topflightpro

My SRMs read lower than my PT and Quarq did.

My two SRMs seem to match each other.

Average power is fine for gauging how hard a ride was overall, but I'm more concerned about power during intervals, which can be a short as 10 or 15s. Not having precision or accuracy at that level would make my PM worthless.

grolby

That's what I (in consultation with The Coach) ended up doing. I had looked at the NP for the test on the Garmin after finishing, so there's some determination of a result there.

grolby

Whereas I'm not super concerned about pacing intervals really tightly by power. I prefer to pace by RPE, though power can be a rough guide. It's all about being aware of how the power meter works for your methods and what its limitations are. I have a Stages and what I've seen seems to pass the basic sniff test in consultation with other people, but I try to remain aware that below 5 minutes or so it can read very differently from other PMs. In general, I think it's probably smart to regard what you're calculating for W/kg at any given duration with a grain of salt.

I think the point about historical utility of data is an interesting one to consider, but I also think that it's probably worth getting one of the less expensive power meters vs not having one at all. But you have to be aware that it might read high (or low, I suppose), or otherwise is probably giving a less than 100% accurate picture of your output.

Hls2k6

It's only a matter of time before I take the leap and order an SRM, and every time I read threads like this that time grows sooner. I remain certain, however, that the market is going to continue to force price adjustments, and that SRM will jump on the wagon the day *after* I do.

shovelhd

A used SRM is money well spent.

I also have a Stages on another bike. If I had a second head unit I could compare them side by side as they are both BB30. However by RPE they appear to be pretty close. A lot closer than 20%. 250w feels significantly different to me than 225w. If the Stages was that far off I'd know it. For the few times I rely on it for accuracy versus my SRM standard, it's fine. Even if I undershot or overshot my interval by 10% that day because I was using the Stages, what's the net effect? Not much. What had a profound effect on me was when my last Quarq was drifting low over time. Workouts at the same level kept getting harder and harder so I kept adding rest, which helped for the first day back but the next day was hell. It was demoralizing and counterproductive. This is why I say that accuracy is important but stability is more important.

Hls2k6

Just sent some questions to a seller on eBay about a used one. Nearly half price would be great, assuming I can still get it serviced by SRM USA.

shovelhd

SRM Colorado will service any modern SRM no matter where you bought it.

revchuck 

Okay, so last Friday I had a flat on a tubular Gatorskin. The inflator can of Effeto Mariposa Espresso pretty much refused to go in, so I ended up riding gingerly about two miles on the mostly-flat tire to my truck. I put part of a bottle of Stan's in the tire at the shop - used the whole bottle, but much of it ended up on the floor - and at first it seemed to not have helped, but now the tire is holding air.

Is this tire okay to ride, or did I kill it by riding it mostly flat? Externally it looks okay, no lumps or bumps.

shovelhd

It's a Gatorskin. Garden hose. If it holds air, ride it.

Doge

The Stan's plug may blow out at some time. Carry more Stan's. That stuff does get the wheel off balance. Common to race, get a flat, use Stan's then use for training.

revchuck 

When the tire went flat and slid out from under me on a corner, I wasn't sure if it was because it was a flat, or...well...because it was a Gatorskin. The 303s came with these things glued on and almost no miles on them. I keep talking myself out of replacing them because they're so unworn. Don't know how much longer I can keep that up.

tetonrider

Damn. That sucks.

We had a whole thread a while back where I got bashed for citing data integrity as one reason I liked the pc7 (many felt it was overpriced and could not get over lack of GPS). A few chimed in that the garmin corruption thing is a non-issue (same with the press-start-to-record and God forbid you don't hit stop and hold reset before you power off). Always seems to happen on the important files and never the recovery rides.

Once is too much.

tetonrider

Talk to me before you go used. Used meters can be amazing deals, and I steer many people that way vs some other devices. 2015 prices dropped a bit. May be able to help you out depending on model.

tetonrider

its not so much about pacing by power as it is data analysis after the fact and historical trends.

You can't really pace a 10" effort by power.

His stuff can matter a bunch or not at all, depending on who you ask. When I coach people, data integrity and the type of meter they use is very important. I am not riding with them and have to read quite a bit into the ride based on small things in their files. If their data is bad, then those small differences can get lost, and much of the valuable stuff (subtle nuances that tell me things about how a rider is riding) are lost.

Of of course some folks just need AP and TSS and call it good.

Hls2k6

Thanks very much. Apparently, I don't post here enough to send a PM, but I tried. If you PM me an email, I'll write there. In the meantime, I ride Dura Ace 9000, so I doubt new pricing would be very favorable, but I'd be happy to be proven wrong. Anywhere between 175 & 180 (with longer best) in traditional gearing.

canuckbelle

You can PM after 50 posts. You're nearly there.

shovelhd

I ride 9070 and use a Sram SRM with Red 22 rings. Works fine. I'd love a 9000 SRM but even with a killer discount I don't have that kind of coin.

shovelhd

We just like to bash you.

grolby

Yeah, I see where you are coming from. For me, for the time being - my coach knows me, which helps, and I'm not super concerned with the specific details of my power at durations below 5'. Not that it isn't nice to know, to get an idea of where I stand, or what happened in a given race (e.g. looking at 2-3 minute intervals in a road race where I got dropped the third time up a really steep climb). Shockingly, different people have different needs! So I can see why the problems with something like a Stages would be more concerning to someone else. It does ease my mind that the numbers I've seen with it even at short durations are consistent with previous measurements I've made, but the thing is that could still be off by 20 watts one way or another and I wouldn't be able to tell. Still, I'd rather my 3' power be off by 20 watts than my 20' power!

tetonrider

oh, no, it is absolutely not shocking at all. the thing is sometimes someone new to power (or anything) doesn't realize what will be important down the road. and i get it -- it is hard to know what we don't know.

it's why the precise-but-not-accurate-is-ok argument works; that user has not been through the cycle of a warranty repair, a 2nd unit, an upgrade, etc.

what measurements?

you can tell if you spend 5' calibrating your meter. (if stages allowed it, that is.)

why? if one is off, how can you have any confidence in the other?

these are earnest questions. not picking on you. i've made many mistakes with power early on and it cost me time, data and money. one reason i help many people (mostly offline) is that i enjoy seeing them get right to what is important without stumbling, wasting time, losing data and/or $$$.

tetonrider

makes me feel comfortable, kind of like hanging with my family.

Matt2.8NJ

Great info, thanks!

Let me rephrase the question:

You have two bikes, A and B. A is your nice race bike, with an SRM. B is your retired race bike, turned commuter, with PT. The SRM reads significantly lower than the PT. However, you spend most of your time on bike B training/commuting (75% of hours).

So the data gathered from the SRM at races is massively lower than your training, making it less than useful.

Ideally, I'd like the two to read as closely as possible in order to have seamless data gathering.

Phrased in this situation, would you still not recommend tweaking the slope of the SRM until the data gathered is roughly the same?

Matt2.8NJ

Proof of the pudding is in the _________.

Rather than spending a bunch of money on a known weight... maybe it's just easier to measure a known quantity of water as the test mass.

tetonrider

i just got home. will send you a note. basically it is up to you to say what you need. a nice thing about SRM 9070s is that one can choose the rings they want off the bat (50/34, 52/36, 53/39, 54/42, 55/42)--especially so for people who want, say, a TT setup; they don't have to buy 53/39 rings they won't use.

as shovel says, below, other than "matching" there is no reason you can't use another crankset, like sram, FSA, etc. there are cheaper models.

DA rings are amazing, though.
hard sayin', not knowin', as they used to say up in alaska.

tetonrider

under no circumstance do i recommend adjusting a device -- particularly one that has been calibrated in the last year (and calibrated SRMs tend to hold it) to match a non-tested meter, no matter the brand.

either test your slope (PT) and then send to saris, or just send it to saris for testing....but don't tweak a known-good meter.

accept the data corruption and start collecting good data going forward.