Trek speed concept bicycle (aeromodding bicycle)

[jtbo]

I'm still amazed how big difference that triathlon bar makes, today I barely could go forward on upright position when there was strong gust of wind, then I changed position to lean over triathlon bar and surely there was slight resistance from wind, I could hear and feel air going around me, but it provided very small amount of resistance, I could coast to head wind, but when I got upright position bicycle stopped in few seconds in strong gust.

That is ridiculous amount of improvement and bit difficult to explain why it is so large effect, maybe frontal area becomes just so much less from leaned position and maybe rear section then leaves air much easier, but effect is huge. Can't wait to test and see what effect is with my main bicycle when I get it going again at next week.

I bought my triathlon bar here, but shop around to see if you can find better price locally, well worth a price, imo.
Bike Bicycle Rest Handlebar - Free Shipping - DealExtreme

[Grant-53]

The air hitting the chest is the main source of drag. The aero bars help in two ways. First the shoulders are lower for less frontal area. Second if the hands are closer together the air flows around the arms and away from the chest.

[jtbo]

Originally Posted by Grant-53

The air hitting the chest is the main source of drag. The aero bars help in two ways. First the shoulders are lower for less frontal area. Second if the hands are closer together the air flows around the arms and away from the chest.

I would consider most drag being on back's side as in aerodynamics it is more important how object leaves air rather than how it enters.

One can experiment this with triangular long rod, having taper towards direction of motion is nearly same resistance when swinging it than I shaped plank of same size, but have taper behind (enough low angle of course) there is clearly less resistance when swinging thing in air.

Front has of course a role in it too, but not so great as often is thought.

With bicycle one creates kind of parachute in upright position, arms closer reduces this effect and lower position reduces further rear area that causes lot of drag, of course also frontal area is smaller that is big contributor too, but if rear would be perfect shape frontal area's effect can be minimized.

CwA is Cw multiplied by frontal area, thus reducing either one is reducing effect of other one, leaned over with triathlon bars area becomes 2/3-1/2 of original I guess, Cw is probably also less and even Cw would not be greatly less as area is it is reducing a lot of drag, same could be applied by upright position with fairings that reduce Cw by relatively similar amount.

That is why added Kammbacks in cars also work so well, they reduce Cw, not area, by reducing rear area and making air leave more cleanly rear of vehicle, it is helping great deal.

So I believe that thinking of chest being big part is perhaps bit misleading, I would consider back being more important in upright position, what do you think?

Yesterday it was 22km/h headwind with over 30km/h in gusts, I did ride 25km/h against that in relatively small effort, so in gusts airspeed was more than 55km/h that is bit over 34Mph, now one must think that it is equal to ride 34Mph at calm weather.
That makes quite a difference to importance of aero compared to if you would forget wind aspect.

Very windy day it can be 36km/h headwind with gusts of 60km/h, that would mean easily 50Mph airspeeds in gusts and it starts to get frustrating to ride in such weather, but such happen every now and then. 30km/h gusts and 22km/h headwind is quite common, but then again it can be week or two with only 12km/h wind.

[Grant-53]

Thanks for your ideas. I have been experimenting for years and believe your conditions are similar to mine. We do a lot of sailplane soaring here in Western New York state. 72W 42N. I wish there was more hard data for upright bikes with the rider's back angle 45 to 55 degrees (50-60 grads) from horizontal. My observation is that the rider's torso, arms and legs form a shape similar to a pump vane or scoop. A rider with a back angle close to zero has a much different chord to length ratio and the rump has a larger radius compared to the rib cage front to back. Again observation versus hard data. So far my fairings have been for city bikes with my back angle at 55 degrees. My aero bars are homemade and I am planning to build an inexpensive triathelete style bike using a mixte steel frame to test a full body fairing. The profile will be a 1:4 inverted wing truncated 25% for kamm effect.
Front fairings have been popular more for rider protection than for drag reduction on motorcycles. Getting a leg over the seat or top tube is an issue for older riders when there is a rear fairing shoulder high. So far the best option is to have a pivot point near the head tube.

[jtbo]

Today new parts came and I did put everything together, took 3 hours, my first ever:
Chain swap
Rear gear install to hub
Front gears, cranks swap

New parts are all gears, chain, cranks, triathlon bar, rear wheel + hub, rear tire and pedals.

Front tire and wheel assembly is new for this bicycle, I recycled parts from one older bicycle, which had new tire and straight front wheel.

Even brake pads are new and everything is serviced and lubricated.

It was wet weather, bit of fog/mist kind of rain, wind was almost the same as before, maybe bit less gusts.

Might be that my legs were not working quite perfectly after long bicycle installation session, also I had one 9km quite fast trip on my belt for morning, uphill speed was certainly less than before, legs had no fire in them and I took my time to adjust seat height at the beginning of the trip, total time was similar than with grandmother bicycle, but on level ground with tailwind I could easily keep up 40kph speed, 30kph was child's play, where before that was limit with this bicycle and old gearing, crank rpm became too high that limited speed, but now that was not an issue, there was always bigger gears available. I could reach 53kph but felt that there would of been much more if my legs would not been so numb.

However wind seems not to go around me as well as it did with grandmother bicycle, perhaps handlebar should be lower, but then again it is at lowest position already, pushing head down I could feel wind easing up it's grip around my ears as wind noise did go lower and turbulence I could feel got lot less, so I guess that position is still bit too much upright and head pokes up into airstream instead of being level with torso and being at low velocity area.

So speed is around 10kph more at level ground now and gearing is plenty to support that, so it is step to right direction already, but need to try and see if I could improve from there, aerodynamic panniers to rear is something that refuses to let off from my mind, so I guess that is one thing to experiment with as my current panniers are bit small for all the stuff I need to haul from shop (like cat sand) so it would serve another purpose as well, I have tools and materials for making those from thin metal as they need to be rather strong, only thing I lack is skills, but those came when one fails enough many times, which means I must attempt to build something like that soon

edit: Today I found flat tire, well it did last 8km or so.
Put new tire in so that I could visit a shop, initial impression was that it did roll more freely, however again I felt that it was harder to go speeds that I did before, surely there was bit of head wind too, 30kph and as I did rode 10kph or bit more that worked out as if I would of cycle 40kph.

When coming back I did cycle 2km distance with average speed above 40kph and 2.5km distance with average speed above 35kph. Can't really tell much from performance, wind is messing things up greatly, but somehow it feels slower than it should be when climbing and riding against the wind. Forecast tells again that tomorrow should be less windy, let's see how it really is, but tomorrow I plan to do standard test route again, maybe I can get gps with me and do coast down test if there is zero wind, it might give some information about rolling resistance.

Should be easy to maintain 25kph travelling speed and should be no trouble climbing 15kph or more on those not so steep hills, top speed should be around 60kph, however must wait and see results to know.

[Grant-53]

Take some time to search online for bicycle fairings projects from colleges such as:
HPV2009-ASME_FinalDesignReport.pdf
Tailwind panniers may not be available any longer but the concept is a starting point. The rear rack fairing could integrate hard shell storage.

[Grant-53]

I tested my front fairing this week. It is a cut and tuck coroplast piece made to look like a motorcycle Windjammer. I ride a Jamis Aragon city bike with 700Cx32cm front and 38cm rear. Tire pressures are 85 psi front and 78psi rear. My weight is 250 lbs. My easy cruise speed on level ground is now 14 mph up from 10 mph measured by an electric bike computer. With a brisk head wind on the front quarter I could still comfortably keep 12 mph. Since it attached to the frame there is no steering effects.
I have some smoothing and minor adjustments to do. Pictures and test data from coast downs will be posted. Then I will add a tail box and more testing for each component separately as well as in combination.

[Stan]

Originally Posted by Grant-53

I tested my front fairing this week. It is a cut and tuck coroplast piece made to look like a motorcycle Windjammer.

Would love to see a snapshot or two, Grant!

[jtbo]

Originally Posted by Stan

Would love to see a snapshot or two, Grant!

2nd that

Few days ago I visited a shop, coming back there is downhill and some gusty head wind. At place where I get over 30kph reliably when coasting at aerodynamic position and without much of wind I got speeds of 15kph with pedaling normally (not agressively, quite lightly actually) as gust of wind hit against me at upright position and this was downhill.

There are those days of wind, somehow my bicycling happens to be on those times and days, right now there is 0 wind and no clouds either, temperature is +8C, last night it was +5C, too easy to find excuse not to ride

Work with bicycle has been rather little as there has been some other things, like game designing and house reconstruction taking considerably time from days.