Stages PM Question
 

I've had a Quarq for the past 2 years and because it's a tank (weight wise) and also because I want to have power on a compact setup on a CX bike, I got a DA Stages. I've read a lot of talk about the left/right balance "debate".

I'm looking for a check on my understanding. If I did an interval at say 500 watts (250 of that from the left) and then came back a week later and did 500 again would I really know that I've stayed the same or is that the crux of the Stages "problem"? Would doing the same two efforts with my Quarq really be any more accurate?

nobody can tell you a definitive answer to this. No one can tell you definitively that the same power on the same power meter 2 weeks apart is actually "the same".

Stages work on the idea that your legs develop at about the same rate and that most people have about 50/50 balance naturally. Quarqs fluctuate on temp/calibration/slope slip, etc. Nothing is perfect. Power meters are an improvement, but there is an aspect of feel and trust and that the thing will work within a reasonable margin of error.

from what I have heard from people, Stages are "fine" and serve the purpose as well as any other meter. (inb4 SRMs never go bad)

So to clarify, if you had a 5 or 10 watt improvement in one FTP test to another, that's probably more or less as valid as it would be with anything other than SRM ;) ?

Yep

the data seems to suggest that stages have certain inconsistencies (spikes) which could be a big deal depending on what you monitor. There's also, as I understand, no way to test and change the slope which is the kind of thing one would do with an SRM (and presumably other PMs) to maintain the consistency of the data.

I would not suggest putting too much stock in readings from different power meters. One should be your primary, the one you race and test with. The other can be on your backup, commuter or rain bike and used for data gathering but assume that there is correlation error.

it's why if one is going to own multiple meters, they should purchase ones that can be calibrated--whatever brand they choose. accuracy matters here.

that's the reason to scrap a quarq?

for a few units that have spiders that are distinct from cranks, i've measured that the quarq adds about 60-90g over a regular spider. now, i guess that could be a 'boat anchor' for someone...

if you're using a DA stages, you're not exactly in weight-weenie territory. shimano cranks are awesome, but light they are not.

In the scenario I laid out, it really doesn't. If your primary meter is calibrated and stable, then doing secondary activities on the other meter isn't going to mess things up much unless it's way off or drifting. You will know that via RPE. I don't need to know if the last ride I did on the rain bike had a TSS of 89.6, as long as it's between 85 and 95 I'm not going to mess up the plan if most of my rides were using the primary meter.

What is much more important to me is stability of the primary meter. If it cuts out intermittently or drifts that can cause havoc with the numbers.

with all my SRMs calibrated together I don't see a difference meter to meter.

I am the poster boy for Stages. I have 4 of them, on 4 different bikes (long story). I haven't seen data spikes. The only data problem I have had is that the Cannondale version seems less accurate than the others, possibly because of the way their crankarms are constructed.

All else being equal, the Stages is probably less accurate than a Quarq or SRM, and as a user you can't recalibrate the slope. If you already have the Stages, I would say don't worry, be happy. I'm certainly happy with mine, and I love that I can afford to have one on every bike, including my cross bike and my winter single speed. If you are still shopping around, and accuracy is of high importance to you relative to other factors like cost and ease of installation, then you might prefer other options.

I agree with ygduf's comment about how at some point you have to accept the measuring tool for what it is.

If I didn't have a PM I'd probably give Stages a go. For me it didn't make any sense to get a stages as a second. I got such a good deal on my second SRM that when you consider that I'd have to buy a garmin for it (unless I have bad info I couldn't pair a PC7 with a stages) that it would have cost me almost as much to get a stages (second bike so I'd need the full crank).

I suppose I could sell all my SRM stuff, replace it with Stages and a head unit or two, and walk away with a bunch of spare cash.

Having used a PowerTap, Quarq and SRM, I can say that it is not uncommon to get different number from each. My FTP and power zones were different on each meter.

In my case it was 1/2 pound more than the Stages option. I left out an equally important reason; my old Quarq really drifts with changes in temp and is basically useless in any kind of wet weather.

Having said all that, I've decided to get a newer Quarq with active temp comp. As I thought more about it just doesn't seem like Stages solves for a hard interval done at say 90rpm and the same interval done at 70rpm, which is to say nothing of the intensity they're done at. By "solves" I mean how do you account for the almost certain leg imbalances. Also, my legs are both (knock on wood) in good nick now but what if one of them does go bad? Anyway, if I'm bothering with power, I'm sticking to Quarq et al..

Unless you're throwing down $$ for the Elsa, how are you going to assess leg contribution to power? Sure, the Quarq measures total power, but it's not telling you xx%L and yy%R, just total power.

I don't care about left/right balance. I'm more concerned that depending on intensity or cadence the contribution of each leg will be different, so what looks like the same number might not be.

Another damn Safari crash wipes my reply. Short version. I want power on my winter road bike but won't spend over a grand for it. This is the Stages sweet spot.

First post, long time lurker who has learned a lot from you guys (thanks, by the way). Been racing in Tucson for a couple years. I have been using the Stages PM (Ultegra) since January. I did a little "experiment" earlier this year and I'd be interested in what other's thoughts might be...

Indoor on trainer, maintaining constant cadence, single leg drills (1-minute long each leg) at multiple power outputs (40%, 60%, 80%, 100%, and 120% of FTP). With the PM only measuring left-leg power, assuming an FTP of 250, the results *should* be:

[TABLE="width: 300"]
[TR]
[TD][/TD]
[TD]Both[/TD]
[TD]Left[/TD]
[TD]Right[/TD]
[/TR]
[TR]
[TD]40%[/TD]
[TD]100[/TD]
[TD]200[/TD]
[TD]0[/TD]
[/TR]
[TR]
[TD]60%[/TD]
[TD]150[/TD]
[TD]300[/TD]
[TD]0[/TD]
[/TR]
[TR]
[TD]80%[/TD]
[TD]200[/TD]
[TD]400[/TD]
[TD]0[/TD]
[/TR]
[TR]
[TD]100%[/TD]
[TD]250[/TD]
[TD]500[/TD]
[TD]0[/TD]
[/TR]
[TR]
[TD]120%[/TD]
[TD]300[/TD]
[TD]600[/TD]
[TD]0[/TD]
[/TR]
[/TABLE]

If the power ouput for the left-leg only portion is higher than expected, this would mean my right leg is providing more power when pedaling with both legs. Conversly, if the power output for left-only is lower than expected, my left leg provides more power. This would also show whether my legs provide different %'s of power at differing power outputs.

When I did this, my results showed that my legs are within the PM's 2% accuracy of being equal -- which of course was of great dissapointment as I was hoping my embarrassingly low FTP could be explained by my power meter's innability to accurately account for my incredibly strong right leg.

The new PM from 4iiii might be another good option to look at if anyone else is in the market.

It's not out until next year, is unproven, and won't work with all crankarms.

Yep, as someone who doesn't currently have a PM and has a small bike budget, Stages is pretty much the front runner as I contemplate a PM purchase. Stages has some known weak points compared to its more expensive competition, but they don't seem to be a problem for most of what people need a PM to do.

I wouldn't have a great deal of confidence in that experimental design due to the fact that pedaling with one leg at a time is proprioceptively very different from pedaling with both.

Yeah I agree it's definitely different, just wasn't sure how different. I would assume my pedaling efficiency goes down when one-legged, which would mean more watts for the same RPM. For me it all seems to end up within the noise of the PM's accuracy anyway.

I'll just continue to assume then that my right leg is superhuman. :)

I own 2 Quarqs (S975 and Riken) and a Stages. I bought the Stages for my 'cross bike and for my rain bike so I could get power data (WKO purposes) on rides that might be a little more abusive to a power meter.

For steady state stuff, where the power doesn't fluctuate as much, they're all pretty close workout to workout, with the Stages reporting ~10W lower on average for the same type of ride (YMMV). Granted, I have not done an A?B test like DC Rainmaker to check the comparison, but on the same bike, on the same course, under similar conditions, the Stages reports slightly lower for me.

For 30sec-1min VO2max intervals, the power difference is more significant (as much as 80W). This does throw off the IF a bit.

This winter I plan on doing a range of workouts on the trainer, with the Riken and the Stages going at the same time. This will allow me to identify what ranges are similar for me and what ranges are different. Then I can do the math in my head to keep within range no matter what power meter I'm using. That's the idea, at least.

I've got 2 Elsas, one compact and one standard each on different bikes. I alternate pretty regularly for training and racing. I calibrate before each ride (the standard reads about 480 or so and the compact reads about 1451 or so, both before and just shortly into the ride). Are the different readings from each bike suspect?

To complicate matters I'm looking at a TT bike with a Rotor 3D, and the only compatible meter I can find is the Power2Max, which would make 3… I know, I know, first world problems.

not your fault, but garmin perverted the use of 'calibrate'. you are simply checking the zero offset of the meter (which is one thing you should do before a ride), but it has no bearing on calibration.

a reading of 1451 on a quarq is definitely suspect, but as long as it does not fluctuate much that is better than high and rising (or dropping).

an analogy for zero offset is this: remember analogue scales? let's say you actually weigh 165 pounds. you step on a scale and it reads 170. you step off and it reads 5# with no one on it. ZO is the power meter equivalent of checking what the scale reads when no weight is applied.

calibration has to do with taking a reading at zero then taking a known mass (a large mass that is known to a high degree of precision) and measuring the unit's response to it. this defines a line from which you can extrapolate how the meter responds when any force is applied. power then comes from the force and cadence.

EDIT TO ADD: just because one zeroes their meter at the start of a ride and therefore it reads 0W when the only weight is that of a pedal has no bearing as to whether a meter is accurate when another force is applied. that's what true calibration is for.

anyway...your 2nd meter could be suspect. it raises a yellow flag for me.

cervelo? rotor makes a nice BB which allows you to run a 24mm crank on a BBright frame w/o any adapter. i put shimano SRMs on them. it's a special BB and a little hard to find -- the part #s are confusing.

also installed a rotor SRM on a friend's foil. it was their BB for bb89 & bb92 frames, if i remember correctly.

reach out if i can help you investigate SRM options. you might be surprised.