Now here is a subject that has never been discussed on this forum. try doing a search on the subject you will get a lot of hits.



By the way, Zipp rules.

"Zipp rules. "

Kraig Willet tested a Zipp disc against a CH Aero cover in a wind tunnel. The results are available on his pay site for a few dollars. Makes an interesting read.

http://www.biketechreview.com/tunnel_main.htm

Dave, I have owned both. The Zipp is very nice, but my major problem with it is brake howl on the carbon surface. The Renn has an aluminum surface.

The aero disc covers are better than nothing, but a Renn is better than the covers. In terms of aerodynamics, they work the same.

I thought I remember John Cobb saying somewhere that a disc is a disc and the differences were minimal. Anyone
recall that?

If the Zipp was a REALLY good deal, that might be hard to pass up, since you might sell it for what you paid.

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_________________
Dick

Take everything I say with a grain of salt. I know nothing.

"Anyone
recall that? "

Are you sure it wasn't one of my 9567 previous posts on the subject?

In terms of aeroness a disc is a disc is a disc. The only advantage which is very slight is lenticular vs flat. In terms of quality, lightness and bragging rights then do definately go with the Zipp. Just don't think you'll be any faster.

Sorry, I knew it was someone.
When I get better I'm going for a Renn tubie.

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_________________
Dick

Take everything I say with a grain of salt. I know nothing.

Ya know I think you are so well rehearsed with the ch aero cover / disc debate that you should have lobbyist credentials.

I bought one and can tell a big difference, even going uphill.

My only concerns with the covers are:

1) slight rubbing from the chain in the biggest sprocket.

2) They only fit plain box rims.

3) Slightly anxious about something coming loose or breaking in a race.

But there is definitely an improvment in aerodynamics.

Actually, I made the covers work on my Bontrager aero rims. You have to cut the outside lip off and then attach the discs with lots of electrical tape. However, the result is a actually a much cleaner transition than what you get with a box rim.



-- Jens

If aerodynamically they are both the same why is the Renn better?

I like my Renn Disc so much that at after the first few months of use I called the guy (isn't his name Frank) and asked if he would sell me the business. Frank politely passed on my offer... damn! True story.

Ron

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Is it a wash?

No, the Zipp is lighter. period.

The Renn is a GREAT bargain....but if money isn't an issue, get the Zipp.

Here's the plan see...buy the Zipp at the super deal...sell it off for more than you paid for it..then buy a Renn..spend the extra money on something else..like an aero front wheel..sold

"I bought one and can tell a big difference, even going uphill."

A big difference in what? Not speed. Read Kraig Willet's and Jim Martin's articles that I posted. Both the aero issues and the difference a half lb in weight will make is covered.

I won't argue that there may be aesthetic or quality differences in a "real" disc, but there is absolutely no performance advantages - none whatsoever.

Like I said, the cover/wheel is about 600g heavier that a 909.

That said, the RENN is such a deal that it is hard to pass on.

I haven't read the article....but perhaps you can enlighten me about what they say about uphill weight? I can understand that "aerodynamics" aren't effected...but surely rotation weight is.

If it's moot, I'm selling my 909s and going back to box rims.

I should clarify...

"one" = ch aero cover.

I heeded your aero cover evangelism!

I think the aero cover is a fine alternative to the disc. The aerodynamic improvements were noticeable to me right away. I was suprised to notice the improved aerodynamics going uphill.

If I could spend the money on the 909 without any compunction I would, but for now that would make me the equivalent of the guy who lives in a shack and drives a Ferrari.

Oh wait a minute, I am already the guy who's triathlon bike has a higher resale value than my car!

My bad.

it's moot. aero trumps weight for anything short of a 100% uphill TT at Alpe d'Huez grades. rotation weight meaningless for anyone other than trackies, crit specialists and other anal-retentive roadies. read it all here: http://www.rickdenney.com/october_1999.htm



Carl - Renn devotee, but also in possession of several pairs of the pre-CH Aero soft wheel covers by UNI-Disc.

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Carl Matson

Hello,

My how I hated Uni Disk covers. While I'm sure that they were better than spoked wheels they would never seal tightly to the rim. Plus I hated installing them.

I agree that CH aero covers are a good alternative, but I still think that a disk is slightly better due to a better disk rim interface.



Styrrell

Assumming your statement is true (which I would argue)....

The part that you are missing is that if both wheels had the same aerodynamic properties...the lighter wheel would be faster b/c of less resistence (gravity).

Congrats to Zipp.

Yes, if :09 or :20 up Alpe d'Huez is important to you, pay the extra $$$ for the high zoot disk wheel. Will you notice the difference on any triathlon (or non-hill climb TT) you are ever likely to do? No.

Do you own a disk? Which kind?

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"Go yell at an M&M"

I agree with the assessment up a steady climb, but the articles I have read always discount accelerating a heavier wheel as unimportant. They say you only do it once at the beginning.

Realistically looking at IM Wis ypu are constantly climbing, desending or turning. I suspect that the total climbing is on the order of L'Alpe L'Huez or even more, and I suspect that the averge age grouper is accelerating 5 -10 mph dozens of time. If I were to estimate the time savings for a light disk vs a heavy disk I would say 1 - 2 minutes for an IM.

Now is that worth the $. To me no, but IMH isn't a priority (even if I was to qualify I would go). To someone who has a lifelong dream to qualify and gave up sportscar racing or the yacht to do IM seriously, why not?

As a disclaimer, I bought a used zipp with outdated threading and had it converted to 9 speed cassette at a cost much less than even a Renn so i got the best of both worlds.



Styrrell

you are correct. I maintain that the effects are negligible for tri purposes. focusing on the weight delta between the disks rather than considering the bike&rider system as a whole is silly. I suspect also, tho I won't take the time to prove it right now, that even if the scant ounces of weight difference between the two are truly that important, there are cheaper ways to get the same benefit. CH-Aero's on a Mavic Helium (or equivalent) come to mind...

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Carl Matson