koiboy4343

hello

here's the situation: I am on a school team that races solar assisted bicycles in Ogata japan

here is our teams webpage: https://sites.google.com/site/bhssso.../photo-gallery


and here are the questions

1. should we use aerobars on our bike?
2. if so what are some drawbacks and things to watch out for when using aerobars?

info: we will be riding long distance or pretty flat ground at speeds around 25 MPH and a max of 35 MPH. since things become exponentially less efficient the higher their speed, do the benefits of the aerobars outweigh the drawbacks at the speeds we will be traveling at?

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carbon clinchers

you usually see pro's using them but they tend to be a pretty controversial subject due to their drawbacks


pro's

1. more aerodynamic in a straight line
2. supposedly more comfortable to ride

con's

1. more mass and therefor more inertia.
2. carbon fiber has worse braking characteristics than standard wheels.
3. in a crosswind the benefits are more than negated by the aerodynamic characteristics caused by a crosswind.

info: because clinchers have more mass(more specifically, inertia) it requires more energy to accelerate them to an equilibrium than a standard pair of wheels.

the goal of the team is to create the most efficient long distance bike, not the bike with the highest theoretical top speed under the right circumstances. so does the benefit of the clinchers (straight line aerodynamics) outweigh the drawbacks (requires more energy to accelerate or decelerate, worse braking, worse in a crosswind)?

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and lastly do you know of any super eficiant aftermarket axles and bearings for bikes,as that would make the biggest difference overall.

TY

Elvo

I'd go with a recumbent with a full fairing and focus on the rider's fitness.

koiboy4343

probably should have mentioned this but recumbent bikes are not allowed

jeff@work

I'd recommend looking at how the pros setup for long TT's and Ironman competitions.
Aerobars will definitely be more efficient but the drawback is they make the bike a little more unstable and you'll need to practice on them to become comfortable. Actually I didn't look at the bikes but you should be on a TT style bike as that will let you get your body in a more aero position.
For wheels... Unless it's a super windy area then a disc rear wheel and deep carbon front. Weight won't matter much, especially on flat roads. Aero tires with low rolling resistance are important... GP4000's are pretty popular for that.
Don't forget the rider... Aero helmet, skinsuit, and good position.
I wouldn't worry about the hubs... The difference in it won't be noticeable unless you're riding on just awful wheels.

carpediemracing 

Some misinformation there.

First, if clinchers aren't standard wheels then what are standard wheels? Tubulars?

Carbon clinchers can be lighter than regular clinchers. Tubulars can be lighter than both.

25-35 mph speeds without a recumbent bike means this will be all about aero. Aero bars will be worth it if you optimize the position. If you don't then they may not be beneficial at all.

Bearings will be negligible - you can do some research but it'll be worth a few watts, that's it. A good aero helmet or a good aero position might be worth 100w at 28-30 mph, if not more. A waxed chain could give you 4-6 watts or something, but if you think about it the chain is a 100+ bushing type pivots, a really inefficient thing compared to bearings in the hubs or bottom bracket. Fancy bearings are great for high rpm applications, not the low rpms a hub or BB sees.

If you can use a fairing that would probably make the biggest difference. If a fairing isn't allowed then keep reading below.

Even if fairings aren't allowed some "shaped battery holders" might give you similar benefits. Aerodynamic pannier (bags) have been tested to be faster than just the bare bike alone. This is a while back but the evidence was compelling. So, for example, if you use aerodynamic panniers to hold your batteries or whatever then you'll have the partial benefit of having fairings. Generally speaking you want to mount the weight close to the pivot center of the front wheel and down low is better than up high. The aero panniers mounted basically centered on the hub on the forks. A matching handlebar bag helped deal with the aero mess up higher. Once the wind hits the front of the bike it gets swirly so you don't get as much benefit doing aero stuff towards the back.

Round tubes are less aero than aerodynamically shaped tubes. If it's within the rules you should strive to find a narrow, aero tube frame. There was an article in Velonews recently on this. Based on this if the bike were disposable or inexpensive I'd be looking at narrow tube forks (the old Schwinn Continental and similar steel forks were super narrow). I'd use aero seat posts, aero top bars (meaning the tubing is flattened out), etc. If building a frame you can get narrow aluminum tubing or you can mold something from carbon.

Once up to speed (since it's human assisted you can use some power there) a heavier wheel is easier to keep going, at least for an imperfect motor like a human's legs.

Speaking of human's legs, Specialized has wind tunnel data to show that shaved legs save a substantial amount of drag, to the tune of about a minute over a 40km distance. Facial hair is not as significant. Pony tails I think are inefficient as well.

Aero wheels, whether carbon or carbon/aluminum, clinchers or tubulars, typically have a crosswind advantage, up to a point, their "stall point". That's where aero benefits drop off dramatically. In a direct headwind aero wheels aren't that helpful, it's in a slight crosswind that they're the best. Go to HED's site and look at their aero charts.
HED Cycling - Tech.asp*
Also if you select a wheel click on the aero data tab, it gives you a good visual on stall angles.

Having ridden an electric bike a bit I know just how powerful the motors can be. If that's the case then speed will be pretty high which means that aerodynamics is absolutely the most important limiter as far as the "bike" is concerned. Efficient motor, powerful batteries, proper energy management, etc will play an enormous role as well.

koiboy4343

we have tested our bike in a wind tunnel against a cannondale slice and the drag coeficient difference is somthing like .05 which is almost nothing according to the technition, and definitly not worth spending upwards of an extra 5K to get a .05 drag difference. so we are focusing on ways to change aero proportys (clinchers and aero bars) without spending stupid amounts of money for a barely noticeable change.

this research:
https://www.altairhyperworks.com/html...431_MNGodo.pdf
showes that maximum eficiancy happenes at a yaw of around 12 degrees and then drops sharply from there on wheels with the carbon clinchers only.

shaveing legs: 5 seconds difference on a 40K not 1:30.
https://www.sheldonbrown.com/rinard/a...rodynamics.htm
.

also you would be suprised at how much efficiancy is lost due to hubs. besides wind resistance that is the largest loss of eficiancy from the whole bike.

koiboy4343

****, let me clarify

when i said clinchers i ment carbon clinchers like here

https://www.wigglestatic.com/product-...800&h=1800&a=7


when i said "regular" wheels i ment this kind (smaller side profile):

https://www.mountainbikebitz.com/imag...135mm_rear.jpg

also,aero helmets,suits have already been purchased.

carpediemracing 

It might be that your English isn't allowing you to express yourself clearly, but "carbon clinchers" covers such a wide assortment of wheels that it's impossible to generalize that they drop off at 12 degrees of yaw. For example, if you go here and click on aero data, you'll see the drag reduces well beyond 12 degrees yaw. I understand the company has a vested interest in showing their wheels help but you'll find that although the exact values may be off here and there the general trends will still be there.

A recent wind tunnel test by Specialized. They have a distinct interest in showing that buying their equipment is best but in this case they found that a very simple act will give a bigger benefit than buying some of their equipment. I can't tell you how their testing protocol differs from other tests, like the one you cited (which I have seen before as it was significant when it first came out).
https://www.youtube.com/watch?v=DZnrE17Jg3I

I'm not trying to give you a hard time, I want to help. I think that this is a really interesting challenge and pertinent to my own transportation thoughts/needs/wants.

gsa103

As someone with a background in physics, I'm curious about the solar aspect of this. Considering the small panel area, it seems like you'd be challenged to generate more than about 20-30W of solar power while pedaling. With that power, one has to question if you would be faster by dropping all the solar equipment and running purely human powered, since you wouldn't have the weight and drag of the panels.

Solar powered vehicles are a different story, because the cross-section is significantly smaller and the panel area is huge (several m^2).

wphamilton

Yes, you want the best position possible to reduce drag.

A suggestion, I haven't tested it but I believe that a small fairing built around the aerobars and extending at least as far back as the handlebar would have a significant drag reduction. There would be some issue with restricting your control, so careful testing - or designing in a flex - would be necessary.

Full length fairing is your best bet, even with the diamond frame geometry.

drawbacks: Solar powered vehicles seem to all be ultra-light. So the choice of bike, components, wheels and accessories including the aerobars will need attention with respect to weight as well as aerodynamics. And will be expensive.

TrojanHorse

How on earth are you going to be going 25-35 mph? You can't be generating THAT much power from a tiny solar cell.

koiboy4343

the bikes are solar assisted not 100% solar. the race is several hundred miles or so but we train to be able to do century's on normal bikes.

as for the pannels, they are located behind the rider in the low pressure zone created by the riders body which lets us generate more energy than we lose from the weight and aero propertys of the pannels and other equipment.

and the pannels arent too tiny, but they arent huge either.

wphamilton

Just a suggestion, if you build the panels (flexible solar) on something like this

then there won't be any aerodynamic penalty. to give you an scale and position, the vertical edge is around the seat post, and the slanting front edge is attached to the seat stay on both sides. Extend it as far back as the farthest point on the wheel.

If on the other hand you just hang some vertical panels back there behind the rider, you will have an aerodynamic penalty and you'll also have some issue in windy conditions.

koiboy4343

Thank you very much! I will relay this to the team leader. our array is already somewhat aero, but I like your suggestion.

https://plus.google.com/photos/115750549596716615765/albums/5774465054888834337/5774466639766842562?banner=pwa&authkey=CI6465aLhe20FA&pid=5774466639766842562&oid=115750549596716615765

TrojanHorse

Your picture is private, can't see it.

So how many watts of assist do you get out of your solar/battery motor? Do you get to start with a fully charged battery or is that something that has to be charged as you ride? I imagine that flat panel will be a bit of an issue in side winds or swirling winds but I guess you've probably tested it plenty so far.

GhostSS

You know what's funny? I work for an electrical engineering design/build company that does a lot of photovoltaic installation and I love bikes, but I never thought that combining the two was a thing. I thought all solar bikes were velomobiles.

When using aerobars the first thing that has to change is your layback positioning. You have to consider the type of setback on your seatpost and the layback of the saddle in order to get the right position on full aerobars. This setup is entirely different from a typical roadbike setup and can prevent effective climbing when out of the saddle due to the proximity of your legs to the handlebars for some people.

What kind of terrain will you be cycling on? I suppose if everything is mostly flat with few turns aerobars on a solar assisted bike with have no disadvantages.

Vertical solar panels are nearly useless in terms of wattage per hour efficiency as well.