# Rear 'disc' cover - worth it?



## strat_man9 (Sep 17, 2007)

Hi all,

I'm a university student who does triathlons on the side (no professional aspirations here). I was wondering if putting one of those disc covers (like the CH or wheelbuilder ones) on my rear wheel is really worth the time, effort, and (minimal) cost. I've seen used carbon trispokes occasionally go on Ebay for ~$200, so how does a $60 wheel cover compare to waiting and getting my hands on a used rear trispoke?

To give you an idea of my current setup, I've got a softride TT classic with full ultegra, with all the usuals (cowhorns, bar-end shifters, etc) and 'aerohead pro' wheels (21mm rims). I know my wheels are currently my weak spot gear-wise, but being a university student, my wallet is my biggest weak spot. So the thought of spending under $100 for 'disc...ish' performance sounds good to me, if the covers do what they're supposed to. Oh yeah, and do they make any noise like regular discs do? I imagine not, but that would be cool :thumbsup:


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## ergott (Feb 26, 2006)

It actually helps a lot. It's cheap and snobs will look down on you, but don't fret. You saved a lot of money and get a pretty fast wheel.

-Eric


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## strat_man9 (Sep 17, 2007)

Cool, I'm glad to hear your opinion! I'm quite the newbie so I can understand the idea behind it, but had no idea if it actually made any difference. I don't care if it's ghetto, I'm a student who can't afford a disc wheel and I'm not ashamed to admit that.

Do you know if they make that crazy disc sound that heralds the hardcore bikers as they fly by me? :blush2:


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## ergott (Feb 26, 2006)

Not that I remember.

-Eric


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## estone2 (Sep 25, 2005)

strat_man9 said:


> Cool, I'm glad to hear your opinion! I'm quite the newbie so I can understand the idea behind it, but had no idea if it actually made any difference. I don't care if it's ghetto, I'm a student who can't afford a disc wheel and I'm not ashamed to admit that.
> 
> Do you know if they make that crazy disc sound that heralds the hardcore bikers as they fly by me? :blush2:


They aren't nearly as loud. But they're nearly as fast as a normal disk!
Much faster than a trispoke. And I actually find them to be more predictable than riding with a trispoke - riding with dual trispokes is downright terrifying, riding with a trispoke and a normal rear wheel is a bit weird, but riding with a trispoke and a disk is quite normal. The disk seems to actually have a calming effect on trispokes up front.

I would get a front trispoke and a rear wheel cover if I were you.


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## Kwantani (Sep 26, 2002)

The question you really need to ask is what kind of rim on the current rear wheel?
Disc wheel cover only works well on shallow rim or "flat" rim, the flatter the better. It'll be very awkward to attach to any aero deep dish rim, cause the cover's lip does not line up with the rim and you may end up not getting the aero effect. So if you want to use disc cover, make sure getting a non-aero rim rear wheel.


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## tanhalt (Nov 9, 2005)

Kwantani said:


> The question you really need to ask is what kind of rim on the current rear wheel?
> Disc wheel cover only works well on shallow rim or "flat" rim, the flatter the better. It'll be very awkward to attach to any aero deep dish rim, cause the cover's lip does not line up with the rim and you may end up not getting the aero effect. So if you want to use disc cover, make sure getting a non-aero rim rear wheel.


They can be trimmed to fit deeper section wheels. In fact, this guy will do it for you:

www.wheelbuilder.com

Some folks I know run them on rear Zipp 808 PT wheels. That setup actually measures to be lower drag than most any disc except for the brand new Zipp "bump" disc that apparently produces negative drag at 12-15 deg. of yaw.:thumbsup:


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## strat_man9 (Sep 17, 2007)

Kwantani,
I have 650c wheels, so the CH won't fit in any case. The one at www.wheelbuilder.com has an option for them to custom-trim the cover for your rims, and since they sell velocity aeroheads, I'm sure they can cut one that fits. Hell, here's a picture of one of their covers fitted to a 404 with a power tap! https://www.wheelbuilder.com/images/PowerDisc.jpg 
Edit: Tanhalt beat me to it!

I had no idea that a cover could be faster than a trispoke (but heavier I believe). And estone2, thanks for your input! I never thought about how different types of wheels would interact handling-wise. I'll probably start with the cover, and if a killer front trispoke deal happens to come my way when I have the cash to spare, I just might pick it up.


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## kbiker3111 (Nov 7, 2006)

Um, if you're super ghetto, you could do it yourself? Its really easy with PVC plastic, glue and some scissors. http://www.recumbents.com/home.asp


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## thelivo (May 14, 2007)

tanhalt said:


> They can be trimmed to fit deeper section wheels. In fact, this guy will do it for you:
> 
> www.wheelbuilder.com
> 
> Some folks I know run them on rear Zipp 808 PT wheels. That setup actually measures to be lower drag than most any disc except for the brand new Zipp "bump" disc that apparently produces negative drag at 12-15 deg. of yaw.:thumbsup:



I heard about this - i will check out the website later but did Zipp somehow inadvertently invent a perpetual motion machine?


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## estone2 (Sep 25, 2005)

The question is if that would actually be any more aero...


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## tanhalt (Nov 9, 2005)

thelivo said:


> I heard about this - i will check out the website later but did Zipp somehow inadvertently invent a perpetual motion machine?


Nope. The bike and rider still generate a drag force in the direction of travel. The disc just generates enough "lift" that the component of the lift force in the direction of travel is greater than the component of the drag force in that direction...but it is nowhere near enough force to overcome ALL of the other drag forces in that direction.

You still have to pedal


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## RHRoop (Nov 1, 2006)

*Just got Aero Covers*

I just got some Aero covers and I am quite pleased with the result.

I had to get a Mavic Open Pro rim as the rim I intended to use seemed a bit to tall to get the ideal fit. That set me back an additional $125 (thanks to my sponsor discount) but still hundreds short of an actual built to purpose disc.

If you are concerned about looks from gear snobs don't be. They won't be able to tell that you spend hundreds less when you pass them. They look the same at speed.

All that said, the success I had with the wheel has only encouraged my evil twin to start plotting on how to get a Zipp 909.


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## Keeping up with Junior (Feb 27, 2003)

*Rules?*

You might read the rules and determine if they are going to be enforced at your event. IIRC you cannot use covers in a USCF time trial, but that was a few years ago. Not sure what the Tri sanctioning body has to say.


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## tanhalt (Nov 9, 2005)

Keeping up with Junior said:


> You might read the rules and determine if they are going to be enforced at your event. IIRC you cannot use covers in a USCF time trial, but that was a few years ago. Not sure what the Tri sanctioning body has to say.


Not true. For the vast majority of USCF TTs, except for NRC races and Nationals, using a wheelcover is just fine. In fact, for any USCF TT that isn't under UCI auspices, pretty much anything short of a recumbent is OK. Here's the relevant rule out of the 2007 USA Cycling rule book about when UCI regs are required:


> 1J1(e) Bicycles must meet current UCI technical
> regulations at events that select 17-18, U23 and elite
> riders for international competition or national
> teams. As of January 1, 2008, all bicycles used in
> ...


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## azdroptop (Jun 6, 2006)

The question for me would be is the 60 bucks worth the small amount of time gain you will get with the cover. It might be worth it over 100 miles, but for a shorter distance tri I doubt it.


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