Some kilometres are longer than others

With the spate of attempts at the UCI world hour record over late-2014 and into 2015 due to the revised UCI rules making the record within reach of more riders, it has naturally sparked interest in discussing what matters for best performance in the event.

Jens Voigt started the latest round of hour record attempts at the UCI's Aigle track

I recently saw some chat on a triathlon forum speculating about who could do what distance and so on. All in good fun, but none of them actually go to a track to find out. If they did, they'd realise it's not quite as simple (or as hard) as they might make out.

It pretty much comes down to optimising four main elements:

• maximising sustainable power output for an hour
• minimising the physical resistance factors of riding on the track
• technical execution / skill
• logistics & resources

Some might add psychological factors to that list, but ultimately I consider these to be expressed within the outcomes of each of the above.

Regarding logistics, there are of course UCI requirements to be permitted an official attempt an hour record, e.g.: minimum time in anti-doping bio-passport program is mandatory at elite level or dope testing at age group level, application submitted in advance for approval to relevant levels of cycling administrations, all the technical requirements including international level commissaires to supervise, a UCI approved track, use of timing equipment, start gates, specified date and time of attempt, etc. You can't just rock up and ride whenever you like. Well you could but it would never be a sanctioned attempt.

Then of course you need to factor in enough solo rider time on track for preparation, and that costs money and time as well. Quality indoor tracks are not always local, and even if they are, getting solo time on the track is not always so easy, let alone cheap. For an elite professional rider whose job is to race on the road, it may be difficult to devote sufficient time to the task of preparing properly for a track event.

Of course assuming the paperwork is all in order and you can do your training, then sustainable aerobic power and aerodynamics are king and the rider's ratio of power to aerodynamic drag area is the single most important factor for how far they will go in the hour. But W/m^2 is not the only factor.

There are other physical resistance force factors, like the influence of air density which is a function of altitude, temperature and barometric pressure (and to a much lesser extent, humidity) and the rolling resistance of the track and tyres chosen. I discuss some of these in the following items:
Altitude and the Hour record Part I
Altitude and the Hour record Part II

Which leaves us with technical execution and skill factors, of which there are a couple of key items, namely:

• pacing, which I covered in this case study of the masters hour record by Jayson Austin, and 
• riding a good lines around the track.

Riding good lines

Riding a good line involves a couple of components, one is pretty obvious and involves not riding further than you need to around the bends. Ride wide and you ride further. Pretty simple given the track is all but two semi-circles joined together with two straight sections. OK, the actual shape of tracks are more subtlety curved but that's close enough to describe why riding wide adds distance to your travels around a lap.

Design of the Glasgow Velodrome

If you ride 10cm wider in the turns, you add 10cm x 2 x PI = 62.8cm per lap.

If the extra width is measured on the track's surface, well the actual addition to the distance the wheel travels is reduced by the cosine of the banking angle. e.g. say the track's turns are, on average, banked at 40 degrees, and you ride 10cm above the black line. Then the actual additional track radius ridden is cosine (40 degrees) x 10cm = 7.7cm, and the additional distance per lap = 7.7cm x 2 x PI = 48.1cm. Nearly half a metre.

Do that over 200 laps or so for an elite hour record and you'll ride ~100 metres more than you need to. And that's for riding only a hand's width above the black line.

London Velodrome used for the 2012 Olympics

Another more subtle ride line factor involves the shape and design of the banking and in particular the transitions from the straights to the turns and back again, and whether it's advantageous to ride a slightly wider line in the straights to aid the transitions. On the straights you don't suffer the same severe distance penalty of riding a wider "radius" as you do when riding wide in the turns, so you can explore marginal gains in this manner.

However there is no simple or single answer to this, it depends on the rider and the track geometry - all of which have subtle differences. This is a somewhat more complex optimisation problem and I'm not going to delve into it here.

So putting aside these subtleties, the shortest distance around the turns is to ride the track's black measurement line* - ride any further out from the black line and you ride more distance each lap than is necessary. For the hour record you only get credit for the official lap distance each lap, which is typically 250 metres per lap on most modern standard indoor velodromes although some tracks are shorter and some are longer.

* it is possible to ride inside the black line, however in such timed track events like the hour there are foam blocks placed around the inside line of the track to ensure the riders don't. Very skilled riders can however ride fractionally under the black line on some tracks but it is risky as hitting the foam blocks can disrupt your effort and wash off some speed. The shape of the track in that small space between the black line and the wide blue section varies from track to track and it can be good or not so good to ride in.

Foam blocks discourage riders from riding inside the black measurement line.

Now why are some kilometres longer than others?

Office distance for the hour record =
(Official lap distance)  x  (Number of full laps completed within the hour)
+ a pro-rata distance calculated for the final incomplete lap

I won't go into the formula used by the UCI to calculate the pro-rata distance of the final lap (that's actually deserving of a blog post on its own as the regulations are remarkably confusing).

It matters not how far you actually ride, you'll only be credited with the official minimum lap distance per lap. This is why track riders and coaches are focussed on lap times and not with bike speed, since lap times are the integral of all performance elements. Power meter and other data loggers are of course valuable in parsing out the individual elements of performance that go into attaining lap times, and helping to prioritise development opportunities.

How good are riders at riding the minimum distance necessary?

It varies. Quite a lot. Skilled track riders are typically much better, which is what you'd expect. But what sort of penalty would an unskilled rider face if they started out on a track effort?

Of course we can do lots of maths to figure out how much extra distance on average a rider might cover if they ride wide by so much, but in reality riders move up and down the track, sometimes riding a good line, other times not so good. Some riders are just better at it than others and some adapt to the track more quickly than others.

It'd be so much better if we could simply measure what people actually do rather than speculate.

Which had me thinking. I have some data like that already...

Not so long ago I was doing some performance testing involving half a dozen pro-continental road racers at an indoor 250m velodrome. One of the features of the data logging system used for the tests is an ability to calculate the distance ridden per lap using the wheel's speed sensor data combined with track timing tapes to know precisely when they pass a specific points on the track. With some clever maths this is enough to nail the actual distance ridden each lap to high precision.

In amongst the test data were some solo efforts of at least 10% of the distance of an elite hour record attempt (i.e. 20+ laps of consistent effort) and several such runs by each of the six riders. I figured the runs needed to be long enough to reasonably approximate what a rider might be expected to do over a longer distance/duration.

Of course absolute accuracy of the distance the wheels travel depends on having an accurate wheel circumference value and that value not changing a lot while riding. So I'm not going to assume that the absolute accuracy was perfect, even though the absolute error might typically be somewhat less than 1%. More than that would require an error in tyre circumference assumption of 20mm, which is a lot for those used to measuring such things. However in our favour is that even if such an error existed, it would be a consistent bias error.

So rather than concern myself with absolute accuracy, I thought I'd compare the measured average lap distance for each run with the shortest recorded legitimate lap. In this way if there is any bias error, it's impact on this analysis is minimised (i.e. both measurements would be out by the same proportional amount). By legitimate lap, I mean a full lap not ridden below the black line.

Here's a table summarising data collected from the six riders (in no particular order). Each rider has multiple runs although I haven't identified the riders in the table. What the first column shows is the average lap distance per run less the minimum legitimate lap distance for that same run. The distances are of course distance travelled by the wheel.

Now the riders possibly could ride a tighter line than they actually did for their shortest legitimate lap, meaning that these distances likely underestimate the extra distance ridden when compared with riding very tight to the black line.

For the moment though let's assume the shortest lap they rode during each run was the best they are capable of doing. Since they actually did it, I think that's a reasonable assumption.

The average extra distance ridden per lap varies from one rider to another. One rider consistently rode only 0.3-0.4 metres more per lap than their shortest distance lap, while another was consistently riding more than 2 metres extra per lap on average compared with their shortest legitimate lap. The rider with smallest extra distance per lap had a track racing background.

The second column shows what that average extra lap distance would mean if extrapolated to riding 200 laps of a 250m track (an official distance of 50.000km). For one rider they would be riding nearly half a kilometre further than their track skilled team mate. Yet if both completed exactly 200 laps in the hour, each would be credited with riding precisely 50km, even though one rider's wheels had travelled nearly 500m further than the other's.

In this case, 50.5km = 50.0km. Some kilometres are longer than others.

So what's that extra 500m cost in power terms?

Well for a rider with a CdA of ~0.23m^2, that extra 500 metres travelled requires they output ~11-12 watts more than if they were able to ride a a better line.

Or they'd need to find a 3% reduction in CdA to make up for their skill deficiency.

Remember these were well skilled, well trained and experienced pro-continential road racers and finding an extra 10W or losing another 3% of aero drag coefficient isn't such an easy thing to do.

So no matter your current skill level and experience, if you're expecting to ride such an event yet you have never trained to become proficient riding on the track, well you might want to chop half a kilometre or so from your estimated distance covered based on your power and aero data alone.

Better still, just get to a track a find out what you can actually do.

Likewise, when estimating power, or W/m^2 from the official hour record distances, you might need to add some watts for the technical proficiency of the rider. The less proficient, the more power is required to attain the same official distance.

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Positioned for Speed

Last week I had the pleasure of co-delivering the first "Positioned for Speed" Course held in Australia, which is part of Retül University's growing list of international course offerings. Many thanks to Matt and Nick at Retül and Andy and the guys at Alphamantis for the opportunity, it was a lot of fun. Looking forward to doing more of them (if they'll have me back that is!).

The two day course was aimed at bike fitters and coaches primarily, and gave attendees an introduction to the theory of aerodynamics relevant to cycling, an understanding of how the theory applies to the practical considerations of bike fitting, what elements of aerodynamics we can influence and improve, how we quantify the impact to performance, as well a chance to design and conduct an aero testing session with a test subject.

I had fun explaining the theoretical aspects, then helping the participants understand and experience exactly how to translate these into actual testing scenarios, and using the Alphamantis track aero testing technology to measure the impact they have on a rider's performance.

We tested bike position options, equipment options (helmets and wheels), body shaping options while riding, and clothing options. Over the course of the session, incremental improvements in the rider's aerodynamics were identified, all while ensuring the rider's position was still bio-mechanically effective and comfortable for the rider when considering the events they are targeting.

Thought I'd share a few examples of comparison test results along the way. I can't say much about the rider, or the exact details of each options tested, but suffice to say they are targeting road time trials and track endurance events.

Put a lid on it

Aero helmets are known to give good aerodynamic benefit but which helmet is best for any individual is quite variable. In any case, the team immediately saw the sizeable benefit of one aero lid over the rider's existing standard "mass start" helmet. These were not the only options tested but just shown as a comparison example.

Putting that into perspective, at this rider's Function Threshold Power, that's a gain of more than 0.6km/h or 1.1 seconds per kilometre on flat road terrain. Some people will gain more speed and some less from an aero helmet, and no one helmet brand or model is the best choice for every rider. Some provide more speed gains than others.

The value of a good shrug

Next example is how you can gain speed by "shrugging" (or "turtling") such that you bring your head down and narrow your shoulders while riding in the TT position, but do so without compromising your power output. Sometimes riders learn to be able to do this for extended periods of time, but it's a technique mainly for shorter road TTs and individual pursuit, not so much for the Ironman athletes out there. The gains can be well worth it if you are able to hold onto a shrug for a while.

In this rider's case, they can increase road time trial speed by nearly 0.5km/h or gain nearly 0.9 seconds per km while they shrug. For some riders there are bike position set ups and helmets that enable the rider to shrug more easily or hold it for longer. Ideally you'd like to set up the bike such that the effect is a full time enhancement, however this is not always feasible, so being on the lookout for more free speed-gaining opportunities is worth a go.

Skinsuits. Choose wisely.

The final example I thought I'd share from the testing session was some skinsuit options. Here we can see the difference between three suits tested.

The best suit is about 0.4km/h or 0.6 seconds per km faster than the team issue suit at this rider's pursuit power on a track. That gives them a 25 metre lead over the slower suit by lap 12.

Overall we identified a 0.033m^2 reduction in this rider's coefficient of drag area, which is equivalent to a 35 watt power saving, or a little over 3 seconds per km or a speed gain of 1.7 km/h.

Talk about a winning margin.

Discussing track test routine with one of the course participants.

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Crash test dummies

Following my Aero Testing for Dummies post the other day, I've been getting questions about aero testing services and when people can start getting tested, as well as general interest in progress with the project. I won't go into business plan detail but will post casual updates here every so often, and eventually when it's ready for full professional service delivery, I'll update our website (this is a primarily a personal blog, not a commercial one).

This is a sample of the comments:

Sounds like a terrific service. Good for you Alex, am sure it will be a big hit. Be cool to incorporate with a 'dynamic bike fit' service too - make a change to bar drop/saddle height etc, do a lap while you test comfort and aerodynamics. 

It's right up my alley - am trying to think of an excuse to get back to Sydney now.

This technology and service is a perfect complement for bike fit services.

I have no personal desire to do professional bike fitting, I'd rather provide aero test consulting services to professional fitters and/or work in tandem with them. Indeed I'd prefer a bike fitter be involved, so they can learn about the impact of their fitting and equipment decisions on the rider's aerodynamics, power and speed, and make the adjustments with the benefit of my analysis, feedback and advice. I'm sure over time they will get better for seeing such information, as will I.

I can't say much about what's in the pipeline but I expect the system may well ultimately integrate with professional fitting tools so that rider/bike fit and aero data can be managed for ongoing reference and development.

And similar to bike fitting, much of the quality comes with the knowledge and professionalism of those providing the service. The tools are an enabler and/or help with efficiency. The difference with this tool is the results are immediately apparent, objectively measured and precisely quantifiable.

Next up for me is what I've called Phase II - Demonstration testing

This is where I'll do some properly controlled testing over next month or so, but the emphasis will be on nailing the process, getting good aero results and giving people the opportunity to see it in action, and not so much on commercial considerations beyond refining operational processes for efficient use of testing time.

I already have some crash test dummies lined up.

Once I am satisfied with that I'll move to full professional service delivery, and provide some clearer guidance on services and pricing.

I'm hoping to get to Melbourne at some time before long and there's reasonable a chance I might be heading to Tour of Bright to work at the race and perhaps I could do something at the Wangaratta track around that time if anyone is about and logistics can be arranged - but that's just a thought bubble for now.

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Aero Testing for Dummies

Just lately I've been having some fun with the Alphamantis aerodynamics testing system here in Australia.

In a nutshell, this system enables me to precisely assess changes in a rider's aerodynamics in real time while they are riding their bike.

The rider does not need to do anything special other than ride their bike around a suitable track. Any regular oval-like cycling track or velodrome will do, although an indoor velodrome is preferred as environmental conditions are far more predictable indoors and of course you won’t get rained out.

All that's needed is an ANT+ power meter and speed sensor on the bike, and a clear track to ride around, one where the rider can maintain position and does not need to brake.

Do a handful of laps, and we have your CdA baseline number. Then make a change to your bike position or change a piece of equipment (e.g. helmet or wheel), do a few more laps and we can tell immediately if you are getting an improvement, and by how much. Lather, rinse, repeat.

Test while riding, know if the position is rideable, how it feels at race pace, as well as whether or not it is faster for the power you have, and by how much.

Simple.

Here's a 7-minute long video showing a sample of it in action, with me explaining in voice over.

That's just a sample of the data capture, there are lots of other things but that's the essence of it.

I've been in a systems testing phase these past couple of weeks, and have successfully tested the system with two riders using different power meters (one an SRM, the other a Powertap) at the Dunc Gray Velodrome. Apart from Rod, who's data was featured in the video, the other rider was my mate Tony. It was only a systems test, not a properly controlled aero test, nevertheless we were able to quickly discern for Tony a difference between two good aero helmets.

The next phase will be to demonstrate for those interested in seeing it in action, in particular those with a professional interest in aerodynamic related cycling performance improvement such as bike fitters, coaches, squad development people, and organisations that have tracks. Australia has over 90 velodromes/tracks to choose from!

The system is portable, meaning I can set it up anywhere with a suitable track, so if there is sufficient interest and access to a clear track, I can travel. All I need is access to a regular 240V power outlet and maybe a table and chair for convenience.

How it works:

Power and speed information from your bike's ANT+ device is transmitted wirelessly to special software on my laptop which, along with various parameters (e.g. rider morphological data, track geometry data, rolling resistance and environmental data) and track timing tape data, calculates and plots charts of power output, speed, CdA, exact track position and so on. It does all this in real time.

There are lots of calculations going on underneath (viewable if desired) such as centre of mass speed, lean angles, precise lap distance actually ridden and so on. And more work is being done to further refine the already sophisticated physics modelling, e.g. modelling the intra lap variation in rolling resistance/tyre scrub, as well as integration with individual track timing data systems for even more frequent precise positional data.

The system also works with the Alphamantis "aerostick" device that can additionally capture the relative wind speed and yaw angles, enabling the software to parse out the effects of any wind during testing.

All the data is also captured for reporting, additional analysis, as well as replaying the data to the rider afterwards if desired.

It is, very, very cool.

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