Aerodynamics, Rolling Resistance, Weight, and Return On Investment with Sebastian Schluricke | EP#90
Cycling aerodynamics and rolling resistance is almost like a discipline of its own that triathletes need to master in order to be faster. Sebastian Schluricke of Aerotune breaks down the time savings per money spent on different equipment upgrades, to help you create a bang-for-buck shopping list.
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In this Episode you'll learn about:
- How having the right tires is almost off the charts in terms of minutes saved per money spent
- What tire pressure should you really be using?
- How much time can you save per kg you get rid of on yourself, your bike and your equipment on a typical Ironman course. The answer is probably a lot less than you may think.
- Top-priority aerodynamic upgrades to make in terms of time saved per money spent
- The mistakes triathletes make with their water bottle setup
- How much time are you throwing away in an Ironman because you didn't get a bike fit?
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About Sebastian Schluricke
- Co-founder and CEO of Aerotune
- Engineer and enthusiastic triathlete with a wealth of knowledge in aerodynamics
What can you tell us about rolling resistance and what are the factors that affect it?
- Rolling resistance can make a significant difference. The difference between having a good tire and a bad tire translates to a 10- to 15-minute difference for a 100 kilometer distance.
- The great thing is that good tires aren't very expensive either. For example, at the moment of writing you can get a Continental Grand Prix TT for 57 euros.
- Sebastian's tire recommendations
- Continental Grand Prix TT (9.9 W rolling resistance according to Bicycle Rolling Resistance testing)
- Specialized Turbo Cotton (10.1 W)
- Vittoria Corsa Speed Tubeless Tires (7.7 W)
- As a comparison, a tire like Continental Gatorskin has a 19.3 W rolling resistance penalty. Around 10 W more than the tires recommended above.
- Check out the website Bicycle Rolling Resistance to find out which tires have the least rolling resistance based on objective testing.
What is the optimal tire pressure?
- Sebastian usually rides with a tire pressure of 8 bars (116.03 psi).
- However, different tires have different optimal tire pressures so it is best to check what your tire manufacturer says.
- Tire pressure is also dependent on the condition of the roads where you are riding:
- inflate to higher pressures when you are riding on very smooth roads in good condition.
- inflate to lower pressures when you are riding on rough roads in not so great condition.
- Roads that aren't very smooth require low pressures on the tire so that the tires can "deform" and adapt to the contours of the surface. Lower tire pressure will lead to better rolling resistance in those conditions.
- The athlete’s level of comfort is another consideration. If the change in pressure does not result in a significant change in speed, then the athlete’s comfort level becomes of higher priority, which may mean slightly lower tire pressures.
Rolling Resistance coefficient (Crr) vs. Tire Pressure by road condition - Click to zoom
Factors that affect aerodynamic drag
There are 2 main factors that affect aerodynamic drag:
- Frontal Area - the surface area of you and your bike that the wind "sees"
- Geometric Shape - different "shapes" of bike and cyclist cause different amounts of turbulence around you that increases the power you need to overcome aerodynamic drag.
Best Ways to Minimize Aerodynamic Drag and CdA
- A triathlon bike or time trial bike is a must if you want to minimise CdA
- Keeping a good riding position. A new bike can be a poor investment if you cannot ride it in the right position. A new bike will only be able to give you beneficial return when it allows you to get into a better riding position.
- Improving your hydration system is perhaps the most cost-effective way to minimise CdA.
- the conventional water bottle shape and placement on the down tube and seat tube are not beneficial for the goal of decreasing aerodynamic drag
- remove water bottles and water bottle cages from the bike frame and use either between the arm aerodynamic bottles, integrated hydration in the bike frame, or place the bottles behind the saddle.
- for behind the saddle bottles, ideally you want the bottles positioned with horizontal alignment from under the saddle rather than sticking up into the wind flow.
- On average, this saves 5 to 10 minutes at a cost of about €20 per minute.
Horizontally aligned saddle bottle.
- Wearing the right helmet according to one's riding position
- Riders who ride with their head more upright and looking ahead will likely benefit from a longer aero helmet.
- Riders who ride looking down will likely benefit from a short aero helmet.
- Performing an aerodynamic test and getting fitted for a bike. This can save about 10 to 20 minutes over an Ironman at a cost of about €10 to €20 per minute if you've never had a bike fit before, or have a poor fit for whatever reason.
How weight affects your bike performance
- It depends on the course
- On a relatively flat course 1 kg less can save 30 seconds over an Ironman.
- On a very hilly course, like the Norseman for example, 1 kg less can save 2 minutes over an Ironman.
- To save 1 kg on lighter equipment is very difficult, and very expensive. Getting to race-weight is probably the best way to lose that weight.
ROI of a new bike and new wheels
- Getting a new bike is in general the worst investment you can make if you are already on a triathlon bike and have a good riding position.
- The cost per minute saved on an Ironman is roughly €1000 per minute
- The caveat to this is if you don't have a triathlon bike, or your triathlon bike doesn't allow you to have a good riding position.
- New wheels, assuming they cost around 2000€ per wheelset can save you 5-10 minutes if your previous wheels aren't that great, but that's a relatively big investment compared to e.g. a good helmet. The wheels cost per minute is roughly 200€.
Brief Explanation of Aerotune's Aerotesting
- Aerotune's aerotesting is an aerodynamic test an athlete can perform on their own to find their CdA in different riding positions and with different equipment and equipment setups.
- To do the test, you will need:
- a scale to measure the your weight prior to the test and to measure the bike's weight
- a GPS-device (if you have a Garmin device you can use Aerotune's Garmin application directly)
- a power meter
- a straight and flat road that's 1 km in distance (be sure to have enough space before and after the 1-km strip for acceleration, turning and deceleration)
- Markers for the beginning and end points of your 1-km strip
- Aerotest results contain your CdA (aerodynamic drag) and RR (rolling resistance) values.
- If you are training for a specific race, you can get a prediction on how long it will take you to finish. You will also get the time advantage of of one test compared to another to find the fastest setup for you.
Current developments for Aerotune
- Aerotune is currently working on a subscriber-based platform where your aerotest results can be delivered in a matter of seconds to your Garmin device. Alternatively, you can use their web-based application to get your analysis by uploading the files from your GPS-device.
- That same application also includes a feature where you can compare your CdA with other athletes and even with pro-athletes.
Favorite book, blog, or resource related to triathlon or endurance sports:
- Bicycle Rolling resistance website
Favorite piece of gear or equipment:
- His disc wheels
Person in endurance sports that you admire or look up to:
- Jan Frodeno
Links, resources and contact
Links and resources mentioned
Connect with Sebastian Schluricke
- Aerotune website www.aerotune.com
- On Facebook
- On Twitter - @afasteryou
Connect with host Mikael Eriksson
Hi! I'm your host Mikael,
I am a full-time triathlon coach and an ambitious age-group triathlete. My goal is podium at the Finnish national championships within the next few years.
I first started the website Scientific Triathlon in autumn 2015 as a passion project to share my learnings with a larger triathlon audience. Later on, in early 2017 I started the podcast That Triathlon Show.
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Let's discuss this episode and the topic in general. Post any comments or questions in the comments below. I'll be here to reply and take an active part in the conversation, so don't be shy!
I'm especially curious, have you done lactate or metabolic testing? If so, what did you find, and how did you use the results to improve your training?
Really interesting podcast on aerodynamics/the impact of weight – albeit I am surprised/confused by the high psi recommendation for tyres which seems contrary to most current thoughts …
I have two questions/comments:
1) would it be possible to post a picture of where nutrition bottles should be fixed “under” the seat rather than behind? Does this require a special type of seat bottle holder … I don’t want to buy a new holder if it the wrong type.
2) given the impact of weight, does it make sense to start an event with 2 full nutrition bottles. They are heavy. Would it be better to start with one full and one with just a little nutrition in it as reserve and then aim to replace the main bottle at aid stations?
Also – I really like the concept of your 5-15min intro pods for beginners. The full pods are very interesting. But a intro pod, I think, will bring it back to practical basics – good for newbies and less pro participants such as myself.
Thanks Lawrence! My interpretation is that those high psi recommendations may be ideal on smooth roads in very good conditions (aka Germany…)
1) I googled this the other day, and found one image, but I didn’t save it. And now I can’t find it. I’ll reach out to Sebastian and ask if he has an image.
2) Actually, the point of the discussion on weight is that it really is NOT that important, unless you’re doing a really hilly course like the Norseman. So (again, my interpretation) is start with 2 full bottles, no question about it.
Thanks for the feedback on the beginner episodes, I appreciate it!
Lawrence – I updated the blog post since getting a reply from Sebastian.
It is actually a pretty normal setup. The misunderstanding was that the bottles are not supposed to be positioned vertically, but horizontally, protruding from under the saddle. Look at the image to see what I mean.
Also, Sebastian sent me a nice chart for tire pressure recommendations on different road conditions that I added to the post. Have a look! On coarse asphalt, 90 psi is a good option.
I am quite surprised of huge effect of frame installed bottles. If you see the attached picture my head/helmet makes much larger discontinuity (in air flow) than two bottles in frame so I would have an extreme benefit (=10min/180km) of long tail aero helmet? What I wonder too is why my head is so high compared to other triathlonists (pictures can be found in internet)…?
You might, but remember that it’s not JUST the shape of the object itself and how big a surface area it creates, but it’s the overall turbulence. And I imagine that since the bottles on the frame are between the two wheels, that would cause a lot of turbulence relatively speaking, there may be interaction effects of having the bottles there that make the aerodynamic effect of it unproportionally big.
But for you, based on the picture, a bike fit to try and get a lower head position is probably a much smarter investment than a new helmet.