[Closed] GPS Vs Speed Sensor

Probably not that big.

Suggestion is that a speed sensor will stop underreading speed/distance over switchbacks, and there’s the odd place with heavy tree cover where the GPS drops out…

Ah, but a speed sensor doesn't work when your wheels are off the ground 😉

(It also relies on being correctly calibrated for wheel size/tyre size and pressure. )

Ah, but a speed sensor doesn’t work when your wheels are off the ground

Maybe should of stated this is for road. Who cares about recording speed data off-road?

Watching with interest, as I'm getting a bit miffed with Strava/ Wahoo's variance in reporting my rides. Although I just do it from my phone, so not sure what the options are for sensors.

That will be more down to crap GPS in phone (compared to a dedicated GPS unit). Setting GPS recording to 1 second also improves accuracy, but not always an option depending on device (including dedicated GPS units).

(It also relies on being correctly calibrated for wheel size/tyre size and pressure)

don’t Garmins auto-calibrate the wheel size from gps?

Keep meaning to fit my cadence/speed sensor to see how it compares, my Lezyne struggles under heavy tree cover.

Must fit new tyres and calibrate with one wheel revolution with me on bike with typical gear at typical pressure.

don’t Garmins auto-calibrate the wheel size from gps?

Yes they do.

A Wheel speed sensor is probably only really beneficial if you want to know your current speed more precisely, but that's not a field I find all that useful when riding. I'm happy with an Avg speed worked out from GPS alone TBH...

From a recorded data point of view HR and cadence are probably more useful that wheel speed, assuming the trace is reasonable enough to indicate position, it let's you gauge your physical workload/effort at any given point in a ride...

The only time I think a wheel speed sensor is useful is on a turbo trainer perhaps?

I found a speed sensor helped at the lower speed ranges, the speed reading on my edge would often jump around during slow climbs and there was more of a lag detecting speed changes

@docgeoffyjones - was your Edge set to record every second? And does it have auto-pause activated?

No auto pause, i don't think the edge had every second recording

The only time I think a wheel speed sensor is useful is on a turbo trainer perhaps?

I found a speed sensor helped at the lower speed ranges

I get this on my gravel bike. Slow climbs and hike a bike and the ride auto pauses, thus missing out moving time.

I’m happy with an Avg speed worked out from GPS alone

But dotn you need accurate current speed to get accurate avg? That's another question. Does the GPS recalculate at the end of the ride? Like does it know how far you have travelled (including the parts under tree cover etc) and time taken to give you average speed etc? Or does it calculate on the fly and use the final figure when you stop recording? Does that make sense?

DickBarton
Subscriber

That will be more down to crap GPS in phone (compared to a dedicated GPS unit).

Ah, good to know. Gives me an excuse to find a decent sub £100 GPS to use

Or does it calculate on the fly and use the final figure when you stop recording?

I think the GPS just records where you are and at what time at frequent intervals (as well as recording whatever stuff it records, like HR etc.), then calculates everything else from that.

I think the GPS just records where you are and at what time at frequent intervals (as well as recording whatever stuff it records, like HR etc.), then calculates everything else from that.

So then tree cover will have little effect unless it's at the very start or very end of the ride or on a sharp bend where the GPS will cut the corner.

But dotn you need accurate current speed to get accurate avg?

Not really TBH if I pedal harder for a mile I notice the avg creeping up by 0.1mph, that is all I really need, a general indication of what a given level of effort is achieving.

Of course if my HR is in zone 5.4 and my cadence is dipping too low then I know my effort isn't sustainable and/or my gearing is too high, wheel speed is far less useful than knowing if your engine is about to blow a gasket...

Post ride avg as shown on strava is probably just down to the accuracy of the GPS trace, which will of course have time stamps taken from the GPS signal, the distance recorded is the distance recorded (inaccuracies and all), it more than likely disregards the wheel Speed sensor when calculating distance travelled...

The real question is how "accurate" does it really need to be? What changes for you if it says you did a 42.2 mile ride at 17.2mph avg when it was really 17.3 avg over 42.1 miles?

There is an inherent lack of precision with GPS, your relying on a matchbox sized receiver/processor picking up and recording the signals from satellites 12.5k miles overhead, +/- a couple of hundred metres over 50 odd miles is an acceptable margin of error IMO and affects the record taken minimally...

There is an inherent lack of precision with GPS, your relying on a matchbox sized receiver/processor picking up and recording the signals from satellites 12.5k miles overhead,

There are lots different levels of precision with GPS etc. Absolute location is lowest, relative location will be better as absolute errors/offsets drop out. I suspect a lot of perceived problems are just a low sampling rate, which is configured to maximise battery life.

Differential GPS, used for surveying is accurate down to around 1 cm.