or even your steepest local climb, and you'll feel like a million dollars. Get on a brand new bike with enough aero tube shaping to save you 20 watts, on average over a flat 20k time trial, and you'll maybe finish 20 seconds sooner. But it'll feel precisely the same.

Avatar
peted76 [798 posts] 4 months ago
7 likes

@handlebarcam - did you actually read the article? 

It says what many others have said over recent years, aero trumps weight almost all the time for almost everyone, the caveat being unless you live at the base of a mountain and just climb hills all day.

Of course that doesn't stop me wanting to buy a lightweight bike over an aero bike and losing a few pounds, but I nonetheless accept the science.

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DrJDog [432 posts] 4 months ago
1 like
Quote:

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.

Is that talking about overall packages, or just the bike?

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boardmanrider [100 posts] 4 months ago
3 likes

And yet the second guy on the podium of this years Tour de France was on a 'non' aero bike. Uran rode the Cannondale SuperSix Evo while has aero features isn't in the same league as the Reacto, S5 etc.

Does it really matter in all honesty? At the end of the day for the vast majority it's about swinging your leg over the top tube and going for a ride. Ride what you want, what your budget will allow and have fun. 

 

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trohos [52 posts] 4 months ago
1 like

 If in your area there are side winds?

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wellsprop [507 posts] 4 months ago
0 likes
peted76 wrote:

@handlebarcam - did you actually read the article? 

It says what many others have said over recent years, aero trumps weight almost all the time for almost everyone, the caveat being unless you live at the base of a mountain and just climb hills all day.

Of course that doesn't stop me wanting to buy a lightweight bike over an aero bike and losing a few pounds, but I nonetheless accept the science.

You said what I was thinking more or less! Aero is far more important most the time.

Avatar
ChrisB200SX [565 posts] 4 months ago
1 like
DrJDog wrote:
Quote:

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.

Is that talking about overall packages, or just the bike?

Both, really. You've got to apply it to both scenarios to compare them but the bike doesn't ride itself so a % reduction in bike weight doesn't really mean much unless you are actually carrying it over fences and such.

1% reduction of total mass is going to be around 1kg.  1% total drag reduction would still be far faster for normal riding.
Realistically though, most bikes are quite light and quite aero these days, improving either mass or aero isn't going to make a huge difference, but some of us love marginal gains  1

Avatar
davel [1988 posts] 4 months ago
1 like
wellsprop wrote:
peted76 wrote:

@handlebarcam - did you actually read the article? 

It says what many others have said over recent years, aero trumps weight almost all the time for almost everyone, the caveat being unless you live at the base of a mountain and just climb hills all day.

Of course that doesn't stop me wanting to buy a lightweight bike over an aero bike and losing a few pounds, but I nonetheless accept the science.

You said what I was thinking more or less! Aero is far more important most the time.

I'll choose aero any day of the week for my  road riding: I'm an average TTist, not a mountain goat. I also happen to think that aero bikes look ace and I'm happy with any article that vindicates me jumping on that bandwagon earlyish, when I bought it for geometry and looks rather than the science (I have a Reacto from a few years back).

However, this is another one of those topics that it's really difficult to 'real worldify'. I'm guessing not many readers raced at the previous TdF, which forms the basis of Merida's justiification for race bike choice. If I was buying a bike mainly for a Sunday run, which is a hefty chunk of the Mamil market, and that run is likely to involve crosswinds and a fair few accelerations due to  junctions, lights, a cafe stop and waiting for your ridemates to do various things, I'd still be tempted to opt for the *feel* of lightweight.

Avatar
don simon [1549 posts] 4 months ago
1 like
boardmanrider wrote:

And yet the second guy on the podium of this years Tour de France was on a 'non' aero bike. Uran rode the Cannondale SuperSix Evo while has aero features isn't in the same league as the Reacto, S5 etc.

Does it really matter in all honesty? At the end of the day for the vast majority it's about swinging your leg over the top tube and going for a ride. Ride what you want, what your budget will allow and have fun

 

Why worry about bike weight if your body fat is anything over 4%?

Get bike.

Ride it.

Enjoy it.

Then again, if splashing the cash and swallowing the marketing crap make you happy, who am I to complain?

Avatar
jhsmith87 [37 posts] 4 months ago
1 like
boardmanrider wrote:

And yet the second guy on the podium of this years Tour de France was on a 'non' aero bike. Uran rode the Cannondale SuperSix Evo while has aero features isn't in the same league as the Reacto, S5 etc.

Does it really matter in all honesty? At the end of the day for the vast majority it's about swinging your leg over the top tube and going for a ride. Ride what you want, what your budget will allow and have fun. 

 

 

Using the pro's as an example can be difficult given how much of the time they stay in a group. However the same can be said for some riders who only ride on a club run. It all comes down to what you do on your bike. I live in Cambridgeshire where the highest hill is 154m. An interesting thing to do is to ride at a consistent effort but to see the difference in speed you can get from changing to a more aero position. Aero makes a big difference in most conditions other than climbing a mountain.

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turnerjohn [46 posts] 4 months 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 !

Avatar
simonmb [565 posts] 4 months ago
3 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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dave atkinson [6330 posts] 4 months ago
4 likes

turnerjohn wrote:

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 !

TdF riders are notorious luddites who have resisted pretty much every single technology shift since the race started. my favourite story of recent times was of a worldtour team mechanic who had some 25mm tubs labelled as 23s by the factory because he knew they were faster but the team refused to ride on 25s. unsurprisingly, the team loved the 'new 23s'.

Avatar
handlebarcam [1064 posts] 4 months ago
3 likes
peted76 wrote:

@handlebarcam - did you actually read the article?

Did you actually read my comment? I was explicitly talking about sensations not performance.

Avatar
abrooks [21 posts] 4 months ago
3 likes
turnerjohn wrote:

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 !

Here are the 2017 TdF bikes:

http://road.cc/content/feature/224475-tour-de-france-bikes-2017

Not a single wheel that is not deep section

Avatar
flobble [127 posts] 4 months ago
1 like
boardmanrider wrote:

And yet the second guy on the podium of this years Tour de France was on a 'non' aero bike. Uran rode the Cannondale SuperSix Evo while has aero features isn't in the same league as the Reacto, S5 etc.

Said second guy on the podium rides for Cannondale-Drapac. Since Cannondale don't make a proper aero bike, he really didn't have the choice of riding one. Had he done so, he might have been on a different step on the podium...

Avatar
turnerjohn [46 posts] 4 months ago
0 likes
abrooks wrote:
turnerjohn wrote:

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 !

Here are the 2017 TdF bikes:

http://road.cc/content/feature/224475-tour-de-france-bikes-2017

Not a single wheel that is not deep section

the majority of those wheels are not deep section....majority around the 45mm....deeper than a box rim granted but not a huge aero advantage than compared with running proper deep rims 

Avatar
Simon E [3154 posts] 4 months ago
1 like
turnerjohn wrote:

the majority of those wheels are not deep section....majority around the 45mm....deeper than a box rim granted but not a huge aero advantage than compared with running proper deep rims 

From what I've read, rim profile is probably more critical than depth. Flo demonstrated that real world gains between 30mm and 60mm on the front aren't that great. Rear is even less so. With the 2016 carbon models they found the 60+60 combo was a fraction faster than the 90+90.

Their (long) aero v weight article is here.

However, all the aero gains in the world are worth nothing if you have a flapping jersey or when you sit up to take a selfie, a swig from a bottle or fumble with food in your pocket.

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dottigirl [808 posts] 4 months 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?

Avatar
Jack Osbourne snr [680 posts] 4 months 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...

Avatar
alansmurphy [1242 posts] 4 months 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...

Avatar
dottigirl [808 posts] 4 months 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...

Avatar
alansmurphy [1242 posts] 4 months ago
1 like

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

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davel [1988 posts] 4 months 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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fenix [837 posts] 4 months 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

Avatar
wellsprop [507 posts] 4 months ago
1 like
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.

Avatar
I love my bike [211 posts] 3 months 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!

Avatar
Jimnm [269 posts] 3 weeks ago
2 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 [1135 posts] 3 weeks 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.

Avatar
HenHarrier [9 posts] 3 weeks 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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