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

agreed on the UNI's in general...tho I only hated installing the original non-stretch nylon versions. the later lycra style didn't require you to pop the freewheel off.



with a moderately deep section rim and CH-Aero's you just need tape (like someone else already said) and voila the interface at the rim is really no different than a disk.



as for the hills at IM-W (a course I've ridden in training but not on raceday) I seriously doubt that there's all that much rider-caused acceleration going on. what does Slowman preach? constant power output...shifting as needed for climate and terrain, but keeping that wattage steady, right? are you trying to tell me that at the top of a climb you're going to actually stomp on the pedals (i.e. accelerate) into the following downhill rather than letting gravity do the work for you? you're going to stomp on the pedals out of every turn like the crit maniacs? those kinds of accelerations are where it makes a difference. besides, even if you DO do that, you're accelerating a system (bike + rider), not just a wheel. the former takes a lot of effort...the latter is a very very small part of it, and the difference between two disc wheel weights is very very much smaller even than that. acceleration is not the player everyone thinks it is, and especially not on a component by component basis.



1-2 min for disk weight deltas in an IM, eh? Whether that's just for the bike, or for cumulative effects (bike split plus run deltas brought on by excess or lack of energy attributable to disk weight deltas) I'm guessing that the well-documented Murphy's Law effects for all the other race variables make that 1-2min almost meaningless. How many other things can cause a difference of 1-2min...or more?

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Carl Matson

Just a guess, but given the time you could probably use analyticalcycling to do 200m starts with different weights. Unfortunately analytical cycling is only as accurate as the info you have. Not knowing the moi of a Renn or a Zipp or the speed coming out of a turn, or the number or turns on a specific course, etc a guess is about all you get.

Just out of curiousity, for say, IM Wisconsin with two identical disk wheels except for a 1/2 pound weight difference what do you estimate for a time difference?

Styrrell

Hello,

I take it that you don't ride with a powermeter. No matter how hard you try to ride at a steady 200 watts you will have hugh power variations, but that isn't my point. Even if you could keep power at exactly 200 watts you would still be accelerating and decelerating up and down hill, around corners, and with wind changes. A lighter wheel will accelerate faster, thereby saving you time. Aside from that every pedal stroke is a tiny series of powerpulses. I doubt that this is a big loss of power, but it is some.

Secondly my estimate (and it is just a guess), is for the the bike time savings or a 1/2 pound lighter disk vs a heavier disk. Again 1 -2 minutes isn't a lot, but by the time you add all the little ways you can save seconds in a tri they make a difference.

Styrrell

other than a couple VO2max tests where the resistance steps were based on wattage jumps, no, I don't. is your power measurement at the hub or the crank? if the latter, you could set up on a stationary trainer with your Zipp and a borrowed Renn (hey, maybe I'll volunteer mine) with some measured weight delta, pop in your favorite rolling computrainer course, and record the power data. then you can wow me with the huge (or not) differences in total power applied or time lost/saved for the same ride with different disc weights.



even then, this only isolates a mass difference between wheels. bike plus rider is on the order of 175lbs. I'm just not buying that accelerating 175.5lbs (a difference of 0.3%) adds up to anything meaningful, because the # and magnitude of the accelerations is so small. even for 112mi. RAAM...maybe.



here are a couple of questions: what is the actual magnitude of these "huge" acceleration-based power variations you've seen and how much delta speed do they result in? flat, uphill, down, corners? if you're accelerating every time like a roadie chasing a break then yes, I'll buy everything you're saying. anything short of that, nope...not until I see some #'s.



seriously, I'd like to learn something here...I'm not trying to argue for argument's sake.

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Carl Matson

I've got a Renn. It works just fine. Props to Frank for building a great wheel, but the decals leave something to be desired.

Carl Replied

other than a couple VO2max tests where the resistance steps were based on wattage jumps, no, I don't. is your power measurement at the hub or the crank? if the latter, you could set up on a stationary trainer with your Zipp and a borrowed Renn (hey, maybe I'll volunteer mine) with some measured weight delta, pop in your favorite rolling computrainer course, and record the power data. then you can wow me with the huge (or not) differences in total power applied or time lost/saved for the same ride with different disc weights.

Actually I would love to see more testing like this, but I don't have a computrainer and I live in Mich. I suspect we will see more testing as Allen Lim and others do more cycling specific research.



even then, this only isolates a mass difference between wheels. bike plus rider is on the order of 175lbs. I'm just not buying that accelerating 175.5lbs (a difference of 0.3%) adds up to anything meaningful

Define meaningful, my estimate was for 1 - 2 minutes over a hilly course for two identical wheels with a 1/2 pound weight difference over a hilly 112 mile ride.

because the # and magnitude of the accelerations is so small. even for 112mi. RAAM...maybe.

Again define your terms. For a hilly, technical IM course (wisconsin was my example) I am will to bet that their are at least 100 accelerations of 5mph or greater and maybe a thousand of 0.5 to 1 mph. See Gordon Bryns website for his power data for the most recent IM canada. He was trying to keep power relatively steady.


here are a couple of questions: what is the actual magnitude of these "huge" acceleration-based power variations you've seen and how much delta speed do they result in? flat, uphill, down, corners? if you're accelerating every time like a roadie chasing a break then yes, I'll buy everything you're saying. anything short of that, nope...not until I see some #'s.


Again if you accept analyticalcycling calculations the difference just due to weight up the climbs is about 20 to 30 seconds. That leaves 30 -40 seconds due to the difference in acceleration between the wheels according to my lowest estimate. I never called this "huge". They actually wouldn't increase you speed at all, just your time to get up to speed, and therefore lower your total time.

Styrrell

analyticcycling.com has some worksheets that allow you to compare effect on acceleration due to varying wheel weights (and moments of inertia), such as "Criterium Corner", which takes the example of coming out of a corner in a crit and accelerating with some large wattage; you then can see the effect of the different weights. Plugging in a rear wheel that is 1/2 lb heavier, but the same drag, and an average power of 250W and max power of 400W held for 2 seconds out of that turn (probably more than you'll be doing in an IM) results in a loss of .02m over 15 seconds for that corner. Given 100 of these, you'd lose 2 meters over your 112 mile bike leg. Given 1,000 of these, you'd lose 20m, or about 2-3 seconds due to acceleration of the heavier wheel.

Looking at the course profile, I'd roughly estimate about 700m of climbing overall. If I estimate that this averages around 4%, that gives 17.5km of climbing. The loss due to climbing with a wheel that is 1/2 lb heavier is about 5-6 seconds.

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"Go yell at an M&M"

Not trying to hijack your math (I'm enjoying it as I'm not an engineer type), but would it be accurate to say that you would ride a disc in virtually course?

(as many say discs are not for hilly courses)

In my case, I'll ride my disc no matter what....rode it at Moo & Placid...

Assuming you meant "on virtually any course", absolutely. There's a hill TT here in NJ that is about 1100' of climbing in about 5.5miles, and one of the top Cat 2s did it with his disk last year. I have a 52 mile loop that climbs about 6600' in lots of short, steep hills, and my PR on the course (all of 15.8mph) was with my PowerTap rear wheel with homemade cover (versus my AC 350, which might weigh 800g less).

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"Go yell at an M&M"

I have both. I prefer the Zipp because of the big clicking noise that comes from the hub when I come struttin' my stuff walking my through the transition area with my bike. It's a real attention getter and anything I can do to draw attention to myself is always a good thing. Also, the 'swoosh' sound that comes from the wheel is far more pronounced than the Renn....other racers actually turn around to look as if to say; 'what's that, is it a thunderstorm?' No, it's just Mojozenmaster, happy to distract you as you slow down to watch the freight train roll on by.

On the other hand the Renn is cool to put stickers on; Flames, skulls, bullethole stickers, etc

No stickers on the Zipp though, I don't need the added weight.

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**All of these words finding themselves together were greatly astonished and delighted for assuredly, they had never met before**