Use a power Tap or disk wheel - Page 4

Sure, but he asked if you had any idea how much. In other words, have you done any research to support your ideas, or are you just shooting from the hip? Here's a document right on the Zipp site with the values you need: http://www.zipp.com/tech/documents/A...rviewData2.pdf

The 808s are nearly identical to a disk for any wind angle less than 20-deg off axis, and even then the power difference is miniscule between the two at 30mph. Tell me that you couldn't do better than that through proper pacing.

And the wind vector would, I believe, be calculated relative to bike speed rather than a stationary point, so even a straight crosswind would be at a low angle if you were travelling fast relative to the windspeed. Is that correct aero junkies?

Since you're not afraid to go on the attack, neither will I be. Don't get me wrong, this is an interesting discussion and I don't really want to put you offside.

It's not rough to say 'either it works or it doesn't' - it's wrong. Because we can't observe your pacing ability noone can definitively say that a powermeter will save time. But, I would say that with very high probability having a PM (and learning how to use it) will save a substantial chunk of time. I would also say that with a probability of 1 you will save a small amount of time on a disc over an 808 or a 404 on a flattish course.

It all boils down to this:

Choose between these two options:
(i) I'll give you a dollar, pr=1 (I'll definitely give it to you)
(ii) I'll give you $5, pr=0.5 (say I toss a coin to decide whether I give it to you...)

I can't definitively say you will have more than you began with if you choose option (ii). I can definitively say you will have more than you began with if you choose option (i). However, unless you could buy everything you ever wanted for $1, I think it would be very silly to choose anything other than option (ii).

You seem to want someone to say that a powermeter will absolutely and definitely make a difference or you won't choose it - noone will because it's probabilistic, not absolute. If we follow your logic through, I'm $1.50 richer than you and I win more bike races (controlling for genetic potential).

Obviously the example is stylised and I'm not quite as confident about discs versus PM's as I am about my silly, stylised example. However, I tend to think that the Powermeter is going to be the better choice. I'll take a high probability of a large gain over a 100% probability of a fractional gain anyday.

Yes, I believe that's the case. For a 30mph wind at a relative wind angle of 20-deg or more, you'd need a 10mph straight crosswind.

Roadie_scum is on the right track here and I'd like to extend the discussion. Attributes that will or have the potential of reducing elapsed time in a TT are either certain or uncertain. An example of a certain attribute is a disc wheel versus another wheel. It is certain because the aero characteristics are known and about the only uncertainties are speed and wind (direction and velocity). Basically all equipment would fall into the certain category (frame, helmet, shoes, skinsuit, etc.). Another category of attributes are uncertain in value (time reduction) but not necessarily of less potential value. To assess the value of an uncertain attribute with a virtually unlimited range of outcomes such as pacing with a PM, one must find a way of simplifying the question. In this particular case, I'll posit a simplifying question. The purpose of using a PM in a TT would be to pace oneself better than one can pace oneself without the PM. The net effect of ineffective pacing is that one's NP is less than could have been obtained with more effective pacing. IOW, you finish the ride with an NP of X versus your potential NP of X+Y. So, I propose that the question can be reduced to the value of Y (watts) required to equal the value of the disc vs. the Zipp 808s. Care to speculate on the value of Y?

If i was riding a TT and worrying about power output/pacing and disc wheels i'd look at it like this.

1) if my PT was built into an Open Pro or similar box section wheel and it was a choice of this or a disc, i'd go with a disc without a second thought

2) if my PT was built into deep section carbon rim and it was a choice of this or a disc, i'd go with the PT/deep carbon. No questions asked. I've only been racing for 21 years, and even after this short period of time (having TTed at every distance up to 12-hr TTs), i'm not confident enough about my pacing and slacking off. For e.g., i can ride at my TTpower minus 20 to 30 W and it hurts me (i.e., RPE is the same) as much as riding at my TT power. Without a power meter i'd slack off, and i'd also overshoot (too high a power) at the beginning of the event.

If i'm not using a power meter i better make sure that the difference in aerodynamics is worth the difference in power or poor pacing.

One of the riders i coached had a PT built into a deep carbon rim. They also had a disc. Consistently, they went slower with the disc than the deep/PT for the reasons i posted above. Of course, ymmv, so, i'd suggest that you ride quite a few TTs with both wheels (different days) and see which is fastest for *you*.

Ric

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http://www.cyclecoach.com

I have a VP pacing strategy optimization model under construction. While it's still a bit clunky and requires some hand-holding, it is sufficiently far enough along to provide some insights to your questions. I still don't know how much time you think you will save with a disc versus your Zipp 808s, so I don't have anything to use for a net gain or loss. But, I can address a likely pacing scenario with and without a PM.

Comments from Ric, frenchyge and others plus my own experience suggests that a highly likely pacing scenario without a PM is to take it out too fast, drop back and then try to finish strong. I'm not set up yet to look at more than two segments, so I'll have to defer on that specific strategy. But, I have taken a look at a two-segment scenario of going out too hard (over one's FT) and then finishing at less than FT. My model is entirely based on NP, so one needs to first buy into the physiology assumptions embedded in NP. Specifically, I assumed that one has an FT of 300w, the course is a flat 40K TT and there is no wind. As to pacing, I have assumed that the cyclist rides at 325w for 15 minutes, then realizes his pacing error and backs off. Now, I have given this cyclist super-human powers and he chooses a fall-back pace that brings him across the finish line with an NP for the entire course exactly equal to his FT. IOW, after making his original pacing mistake, his pacing is absolutely perfect. That "perfect" pace turns out to be 289w by my calculations. The time difference of this scenario is 59:57 versus a constant power pacing strategy of 59:33, or 24 seconds slower (I know, you've already done better than this). Personally, I don't think I could execute this pacing strategy. I think I could take it out 25w too high for 15 minutes, but I don't think I could do the "perfect" NP pace from there to the finish. So, I think this is actually a best case scenario and that the more likely scenario would be slower than this.

Again, the time difference of using a PM for pacing will be different for every cylist and I have no idea how good you are at pacing without a PM. This analysis is more of a likely scenario for the typical cyclist than a specific analysis for you. I still say ride your disc because you believe in it.

let's see ... Robert has 404's, a set of 808's with PT, and a disk... quite the collection Maybe he's just a very clever troll?

rmur

Are Ergomo's thought of as too incurate (only left side power) to be suggested as a possible alternative that would let you race with a disk? I see the new Pro model will have better sampling rates. Or are they though of as to unreliebale

I am following the ergomo developments very closely, for this very reason. I think the concept of their approach is very interesting, but results to date have not been persuasive.

Isn't it the same bottom bracket/power meter as in the previous model, with just the computer head vastly changed?

ric

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http://www.cyclecoach.com

That is my understanding, which is why I continue to be only interested but not persuaded. Somebody told me that they have added NP to the computer display options. That's interesting, but I wouldn't trade it for accuracy and consistency in power measurement.

So I take it that the current version is neither accurate or or consistant? - If so is this info gain from owners that have had problems or are there any critical tests/reviews on it that I can read?

I don't claim to be an Ergomo expert. I don't own one and have never used one. I am simply following the progress of this PM. The best info on Ergomo is probably the topicA threads http://lists.topica.com/search/?quer...=msg&x=22&y=10.

Thanks - I will have a look there.