Road Cycling - aerodynamics\speed

At what speed does aerodynamics come into play on a road bike? When does it make good sense to ride in the drops and not the brake hoods?

I read somewhere that 30mph is really when it begins to matter. But how are you going to get to that 30mph? I'd rather be in the drops to get there.
http://www.analyticcycling.com/ may give more interesting descriptions.

Air resistance increases with the square of you speed. The power you need to overcome itw increases with the cube of you speed.

Typically, air resistance is too low to matter much below 20 kmh (12 mph), but after that it starts to go up pretty fast. The difference in power between 30 kmh (18 mph) and 40 kmh (25 mph) is huge.

Air resistance also depends on the size of your frontal area. I have modelled the resistances on a bicycle in an excel spreadsheet, which you can download from: www.uni-bonn.de/~jmlee . Look for the "wattage calculator". There are instructions on the sheet, and some verbage about the physics involved. Read them carefully and you should (hopefully) have a pretty good understanding of what is going on.

You can also do a coast test. Find a is reasonably long (500 m +) hill with a good grade to it. On a wind-free day, coast the hill in one position, and note your maximum speed. Then coast it in the other position, note the max speed and compare them. That'll give you a pretty intuitive answer to your question.

Cheers,
Jamie

A rule of thumb for road bikes I've heard, and it sounds about right, is that at 20 mph, 80% of your effort is applied toward overcoming wind resistance. Any time you're moving fast enough to feel significant wind in your face, you reduce your effort (or increase your speed) by adopting a more aero position.

Originally posted by jmlee
www.uni-bonn.de/~jmlee.
Cheers,
Jamie

FYI, your link has a period @ the end - so it doesn't work. If I may be so bold:

www.uni-bonn.de/~jmlee

BTW - great stuff!!! :)

Originally posted by roadbuzz
A rule of thumb for road bikes I've heard, and it sounds about right, is that at 20 mph, 80% of your effort is applied toward overcoming wind resistance.

I would assume that applies during an otherwise "windless" day? And, perhaps, only on the flat?

after about 24 mph (40kph) I start to get into an "areo" position, I try to get low on the drops and a straight back, with my face just above the handle bars. This works especially well when going down hill, it is very noticalbe when you change your position you begin to gain more speed, although it may not be comfortable it does increase speed and decrese air resistance.

You can feel the air moving around your body, I find a position that minimizes turbulence no matter what speed I am going - assuming I'm not chatting up the ladies, that is. :D

Originally posted by webist
I would assume that applies during an otherwise "windless" day? And, perhaps, only on the flat?

...and a rider/bike weighing x lbs, etc., etc. Yes, I would assume so. The times that I've heard that factoid, it has been in the context of a bicycle being the most efficient form of transportation. I just twisted it around to apply it to the contribution of wind resistance.

A rule of thumb for road bikes I've heard, and it sounds about right, is that at 20 mph, 80% of your effort is applied toward overcoming wind resistance. Any time you're moving fast enough to feel significant wind in your face, you reduce your effort (or increase your speed) by adopting a more aero position


At 20 MPH 80% of my effort is spent going up hill!

Thanks Bac,

I edited my post, too, so that first time readers won't get misled by that stray period.

Cheers,
Jamie

without all the science, i have found out that by ducking my head down when hammering i can definitely feel as if i am cutting through the wind better. i ride like crap in the drops (uncomfortable and i can't get air in my lungs) so i NEVER ride in the drops (too far from the brakes anyway) and instead bend my elbows and RELAX my arms to jello.

when i sit up and have my front right into the wind vs. crouched, there is definitely a difference, even going 14mph when i am toast.

When riding with a group I've noticed that the draft is noticeable going as slow as 14 mph. This explains why Heras and Rubiera were significant factors on climbing stages in the TdF for Armstrong. Even as slower climbing speeds the draft is still a factor for the pros.