Zipp PowerTap disk data differences

Jan 12, 09 17:30

Post #1 of 25 (5083 views)

I recently purchased a 900 Zipp disk with a powertap hub (wireless) for time trialing. I have been using a Zipp 404 or Mavic with a powertap SL (wired) with a wheel cover for 3 years and it has worked perfectly and have won many races including state championships.

I used the disk for the first time yesterday in a TT to get a threshold reading. I have done the TT for 3 years in a row and had the same normalized power each of those years (~375) with little difference in time. Yesterday, using the new disk, I had a normalized power number of 410 and a similar time as the previous years (and a lower HR). It would seem a 9.3% increase in power and a better HR would have equated to a significantly better time.

I am wondering if anyone has had any experience of higher wattage reading with the a wireless disk vs. a wired 404 or the like? I use a different powermeter for training and not sure how I am going to utilize my data? ??? Any thoughts or experience out there?

Re: Zipp PowerTap disk data differences [dgonyer] [ In reply to ]

Jan 12, 09 17:35

Post #2 of 25 (5074 views)

In Reply To:

I recently purchased a 900 Zipp disk with a powertap hub (wireless) for time trialing. I have been using a Zipp 404 or Mavic with a powertap SL (wired) with a wheel cover for 3 years and it has worked perfectly and have won many races including state championships.

I used the disk for the first time yesterday in a TT to get a threshold reading. I have done the TT for 3 years in a row and had the same normalized power each of those years (~375) with little difference in time. Yesterday, using the new disk, I had a normalized power number of 410 and a similar time as the previous years (and a lower HR). It would seem a 9.3% increase in power and a better HR would have equated to a significantly better time.

I am wondering if anyone has had any experience of higher wattage reading with the a wireless disk vs. a wired 404 or the like? I use a different powermeter for training and not sure how I am going to utilize my data? ??? Any thoughts or experience out there?

First, you should compare average powers, not normalized powers. Average power is what actually gets you down the road, normalized power is just an estimate of the "metabolic cost" of a variable effort in terms of a constant effort.

Second, have you statically checked the torque of either wheel? (i.e. a "stomp test")

Third, and just out of curiosity, but what PM do you use for training?

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Re: Zipp PowerTap disk data differences [Tom A.] [ In reply to ]

Jan 12, 09 19:20

Post #3 of 25 (5030 views)

Thanks for the ideas. In all my TT's avg power is almost exactly the same as normalized. It was true with this one compared to the previous years as well.

I have not tried a stomp test...what is that?

The PM I use for training is a PT as well.

Re: Zipp PowerTap disk data differences [dgonyer] [ In reply to ]

Jan 12, 09 19:35

Post #4 of 25 (5028 views)

Maybe the 404 with the disc cover was faster. I know I have seen stranger things happen.

Re: Zipp PowerTap disk data differences [trainhard] [ In reply to ]

Jan 12, 09 20:43

Post #5 of 25 (5001 views)

In Reply To:

Maybe the 404 with the disc cover was faster. I know I have seen stranger things happen.

Clearly I haven't been around this forum enough lately. There is absolutely no question that a 404 with a cover is faster. Why do you think Zipp started making their disks look like 404s with covers?

In fact I still maintain the combination of the lens-shaped covers and the 404 bump is still faster than the Sub 9. (You'll never get Zipp to admit this)

Last edited by: jens: Jan 12, 09 20:44

Re: Zipp PowerTap disk data differences [jens] [ In reply to ]

Jan 12, 09 21:02

Post #6 of 25 (4989 views)

The question I posed is not one of which is faster....it was why the discrepancy of wattage between the two meters.

Re: Zipp PowerTap disk data differences [dgonyer] [ In reply to ]

Jan 12, 09 21:14

Post #7 of 25 (4979 views)

No, but if you were riding a significantly slower wheel it would take more power to ride a similar time. Good news is if you are actually making more power you can switch back to the other wheel and go even faster.
Jens- ever test an 808 w/wheel cover vs. 404 w/wheel cover?

Re: Zipp PowerTap disk data differences [dgonyer] [ In reply to ]

Jan 12, 09 21:15

Post #8 of 25 (4979 views)

In Reply To:

The question I posed is not one of which is faster....it was why the discrepancy of wattage between the two meters.

Yes, and you pointed to the higher power but similar times as an indication of the discrepancy. I just answered that. There's no discrepancy: your power was probably higher, but your equipment was probably slower.

Of course, there are also all the other variables of barometric pressure, humidity, temperature, wind, etc.

To expand, as long as you zero a powertap, it's either completely on or it's way, way off (like by 100 watts). Doesn't matter if it's wireless or not.

My latest book: "Out of the Melting Pot, Into the Fire" is on sale on Amazon and at other online and local booksellers

Re: Zipp PowerTap disk data differences [bootsie_cat] [ In reply to ]

Jan 12, 09 21:19

Post #9 of 25 (4976 views)

In Reply To:

No, but if you were riding a significantly slower wheel it would take more power to ride a similar time. Good news is if you are actually making more power you can switch back to the other wheel and go even faster.
Jens- ever test an 808 w/wheel cover vs. 404 w/wheel cover?

I never tested them head-to-head -- they both beat other disks head - to -head. The 808 by a little more.

Re: Zipp PowerTap disk data differences [jens] [ In reply to ]

Jan 12, 09 21:24

Post #10 of 25 (4975 views)

I check underground weather for the 3 years and it was very similar. The pressure was a little higher because of a santa ana we had this weekend in so cal.

With regards to my power during yesterdays race...I am behind in my training this year and am not getting any younger at 45. I am not convince my power output increase by almost 10% especially this early in the season. Also, I don't believe the disk would be 10% slower v. the 404 and wheelbuilder wheel cover.

Re: Zipp PowerTap disk data differences [dgonyer] [ In reply to ]

Jan 12, 09 21:29

Post #11 of 25 (4973 views)

Anything else different about position or other equipment? Bike, helmet, skinsuit, front wheel, aero bars, etc.?
Similar heartrate values?
Were previous efforts maximum efforts?

Re: Zipp PowerTap disk data differences [dgonyer] [ In reply to ]

Jan 12, 09 21:32

Post #12 of 25 (4971 views)

Sorry, you already answered my heartrate questions.
Was the course exact same distance?

Re: Zipp PowerTap disk data differences [dgonyer] [ In reply to ]

Jan 12, 09 23:52

Post #13 of 25 (4953 views)

In Reply To:

I have not tried a stomp test...what is that?

http://www.midweekclub.ca/powerFAQ.htm#Q23

_________________________________________________________________________________
Training Plans -- Power Meter Hire -- SRM Sales Australia -- cyclecoach.com -- My Blog -- Sydney Turbo Studio

Re: Zipp PowerTap disk data differences [Alex Simmons] [ In reply to ]

Jan 13, 09 6:24

Post #14 of 25 (4899 views)

In Reply To:

http://www.midweekclub.ca/powerFAQ.htm#Q23

I've had difficulty getting consistent values when standing on the pedal. I always get much more repeatable results when I clamp the bike into a trainer and hang a known mass from the pedal. That power FAQ ought to be edited sometime.

Re: Zipp PowerTap disk data differences [dgonyer] [ In reply to ]

Jan 13, 09 7:37

Post #15 of 25 (4873 views)

In Reply To:

I recently purchased a 900 Zipp disk with a powertap hub (wireless) for time trialing. I have been using a Zipp 404 or Mavic with a powertap SL (wired) with a wheel cover for 3 years and it has worked perfectly and have won many races including state championships.

I used the disk for the first time yesterday in a TT to get a threshold reading. I have done the TT for 3 years in a row and had the same normalized power each of those years (~375) with little difference in time. Yesterday, using the new disk, I had a normalized power number of 410 and a similar time as the previous years (and a lower HR). It would seem a 9.3% increase in power and a better HR would have equated to a significantly better time.

I am wondering if anyone has had any experience of higher wattage reading with the a wireless disk vs. a wired 404 or the like? I use a different powermeter for training and not sure how I am going to utilize my data? ??? Any thoughts or experience out there?

The most likely culprit is not properly zeroing the PT before your race. Did the download file contain any periods of coasting just before or after the TT where you can check for non-zero torque?

Secondly, there *could* be some data spiking going on. Add on a few spikes to 2048 (or whatever the absolute max. wattage is) and your AP/NP could be inflated. Have you looked at the data closely?

Re: Zipp PowerTap disk data differences [dgonyer] [ In reply to ]

Jan 13, 09 7:47

Post #16 of 25 (4864 views)

My hunch is that there is a difference in the baseline torque...one was probably zeroed while the other one wasn't. The Cycleops Powertap manual explains how to do this. I use the same head unit between a couple of Powertaps and need to remember to zero it otherwise my watts will be off.

"Most of my heroes don't appear on no stamps"
Blog = http://extrememomentum.com|Photos = http://wheelgoodphotos.com

Re: Zipp PowerTap disk data differences [dgonyer] [ In reply to ]

Jan 13, 09 9:05

Post #17 of 25 (4833 views)

I have both a SLC and PT disc. I benchmarked them both against an SRM with basically identical results.

"Non est ad astra mollis e terris via." - Seneca | rappstar.com | FB - Rappstar Racing | IG - @jordanrapp

Re: Zipp PowerTap disk data differences [Rappstar] [ In reply to ]

Jan 13, 09 9:40

Post #18 of 25 (4816 views)

In Reply To:

I have both a SLC and PT disc. I benchmarked them both against an SRM with basically identical results.

When you say "benchmarked," what do you mean? Did you make CdA estimates?

Re: Zipp PowerTap disk data differences [dgonyer] [ In reply to ]

Jan 13, 09 9:55

Post #19 of 25 (4803 views)

You can ask MarkyV. He seems to have had a similar issue with a training PT vs. race PT (you'll have to ask him to clarify) - but I know he switched to SRM. You could PM him.

Dave

Re: Zipp PowerTap disk data differences [jens] [ In reply to ]

Jan 13, 09 10:28

Post #20 of 25 (4787 views)

Whether a flat disc, a lenticular disc or a "bump" disc is faster also depends on the frame you are using. Has to do with the "gap", width/clearance of seat and chain stays, and or lack of these, ie beam bikes. Each disc has its "best" fit to a frame.

.
.
Paul

Re: Zipp PowerTap disk data differences [zipp] [ In reply to ]

Jan 13, 09 11:22

Post #21 of 25 (4769 views)

In Reply To:

Whether a flat disc, a lenticular disc or a "bump" disc is faster I THINK also depends on the frame you are using. Has to do with the "gap", width/clearance of seat and chain stays, and or lack of these, ie beam bikes. Each disc has its "best" fit to a frame.

I corrected your post for you...

:D

g

greg
www.wattagetraining.com

Re: Zipp PowerTap disk data differences [gregclimbs] [ In reply to ]

Jan 13, 09 11:33

Post #22 of 25 (4765 views)

I can't mention sources but its not "I think".

We'll now need to agree to disagree.

: )

.
.
Paul

Re: Zipp PowerTap disk data differences [zipp] [ In reply to ]

Jan 13, 09 11:38

Post #23 of 25 (4761 views)

As the sign on my desk says:

"Without data, it is just an opinion"

:)

G

greg
www.wattagetraining.com

Re: Zipp PowerTap disk data differences [gregclimbs] [ In reply to ]

Jan 13, 09 12:38

Post #24 of 25 (4739 views)

: )

Thats OK with me!!

.
.
Paul

Re: Zipp PowerTap disk data differences [RChung] [ In reply to ]

Jan 15, 09 13:02

Post #25 of 25 (4674 views)

In Reply To:

In Reply To:

I have both a SLC and PT disc. I benchmarked them both against an SRM with basically identical results.

When you say "benchmarked," what do you mean? Did you make CdA estimates?

No, I mean that when my SRM read, for example, XXX watts, both my 404 laced to my SLC and my PT disc read an equivalent value of YYY watts. The "conversion" for both was ~6% (of course, at lower values it is a higher number and at higher values, the conversion is a lower percentage).

"Non est ad astra mollis e terris via." - Seneca | rappstar.com | FB - Rappstar Racing | IG - @jordanrapp

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