caloso

Bend your elbows more.

https://offthebackistan.tumblr.com/po...s-eddy-is-more

hyhuu

For my commute, being aerodynamic is highly important: long ride, few traffic stops and headwind.

pallen

The trouble with getting more aero beyond position on the bike is finding what is good in all conditions. Something that is great for a headwind might be unsafe in a stiff crosswind. I will say aerodynamics was a big part in choosing my Linus panniers and the narrow Streamliner rack. I don't need to carry much back and forth to work and the low profile makes for less drag that big bulky bags. These don't stick out any further than my legs.

imi

Bent

henkie327

I commute on a recumbent bike and have my seat tilted as far back as possible. The bottom bracket of my bike is a little bit above seat height as well so combined it provides a relatively small cross section which helps tremendously in picking up speed and keeping speed. Be that as it may, my main priority was/is to get to work on a bike in relative comfort and ease, without pain in the butt, so to speak . The aero benefits are simply an added bonus

alan s 

I have a similar commute, and used to be more concerned with this. Getting somewhat aero is great, but beyond that, is not worth the time or expense for marginal benefits.

wphamilton

Not impossible, but too dang hot for this time of year. The other downside, that you wouldn't naturally think of, is the restriction of large body movements which makes riding it completely different from a normal bike.

i think you can put a streamlined tailbox on without issue though. Other than the odd appearance.

spare_wheel

My two "hybrids" have flat bars set ~4 inches below the saddle and if I place my arms on the bar I can adopt a full aero tuck. Moreover, since my bars are ~420 mm wide my arms are most definitely not overly separated. The real advantage of using a flat bar is that you can lop off ~200 gms of steering weight (drops+STIs can be boat anchors). This makes a very big difference in manoeuvrability and is the main reason I commute on flat bars. Its akin to the difference between running a 600 gm carbon fork vs an 800 gm alloy fork.

RubeRad

I've heard from multiple sources that aero doesn't begin to matter until about 20mph; is it possible to develop a rule-of-thumb graph (from measurements, not speculation) that shows aero drag as a function of airspeed? (rather than ground-speed, which would be more useful for considering the very important drag of rolling resistance -- if you consider airspeed instead, you can automatically account for headwind/tailwind)

tjspiel

42 cm Ritchey carbon drops only weigh about 220 grams (there are definitely lighter models) and mid-range Campy shifters are lighter than Shimano trigger shifters + brake levers so that 200 gram weight savings is hardly a given.

Also, I'm not sure how 42 cm flat bars would make a bike more maneuverable than 42 cm drops but I do know that riding with your arms on flat bars isn't going to be as comfortable over a distance as riding in the drops nor would you have fingertip access to brakes and shifters.

Obviously drops are going to involve more tubing so there is some potential weight savings there with flat bars but most flat bars are significantly wider. You can cut them down but then you lose space for controls, lights, etc plus most of the advantage flat bars give you in terms of leverage.

tjspiel

Runners draft and they aren't usually going 20 mph, so it matters at slower speed than that. How much it matters is the larger question, especially when it comes to commuting.

Also as you've implied a moderate 10 mph headwind with a 10 mph pace means a 20 mph air speed.

xuwol7

Thanks for posting Darth Lefty, I thought of posting the same but didn't want to hear the flames..lol
Thanks for taking the heat.

I commute on a 2 different MTB'S both have rear racks and I don't care for a back pack.
1. single speed coaster with studded tires and fenders in the winter, swap to 2" serfas drifters for the rain.
2. Nice weather I commute on a 18 speed MTB no fenders and 26 x 1.75 marathon plus, both bikes are vintage 1980's Peugeots.

Aerodynamics are very important and My 27 1/2" nitto handle bars are very wide, I am a big guy 6'1" and 200# not fat but still not pro bike skinny.

A few things that I have found that helped me.

* I don't use aero bars but I sometimes keep my hands very close together and elbows in which helps.
* I am very flexible and stretch my upper body along the top tube with my head low, this may sound funny but coasting down hills in this position I noticed I pick up 4-5 mph+ easy coasting down hill.
* I use an expandable trunk bag, triangle frame bag and seat post bag and since it is all behind me I don't get wind drag.
* keeping my body and head down really helps (If your flexible).

I really like commuting by bike so I really liked DX-MANS post so damn true.
I recently moved from Cali to the Great Plains so commuting is vastly different especially during the winter but what a great workout.

I am interested to hear how others deal with their commute to make it more kind and gentle.




'

RubeRad

Srsly? Never knew that.

Yes, 10+10=20, and 10mph wind is quite moderate (and 20mph with with 10mph TAILwind is still 10mph headwind), still like to see some concrete, measured graph showing airspeed vs drag for some typical bicycling setup (average size/shape bike, average size/shape rider, known/varied riding position, clothing, controlled/measured wind etc...)

wphamilton

The equations work, and have been verified. https://www.kreuzotter.de/english/espeed.htm is very good.

old's'cool

For some of us, being as aero-optimized as practical is quite important, and worthwhile. In my case, the reasons are:

• I bike commute in order to get a heavy workout on a fairly regular basis, with the minimum net investment of time
• that means I want to go as fast as possible, within reason
• there is no need for a reasonably aero-optimized commuting bike to be expensive, uncomfortable, or impractical

By aero-optimized, I'm not talking about TT-style..., just the practical measures that Darth Lefty elucidated. And I understand that everyone draws the line between practical and impractical according to their own situation.

Kudos to Darth for presenting such a well-informed guide to practical aerodynamics, as well as to the other posters to this thread for their contributions, both pro and con. It's all good discussion.

dvald001

Jan Heine found that fairings actually increased the air drag. If I remember correctly the fairing basically had double the negative effect that a handlebar bag does.

itsthewoo

Just imagine the upward portion of an exponential graph. The calculation for air resistance is proportional to the square of the relative air speed. The speed at which it "matters" all depends on your situation (i.e. uphill, downhill, heavy bike, how aero you can get).

From personal experience on a commuter bike with drop bars, I'd say that air speed is somewhere between 15-20 mph.

wphamilton

With the important qualification, "It’s obvious that fairings only work if they form one body with the rider. Otherwise, you are just pushing one extra object through the air." - what he tested was more on the order of windscreens than actual fairings. I think he's absolutely right in that context.

One of my old tests shows that full fairings on diamond frames can reduce drag significantly, and even just a tailbox can be a strong improvement:


("with front fairing" just differentiates two different designs) This is simply a coast-down test, coasting unpowered down a hill and recording speed.

itsthewoo

Any half-assed attempt at fairing will likely increase drag. If you truly want to use fairings to reduce drag, you'll need something that, at the very least, nearly meets your body. Ideally the fairing would cover the entire bike in some aerodynamic shape (thereby reducing your drag coefficient while minimizing the increase in cross-sectional area), and that's what they use for breaking speed records and such.

Andy_K 

I like the mini essay as a starting point, but you really need to discuss trade-offs more.

Even on a road bike, I don't generally ride in the most aero position available to me because it restricts my breathing too much (not to mention my comfort). Deep section wheels are great for aerodynamics, but they add weight and so they're bad for start/stop and uphill travel. Skinny tires are slower on uneven surfaces. Then, of course, all of these have to be set on a grid of aero-drag vs. (wind relative) cruising speed. At 5 mph you can nearly get away with carrying an umbrella. At 10 mph, I doubt the backpack vs. kitty litter pannier makes a noticeable difference. At 15 mph, things start to get interesting. Of course, with even a 10 mph headwind we're all going to notice aerodynamics.

If you ever really want to geek out on aerodynamics go watch a time trial. Even the local no-prize variety time trial brings out the tear-drop helmets, full carbon disc wheels, skin suits and shoe covers. Talking to those guys about how much time each piece of equipment saves (and believe me they can tell you), will give you a lot of perspective. For a stipped down rider and bike, there really isn't a lot of payoff beyond the aerobars. The helmet saves a big chunk of time by racing standards, but not enough that you'd commute with it. Panniers are the most obvious piece of equipment with drag, but you need a pretty chunky set of panniers to cause a frontal area change as big as the difference between an upright riding position and riding in the drops of a road bike.

There is a guy around here who commutes with a velomobile. Besides being extremely aerodynamic it's also fairly visible.

I've had people draft me during my commute (which is a bigger gain than any piece of equipment will get you) on windy days. Some even asked if I would mind. It's actually surprising that in cities with big bike commuter contingents you don't see organized pacelines of commuters. It would be very sensible, and maybe even fun.

RubeRad

That right there is very helpful (except replace "exponential" with "quadratic"...). Now I can go out and make measurements myself on an out-and-back windy route (for example, the Silver Strand bike path (Bayshore bikeway?) to Coronado island), and use the airspeed^2 relationship to get an understanding of how my bike/posture/clothing/etc is affected for lower/higher airspeeds. If I ever do anything quantitative I'll report back with method/results...

If nothing else, this thread has convinced me to eventually replace my panniers with collapsing baskets. I've always thought they were really cool anyways, now I understand they'll give me some amount of aero benefit (that I can pretend is significant)!

Andy_K 

From https://sheldonbrown.com/rinard/aero/formulas.htm



It's interesting to see that a Dutch-style upright is "distinguishing" itself at speeds as low as 10 kph, while the racing bike hangs with its more aerodynamic cousins until about 15 kph and even then only slowly diverges from the "aero bike" (which I'm guessing is a time trial bike).

tjspiel

Given that panniers are sitting behind your legs (which granted are moving up and down), how much difference does it really make?

Anyway, here's a chart from active.com regarding aerodynamics and triathlons. While you won't find folding baskets vs. panniers, you do find upright (relatively) vs aero bars. The difference isn't that huge over typical commuting distances.



I'm kind of surprised that a skin suit makes that much difference over standard bike shorts and a jersey.

RubeRad

That's why I said "pretend"...

But thx for the table, that's the kind of thing I was looking for!

Also Andy_K, super thx for the graph, should have known SB would have something! I guess me and my CrossCheck are going to fall somewhere between "Dutch upright" and "Racing Bike" (maybe closer to the former, as even though my bike is American and Japanese, I am half Dutch, and relatively Upright...)

Andy_K 

The Jan Heine link claims that a "full aero tuck" makes a 38% difference in wind drag compared to riding on the hoods, which doesn't quite square with the otherwise reasonable looking numbers in that chart. I have to wonder what the "upright, on bullhorns" position really means.

Anecdotally speaking, I can tell you that dropping from my normal position on the hoods down to a semi-tuck on the drops is usually good for an instant 1 mph boost. In a stiff headwind, the difference in effort between those two positions is huge.

I've also done some relatively unscientific measurements on the max speed I reach coasting down the hill from my house from a stop at a fixed location. I did this thinking I would measure tire rolling resistance that way, but the only thing I found that changed the numbers in a repeatable way was whether or not I was wearing a loose, flappy coat. Panniers versus trunk bag versus backpack didn't seem to make a significant difference. The flappy coat took me from ~37 mph to ~34 mph top speed.