shovelhd

That's pretty much what a Powertap uses without an external cadence sensor to override it. It works.

slynkie

I remember the cadence data from my powertap being pretty sketchy. Granted it's been a few years. I think it's pretty different, anyway, since the PT's accelerometer isn't directly measuring crank cadence it has to do quite a bit more interpretation..

globecanvas

I don't think that's quite right. A powertap has an accelerometer which it uses to measure wheel RPM, and from that calculate power. It can also infer pedaling cadence by looking at peaks in the power reading, but that calculation is not an input to the power calculation, and can be unreliable (I recall frequently seeing cadence numbers that were 2x what they should have been).

If a cadence/speed sensor is present, you can set a Garmin to ignore the powertap inferred cadence, but the PT is still using its accelerometer to measure wheel speed and calculate power internally.

Stages and Garmin Vector use accelerometers to measure pedaling cadence and therefore power, and those cadence measurements are accurate because the accelerometer is on the spinning part that it's measuring. That is what I believe the Quarq will do in the absence of a cadence magnet.

abhirama

I see Quarqs at nicely discounted prices. Any idea if they're releasing something new sometime soon?

burger0014

Where are you seeing Quarq's at discounted prices? I'm looking for a Riken BB30

abhirama

Glory Cycles.

ShutUpLegs

Hey guys got a set of ENVE 6.7s with a powertap G3 laced in. Just got them from another local rider and they were minimally used. First two rides I noticed that my Garmin 500 will Auto Pause/Resume during the ride. Seems like the power drops out causing the garmin to think I have stopped and then it will resume again. It did this about 7-8 times during my hour recovery ride the other day, just really annoying. Is has calibrated @ 506 so that doesn't seem to be off. Any ideas?

shovelhd

When you are training with power you should shut auto pause off. You want to measure your stop time. It affects the cumulative metrics like IF, TSS, etc.

valygrl

It shouldn't do that. Have you changed the battery?

LAJ

When the battery in my Powertap starts heading south, that's the first warning.

waterrockets 

That's better than the LYC's warning system. I put in a new battery and get the low battery warning in about 2 weeks. Then it blinks at me for 6 months or so, when it finally stops working.

ShutUpLegs

I'll double check the battery, that was my first thought, but friend at the shop told me he was pretty sure he just replaced it. But small expense to make sure.

ShutUpLegs

Good point shovel

mattm

But on the flip side, I got annoyed that all of my stopped time was counted towards my total training hours. Too many stoplights around here.. and they're super long.

Ygduf

cycling analytics and strava both cull out 0mph time from training hours.

Creatre

I still have auto pause on. I don't train sitting at stop lights, I train moving. And my garmin won't show me time without 0mph in it without having auto pause on.

misterwaterfall

I have it off, and just hit the start/stop button if I end up sitting at a light for more than a few seconds.

Creatre

That kind of defeats the purpose of having auto pause off and is way too much work.

Ygduf

I only recently turned autopause off because I was testing to see whether the pause-at-time-of-stop was contributing to the disappearing ride phenomenon.

wsuhoops1000

Any thought on doing 8 mile time trials, there and back, as suggested in the friel book? I don't have any roads other then rolling hills I can do for 8 miles straight..

Not pedaling for 10 seconds to do a quick 180 wouldn't throw things off too bad would it?

edit - I'm talking for FTP testing. Sorry

waterrockets 

8 miles is a handy distance for power tests. I wouldn't worry about the short pause in the middle, and I wouldn't worry about the rollers. Learn to hold power on the descents -- it's just pedaling like all the other stuff. You can also pedal into the brakes approaching the turnaround, and maintain power throughout. Many prefer pure climbing power tests, but they are not necessary, nor necessarily preferred.

tetonrider

a magnet is always going to be more accurate, no? even quarq says that users should keep their magnets (but of course many are already removing them).

then again, a magnet forces one reading per revolution (which ultimately gets down sampled by most headsets to 1 reading per second). cadence could vary within a single revolution, which devices with accelerometers have the potential to detect, but the protocol for recording still winds up in downsampling to 1 # (is it averaged? is it a random value from the rotation? we don't know).

i'd think the accelerometer method, due to it's inherent nature, has more points of failure.

tetonrider

a few years back, i had a ton of friends claiming big, big riding hours. it scared me because i had to train indoors (so minimal hours), and even when i rode outdoors they were riding WAY more than me. wasn't until i took a ride with one of them that i realized how much time could be eaten up just getting out of the city in which they lived to a place where they could really ride.

these guys did live in a city, so it's probably worst case, but the amount of stopped time was shocking.

tetonrider

a small feature i appreciate of the SRM when used WITH their head unit is that every time you plug it in it gives you an estimate of how many hours are left.

you can see it gradually drop and have a better idea of when it might be done / when you might need to send it in. (sending it in is annoying, but with battery life of 1,900 or more hours for most units, it takes a while.)

tracks pretty well with actual training time. i suspect it is using voltage readings but don't know for sure.

tetonrider

i know they replace units pretty readily, but this took YOU figuring out that there was a problem. if you only had that one PM, you would never know there was an issue, until perhaps years later when you replaced it with another device and then could never hit those #s . (frustrating!)

i'd say good customer service would have been THEM reaching out to people who have these units to let them know the readings are off, or at least there is the potential.

we're not talking about safety issues or life-saving equipment, but lots of cyclists live and die by these numbers in their training sessions.

the scenario you described is similar to what caused me to lose faith in quarq. they replaced lots of units, though.

yes, it is just that--a fail-safe.