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Re: "Best" power meter - money no object [Tom_hampton] [ In reply to ]
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Sounds cool. I saw where one person recommended Stits aircraft covering. That should be really tough but probably heavier.

Is the cover very uniform on each side? What I'm concerned about is wobbles or unevenness in the surface when you spin the wheel that would cause flow separation and defeat the purpose.
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Re: "Best" power meter - money no object [jaretj] [ In reply to ]
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jaretj wrote:
Garmin does now:

https://buy.garmin.com/en-US/US/p/546361

Do they similar for Vector 3 ?

Have kept this a bit quiet considering how many use Shimano cleats
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Re: "Best" power meter - money no object [rruff] [ In reply to ]
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Mostly that's a question of workmanship. A slightly deeper rim would make it easier to manage. The R460 doesn't leave much room to work. So a slightly deeper section would just make it a littler easier to work with.

But, I think you are splitting hairs. Not that there is anything wrong with that. That IS sorta what we do around here.

Of course, I did fare the battery cover on my powertap. And it annoys me that it is a concave faring. So, I might be the pot calling the kettle black. :=)
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Re: "Best" power meter - money no object [Tom_hampton] [ In reply to ]
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IME a rigid cover is never quite right. I seem to have more trouble with the DS, but can get the NDS pretty good. That's my main motivation for looking at Monokote or something similar. The current rim is a XC279, 23w, 28d. I've been debating getting a cheap 80+mm carbon rim and putting a cover on that... because it should be easier to get a good fit on a deep rim, plus better chainstay and derailleur clearance. And in Wheelbuilder's tests, the cover on a deep rim was much better... although I believe fit was probably the only reason for that. Fit is important! Seems like the Monokote would be uniform so long as you get the glue lines uniform. I don't know how hard that is though. And the dish! Not sure about that either...
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Re: "Best" power meter - money no object [rruff] [ In reply to ]
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If you want perfect glue lines, just mask off the edge near the spoke nipples with tape. You can spend all day on that if you want, to get it perfect. Apply the contact cement, let dry, and peel the making tape. Then apply the monokote. Should be near perfect.

The hardest part of the whole process is minizing wrinkles on the rim. Just takes some patience. Apply at 12,6,3,9 and the divide. You can use your heat gun to shrink between divisions to pull out the slack as you work around the rim. As noted, monokote is cheap... So, if you aren't happy you can retry your process until you are... Several times before you even get close to the cost of a cover. It's easy to work with, so worst case I'd guess it takes one extra roll to get the process perfect like you want.

The material shrinks a LOT. So, it will be drum tight and glass smooth when you are done. The dish is no big deal. It has no impact on covering either DS or NDS. No drama.

Your xc279 looks almost identical to an r460. Its actually 4mm deeper according to one drawing I found. So, seems fine.
Last edited by: Tom_hampton: Mar 8, 19 19:50
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Re: "Best" power meter - money no object [Tom_hampton] [ In reply to ]
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Tom_hampton wrote:
Apply at 12,6,3,9 and the divide. You can use your heat gun to shrink between divisions to pull out the slack as you work around the rim.

The divide? Can you explain that some more?
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Re: "Best" power meter - money no object [rruff] [ In reply to ]
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Almost any Monokote disc should be better than this: https://forum.slowtwitch.com/...ost=3487234#p3487234
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Re: "Best" power meter - money no object [RChung] [ In reply to ]
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That's.... amazing ;) If you check the spreadsheet, the CdA (yes he took it to A2) was surprisingly low compared to a box-rim wheel.
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Re: "Best" power meter - money no object [rruff] [ In reply to ]
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Sorry. Typo. Sound have been "then divide".

The idea is to adhere the monokote just at each point on the clock (12,3,6,9). Then subdivide each of those areas. Keep subdividing until the sections are about 4-6" long. Once you are down to these short sections use the heat gun (or iron) to shrink the perimeter enough to avoid wrinkles as you smooth down a section at a time.

Then use the heat gun to begin slowly working out the slack. Take your time and work fairly large areas until it begins to get taught. Concentrate more on the perimeter more than the center. From then on work smaller areas that are showing wrinkles. Just keep the heat gun moving. Don't over shrink it. Just enough so it's taught, and not showing wrinkles.

Seasonal temp changes may cause it to go a little slack and show wrinkles. 30 seconds with the heat gun will tighten it back up. I check the night before the race and touch up with a heat gun if I find any wrinkles.
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Re: "Best" power meter - money no object [Tom_hampton] [ In reply to ]
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Thanks for the info. Been reading that Monokote is pretty fragile. Since I ride on roads that have gravel scattered on them, I might try dacron cloth used to cover aircraft. Looks like the same idea, only I'd need to coat it with something after it's made.
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Re: "Best" power meter - money no object [rruff] [ In reply to ]
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Yes. I've done the silk and dope thing on a model RC aircraft. It's more work, and I don't think it would be any better. My silk and dope rc is much more fragile than my monokote.

Don't know why someone said monokote is fragile, because it is not. My first cover lasted over a year. I had to remove it to fix my PT hub, but it was fine. The replacement has also lasted over a year. I ride it all the time. It's my training wheel. The only punctures I've gotten were from me being careless with a screw driver or something. Even then it was just a hole and didn't lead to total failure. It does not just tear like mylar or celophane once punctured. It just leaves the hole.

As I said above, small holes can be patched with electrical or packing tape. Larger holes can be covered with a piece of monokote. It has a heat sensitive adhesive backing. So, it will iron onto the existing cover.
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Re: "Best" power meter - money no object [wintershade] [ In reply to ]
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Why no love for Vectors? Anyone gone from garmin to faviano?

My vectors have been pretty solid for 4+ years now and I “feel” (as measured vs my Neo) consistent.

Never used another brand

Not seen anything yet w these tho that makes me want to upgrade
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Re: "Best" power meter - money no object [rruff] [ In reply to ]
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rruff wrote:
MTM wrote:
I think they did, but I'm not that versed in Powertap offset values. I was wondering what one unit in the offset (as showed on my Garmin) corresponds to.



Looks like N-m if using Ant+. https://www.powertap.com/...tes-to-offset-values

If I'm reading that correctly each increment is 1 Nm (for both ANT+ and BLE, you just have a decimal point in the reporting value when using BLE). That's extremely blunt at ~10W for each step at 95rpm. Unless your powermeter is quite unstable, better not touch the zero offset at all if that is correct!
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Re: "Best" power meter - money no object [mvenneta] [ In reply to ]
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I have 2 Quarqs and PT G3 that have served me well for several years.

I believe though based on the original thread title that SRM has been a tough one to knock off that “gold standard” of power meters podium especially when cost is not a factor.
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Re: "Best" power meter - money no object [MTM] [ In reply to ]
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MTM wrote:
If I'm reading that correctly each increment is 1 Nm (for both ANT+ and BLE, you just have a decimal point in the reporting value when using BLE). That's extremely blunt at ~10W for each step at 95rpm. Unless your powermeter is quite unstable, better not touch the zero offset at all if that is correct!

Actually it's more like 40 W/Nm at TT speeds. Something doesn't add up here! Unless the number displayed is much more crude than the number stored... ?
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Re: "Best" power meter - money no object [rruff] [ In reply to ]
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rruff wrote:
MTM wrote:
If I'm reading that correctly each increment is 1 Nm (for both ANT+ and BLE, you just have a decimal point in the reporting value when using BLE). That's extremely blunt at ~10W for each step at 95rpm. Unless your powermeter is quite unstable, better not touch the zero offset at all if that is correct!


Actually it's more like 40 W/Nm at TT speeds. Something doesn't add up here! Unless the number displayed is much more crude than the number stored... ?

Yes, I calculated it as was it the torque at the spider, not the hub, so my number is off. 4x that sounds right when using the hub, which sounds absolutely huge. Maybe Chung's post about it being in 0.1 Nm steps is correct? That would still be 4W/step, so definitely still quite coarse.
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Re: "Best" power meter - money no object [MTM] [ In reply to ]
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He showed a photo of his calibration screen showing "Raw Torque" in 10ths of an in-lb. The offset was still in whole in-lb though. There are 8.85 in-lb/N-m, so 10ths of an in-lb would be ~0.5W resolution.

I have the same computer (Joule GPS) only mine shows raw torque in whole in-lb on that screen. This is also reflected in the .csv files. Even though the torque field is in N-m, it's obviously converted from whole in-lb increments. So resolution is more like 5W at TT speeds.
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Re: "Best" power meter - money no object [rruff] [ In reply to ]
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rruff wrote:
He showed a photo of his calibration screen showing "Raw Torque" in 10ths of an in-lb. The offset was still in whole in-lb though. There are 8.85 in-lb/N-m, so 10ths of an in-lb would be ~0.5W resolution.

I have the same computer (Joule GPS) only mine shows raw torque in whole in-lb on that screen. This is also reflected in the .csv files. Even though the torque field is in N-m, it's obviously converted from whole in-lb increments. So resolution is more like 5W at TT speeds.

Doesn't Powertap statae +/-1.5% accuracy for their G3 hub? It's interesting that their stated accuracy is on the same order as their zero offset steps. Doesn't leave much room for inaccuracies in the rest of the measurement path!
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Re: "Best" power meter - money no object [rruff] [ In reply to ]
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rruff wrote:
He showed a photo of his calibration screen showing "Raw Torque" in 10ths of an in-lb. The offset was still in whole in-lb though.
Hmmm. You know, now that I think about it, I'm not sure what units the offset number used, or why it was "centered" at 512.
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Re: "Best" power meter - money no object [RChung] [ In reply to ]
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RChung wrote:
rruff wrote:
He showed a photo of his calibration screen showing "Raw Torque" in 10ths of an in-lb. The offset was still in whole in-lb though.

Hmmm. You know, now that I think about it, I'm not sure what units the offset number used, or why it was "centered" at 512.

When mine is calibrated and no load I show 509.0 in the raw torque field, and 509 in the offset. Even though the raw torque shows 10ths, it's always a zero to the right of the decimal, even if I apply torque. Both numbers are in-lb.
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Re: "Best" power meter - money no object [rruff] [ In reply to ]
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When mine is calibrated and no load mine shows 0.0 in the raw torque field.
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Re: "Best" power meter - money no object [RChung] [ In reply to ]
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I'm guessing the difference is I have an SL+ and yours is a G3.
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Re: "Best" power meter - money no object [rruff] [ In reply to ]
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A long time ago I had a PT Pro with the LYC, but I don't recall seeing raw torque on a base of the offset.
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Re: "Best" power meter - money no object [RChung] [ In reply to ]
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RChung wrote:
rruff wrote:
He showed a photo of his calibration screen showing "Raw Torque" in 10ths of an in-lb. The offset was still in whole in-lb though.

Hmmm. You know, now that I think about it, I'm not sure what units the offset number used, or why it was "centered" at 512.


I can only speculate but considering we are talking about days when processing power and memory in a cyclo-computer was at a premium...

If a display can't show negative numbers (my old PT Cervos didn't), best then to use a large enough positive value as the baseline as well as large enough to provide some reasonable level of resolution at the unit level.

That and 512 is a power of two in binary number system which (along with all units up to 1023) can be stored with just 2 bytes.

Baseline:
(512)₁₀ = (1000000000)₂

One unit above:
(513)₁₀ = (1000000001)₂

One unit below:
(511)₁₀ = (0111111111)₂

http://www.cyclecoach.com
http://www.aerocoach.com.au
Last edited by: AlexS: Mar 11, 19 14:07
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Re: "Best" power meter - money no object [AlexS] [ In reply to ]
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IIRC, Quarqs used to report their calibration numbers in units of 1/32nd of a Nm.
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