I have a Carrera Crossfuse with a Bosch Purion display plus a Livall Bluetooth helmet which pairs with the Livall app. When I use the bike, I see a different speed on the Bosch display (which presumably picks up speed from the sensor mounted on the rear wheel) to the speed displayed on the app (which presumably uses GPS). Does anyone else see the same thing happening? Which speed is correct?
Speed Difference
- Thread starter pauls
- Start date
Unless you have a poor GPS its speed should be pretty accurate. However, a small jitter error on GPS can lead to grossly distorted speed reading (like being stationary and being told you are going at 3mph). When I had a mid-range LG (?LG-G3?) the GPS was pretty poor; my cheapo Numo 20 is much better for GPS (partly why I chose it).
The Purion display speed could be wrong if the wheel size is wrong (even fitting different tyres changes it a bit), otherwise it should be accurate too. You haven't said how big or how consistent the difference is.
The Purion display speed could be wrong if the wheel size is wrong (even fitting different tyres changes it a bit), otherwise it should be accurate too. You haven't said how big or how consistent the difference is.
To check the GPS
1) stay still for a while and see what speed it registers
2) record a track while riding a straight road, and then look at it really zoomed in to see how straight the recorded track is.
There have been a few complaints about incorrect speed reading on the Purion: it looks as if you can't even query the wheel size setting, let alone change it.
1) stay still for a while and see what speed it registers
2) record a track while riding a straight road, and then look at it really zoomed in to see how straight the recorded track is.
There have been a few complaints about incorrect speed reading on the Purion: it looks as if you can't even query the wheel size setting, let alone change it.
Should be but probably a generalisation based on average tyre, tyre pressure, tyre profile ......
And what speed are you seeing this difference at?
GPS requires a bit of time to do the calculation - such a small error is splitting hairs imho.
if you want the right speed then use something else as the bosch purion display can be out 1-2mph either way same as the old one.
a dealer can dial it in with the wheel size if i remember as i was able to do this with the intuvia display but not a option with purion.
a dealer can dial it in with the wheel size if i remember as i was able to do this with the intuvia display but not a option with purion.
I would think the most accurate device for measuring your speed is something like one of the Cateye cycle meters in which you can enter the exact (to within a cm) circumference of your cycle tyre. Update rates are very fast too.
I'd rather believe a garmin GPS, but it has to be in non power save mode, have a lock on at least 8 satellites, and take the average over a minute or so. Oh, and you have to be under 600mph (?) or something, else you need a military version.
Under proper conditions it gets the right answer regardless of wheel size, tyre spin, or ebike electronic optimism. I use an ancient gpsmap 62.
I notice the difference at about 9-10mph. At that speed, the difference is about 10% so the trip and range could also be 10% out.
Uncertainty principal applies to any instantaneous measurement.. If you count wheel revs per unit of time you have a +/- 1 rev error, and if you time one rev you maybe have speed changing every second or two, which would be confusing as heck. You really need to worry about the average over a reasonable period or distance..
Easiest way to check is over distance. The further you go the more the difference becomes. I found that every bosch bike I have owned shows around 1mph above.
I ride somet
I sometimes cycle with a friend, him Bosch me Yamaha. At the end of the ride he’s always completed abut 1-2miles further than me comparing odometers.
The Bosch system registers the speed using a simple magnet attached to one of the spokes on the rear wheel as it passes a sensor. I'm wondering if I adjusted the location of the magnet it might correct the inaccurate readings? Do I move it towards the centre of the wheel or towards the rim? Not sure?
One thing to bear in mind, even if the wheel size is set correctly, tyre type can make a significant difference...eg a 700c wheel with a 20-622 tyre is 2100mm circumference, whereas a 60-622 is 2340mm.
www.schwalbetires.com
So it's important to set up your circumference properly on your speed gauge. CatEye allow you to put this value in. But don't believe the tables for circumference, measure it yourself with a tape measure, or a piece of string and then measure the length of the string.
Tire Dimensions | Schwalbe Tires North America
What is the exact circumference of my tire? Why are tires often narrower than the stated tire size?
So it's important to set up your circumference properly on your speed gauge. CatEye allow you to put this value in. But don't believe the tables for circumference, measure it yourself with a tape measure, or a piece of string and then measure the length of the string.
It won't matter, one revolution is one revolution, so long as pulses are not missed because of the gap being too big between the magnet and the sensor.
How do I set the wheel size. I believe the wheel is 700c but the bike is new so I'm assuming that this will have been set by Bosch / Carrera / Halfords? I can't see any way to adjust this setting in the Bosch controller.One thing to bear in mind, even if the wheel size is set correctly, tyre type can make a significant difference...eg a 700c wheel with a 20-622 tyre is 2100mm circumference, whereas a 60-622 is 2340mm.
Tire Dimensions | Schwalbe Tires North America
What is the exact circumference of my tire? Why are tires often narrower than the stated tire size?
So it's important to set up your circumference properly on your speed gauge. CatEye allow you to put this value in. But don't believe the tables for circumference, measure it yourself with a tape measure, or a piece of string and then measure the length of the string.
It makes no difference where you put it, it's still one pulse per rotation. If you put it too far from the sensor, you'll get an error code come up and the motor will stop.
That's annoying...so if you change your tyre type it's back to the dealer and hand over cash if you want the thing to report properly.
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