so im wondering if its just me or if its some well known fact and i just missed the boat. my 2 fastest bike splits in races have been on crazy windy days. most recently, the chicago triathlon where i held a 23.5 mph average, and prior to that, a sprint race in florida on an unprotected key/island. both races were by far the 2 windyest races i have done. is it normal to be faster on windy days? i guess it makes sense that while you spend half the time into the wind struggling along at 20mph and then turn so the wind is on your side and flying back at 30 would increase your average speed. but it also seems like a consistent ride would be faster and more economical… any insight? thanks in advance!
No matter which way you cut it, you should be slower on a windy day…excluding 2 rare scenarios.
- It is a point-to-point ride
- All headwind sections are extremely protected, and tailwinds sections are very open
Friction (even air) always works against you.
I should have expanded…the best way is to look at the basic fluid dynamics equation for drag. Drag = 0.5rhoACv^2 (rho, A, and C are all constants that essentially won’t change if you’re the same person riding the same bike, etc…). But v is velocity as perceived by the moving body. to simplify everything…say 0.5rhoA*C = 1 in both cases…so all you care about is v^2)
So I’ll give two over-simplified examples that yield a meaningful result: 0MPH wind, and 20MPH wind, with your avg speed ~20MPH…on an open out/back course.
Case 1: No wind, so you have an effective 20MPH wind hitting you at all times. On both out AND back you get 20^2 = 400. So overall ‘drag’ is 800.
Case 2: With the 20MPH tailwind, you have 0MPH effective wind. With the 20MPH headwind, you have 40MPH effective wind. On the way out you have a ‘drag’ of zero. On the way back you have a drag of 40^2 = 1600. So, on the windy day there is more air resistance due to drag/you have to put out more power to go 20MPH. This result will go for any wind/speed value you choose.
Hope that makes gives some level of explanation.
No matter which way you cut it, you should be slower on a windy day…excluding 2 rare scenarios.
- It is a point-to-point ride
- All headwind sections are extremely protected, and tailwinds sections are very open
Friction (even air) always works against you.
While I’m sure it’s true that most of the time you are slower when it’s windy, I’m not convinced it’s all that rare to be faster on windy days in certain areas. Where I live in Massachusetts, it’s wooded with rolling hills, with intermittent open fields. The loops I do around my house tend to have certain directions which are more wooded and certain directions which are more open due to the topography of the hills. When the wind is in certain directions, it feels faster to me due to the headwinds being on the wooded sections and the tailwinds being on the open sections. The headwind sections aren’t extremely protected; but they are protected enough to make a difference.
You may be quicker but you will have used more power to go even the same speed on a windy day than on a still one. No matter what crazy ideas you come up with you are not going to beat the laws of physics.
Modern aero bikes and wheels do have less drag when at certain yaw angles.
Science and logic says this can’t be the case, but the same people say bees can’t fly. The same thing used to happen to me but I think I have understood why and this has led me to put things in place to prove the science right.
At times very strong winds naturally break up a ride into smaller segments, and I feel on very windy days this is very much the case, the slightest turn in the road throws up a new scenario. Driving into the wind can often get us really focused on what we are doing to keep moving forwards, position, right cadence gearing selection, pacing etc… I think at times this elevates the average rider to new levels. When they turn into a side or tail wind they simply keep the movement patterns going. In another way it is also easier to deal with the ride because it is in bite size segments.
I also had this phenomonon until I started to really focus and break my rides up into smaller segments. In many ways the hardest ride of all for me is a 150km plus challenge on the flat on a nice calm warm day, it is so much of the same! It takes mental strength to keep performing in this type of scenario, and this takes practice and patience to develop. I am by no means there but focus is something we all need to work on. These rides simply highlight I feel the fact that you find it hard to focus on everyday rides. Break rides down, always start off with a warm up segment, my next one is always about form and focusing on drills if needs be. My next segment is about geting into the right heart rate zone/zones for the day, and I take it from there remembering the last segment is a cool down so I can come back tomorrow if needs be and do it all over again.
It does somewhat depend on how much you draft…
As a serious point, then in very strong headwinds then you may be ‘legal’ but gain some advantage from following other riders just out of the zone upwind, then of course be wind assisted with the wind.
or it is an out and back where it is a light to medium crosswind the whole way.
many bike+riders will have less drag at non zero yaw angles.
for instance, Dave Z on all of the super bikes:
No matter which way you cut it, you should be slower on a windy day…excluding 2 rare scenarios.
- It is a point-to-point ride
- All headwind sections are extremely protected, and tailwinds sections are very open
Friction (even air) always works against you.
Science and logic says this can’t be the case,
no it doesn’t
but the same people say bees can’t fly.
no they don’t
.
You may want to first consider that it is blatantly obvious there is less drag at (for all intensive purposes) any non-zero yaw angle. Take 9th grade math…if the wind is X MPH and your angle is Y, then the projection of wind resisting you is: X*cos(Y). So this is maximized at Y = 0° (cos(0)=1), min at Y = +/- 180° (cos(180)=-1). But what about ZERO wind…ummm…less drag.
A yaw angle having less drag is how it SHOULD be. But certain yaw angles don’t have negative drag. These are basics of most upper level HS or College math/physics/engineering class. I’m not attacking you, I’m letting you know I’m not BS-ing you.
As for the mental aspect, people are correct that wind is a game changer. But you will still be doing a greater amount of work to complete a windy course in the same time as the same course on a calm day. It’s possible to be faster on a windy day, but is impossible to do less work to achieve the same time.
You may be quicker but you will have used more power to go even the same speed on a windy day than on a still one. No matter what crazy ideas you come up with you are not going to beat the laws of physics.
So the laws of physics say it’s not possible to be faster on a windy day on a course in which the headwind sections are sheltered and the tailwind sections are open? Whatever…
tttiltheend, you are right in that there are rare circumstances that could cause you to be faster due to winds. But the idea is that those are rare and generally speaking, wind makes you slower. Additionally, the chance that reefman77 had two of these types of courses is even less. So wind slows you down, unless you are one lucky guy. If you know of a course, let me know…I’d like to hammer a solid 40K TT :).
There are so many other factors.
Did the “windy” courses also have fewer hills, turns, or an easier path in/out of transition?
Did you put down more power on those days?
Just from experience biking and running, a windy course has a net negative effect. Hurts you more going into the wind than it helps you when you have a tailwind.
At Chicago, most areas are blocked from the wind by traffic and people. Depending on when your wave leaves, you will almost always be in the 15" passing zone of somebody. It’s not really illegal drafting - it’s just the nature of a race with 9000+ people (or whatever the number is) on a 2-loop 40k course.
Traffic on Lakeshore drive is almost always slowed/stopped during the race, so vehicles are going to block a lot of the wind off the lake. I think the course itself is pretty fast with a lot of false-flats and no significant hills.
Not sure what your races looked like, but hills slow me down much more than wind. I am much faster on a windy flat course than a hilly calm course.
playing around with the hed yaw angle calculator: http://s321476941.online.de/hedgermany/aerodynamics_technology/yaw_calculator.asp
and looking at the yaw angle sweep of the P4 with DZ on it, I’m seeing that very slight crosswinds, even at 30mph, can cause large drag reductions with very small increases in total apparent wind speed.
shall we do the math? I can fire up a spreadsheet.
but is impossible to do less work to achieve the same time.
playing around with the hed yaw angle calculator: http://s321476941.online.de/...y/yaw_calculator.asp
and looking at the yaw angle sweep of the P4 with DZ on it, I’m seeing that very slight crosswinds, even at 30mph, can cause large drag reductions with very small increases in total apparent wind speed.
shall we do the math? I can fire up a spreadsheet.
My n=1 experience with wind/no wind on the dead flat loop of the Fiesta Island TT course showed me that my power vs. speed was basically the same either way…whereas others tended to be more affected by wind being present.
I guess I sort of “sail” just like DZ 
I’ve been pointed to a journal that tackled this very question:
Kyle CR. The effects of crosswinds upon time trials. Cycling Sci 1991; Sept/Dec: 51-56.
Which came to the same conclusion I guessed at. Due to the way cda varies as a function of yaw angle, a little wind can in fact be faster than no wind at all.