Much point using Garmin wheel speed sensor?
Discussion
Can understand the point in a wheel speed sensor for those using turbo trainers perhaps, but what about for riding outdoors when I have my GPS unit? Can't imagine it'd be that much more accurate? I've just got a new bike and will likely swap between the 2, and don't fancy faffing about changing the sensor between bikes each time, or buying another if there isn't much point.
Cheers
Cheers
I had one fail last summer and it showed in some really weird peaks and troughs in the speed traces on Strava as the GPS signal dropped in and out; it also meant an awful lot of false auto-stop/auto-start moments on slow climbs and the beeping drove me up the wall after a bit - so I bought another one and have them on all the bikes.
I may be wrong, but I don't think the wheel speed sensor makes much of a difference to the overall numbers at the end of a ride. That's all based on distance, time, and some basic maths, using GPS pin-points on a map trace to determine distance traveled and average speed etc.
As I understand it, the wheel speed sensor is meant to make your instantaneous speed red-out more accurate. The GPS plots points on a map and calculates speed based on the distance between your last few reference points. As such it's always going to be slightly behind the curve, reporting what your speed WAS not what it currently IS. The wheel speed sensor simply counts revolutions, so reacts quicker to changes in speed.
As I said, though, I'm not an expert and am happy to be corrected if I'm talking out of my 'Arris on this subject.
As far as sensors go, I have a custom Bontrager sensor on my Trek Emonda - it's recessed into the non-drive side chainstay and measures wheel speed and cadence at the pedals. The sensor that came with my Garmin is on a second (currently unserviceable) 'winter' road bike, cable-tied to the chainstay (but was) doing the same job. My third bike, a Giant Anthem MTB, has no speed or cadence sensors fitted.
I don't really use the cadence data much anyway. I've tried to use the sensors to train myself to pedal faster in lower gears, but I haven't had much luck. So I would probably be entirely happy riding without sensors of any kind really. I don't think it would alter my approach to bike riding at all. And I certainly don't see the need for cadence/wheel speed data on the Garmin display while MTBing - it'd be a massive distraction when my attention ought to be focused on the trail ahead, not doing mental maths with the numbers scrolling on GPS screens.
Anyone who remembers riding with me on the PH 'Tour de France' ride from Cambridge to London will remember the very irritating speed and cadence alarms that were beeping and chirping the whole ride through because I had failed to learn how to disable them (they were set up by the Garmin's previous owner who sold it to me on ebay). The "Tour de PistonHeads" was back in May 2015, yet I'd had the GPS since late 2013, and didn't finally get around to disabling the cadence alert until the start of the #Festive500 in late December 2017.
As far as accuracy of the speed sensor goes? Well I've come back after a few rides and uploaded data only to find Strava showing that I've (momentarily) achieved insane speeds, right up to 70, 80, or 90+ mph. Yet the GPS head unit didn't display anywhere near such silly speeds. So I think it might well give you a more realistic idea of your actual speed in moments where GPS drift or a momentary glitch might suggest otherwise. I'm fairly certain, though, that it doesn't record the instantaneous read-out nor incorporate it into the GPS file data...
As I understand it, the wheel speed sensor is meant to make your instantaneous speed red-out more accurate. The GPS plots points on a map and calculates speed based on the distance between your last few reference points. As such it's always going to be slightly behind the curve, reporting what your speed WAS not what it currently IS. The wheel speed sensor simply counts revolutions, so reacts quicker to changes in speed.
As I said, though, I'm not an expert and am happy to be corrected if I'm talking out of my 'Arris on this subject.
As far as sensors go, I have a custom Bontrager sensor on my Trek Emonda - it's recessed into the non-drive side chainstay and measures wheel speed and cadence at the pedals. The sensor that came with my Garmin is on a second (currently unserviceable) 'winter' road bike, cable-tied to the chainstay (but was) doing the same job. My third bike, a Giant Anthem MTB, has no speed or cadence sensors fitted.
I don't really use the cadence data much anyway. I've tried to use the sensors to train myself to pedal faster in lower gears, but I haven't had much luck. So I would probably be entirely happy riding without sensors of any kind really. I don't think it would alter my approach to bike riding at all. And I certainly don't see the need for cadence/wheel speed data on the Garmin display while MTBing - it'd be a massive distraction when my attention ought to be focused on the trail ahead, not doing mental maths with the numbers scrolling on GPS screens.
Anyone who remembers riding with me on the PH 'Tour de France' ride from Cambridge to London will remember the very irritating speed and cadence alarms that were beeping and chirping the whole ride through because I had failed to learn how to disable them (they were set up by the Garmin's previous owner who sold it to me on ebay). The "Tour de PistonHeads" was back in May 2015, yet I'd had the GPS since late 2013, and didn't finally get around to disabling the cadence alert until the start of the #Festive500 in late December 2017.
As far as accuracy of the speed sensor goes? Well I've come back after a few rides and uploaded data only to find Strava showing that I've (momentarily) achieved insane speeds, right up to 70, 80, or 90+ mph. Yet the GPS head unit didn't display anywhere near such silly speeds. So I think it might well give you a more realistic idea of your actual speed in moments where GPS drift or a momentary glitch might suggest otherwise. I'm fairly certain, though, that it doesn't record the instantaneous read-out nor incorporate it into the GPS file data...
Edited by yellowjack on Tuesday 9th January 09:20
I'll order another one then I think My Garmin hub mounted one still works but doesn't auto turn off, so it gets removed and the battery door opened every ride.
GPS speed can be effected by plenty of things so I always prefer to have a wheel mounted one. I do find the edge 1000 terrible for battery so on long rides I have disabled speed and cadence and just left HR and power connected, you can normally eek out a few more hours with less things connected.
When you are climbing steep climbs GPS can get confused.
Saying that I have recharged the Edge on the go now so that is less of an issue. May get a Wahoo speed sensor as the Garmin ones seem to only be available with a cadence sensor.
GPS speed can be effected by plenty of things so I always prefer to have a wheel mounted one. I do find the edge 1000 terrible for battery so on long rides I have disabled speed and cadence and just left HR and power connected, you can normally eek out a few more hours with less things connected.
When you are climbing steep climbs GPS can get confused.
Saying that I have recharged the Edge on the go now so that is less of an issue. May get a Wahoo speed sensor as the Garmin ones seem to only be available with a cadence sensor.
Jeez, didn't realise they were £30 or so! Mind you, I've spent £4500 on the bike, £650ish for power meter, £150 for a new saddle, £30 or so for a raceware garmin mount, £100 for some ultegra pedals, £60 for a different cassette for the bike and again another £60 for a cassette for my Wahoo kickr and Christ knows what else....another £30 won't do much harm 
I just bought a couple of Chinese sensors from aliexpress so I can have stuff set up on all my bikes. They do one for about a tenner and you can switch it between it being a speed or a cadence sensor. Whip the battery out and put it back in again to switch between the two. So far they seem to work fine and have reasonable reviews. They look quite a lot like the garmin cadence sensor.
They are called the Magene Gemini 200
https://www.aliexpress.com/item/MAGENE-Computer-sp...
They are called the Magene Gemini 200
https://www.aliexpress.com/item/MAGENE-Computer-sp...
The thing about GPS is that at any time your reported GPS position could be anywhere within a 'sphere of positional noise' for want of a better description depending on how many satellites you are receiving (you need a minimum of 3 to calculate position), if you are travelling at say 40km/hr and the GPS unit is calculating speed based on positions taken every 10 seconds then a 5m error in a GPS position will give about a 5% error in the calculated speed. The calculated speeds are averaged out so are accurate over time. I imagine most devices will also throw away some readings.
Where this becomes more of a problem is if you slow down, it takes longer to get an accurate speed which really becomes a problem for those of us who run as not only are we going much slower but we also don't want to have to wait ages to get an accurate measurement of pace!! The answer is to use a stride sensor which is the running equivalent of your wheel sensor!!
Basically, if you are really interested in accurate pace readings then use a wheel sensor! It will also keep working when the road goes through an avenue of trees.
Where this becomes more of a problem is if you slow down, it takes longer to get an accurate speed which really becomes a problem for those of us who run as not only are we going much slower but we also don't want to have to wait ages to get an accurate measurement of pace!! The answer is to use a stride sensor which is the running equivalent of your wheel sensor!!
Basically, if you are really interested in accurate pace readings then use a wheel sensor! It will also keep working when the road goes through an avenue of trees.
A consideration you need to make is how GPS is affected by ‘dead zones’. If you find yourself in a very remote / built up / shielded by terrain / trees area, the GPS sensors can go very screwy. The wheel speed sensors don’t differentiate, so you’re far more unlikely to get screwy data.
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