DIY aero/stealth disc skinning a rear hub wheel..

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DIY aero/stealth disc skinning a rear hub wheel..

Postby vanilla ice » Sun Jun 28, 2009 2:31 am

I know the polo guys do cheap rough-looking DIY disc wheels for protection, but I was thinking something halfway between that and the fancy aero wheels would be neat. Not a $1 budget, but not a $1000 budget either.. anything in between really. I remember seeing some relatively affordable "CH aero" commercial covers, but I guess those are gone. I even saw a guy on YT that did a duct tape version.. Anyway, ideas on which methods/materials/sources would work out?

The large hubs actually make things easier, half the spoke area to cover, no sprocket removal.. I was figuring drill and tap the rim and hub for some small machine screws. Maybe even tape or spoke ties? Not certain what kind of plastic to use.
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Re: DIY aero/stealth disc skinning a rear hub wheel..

Postby TylerDurden » Sun Jun 28, 2009 7:51 am

Coroplast is cheap and comes in lots of colors.

.25" x 48"x96" ~$20 at your local sign shop or plastics supplier.
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Re: DIY aero/stealth disc skinning a rear hub wheel..

Postby John in CR » Sun Jun 28, 2009 8:48 am

By stealth I hope you don't mean to cover the motor too, because that will cause a serious heat issue, since the hub needs as much exposure to airflow as possible.

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Re: DIY aero/stealth disc skinning a rear hub wheel..

Postby Drunkskunk » Sun Jun 28, 2009 8:51 am

Monocote, like they use for RC plane wings. its cheep and light weight.
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Re: DIY aero/stealth disc skinning a rear hub wheel..

Postby TylerDurden » Sun Jun 28, 2009 9:03 am

Q: How thick is monokote?

(couldn't find spec.)
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Re: DIY aero/stealth disc skinning a rear hub wheel..

Postby spinningmagnets » Sun Jun 28, 2009 9:20 am

Whatever method and materials you choose, John brings up a good point about heat. But I think its possible to make your aero-disc a positive. Imagine that you've covered not only the spokes, but the motor sides too, but you've also left a co-axial small space open near the axle and also at the rim. Then you add several radial vanes attached to the spokes.

This would mimic the shape of a cars ventilated front brake disc. Air trapped inbetween the discs and vane-chambers is flung outwards. As air exits around the rim, air is then drawn in from the small opening near the hub. The aero-disc would be suspended 1/4" away from the hub sides.

Normally the powered hub rides in turbulent air, I believe its possible for your aero-covers to flow more air across the hub sides per foot travelled than a naked hub. I like this idea of yours as I am a fan of stealth for E-bikes, and this may help with the occasional elusive "hub-cooling" ideas. The air is free all around us, we should use it. It clearly works well for a cars front disc brakes. I realize it may not help a LOT, but it couldn't hurt...

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Re: DIY aero/stealth disc skinning a rear hub wheel..

Postby dogman dan » Sun Jun 28, 2009 9:47 am

Mabye a disk could be made that only covered 3/4 of the diameter of the spokes, hiding the motor, but allowing the cooling. Would lose all the aero advantages though, if that is what you are after. I say screw aero, just pack a few more ah of battery. For me comfort is king at my age. If aero is what you are after, maybe cover the spokes but leave the motor exposed.
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Re: DIY aero/stealth disc skinning a rear hub wheel..

Postby Drunkskunk » Sun Jun 28, 2009 9:49 am

TylerDurden wrote:Q: How thick is monokote?

(couldn't find spec.)

Before it's been heat shrunk, its about 1/3 to 1/4 the thickness of printer paper. its a little thinner but stronger after being heat shrunk.
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Re: DIY aero/stealth disc skinning a rear hub wheel..

Postby vanilla ice » Mon Jun 29, 2009 12:24 pm

I would start the plastic disc as close to the edge of the hub motor as possible for cooling, and also to make things easier for clearance. Drilled hub holes would still be exposed, should cool better than a stock unholed motor even with the disc reducing surface/air area. More worried about how to attach the plastic to the rim. Attachment to the flat hub surface is easier. As far the centrifugal venting goes, you gotsta have a vent for the valve stem anyway, you could balance it out with another one opposite. Not sure what that would do with the air flow.

I remember seeing a dual wheel-disc hub-motor black cruiser posted here a while back.. that thing looked so cool. So if anybody gives this a try, they wouldn't be the first.

Polo cover..
http://www.youtube.com/watch?v=IfoAJicjNJc

Duct tape..
http://www.youtube.com/watch?v=DwJh8Fte4Lw
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Re: DIY aero/stealth disc skinning a rear hub wheel..

Postby urace4me2 » Mon Jun 29, 2009 1:58 pm

I have three of those CH aero covers. Used them many years ago in Time Trials. Now I have a Zipp disk. They would work but the speed gain would be less than 1/2 mph. The big speed jump for aero stuff is:

1 - body position (aero handlebars) 2 mph
2 - front wheel 1/2 mph
3 - rear wheel 1/4 mph
4 - aero helmet 1/4 mph
5 - aero frame 1/10 mph

These are approximate but are close enough to rank your efforts to speed up.

The rear wheel spoke cover would make the bike stealthier looking and may spoof the fuz but it won't give you much extra speed.
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Re: DIY aero/stealth disc skinning a rear hub wheel..

Postby liveforphysics » Mon Jun 29, 2009 2:09 pm

Drunkskunk wrote:
TylerDurden wrote:Q: How thick is monokote?

(couldn't find spec.)

Before it's been heat shrunk, its about 1/3 to 1/4 the thickness of printer paper. its a little thinner but stronger after being heat shrunk.



It gets thicker as it shrinks. It's pleanty strong enough to do a wheel if you could do a neat job and not leave stress risers to start tears. It's pretty tough stuff considering how light it is.
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Re: DIY aero/stealth disc skinning a rear hub wheel..

Postby vanilla ice » Mon Jun 29, 2009 2:54 pm

urace4me2 wrote: They would work but the speed gain would be less than 1/2 mph.


1/2mph at what speed? That can be a good amount of watts saved depending. I admit I'm mostly thinking about looks, but might be worth it just for the watts saved. The faster you go, the more it matters right?
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Re: DIY aero/stealth disc skinning a rear hub wheel..

Postby liveforphysics » Mon Jun 29, 2009 3:03 pm

It matters at the square of speed.
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Re: DIY aero/stealth disc skinning a rear hub wheel..

Postby vanilla ice » Mon Jun 29, 2009 3:16 pm

Right, so if he's saying 1/2mph at 20mph, then at 35mph its a 1.5+mph gain..

Or looked at another way- All of the benefit of a goofy aero helmet, minus the goofiness!
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Re: DIY aero/stealth disc skinning a rear hub wheel..

Postby JS Tyro » Mon Jun 29, 2009 11:56 pm

More like:

new max speed = old max speed + 1/2 mph

Power (watts) will vary with speed cubed, force (and therefore energy) by speed squared - once you've got to the point where almost all extra power/energy goes into fighting air resistance. This is more-or-less over 30 kph (20 mph) give or take. That's why at racing speeds, aerodynamic drag is the big equalizer and you see athletes with relatively large differences in VO2 max showing relatively small differences in speed - VO2 max can be considered a rough measure of power output potential in athletes. Or why wheel sucking (drafting) is so important.
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Re: DIY aero/stealth disc skinning a rear hub wheel..

Postby needWheels » Tue Jun 30, 2009 3:51 am

Halfway strong side winds will knock you over with aero wheels.
Also, nothing draws more attention than an aero wheel on a bike, do you really want more attention or less?
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Re: DIY aero/stealth disc skinning a rear hub wheel..

Postby urace4me2 » Tue Jun 30, 2009 6:27 am

vanilla ice wrote:Right, so if he's saying 1/2mph at 20mph, then at 35mph its a 1.5+mph gain..

Or looked at another way- All of the benefit of a goofy aero helmet, minus the goofiness!


1/4 mph at 29 mph on a real race bike. About 30 seconds on time over a 25 mile course. But that is a full disk not one just covering the short 6 to 8 inch spokes on an e-bike with 26 inch wheels and a huge hub.

Also the weight of that rear wheel will keep you pretty steady in a cross wind. Little people get blown around a little with a disk but big guys or (heavy bikes) hardly notice they are there.

You'll definately save a few watts but for most it won't be enough to be worth the effort unless they like the looks.

Observed tests this May:
I practiced on my TT bike on our state championship course and did 10 and 15 miles test runs for weeks before the event. I used TT bike with regular helmets and regular wheels and average speed was 26 and change. Race day we had much cooler temps and I had skinsuit, aero helmet, $3,000 Zipp disk and deep 1080 front wheel, 160 psi in the tires, tapered my training for the last week and I averaged 27.7. So all that stuff got me less than 1.7 mph. Biggest contributer was training taper and cooler temps, they probably gave me 1 mph. So maybe 0.7 for helmet, suit and wheels? Front aero wheels yield about twice the advantage as rear says other experts. 0.7 mph is huge in a race because it means about 45 seconds over the 25 mile course. Difference between winning and second that day was 30 seconds, but in past I have lost a race by 1 second.

Hope this helps.
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Re: DIY aero/stealth disc skinning a rear hub wheel..

Postby vanilla ice » Tue Jun 30, 2009 10:48 am

Appreciate the solid numbers, have no experience with that type of thing!
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