How aero is aero?

A Specialized Transition looking very aero
Photo ©: Jeff Jones

You want to get faster against the clock. You want to know if you spend X you will get Y time savings in return. Problem is, you're bamboozled by a plethora of marketing hype and scientific data put out by companies who want you to buy their stuff, whether it be snazzy equipment or even time in a wind tunnel. Where do you start? Jeff Jones shines a light on the topic.

Let's break it down into a simple question:

How much time can you save by going from your normal road bike and helmet to adding clip-on handlebar extensions to a full-on time trial bike with an aero helmet? That's it. All other equipment (wheels, tyres, clothing) stays the same.

The answer is quantifiable but finding it is another matter. You need to know what you're doing, and most of us don't. Luckily there are people called engineers in the cycling world whose job it is to find the answers to these questions.

We were given the opportunity to spend a day with Specialized's young aerodynamicist Mark Cote at the A2 Wind Tunnel and Lowe's Motor Speedway in North Carolina. It's NASCAR heartland here, and they put a lot of money into aerodynamic testing facilities. The A2 Wind Tunnel, the smaller brother to the AeroDYN tunnel, is used to test small vehicles and bicycles. It's one of the cheapest in the US at $390 per hour (compared to $800/hr for the San Diego tunnel) and the tunnel managers Mike Giraud and Dave Salazar know exactly what they're doing when it comes to bikes. Plus they can compare wind tunnel data to on road data by using the nearby Lowe's Motor Speedway, a 2.3km banked NASCAR oval.

Lowe's Motor Speedway in North Carolina.
Photo ©: Jeff Jones

For the test, Mark enlisted the help of Nathan O'Neill, eight time Australian time trial champion who has raced for European and US pro teams for the past eight years. He's coming off a 15 month ban (expired November 12, 2008) after testing positive for the appetite suppressant Phentermine, which bizarrely is legal out of competition but illegal in competition. But his experience as a wind tunnel subject, time trialist and of course his availability makes him an ideal test rider.

How it's done

Wind tunnel measurement is currently considered the gold standard of bicycle aerodynamic testing. For best results, you need the rider on the bike to be able to hold their position stable while pedalling. You can test the bike alone, but it makes more sense to have someone on it, because the overall shape will be completely different. You also need to test over a range of yaw angles (wind direction relative to the rider's direction) to account for crosswinds, because aerodynamics are significantly affected by wind direction.

The downside of doing this in a tunnel is that you can't account for handling in a crosswind, because the bike is fixed to a set of rollers.

Testing outdoors is useful because it's closer to real world conditions. That said, it's time consuming and you still need to control as many variables as possible. Even if you have a smooth flat track and precise measuring equipment, like the SRM cranks and mobile weather station that we had, too much wind will give you large errors, even greater than what you are trying to measure.

The 70 watt benchmark

Nathan rides the Tarmac
Photo ©: Jeff Jones

In late July, Cote and his team did a series of tests comparing a standard road bike (Specialized Tarmac SL2 with HED Bastogne wheels) to a full time trial bike (Specialized Transition with HED3 Trispoke wheels and a Specialized TT3 aero helmet).

They compared wind tunnel data with track testing at the Lowe's Speedway and the Asheville velodrome, which consisted of several 10 mile and 1km time trials at a constant speed of 40km/h. They were lucky to have near ideal conditions for the outdoor tests, which kept the measurement errors down to around 2% of total power. The corresponding errors in the wind tunnel are under 1%. From doing this, they found the outdoor testing validated the wind tunnel testing, but did not replicate it.

They also found that outdoors there was a 60-70 watt saving at 40km/h between the normal road bike setup, which required ~280-290W at this speed, and the full time trial setup (~220W). That worked out at between 22-24% in aerodynamic savings. To put it another way, it was 9 seconds per kilometre, 2'14 per 10 miles (16.1km), 5'33 per 40km, and 24'58 over 180.2km, the distance of the bike leg in an Ironman triathlon. Or another way, if you can ride a road bike at 40km/h and switch to a time trial bike and helmet, you can do over 44km/h.

In the controlled environment of the wind tunnel, the savings were greater: between 32-42%, depending on yaw angle. These are aero savings only. About 70% of total power goes towards aero. So 70% of 32-42% = 22-29% of total power. This almost exactly matches the 22-24% from the track The bigger the crosswind, the better off you are on a time trial bike because of the sail affect. Of course, you've got to be able to keep the thing upright…

Drilling down

Nathan rides the Transition
Photo ©: Jeff Jones

So how do we break down that 70 watt saving? How much is position, how much is the bike, how much is the helmet and how much is the wheels? That was the purpose of this test, although we didn't actually test different wheel configurations, so we were looking at ~60 watts worth of savings.

Mark Cote decided on five protocols:
Tarmac SL2 road bike | SWorks Road Helmet | Drop bars
Tarmac SL2 road bike | SWorks Road Helmet | Clip-on aerobars
Tarmac SL2 road bike| TT2 Helmet | Clip-on aerobars
Transition time trial bike | SWorks Road Helmet | Aerobars
Transition time trial bike | TT2 Helmet | Aerobars

For each one, we used the same wheels (Roval) and tyres, and Nathan rode in a short sleeved skinsuit with arm warmers and full finger gloves, but no shoe covers. The mass of the bike + rider was 83kg.

All five setups were tested over two laps (4.6km) of the Lowe's Motor Speedway at as close to 40km/h as we could get. The tests were repeated in the wind tunnel later that day. During each test, Mike Giraud acted as a control, riding his bike around the circuit at ~32km/h, with a wind probe attached to the front of his bike that could measure wind speed and direction. The probe looked like it could double as a harpoon, but luckily there were no whales on the circuit.

It was a clear, sunny November morning but the conditions weren't quite ideal at the Speedway. While we could account for the changes in temperature and humidity, the wind affected things at little.

[CdA = Coefficient of drag x frontal area]

Mark Cote and Dave Salazar analyse
Photo ©: Jeff Jones

Speedway data

On the plus side, the trends were accurate and there was still that big 77W (25%) difference between the road bike and the full TT setup. And it looked as though position would account for about half of that. But as for deciding how much the bike was worth relative to the aero helmet, it was tough. This appeared to be because of an unreliable data point, as the time trial bike plus road helmet should have required about 240W rather than 263W at 40km/h. We suspected this was because of an SRM calibration error, rather than the wind on the track, but at the time of publication this was an known unknown.

Wind tunnel testing

Nathan O'Neill in the tunnel
Photo ©: Jeff Jones

Mark was happier once we got into the wind tunnel. Nice repeatable data that did make sense and gelled with his considerable testing experience. The testing was done at yaw angles of 0 and 10 degrees in 48.3km/h (30mph) wind, which was extrapolated back to 40km/h.

Wind tunnel data

Mike Giraud and Dave Salazar
Photo ©: Jeff Jones

The nice thing about this set of protocols is that there are two separate ways of comparing bikes and helmets. The difference between the Specialized road helmet and the TT2 was 8.6W or 9.4W, depending on which set of protocols we chose. The difference between the Specialized Tarmac SL2 with clip-ons and the Transition was 18.5W or 19.3W. Finally, the difference between a road frame and one with a set of clip-ons on it was a whopping 29.4 watts. This difference is due to rider position (in the drops vs. in the aerobars).

That's 60 watts accounted for in savings. The July tests showed 70 watts, but the wheels were also changed in that one so we can guesstimate that HED 3 Trispokes will save an extra 10 watts over Hed Bastogne wheels. Since there were other differences (wore a TT3 in July vs. a TT2 this time, and a skinsuit vs. road wheels) we have to be careful in making this conclusion. But if it is made, it also shows that the Roval wheels tested about the same as the trispokes and the Roval wheels saved about the same 10 watts the trispokes did.

Finally, to put it in perspective, we can list the wattage savings per unit cost.

How much is it worth? That's for you to decide.

Notes:

• We only used one rider and one set of equipment, which is great for controlling variables but it means we shouldn't generalise too much. We did anyway….
• Apart from the 'high' CdA in the Transition | Road Helmet | Aerobars track test, the other CdAs were all within 3% of the tunnel data. Not perfect but good for power testing, according to Mark Cote.
• Some of the savings going from the road bike with clip-ons to the time trial bike are due to position, not just frame aerodynamics.
• You will save more time but fewer watts at slower speeds with these improvements. The constants are the percentage aero drag savings.
• You can quickly learn a lot from wind tunnel testing, provided you have people who know what they're doing

November is the month the annual Lifecycle Spring Challenge takes place. This is a weekend ride from Brisbane to O'Reillys 1000m up in the Lamington Mountains in the Gold Coast hinterland. Sunday sees the descent of the mountain and a flat ride home. This year saw the third edition of the event and unanimously rated the best by all who came.

  All week the forecast was predicting a wet weekend and early morning weather radar confirmed a huge bank of rain heading towards Brisbane. Our main concern was to try and get on the road before it started. With this in mind the Wombles were lined up promptly at 6am for their departure. They had in mind two things….beating the rain and beating the fast group leaving 30min later!

A little later after packing the support van and getting last minute instructions we were away with our worst fears realised as light rain began to fall. However luck was on our side and the clouds lifted to a nice morning with a touch of tail wind to help us along. Our chances of catching the Wombles were dashed as we got a report from John Schaab , who joined us later that the Wombles were strung out in single file and appeared to be travelling at 40+!

Sure enough they still had a considerable time gap as we got to Canungra so were keen to head off soon after the main group arrived. After filling up on cold drinks and Paula's famous fruit cake a few started sneaking up the road that leads to the top of the mountain.

Not to be outdone the fast group took off soon after in hot pursuit and we were strung out ourselves as a few tried to make a break and get a headstart on the hill. All to no avail as we all came together at the base of the mountain. Here Simone, who had a wager with Blair the old fox as to who would be first to the top, took off in the company of Liam, Jason Reed, Matt Barnes and Major Dave. The rest were soon strung out like Browns cows.

Soon we were into the rainforest and the Wombles were getting caught. Rockin" Rod Stewart was taking his role as photographer fairly seriously and was stopping periodically to take pictures of the field going by….no wonder he was still pretty fresh at the top! A few more succumbed to cramp as the heat took its toll…by now rain would have been welcome!

Jason Reed took the honours at the top followed closely by Major Dave and Simone who had successfully negated Blair's challenge for the $5 wager. Over the next 20 min or so everyone made their way to the top, most in surprisingly good condition.Melissa was really impressive completing the ride to the top hardly out of breath.

After a lunch of sandwiches and fruit juice it was time for a rest. The Rainforest Villas were a huge upgrade on previous accommodation and well worth the extra cost. The showers were awesome and quite a few took advantage of the spa's on the deck. A big storm reminded us we were in rainforest and glad to have made it up in good time.

Soon it was time for Happy Hour in the Irish bar. As we had a couple of Irishmen in the party it didn't take long for a great atmosphere to get going led by Ray and Marshall. Major Dave came through again with cheese and crackers and after a few cocktails the pain of the ride up was remarkably diminished.

  The highlight was still to come. Major Dave had called on all his army trained catering skills and put on a magnificent buffet BBQ. There was way too much food and a few were quietly pleased it was a 30km descent in the morning to start off!

  Morning dawned and the rain was largely gone with a lot of clouds and mist about. The less adventurous took off a bit early as the roads are rough and windy as well as still wet from the previous nights rain.The pace picked up at the back and a few egos were being tested and some rode a little beyond their limit at times. One Jason Moore, in a valiant attempt to be first down slid out on a corner near the bottom resulting in some nasty wounds and cuts.  A ride in the van with Dudley into Canungra was required in case of concussion but after a Big Country Breakfast at the cafe he declared himself ready for the ride home!The Wombles again headed out looking to make good time with the tail wind. The main group took a bit longer route up through Beenleigh before coming back in through Logan Rd. as usual taking a refreshment stop under the freeway near Loganholme.

 Once again the Wombles showed the benefit of another year of training under the belt and were waiting at Lifecycle for the "fast" guys to show up. Time for a few tall tales and then home to rest. Once again a great weekend. Major thanks to Major Dave for his work in the catering department and also to Dudley Cowan who did a great job as support driver. Without that we would not be able to have the ride. 

As many may know Lifecycle identity Josie Loane was involved in a serious accident last Wednesday. She had finshed taking the regular  lifecycle shop ride around Mt Cootha and Josie was heading home to get changed for work at the shop when she had a collision with a car while going down the hill from Ashgrove West. She suffered serious chest injuries including multiple broken ribs and lung damage. It was only due to the prompt action of paramedics that she survived. In an amazing coincidence,if there is such a thing, the same paramedics had been in the shop talking to Josie about bikes the previous day!

Josie was transferred to the intensive care unit at the RBH with  a couple of anxious days for family and friends. The good news is that she has made remarkable progress and is back in the ward although still has a drain from her lungs and a drip in her arm. It is a great testament to her fitness and courage that she is doing so well.

She has appreciated all the vistors and best wishes she has received from locally and all around the world. Knowing Josie she will be back on deck before you know it!