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AASQ #141: Which aero components offer best bang-for-buck drag reduction?

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We know, there’s no such thing as a stupid question. But there are some questions you might not want to ask your local shop or riding buddies. AASQ is our weekly series where we get to the bottom of your questions – serious or otherwise. Hit the link at the bottom of the post to submit your own question.

Welcome back to the Bikerumor Ask A Stupid Question series. This week we delve into aerodynamics, taking a look at which bike components offer the best bang-for-buck drag reduction to improve the aerodynamics of a regular road racing bike. Where is your money best spent? Is it on the wheels, at the handlebar, the fork, or is it actually better spent on improving the aerodynamics of you, the rider? Joining us this week are:

Finally, we also have Sam Pendred joining us from Hope Technology, designer of the Hope HB.TT, a road-worthy version of the Olympic Track Bike built for the British Cycling Team that competed in Tokyo. Though he can’t comment specifically on what gains different components offer, he is able to give an unusual insight into how aerodynamics was considered in the design of the HB.TT. 

Which bike parts offer the best opportunity for improving the aerodynamics of a bike? In terms of Watts saved, where is my money best spent in terms of upgrades? I’ve a standard road bike that I’d like to use for time trial racing.

Swiss Side: Even as a wheel brand, we’d be lying if we said that wheels offer the biggest aero gains. They are super important and high up the list but not at the very top. To answer this question, we need to look at the total bike and rider system and which parts of this system contribute the most drag. In road cycling, the rider is around 75% of the total aero drag, so this is our first point of call.

swiss side aerodynamic testing wind tunnel

The rider position makes the biggest difference and costs nothing. The difference between the ‘cafe position’ (top bars, hands in the middle, straight arms) and an aero position with arms bent with hands flat on the hoods, is around 40W at 35km/h (85W at 45km/h). So, the biggest bang for buck is your yoga class to build core strength to ride lower positions for longer.

The next biggest influencer is rider apparel. A snug fitting one-piece aero suit can bring 14W at 35km/h (30W at 45km/h). Add winter gear and these numbers double again. So, being conscious of what apparel you choose is very important.

swiss side aero road wheel testing wind tunnel
In addition to their own wheelsets, like the Hadron2 Ultimate shown here, Swiss Side also lend their expertise toward development of DT SWISS wheels such as the ARC 1100

Next up are indeed the wheels. A good set of aero wheels deliver in the order of 7W at 35km/h (15W at 45km/h) over a normal set of stock low profile aluminum wheels. And, this benefit increases significantly when there is wind about due to the “sailing effect”. A good front wheel can actually generate thrust (negative) drag if the wind is right.

swiss side aerodynamic helmet testing wind tunnel

Helmets also provide plenty of potential in road cycling (and time trial). Between a good aero-road helmet and a simple heavily ventilated non-aero helmet, we have measured differences up to 5W at 35km/h (10W at 45km/h).

swiss side simplon pride aero carbon road frame developmet
Swiss Side were involved in the development of the Simplon Pride II aero road bike, which Simplon claim is the fastest road bike in the world

Of course, last but not least is the complete bike frame. This is however a big investment and not really ’tuning’. The difference between a standard frame and a top level aero-road bike frame can be up to 20W at 35km/h (43W at 45km/h). This is not including the aero wheels.

Cervelo: The single most effective upgrade is body position. Purchase a set of clip-on aero bars if you haven’t already (these don’t have to be expensive, round alloy ones will do just fine).

cervelop clip-on extension aero bars for time trial triathlon racing
Cervelo’s Clip-On Aero Bar

If you’ve not had a professional fit (either in person or with a number of great apps) it’s worth the investment. Not only will this ensure you’re physically in the best position for your body shape, but also that you’re able to comfortably hold that position, which is arguably more important.

Andy Barlow ripping on the Cervelo Aspero Gravel Bike in some tight fitting lycra

Another low hanging fruit is clothing; you don’t need to go out and find the most expensive skin suit available, just ensure that everything is tight fitting once you’re in the correct position. If it’s a flat course and you’re comfortable with your power output, remove the front derailleur and run the bike 1x.

If it’s a longer course and you need hydration, look at bottles and cages that fit between the arms (clip on aero bar bottle cage) or behind the seat. And finally, tyres and wheels. This will take some serious investment but it’s a fundamentally important next step.

reserve carbon road gravel wheels developed with cervelo
Cervelo were heavily involved in the development of Reserve Road and Gravel wheels

Wheel aerodynamics can easily take up its own article but, in short, look for the right balance between stability, weight and aero performance; narrow and deep for the rear wheel, wide and shallower for the front (if your frame can accommodate it). Ensure that the tyre you choose (brand and width) matches the wheel profile.

Roval: Within Roval’s arsenal of equipment, the rider looking for the best bang for his/her buck when it comes to aero gains on a road bike should think about their leading edge. Obviously, it’s no secret that wheels are a huge aero upgrade.

roval rapide c38 carbon wheelset
The Roval Rapide C38 Carbon Wheelset is tubeless ready with 21mm internal and 26.6mm external widths

Common knowledge has been deeper is faster for a TT, but with our Rapide wheel we focused not only on a super aero 51mm deep front wheel, but ensuring that speed came with the stability necessary to use it – 25% more stable in a crosswind than our CLX50.

Roval Rapide lightweight aero carbon handlebar, more rapid, less weight, Gent Wevelgem photo by Chris Auld
The Roval Rapide Bar weighs a claimed 225g (31.8mm clamp, 42cm)

We also recommend our Roval Rapide bar, offering a 20 second saving over a round bar, with aero details like a recessed step to ensure your bar wrap is flush with the tops and internal cable routing. Another key bar stat to keep in mind when looking for aero gains is width. I’m sure you’ve seen how many pros are going narrower and narrower. It is to reduce the frontal area of your body, and really improve aero.

specialized s-works road bike roval wheels aero riding position

This obviously leads to the overall importance of fit. We asked our Retül fit Guru, Scott Stroot, his thoughts and he said, “Aero bikes and aero components are most helpful if you are positioned in the most aero position your body can hold at the highest amount of power for an extended period of time. If you are not positioned well you can be losing power, aerodynamics or both. This is why a Retül fit is so essential to riders maximizing aerodynamics and power.”

If you’re riding your standard road bike in a TT or off the front w/o aero bars our WinTunnel engineer and Body Geometry Research manager said, “Simply adjusting your body position into a crouched position on the hoods or drops will improve aerodynamics. Crouching so that a rider’s forearms are flat/parallel to the ground can improve aerodynamics in the range of 6-12 W at 40 kph depending on the initial, non-crouched position.”

When it comes to aero gains with equipment across the spectrum wheels, clothing and helmet are the top 3 bang for your buck purchases.

Sam Pendred, designer of the Hope HB.TT:

  • Working on developing the HB.TT further and because of the radical design, we are trying things in the wind tunnel that “usually” give riders a big gain – but the design of this bike can be counter intuitive. We have seen improvements by doing things that would normally be worse for aerodynamics (rider position, especially).

hpe hb.tt front view wide bladed aero fork

  • Working heavily on parts that other brands don’t have the interest/capability to manufacture. Components can be a very interesting one, like the front caliper on the HB.TT – a brand new caliper design that sits perfectly to the fork and behind the axle of the front wheel, with not a single section of exposed hose. We are looking at doing other interesting things like this with more components in the future.

hope hb.tt custom 2 piston flat mount brake caliper

  • Manufacturing capability. This is a big stumbling point for lots of designs where the design is great but you can’t find a way to make it. With everything done in house here at Hope from mould/component machining – to laminating the composite products – finishing & assembly. We have total control over the whole process and it allows us to push it further and try new complex designs (usually) with high levels of success.
hope hb.tt road worthy aerodynamic time trial bike with 8cm wide fork legs carbon everything
The HB.TT was developed by Sam from the Hope x Lotus HB.T Olympic Track Cycling bike raced at Tokyo 2020

Got a question of your own? Click here to use the Ask A Stupid Question form to submit questions on any cycling-related topic of your choice, and we’ll get the experts to answer them for you!

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2 years ago

The answers from the wheel companies are rather self serving. If we’re talking best bang for buck – then getting a set of 30mm alloy wheels achieves the majority of the aero gain available. Going to 60mm carbon is fairly marginal in speed per $ terms. And while outside the remit of this topic – the choice of tyres makes far more difference to speed than the wheels you put them on.

Also, nice of retul to talk about the importance of position then supply an image of a a rider with the saddle rammed all the way up. No good being aero if your back is knackered after a short time.

2 years ago

I had a Retul fit and it was a total scam and waste of money. I had to go elsewhere and pay for another fit as it left me with so many problems. They wouldn’t even adjust my cleats. All they cared about was trying to sell me stuff. When I went for the followup they ignored my complaints about pain and told me to leave and just to email them in future.
Before even looking at me on the bike they tried to get me to buy a new Saddle, custom insoles and handlebar.
It’s just a system to get you to buy Specialized parts.

Either I went to a dodgy place or they need to vet their fitters better.

Mr Pink
Mr Pink
2 years ago

Funny everyone above has left out a key factor here: Your ability to stay fairly still at 30mph for an hour is very difficult for most people. Even amongst top TT age groupers you see a lot of wobbling while tucked In that perfectly tuned aero position…which kills all the gains.

Points to Swiss Side for acknowledging a yoga class is going to be your best investment, and then wheels second.

2 years ago

DB, you’re a little misinformed in your assertions about wheels. A 30mm alloy wheel does not achieve the majority of gain available, or even close to it. He reason carbon is of benefit to wheel design is that there is much more freedom to design a proper shape and size without much penalty in weight. A basic 30mm “aero shaped” alloy rim is simply rounded, not aerodynamic. Better than a rectangular box? Sure, but only a little bit.

Tires must also match the rim profile if you’re to benefit from the work they put into the shape. Use too large a tire and you essentially “break” the aero profile (the rim shape needs the tire profile to be correct to complete the profile). It won’t be “bad” but you’ll immediately be much closer to the aero performance of those $500 alloy rims than what you were expecting to get out of the $2k carbon rims.

2 years ago

Mr Pink, 100% agree with you – Points for Swiss side for their answer, huge minus points for Specialized/Roval for just trying to turn it into a sales pitch.

2 years ago

Disagree with DInger. 30mm alloy rim like Kinlin XR31T will get you most of the way (70-80%) to the performance of a deep section carbon wheel – for a fraction of the cost. It’ll also be much more robust so you won’t think twice about hopping potholes or slamming into other road debris. $2k carbon rims can often make you ride miore conservatively.

2 years ago

Really, and you know this how? I helped my son conduct some research for a university project on wheel aerodynamics. I rode up and down a 500m course @ 40kph over 200 times to study the effect of wheel depth on aero resistance. The 30mm alloy aero rims required around 40w more compared with 80mm front & disc rear

2 years ago

It’s not such much about material as about a) profile and b) depth. As you move away from a box-section profile towards a toroidal shape, or similar, and increase depth, you increase aerodynamic efficiency. It’s perfectly possible to get *most* of the aero gains with an appropriately shaped alloy wheel. Of course, this says nothing about weight – 80mm deep alloys would be anchors – or the availability of such wheels.

I’d also point out that near the top of the article, Swiss Side – who aren’t likely to undersell the effects of aero wheels – suggest 15w saved at 45kph, not 40w at 40kph.

Def Defy
Def Defy
2 years ago

A missed opportunity by some of the professional opinions here. Roval’s response in particular just seems like an eye-rolling press release.

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