Aerodynamics in Cycle Touring - If You Care

[scottg]

A big drag brake or sail, you could mount on the rear rack
would be useful for long mountain descents.

[wheelyhappy99]

Thanks for posting this. It's very helpful to see the relative effect of the various luggage options etc, though I wonder if the quoted numbers overstate the impact for some/most people.

I'm a 'holiday on bike' tourer, rather than trying to achieve speed/distance targets, and the test speeds were noticeably higher than my average. If I recall correctly the faster the speed of travel the higher the proportion of input power required to overcome wind resistance. So at lower touring speeds the effect of any luggage will be smaller than the percentages quoted.

I recall seeing some study a year or two back on a similar topic, though not where, unfortunately. It looked at the relative effect of rolling resistance and wind resistance, concluding that the former had more significance at lower speeds (15mph rings a bell), and wind resistance above whatever the figure was.

Nonetheless, useful comparisons here, and may help with loading for those long spells into headwinds.

[Jdsk]

If I recall correctly the faster the speed of travel the higher the proportion of input power required to overcome wind resistance. So at lower touring speeds the effect of any luggage will be smaller than the percentages quoted.

Enormously so. Aerodynamic drag goes up as the square of speed and power required to overcome it as the cube.

Jonathan

[horizon]

Going through it all again I'm getting the impression that we're talking about roughly a 10% loss or gain due to different aerodynamic set ups (although I cannot quite find out if whether the bike packing bags are of a similar volume to the panniers*). However, that, it seems, is a worst case scenario because you are more likely to be cycling at 20 kph not 30 kph (the clue is in the luggage perhaps) and it is only in headwinds where that would really apply.

So, thinking about some trips today, I generally do 35 - 50 miles per day fully loaded on a camping trip depending on terrain. I might lose say 5% of time on a still day. On say 4 - 5 hours' cycling that's about 12 - 15 minutes. If that ensured me a good night's sleep, extra food, a bigger tent then so be it.

The whole point about the aerodynamics of luggage surely is that you are carrying it for a purpose and that will inevitably slow you down. You could, if speed were that important, take a train, sleep on a park bench, drive, get a motorbike etc. I ask, "What's the rush?".

* If they don't even have the same volume of luggage space then there really is no case for them in terms of aerodynamics IMV.

Having said that, I really liked the article - it was (like the parallel one on weight) very reassuring.in fact (might avoid the flappy clothing though! )

[simonhill]

Thanks, I thought the article would interest most.

My guess is that higher speeds were needed or useful to show up the differences. The article is interesting as it shows 'something' that affects us. Can't see many of us greatly changing our ways.

I already knew that wind resistance is the biggest drag as you go faster and I think this in large part is why I cycle fairly slowly. I'm around 16 kph which is an easy all day speed. If I up it a bit I find it becomes tiring. It's also why checking prevailing wind is one of the first things I check when planning a tour.

[markjohnobrien]

People may be interested in this article. Basically drag of various types of luggage, position and clothes. Not a complete study, but some thought provoking stuff, if you want to shave some time or effort off your days in the saddle.

As for me, I won't be changing anything, but I now know I can blame my rear panniers for my 'relaxed' speed.

https://www.cyclingabout.com/fascinatin ... e-touring/

Interesting article.

[Psamathe]

.....It's also why checking prevailing wind is one of the first things I check when planning a tour.

What sites/sources do you use to check the prevailing wind? Seen it on the MetOffice for UK but not found much for outside the UK.

Ian

[simonhill]

.....It's also why checking prevailing wind is one of the first things I check when planning a tour.

What sites/sources do you use to check the prevailing wind? Seen it on the MetOffice for UK but not found much for outside the UK.

Ian

It depends on where I am going. My recent favourite is Weatherspark, which I think is wonderful https://weatherspark.com/m/32397/10/Ave ... o-Portugal

For most other sites you get a general description saying it is from eg the SW. Some sites are on a daily basis sometimes as detailed as historical hourly, but they are a pain to wade through to get 'normal prevailing'.

I used to use AccuWeather which has good historical data if you dig in, but for wind it's on a daily basis. You have to name a town to start with.

In Oz, the wonderful BoM (Bureau of Meterology) has wind roses. Not seen anything as good anywhere else, but I'm sure there is if you search enough.

For much of my cycling in Asia it is the Monsoon weather system, so that is easy. (Note: Monsoon weather system, not the misuse of Monsoon to mean a lot of rain).

Sorry, no easy answer, but Weatherspark is the best overall for 'averages' of wind and all other aspects of the weather.

[Bmblbzzz]

Interesting, but I wonder if the takeaway is actually "Luggage slows you down but it might not matter". We're not talking huge amounts of time, it seems at most about quarter of an hour over 100km. That's a whole day touring, really (for most, some will obviously like to travel faster, but many prefer to take more time over it). Similarly with the positions on the bars, touring is about an experience not winning a race, so no point prioritising aerodynamics over comfort, efficiency or control.

Then again, reducing drag needn't mean you go faster or further; it could mean you arrive at the same place in the same time but having seen more en route and with more energy at the end of the day, and that's got to be a bonus.

[mattheus]

It depends on where I am going. My recent favourite is Weatherspark, which I think is wonderful https://weatherspark.com/m/32397/10/Ave ... o-Portugal

You tease - I thought you were going to somewhere called Weatherspark!!!

[horizon]

Interesting, but I wonder if the takeaway is actually "Luggage slows you down but it might not matter". We're not talking huge amounts of time, it seems at most about quarter of an hour over 100km. That's a whole day touring, really (for most, some will obviously like to travel faster, but many prefer to take more time over it). Similarly with the positions on the bars, touring is about an experience not winning a race, so no point prioritising aerodynamics over comfort, efficiency or control.

However, it would be important on something like an Audax where time and speed do matter. Of course, Audax riders don't normally carry luggage but on very long Audaxes, a brief overnight stop is required and thus some items perhaps like a sleeping bag have to be carried. Audax riders, so I was told, get round the twin problems of the extra weight and aerodynamics by . . . having their luggage sent ahead by car.

Which, when I found this out, lowered my respect for Audax by about 100%.

[mattheus]

Interesting, but I wonder if the takeaway is actually "Luggage slows you down but it might not matter". We're not talking huge amounts of time, it seems at most about quarter of an hour over 100km. That's a whole day touring, really (for most, some will obviously like to travel faster, but many prefer to take more time over it). Similarly with the positions on the bars, touring is about an experience not winning a race, so no point prioritising aerodynamics over comfort, efficiency or control.

However, it would be important on something like an Audax where time and speed do matter. Of course, Audax riders don't normally carry luggage but on very long Audaxes, a brief overnight stop is required and thus some items perhaps like a sleeping bag have to be carried. Audax riders, so I was told, get round the twin problems of the extra weight and aerodynamics by . . . having their luggage sent ahead by car.

Which, when I found this out, lowered my respect for Audax by about 100%.

...er... was this from a Reliable Source?? It only happens on a minority of events, and even then is usually quite a limited load (e.g. organiser has 50 drop bags crammed into his Honda Jazz along with all the baked beans, loaves, tea-bags ...).
PBP is the most numerous "long" event - by far the majority ride this without support of any kind.

Please don't think I'm getting the hump here, BTW - I've ridden both sorts of events! Have also tried the unsupported Trans Pyrenees Race with luggage for cold October nights in the mountains. I don't do any rides for your respect, but I think you're trolling a bit to say I lost 100% of it (I wonder what your view is on RAAM riders?)

Back on topic - indeed, long Audaxes and Ultra races are the intersection where luggage and speed concerns tend to coincide. It is pretty funny how many people on internet "bikepacking" discussions clearly never ride such events, yet pour scorn on pannier users and the like

[Bmblbzzz]

TBF the reasons for using bikepacking luggage rather than panniers are by no means limited to aerodynamics or speed.

[mattheus]

TBF the reasons for using bikepacking luggage rather than panniers are by no means limited to aerodynamics or speed.

Go on ...

[Bmblbzzz]

Okay. By having weight distributed around the bike rather than concentrated in a couple of places, the handling might be slightly different. By keeping a narrower profile, progress through overgrown paths is easier. Smaller overall luggage capacity forces you to think more carefully about what you take. It also reduces weight (because you've left stuff at home, also because the luggage itself is usually lighter, and because you don't have a rack); this is beneficial in a number of circumstances, not only climbing hills but lifting over fences and gates, loading into trains (especially with dangly bike spaces) and other vehicles. The slimmer profile also makes using trains easier. Lastly, you will be on trend. These are just the ones I can think of off the top of my head, others might become apparent in time.