Actually with a powertap swapping cassettes is really easy. Takes 2 seconds. This also makes disc cover installs a snap.
Swapping cassettes is a pain in the ass so I wouldn’t go the rear hub option. I did and now I’m converting my 10sp road bike into a 11 speed so I can easily interchange the Powertap wheel between bikes. If I were to do it again I’d get a Stages because it’s a simple swap unless you like to complicate things like me. my bikes don’t have the same crank arm length which is why this option is out to pasture for me. I also wouldn’t buy a fancy new bike and then take the advantages a BB30 spindle gives you and convert them to GXP. 24mm vs 30mm is a marginal gain for power transfer IMO.
If I had to do it all again I’d go Vector S and switch my spare pedals to Look Keo’s rather than the Dura-ace ones I have on both bikes now.
I would have easily picked the P2Max, but in this case the sale price put the Elsa a little cheaper for me. I like the battery cover being on the front and can be changed quickly during a ride if needed. The only Quarq that has temperature compensation is the Quarq RS from what I can tell and it was out of what I wanted to spend at this moment. With my Cinqo the bike is exposed while driving to my training courses and if the day heats up I will either rezero the head unit while stopped at a traffic stop or use the back pedal method. I usually don’t too hung up on the temperature drift.
Actually all of the new Quarq chassis-only models (Elsa R, Riken R, Elsa RS, XX1) have the active temp. compensation. Quarq customer support confirmed this when I called inquiring about their upgrade program.
Actually all of the new Quarq chassis-only models (Elsa R,
Riken R, Elsa RS, XX1) have the active temp. compensation. Quarq customer
support confirmed this when I called inquiring about their upgrade program.
I won’t disagree on the disc covers but I hate swapping cassettes. More than anything it’s the whole process of getting the toolbox, grabbing the tools, finding a cassette etc. But I suspect that due to living in a smaller condo in a major city space is the main culprit. If I had a dedicated room to my cycling gear this would become a non-issue. So +1 to you I’m allowed to disagree with myself aren’t I?
No you aren’t listening!
With a powertap hub you don’t need tools to swap a cassette.
Just buy extra freehub bodies, they pop off. Takes 2 seconds, literally.
I won’t disagree on the disc covers but I hate swapping cassettes. More than anything it’s the whole process of getting the toolbox, grabbing the tools, finding a cassette etc. But I suspect that due to living in a smaller condo in a major city space is the main culprit. If I had a dedicated room to my cycling gear this would become a non-issue. So +1 to you I’m allowed to disagree with myself aren’t I?
I just listened to Allen Lim’s 3-min. advertisement for PowerTap and here are a things I don’t quite agree with:
Hub is the most accurate place to measure power - he says that you don’t have any chainring weirdness to futz around with when you’re measuring at the hub, but neglects to mention that measuring downstream of the drivetrain introduces drivetrain losses, which are highly variable. If I take a PT wheel and use it on multiple bikes and get different power readings - is it because I’m actually outputting more/less power or are the drivetrain losses different on each bike, or both?
Not saying that measuring at the crank spider is foolproof or better, just saying that measuring at the hub also has its own issues and isn’t any better or worse.
Auto-zero when coasting - he’s wrong when he says that PT is the only power meter that auto zero’s when you coast. SRM and Power2Max allow the same (with SRM you can turn off auto zero on/off). Quarq allows you to auto zero by backpedaling a number of times.
Regarding #1 - he neglects to mention that drivetrain efficiency confounds the data if you want to know leg power. On the other hand if you are field testing, he is right on, you want to know only the power at the wheel. Assuming you have no broken bearings and a lubed, clean chain on both bikes, the differences due to drivetrain should be on the order of 1 watt max. Either way, if you use a power tap, keep your chain clean and lubed. Should do that anyway =)
Regarding #2 - the crank based meters that can do this either do it poorly (coasting with the SRM and auto zero usually is a bad idea) and obviously having to backpedal is quite less convenient than just getting a free auto zero at every stoplight.
On the other hand the auto zero doesn’t do you any good in something like a hill climb TT, or non technical ironman courses where you don’t coast for hours.
I just listened to Allen Lim’s 3-min. advertisement for PowerTap and here are a things I don’t quite agree with:
Hub is the most accurate place to measure power - he says that you don’t have any chainring weirdness to futz around with when you’re measuring at the hub, but neglects to mention that measuring downstream of the drivetrain introduces drivetrain losses, which are highly variable. If I take a PT wheel and use it on multiple bikes and get different power readings - is it because I’m actually outputting more/less power or are the drivetrain losses different on each bike, or both?
Not saying that measuring at the crank spider is foolproof or better, just saying that measuring at the hub also has its own issues and isn’t any better or worse.
Auto-zero when coasting - he’s wrong when he says that PT is the only power meter that auto zero’s when you coast. SRM and Power2Max does the same thing (SRM allows you to turn/off the auto zero using the PowerControl). Quarq allows you to auto zero by backpedaling a number of times.
I agree that PowerTap is good enough for field testing (I have a PT G3 disc hub on one of my bikes). I’m just saying that Allen Lim is stretching things a bit when he claims that the hub measurement of power is much more accurate than crank-based measurement. Yes it’s more accurate if what you’re measuring is power to the wheel. But most of us just want to know how much power we’re putting to the pedals; measuring power to the wheel is good enough to determine that.
I’m guessing if Allen Lim instead said “I like PowerTap because it’s accurate enough, a lot cheaper than the competitors, and I can use it for training and slap on a disc cover for races” it wouldn’t make much of a compelling advertisement. =)
About the auto zero - no one has really done any studies to determine if the PT auto zero is a good idea or a bad idea. SRM PowerControl lets you see the live zero-offset without actually resetting the ZO; that’s how Alex Simmons was able to find evidence that SRM auto zero was giving him erroneous results. But to my knowledge the only way to check the PT ZO is to reset the ZO first. It’s a moot point anyway (whether PT auto zero is good/bad) because there’s no way to turn it on/off.
My bigger beef with PT is that there is no way to change the PT slope. You can do a static torque test to determine if it’s off, but to actually change it you’ll have to ship it back to PT. This is also an issue with Power2Max.
I’m guessing if Allen Lim instead said “I like PowerTap because it’s accurate enough, a lot cheaper than the competitors, and I can use it for training and slap on a disc cover for races” it wouldn’t make much of a compelling advertisement. =)
hmmm, that’s sorta the list of reasons I bought one…
I’m guessing if Allen Lim instead said “I like PowerTap because it’s accurate enough, a lot cheaper than the competitors, and I can use it for training and slap on a disc cover for races” it wouldn’t make much of a compelling advertisement. =)
hmmm, that’s sorta the list of reasons I bought one…
“PowerTap - measure BOTH of your legs for around the same price as Stages. And we’re almost as easy to swap between bikes. Oh - and you can use your carbon crank arms too.”
Regarding #2 - the crank based meters that can do this either do it poorly (coasting with the SRM and auto zero usually is a bad idea) and obviously having to backpedal is quite less convenient than just getting a free auto zero at every stoplight.
On the other hand the auto zero doesn’t do you any good in something like a hill climb TT, or non technical ironman courses where you don’t coast for hours.
Sorry to keep harping on this, but I disagree. The SRM autozero seems to work pretty well in my experience–better than leaving it off and not manually zeroing the device when it sees changing temperatures. Have you actually investigated this yourself?
IMO the power closet to the wheel matters most to me. That’s the last place it’s possible to measure as it’s moving you forward. That’s the only thing that matters…how fast one is going forward.
As to credentials, I would say it’s pretty hard to argue with Alan Lim’s. Perhaps there are some who may equal here on ST, but not that I know of…
That’s the only thing that matters…how fast one is going forward. .
I disagree. I have a velocity sensor to measure how fast I’m going. I consider power a measure of physiological output, having as little to do with my equipment as possible.
IMO the power closet to the wheel matters most to me. That’s the last place it’s possible to measure as it’s moving you forward. That’s the only thing that matters…how fast one is going forward…
IMO the power closet to the wheel matters most to me. That’s the last place it’s possible to measure as it’s moving you forward. That’s the only thing that matters…how fast one is going forward.
Speed sensors do a fine job of measuring how fast you are going.
I suggest checking PT torque readings when hub is tethered to different cogs. I think then you might reconsider.
As to credentials, I would say it’s pretty hard to argue with Alan Lim’s. Perhaps there are some who may equal here on ST, but not that I know of…
What do credentials have to do with evidence of accuracy?
Is this the same physiologist who apparently couldn’t spot a major doper in his squad?
When it comes to power measurement, there are many people I would pay far more attention to than Lim.
Just so it’s clear, I think Powertap make a fine power meter.
About the auto zero - no one has really done any studies to determine if the PT auto zero is a good idea or a bad idea. SRM PowerControl lets you see the live zero-offset without actually resetting the ZO; that’s how Alex Simmons was able to find evidence that SRM auto zero was giving him erroneous results. But to my knowledge the only way to check the PT ZO is to reset the ZO first. It’s a moot point anyway (whether PT auto zero is good/bad) because there’s no way to turn it on/off.
You used to be able to disable auto zero with the LYC cervo computer. This was specifically so it could be used in a fixed gear conversion. If there is no means to disable auto zero on a Powertap fixed gear set up, you’re screwed.
The PT auto zero is a good idea, but it won’t really help a unit suffering from excessive torque zero drift or with freehub problems. Suggest occasionally manually checking the torque zero behaviour.
The best way to deal with torque zero drift is to use a design that is less susceptible to it in the first place.