Speed/Cadence Sensor

[morrisericd]

Well - my Wahoo Blue SC speed/cadence sensor took a trip off my bike and under the tires of a passing car. Needless to say - I'm looking for a new setup. I have several of the Garmin GSC 10 ones on other bikes that work fine but I'd like to move on to the the ones that don't use magnets.

I'm trying to decide between the Wahoo RPM and the new magnet less Garmin version. Both are around the same price and both get similar reviews. I have the Wahoo Element computer so either will work fine. Any thoughts? I use the speed/cadence sensors partly for cadence, partly for accuracy and partly for when I'm on the trainer.

Thanks

[kramnnim]

Happy with my Garmin magnetless sensors...

[djg21]

Well - my Wahoo Blue SC speed/cadence sensor took a trip off my bike and under the tires of a passing car. Needless to say - I'm looking for a new setup. I have several of the Garmin GSC 10 ones on other bikes that work fine but I'd like to move on to the the ones that don't use magnets.

I'm trying to decide between the Wahoo RPM and the new magnet less Garmin version. Both are around the same price and both get similar reviews. I have the Wahoo Element computer so either will work fine. Any thoughts? I use the speed/cadence sensors partly for cadence, partly for accuracy and partly for when I'm on the trainer.

Thanks

I use the garmin GSC-10s. My wife has the new garmin sensor. I like the older one better. I don't like all the straps on the crank arm, and prefer using a single rair-earth manned affixed to my pedal spindle with the GSC-10. I though about epoxying a small rare-earth magnet to a spoke, but never bothered.

[kramnnim]

I bought a wheelset that had a magnet glued to a spoke, seems to work nicely. I hate the GSC-10, though. (I get cadence from power meters)

[djg21]

I bought a wheelset that had a magnet glued to a spoke, seems to work nicely. I hate the GSC-10, though. (I get cadence from power meters)

I suppose it whichever you hate less: the GSC-10 body on the chainstay; or the big, ugly Garmin speed sensor strapped to your front hub and the cadence sensor attached with black rubber bands to your crankarm.

[R3awak3n]

I like my GSC- 10 and probably more accurate than the magnet less sensors but it is ugly. They are becoming rare and expensive.

I did just get a magnet less cadence sensor from garmin and its pretty nice. Hides well on the crankset and I really do not need that much accuracy when it comes to cadence. On that bike I get speed from GPS.
On the bike with the GSC I get speed from the powertap but I find the powertap pretty inaccurate on the cadence side at certain speeds and that is why I run the GSC-10, not that I need the accuracy but I already have it why not use it (plus I will sit on it until they become like $120 and then sell it :eek:)

[kramnnim]

Wow, I had no idea the GSC-10s were going up in value.

I can't see the ugly hub mounted sensor when I'm riding. :banana:

[djg21]

Wow, I had no idea the GSC-10s were going up in value.

I can't see the ugly hub mounted sensor when I'm riding. :banana:

I use a Powertap G3 rear hub. The speed sensor doesn't fit well on that hub and supposedly interferes with the PT's signal. On the front hub, I have to look at it.

[R3awak3n]

I use a Powertap G3 rear hub. The speed sensor doesn't fit well on that hub and supposedly interferes with the PT's signal. On the front hub, I have to look at it.

why not just use the powertap speed? Its as accurate as the garmin sensor AFAIK (the garmin even picks the powertap speed over its own sensor)

[djg21]

why not just use the powertap speed? Its as accurate as the garmin sensor AFAIK (the garmin even picks the powertap speed over its own sensor)

At least the PT cadence is "vitual" and supposedly not as accurate as a cadence sensor. Don't know about speed.

[Look585]

PT speed in the hub works just like (and as well as) any external sensor. Little magnet passes by a reed switch and sends a "tick". Each tick = ~2095mm and number of ticks per second plus some math is speed.

[R3awak3n]

At least the PT cadence is "vitual" and supposedly not as accurate as a cadence sensor. Don't know about speed.

pretty sure its as accurate or more accurate than the magnet and why it gets chosen on the garmin over the magnet, on the other end the cadence gets priority on the garmin over the PT cadence because it is as you say "virtual"

[morrisericd]

Thanks guys. I'm going to try the RPM - I'll report back. My only concern with both is the attachment - my Wahoo Blue took a trip because the rubber band slipped off. Most likely user error but I was careful when I put it on my bike. Zip ties are much more reassuring!

[kramnnim]

Zip ties break, too... :(

[cdn_bacon]

Use the other garmin Sensor that wraps around the hub and the crank arm with bands.

https://buy.garmin.com/en-US/US/shop-by-accessories/fitness-sensors/bike-speed-sensor-and-cadence-sensor/prod146897.html

Never had a problem with mine.

[metalheart]

The speed sensor portion of my GSC-10 quit working so I replaced it with the Wahoo Blue SC. I looked at the new Garmin and Wahoo sensors and talked to the Wahoo folks and asked if there was a difference in accuracy between the acceleromenter wheel attached sensor and the wheel magnet Blue SC. They replied that they were both the same although the Blue SC sensor could be more accurate for rides on rough roads, which is most of my riding. I believe the Garmin unit is a magnetometer.

The Blue SC paired easily with my Garmin 500 and speed and cadence are working fine.

[11.4]

The only reason for some of the defaults on cadence and mileage sensors is that many people don't bother to calibrate their wheel circumference so they are reading accurate mileage. If you use a magnet-type sensor like the GSC-10 and you calibrate wheel circumference, it'll be dead-on accurate. The default to the virtual setting deals with people who don't calibrate, and also makes initial setup more simplistic.

Chip accelerometers are potentially a good way to measure cadence, but we've found consistently that they miss cycles, especially at high cadence. They also are only as accurate as wheel circumference calibration, of course.

We haven't been excited about virtual calculations, especially virtual cadence. When comparing virtual to real measurements, we've found a frequent 3-5 rpm variance.

I've had GSC-10 sensors for a number of years and never had one go bad or give any kind of problem. On the track, they are critical -- GPS-based distance (and thus cadence) is highly inaccurate on the track and accelerometer-based cadence and speed measurement gets inaccurate at track cadences and speeds. The latter may be because we can measure so precisely on the track -- I know exactly how many pedal revolutions are required for a lap or for a kilo in a particular gear, and starts are programmed around which pedal revolution I happen to be on. The Wahoo unit is nice because it operates on multiple wavelengths (you can run the data to your iPhone if you want via Bluetooth, for example, as well as sending it to a handlebar ANT+ unit). It's nice and so far as reliable as the GSC-10's.

[thirdgenbird]

Wow, I had no idea the GSC-10s were going up in value.

I can't see the ugly hub mounted sensor when I'm riding. :banana:

Are there data points to support that? I couldn't hardly give one away this summer.

[11.4]

New ones are being listed on eBay for prices higher than the originals cost. However, I looked through them and didn't see many of them actually selling. I sold a couple for about $50 each in mint condition. I should have kept them, in retrospect.

This isn't -- or shouldn't be -- about whether they become an investment item (is there anything in cycling, except for a handful of frames, that has appreciated in inflation-adjusted dollars?). It's more that there is only remaining speed/cadence still in production (from Wahoo). I wish we still had the GSC-10's available. There are some applications where they are the best solution.

[R3awak3n]

eBay. Was trying to maybe get one and used ones were going for way over what they cost new

[thirdgenbird]

eBay. Was trying to maybe get one and used ones were going for way over what they cost new

You missed mine then. I think I was $20 or less shipped before I finally got it sold.

[ColonelJLloyd]

Thanks guys. I'm going to try the RPM - I'll report back. My only concern with both is the attachment - my Wahoo Blue took a trip because the rubber band slipped off. Most likely user error but I was careful when I put it on my bike. Zip ties are much more reassuring!

Happy with the RPM sensors?

I'm looking to add some HR and cadence data to my riding. I may end up with a Bolt, but I'd like to try just using the RPM and HRM sensors with my iPhone first.

[shovelhd]

Bontrager and SRM.

[Davist]

Interesting, I didn't have very good luck with the GSC-10 in the past, switched to the all rubber band version and it has been bulletproof. Still have the GSC-10 if anyone's interested..

[Mark McM]

At least the PT cadence is "vitual" and supposedly not as accurate as a cadence sensor. Don't know about speed.

The PowerTap speed sensor must be very accurate to be able to measure power. Like all power meters, the PowerTap doesn't measure power directly - it measures torque, and multiplies it by speed (wheel rpm) to calculate power. So power measurement can be no more accurate than wheel speed measurement. (Although to get road speed, you still need an accurate wheel circumference value.)

Likewise, crank and pedal based power meters must have accurate cadence sensors, because they calculate power by measuring torque and multiplying it by cadence.

[Mark McM]

The only reason for some of the defaults on cadence and mileage sensors is that many people don't bother to calibrate their wheel circumference so they are reading accurate mileage. If you use a magnet-type sensor like the GSC-10 and you calibrate wheel circumference, it'll be dead-on accurate. The default to the virtual setting deals with people who don't calibrate, and also makes initial setup more simplistic.

Some GPS units employ an auto-calibration - after riding some distance, it calculates wheel circumference by dividing distance by wheel revolutions, and applies this value to all subsequent measurements from the wheel sensor. I don't know how accurate this is, however.


Chip accelerometers are potentially a good way to measure cadence, but we've found consistently that they miss cycles, especially at high cadence. They also are only as accurate as wheel circumference calibration, of course.

As noted before, crank based power meters need to measure cadence to calculate power. Some crank based power sensors use chip accelerometers to measure cadence, so hopefully they apply good signal processing circuits/algorithms to get accurate cadence measurements.

For speed/distance measurements, I've found very high agreement between a wheel magnet based speed sensor (Sigma Rox) and the Garmin hub mounted rubber strap sensor.

[Marc40a]

Another vote for the Garmin magnet-less sensors. They're fuss-free, so easy to use.

I'm picking up another set this week for a new bike.

[jruhlen1980]

Another vote for the Garmin magnet-less sensors. They're fuss-free, so easy to use.

I'm picking up another set this week for a new bike.

+1. It helps when you live 40 miles from Garmin and know lots of employees who can get you the employee discount.

[weiwentg]

A follow up question. Say I have a road bike which is going to spend most of its time on tarmac within range of a GPS signal. Imagine I'm either not interested in cadence, or that I'm using a powermeter which supplies cadence. Can I rely on the GPS speed alone?

As an aside, Infocrank has been a strong proponent of magnets (https://www.vervecycling.com/wp-content/uploads/2016/04/RevUp.pdf) over cadence derived from accelerometers/gyroscopes. They did recently implement a magnet-free solution (https://www.bikeradar.com/us/road/news/article/infocrank-eliminates-magnets-with-cadence-measurement-upgrade-46748/) using existing sensors in their cranks.

I frankly doubt that magnet vs accelerometer is going to make a material difference for most riding on tarmac, but I had in mind that I might want to measure power on my CX/gravel bike as well, so I went with a Pioneer left powermeter. Pioneer uses magnets for cadence. So, while I have a GSC-10, I realize I don't need the C. I thought, OK, might as well go with one of those magnetless speed sensors, except that those are also accelerometer based, so whatever problems apply to the cadence sensors also apply here. Hence the question.

[Mark McM]

A follow up question. Say I have a road bike which is going to spend most of its time on tarmac within range of a GPS signal. Imagine I'm either not interested in cadence, or that I'm using a powermeter which supplies cadence. Can I rely on the GPS speed alone?

Rely on it for what? How accurate do you need to measure speed?

I have a Garmin Edge 800 GPS unit. In my experience, the GPS derived speed measurement fluctuates noticeably, compared to a wheel magnet based computer. Furthermore, when riding under dense tree cover, the GPS experiences momentary drop-outs in signal. Does this affect my riding? Not really.

I did eventually get a speed sensor for the Edge 800, for one particular reason: The Edge 800 has a barometric altimeter, and is capable of calculating road grade. When going up steep hills, my speed naturally drops to a very low number, so the GPS-based speed fluctuations are a larger proportion compared to absolute speed, making the grade calculation very noisy and unreliable. The magnet wheel speed sensor smoothed out the speed measurement enough to get reasonable grade measurements at 15%+ grades.

[foo_fighter]

I would probably try the magene magnetless sensors. They can be converted to speed or cadence which makes them more versatile .

[weiwentg]

Rely on it for what? How accurate do you need to measure speed?

I have a Garmin Edge 800 GPS unit. In my experience, the GPS derived speed measurement fluctuates noticeably, compared to a wheel magnet based computer. Furthermore, when riding under dense tree cover, the GPS experiences momentary drop-outs in signal. Does this affect my riding? Not really.

I did eventually get a speed sensor for the Edge 800, for one particular reason: The Edge 800 has a barometric altimeter, and is capable of calculating road grade. When going up steep hills, my speed naturally drops to a very low number, so the GPS-based speed fluctuations are a larger proportion compared to absolute speed, making the grade calculation very noisy and unreliable. The magnet wheel speed sensor smoothed out the speed measurement enough to get reasonable grade measurements at 15%+ grades.

Good question. I was wondering if I could rely on the GPS alone to measure speed accurately in most riding conditions. And I can foresee occasionally being in a forest, where GPS may lose signal.

So, I think you answered my question. GPS speed alone is potentially not accurate compared to a magnet-based sensor. There's likely to be a significant penalty for some terrain. Probably going to get a separate speed sensor of some sort. I realize that while I'm riding, it may not matter what my speed really is, especially if I have a power meter.

I chuckle as I recall a thread you started last year (https://forums.thepaceline.net/showthread.php?t=208053&highlight=cycling+computer+coin+cell) where you expressed some reluctance to go with a full GPS unit at first. Well, you can welcome me to the dark side as well.

[Mark McM]

I chuckle as I recall a thread you started last year (https://forums.thepaceline.net/showthread.php?t=208053&highlight=cycling+computer+coin+cell) where you expressed some reluctance to go with a full GPS unit at first. Well, you can welcome me to the dark side as well.

Unfortunately, I was unable to find a single computer that met all my criteria, so I ended up with a hybrid approach. I've got a non-GPS coin cell computer that I use for all my rides, and on those occasions that I want to either measure power or use navigation, I pop on the GPS computer. My Sigma Rox 8.1 (coin cell) computer has all the other functions I could want (speed, average speed, maximum speed, cadence, ride distance, odometer, time, ride time, altitude, maximum altitude, altitude gain). Batteries last more than a year. Once or twice a week I'd like to add power measurement or moving map navigation, so I add a Garmin Edge 800 in addition to the Sigma. So I'm not quite in the 'full GSP unit' camp, since I rely on the Sigma for the majority of my cycling computer needs.

[sib]

I would probably try the magene magnetless sensors. They can be converted to speed or cadence which makes them more versatile.

I use the Magene as a speed sensor on one of my wheelsets.
It's been faultless so far (approx. 5000km).