aerodynamics in speed/performance

GoldenMotor.com

coryc

New Member
Jun 17, 2011
14
0
0
bullhead city,AZ
so, i've read a good chunk of stuff on this site and 95% has been excellent info and very helpful. BUT....all the discussions on performance and milking every ounce of power out o'these has been on engine tweaks. i liked the guy that said "if you wanna go faster find a big hill and lose 30 pounds". HOW ABOUT BUILD AN AERODYNAMIC BIKE THAT'S FAST TO BEGIN WITH and build an engine for it? you know,low center of gravity, body positioning, fairing, nosecone, wheelwells, etc. ? everybodys got a stiffy for speed while they're pushin' around a cardboard box w/ a race engine.how about some fibreglass guys buiding some fairings and some metal workers chopping up some frames in the style of dragbikes sans the wheeliebars. get it going before i do 'cuz soon these'll be raced competitively and i got ideas. see you in the rearview.
 

Andyinchville1

Manufacturer/Dealer
Dec 26, 2007
502
1
18
Scottsville, VA
HI,

Good idea...I have a set of wheel covers I bought back in the day (probably around 1985 or so)...It is a simple hoop that fastens to the spokes via clips and it had a fabric cover....The manufacturer claims a one or two tooth rear sprocket advantage (i.e. a rider could use a rear sprocket 1 or 2 teeth smaller than they would otherwise use without the cover) because of better aerodynamics / reduction in drag.

It was a relatively low cost mod that seemed to work....

I agree w/ the fairing / nose cone idea...I've heard good things about them but have not personally used them.

If you don't feel self conscious I guess the fastest / easiest way may be a full spandex suit and aero helmet...THAT is supposed to make a big difference for not a lot of effort...

Andrew

PS - Hopefully some metal fabbers out there will respond to this post....
 

Allen_Wrench

Resident Mad Scientist
Feb 6, 2010
2,784
26
36
Indianapolis
If you don't feel self conscious I guess the fastest / easiest way may be a full spandex suit and aero helmet...THAT is supposed to make a big difference for not a lot of effort...
He is right, spandex can make a bit of difference. That said, I can't believe I wore spandex once for a couple years. My ladyfriends of the time talked me into it. I'm really more of a black-jeans-&-leather kind of guy. Lawd, I felt so out of sorts in the spandex. You have no secrets when you wear spandex. You know what I mean. But, yes, aerodynamically speaking, it does seem to work.
 

BarelyAWake

New Member
Jul 21, 2009
7,194
21
0
Maine
Partial fairings for aerodynamics alone are a tricky business as they add weight & tend to create a low pressure zone directly behind them, which can actually increase the overall resistance through induced drag - include the added frontal area and you may well loose a bit of top speed, the larger ones are primarily for comfort & it isn't until you get into fully enclosed velomobiles that you'll see major reductions in wind resistance.

That's not a absolute ofc, much like the suggestions above - small fairings around normally turbulent areas to help guide the air flow around can indeed help, but they're fractional reductions at best, a combination of many little things contributing to an overall effect (reducing/eliminating cables, wheel covers/aerospokes, etc). Aerodynamically speaking what spandex helps with vs "normal" clothing is the elimination of flutter, one of the most severe forms of drag - but wrapped tightly or not, the human form itself isn't ideally aerodynamic, which is why there's the aforementioned aero helmets & custom "speedsuits" with trailing edge inserts, a tapered shape behind the legs & (sometimes) arms to help the airflow rejoin with less low pressure zones & turbulence.

An example would be Markus Stöckl & his downhill world speed record of 130.7 mph;



Ofc, to massively reduce frontal area - there's a plethora of recumbent bike/trike designs, unlike your "dragbikes sans the wheeliebars" they tend to be feet-forward (not always, but usually) to help the rider's visibility (neck cramp etc) and for a more ideal pedaling position. There's some interesting recumbent plans available here BTW: Atomic Zombie Extreme Machines! - Bikes Trikes and Choppers Plans.
 
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coryc

New Member
Jun 17, 2011
14
0
0
bullhead city,AZ
o.k....maybe i don't want to go 130 on my bicycle. just the picture of that guy is scary enough.but after reading the recumbent trike design article, i believe utilizing some of the same engineering principles he discusses on a two-wheel frame you could go a heck of alot faster than i'm reading about these guys going [generally between 40-50mph].i'm not talking about a multi-purpose, cruise around your neighborhood,fun bike. this would be like for quarter-mile or straight dragstrip wide-open topspeed, single pass runs.things like: small bmx front wheel on raked fork, large diameter ten-speed [or granny's 3-speed] wheel in back mounted to a triangulated backend where the horizontal chainstay [using the trikeguys terminology] is about 3-4 inches offthe ground and axle above this like he talks about to lower center of gravity.re-position/alter theseatpost angle and pedal/crank housing up so the pedalling movement is more in the horizontal plane i.e.-kicking out towards rear tire.this would allow you to position the engine closer to the rearwheel and shorten the drivechain, which seemed to be a recurring engineering problem w/ the recumbent design [along drivetrain], stealing precious energy from a limited supply[66cc engine].body would then be more forward, directly above engine in a more prone position distributing weight towards front 2/3rds of bike. again, comfort is low on the priority list here.finally a partial fairing from height of front wheel to handlebars to minimize front profile. anyway....i think i'll stop just short of the spandex outfit and save that for the privacy of my own home...don't the gagballs and the bondage straps create alot of flutter?