How does my E8000 measure km/h?

[pegnose]

Comparing my travel distance with Google maps routing it seems that my bike counts too many kilometers, something like 45 km Google and 53 km Shimano. I was wondering whether my wheel circumference is setup wrong.

However, on the interwebs I read that if that is the case, the bike would stop motor support at the wrong speed. People reported motor support stopping at 19 km/h and that Shimano fixed this remotely via setting the correct wheel size. Mine does stop the support at exactly 25 km/h taken from the display.

I am asking myself: How could it be that the bike has a different speed estimation than from wheel rotation? It can't right? So if the wheel size is set wrong, the bike would not know. It would count more or less km or miles from the same amount of wheel rotations. But it would still report cutting out motor support at the correct speed, as it just can't know better. It has only one way of speed estimation. Is that correct?

 

[Gary]

Yes. The E8000 measures speed from the speed sensor and wheel circumference (just like any non GPS cycle computer)
Wheel circumference is set from the factory (but can be changed via Shimano Steps E-max or 3rd party software like stepsUnlocker App)

Your GPS plots points every 1-3 seconds and then software collates the plotting into data

Neither are hugely accurate.

 

[pegnose]

Thanks, @Gary . So people on the webs claiming that their motor cutting support at 19 km/h display-reported speed getting fixed by correcting the set wheel size cannot be correct.

And my wheel size might actually be set incorrectly (slightly too large it seems).

EDIT: Now I only have to find out the circumference of my Rekon+.

 

[Gary]

I've absolutely no idea whether some random people on the webs claims are correct or incorrect. Nor do I care TBH.

I don't even know what rear tyre you have but yes tyre circumference could well be set incorrectly on your E8000.
On my E8000 wheel circumference is set to 2265mm (the value the bike came with) which equates roughly to a 27.5x 2.7 tyre but in actual fact I run a 27.5x2.3 rear (2200mm circumference). That's 2% out. or close enough that I don't really care. (well not enough to shell out £30 for a license to correct it anyway).

If you want to check yours download @vadII's StepsUnlocker App from the App store for android or IOS. it's £1.49.
if you want to change the value you'll need to buy a license for the App at around £30

 

[pegnose]

The reasoning was that an incorrectly set circumference can't change the displayed speed at which the motor cuts out.

Anyways, thank you. I'll think about it. I am more and more willing to pay for good/helpful software. I also added my tires above, just forgot to press save, obviously. They are the Maxxis Rekon+.

I think I'll first do a cross-check with GPS data or a otherwise specified distance. We have an abandoned air field here with an airstrip of known length. Might be enough to get an opinion.

I am wondering how much the rims, tire pressure, and my weight figure into the equation. Maybe all comes down to use case variance.

 

[Gary]

27.5x2.8 Rekon + will be right around (possibly slightly more than) the 2265mm my circumference is set to from factory.

Personally I'd put that £30 towards some decent tyres first

 

[33red]

A- i have a Rekon 2.8x27.5 on my 40 mm rear rim, it is great for our conditions near Montreal, Quebec.
B- move, here the cut off is 32 km/h
C- stop comparing, pedal, recharge

 

[pegnose]

@Gary That's what I thought. Close to 2300, possibly. Will check on StepsUnlocker today. I will get better tires once I feel they are starting to let me down. This will come with experience, I guess. Currently, I just can't tell. Which ones would you recommend? Depending on where I go I get a good mixture of every terrain, maybe except wet and muddy ground.

@33red I just like to figure out how stuff works. However, I'll strongly consider Canada next time I move. I've heard it is beautiful there.

 

[HORSPWR]

Comparing my travel distance with Google maps routing it seems that my bike counts too many kilometers, something like 45 km Google and 53 km Shimano. I was wondering whether my wheel circumference is setup wrong.

However, on the interwebs I read that if that is the case, the bike would stop motor support at the wrong speed. People reported motor support stopping at 19 km/h and that Shimano fixed this remotely via setting the correct wheel size. Mine does stop the support at exactly 25 km/h taken from the display.

I am asking myself: How could it be that the bike has a different speed estimation than from wheel rotation? It can't right? So if the wheel size is set wrong, the bike would not know. It would count more or less km or miles from the same amount of wheel rotations. But it would still report cutting out motor support at the correct speed, as it just can't know better. It has only one way of speed estimation. Is that correct?

My circumference was set wrong from the factory, my bike was always recording more ks than any 3rd party gps program so I reduced it to match. Those people who state that their assistance cutout at exactly 25kph are correct but the motor will use the speedo to do this, the true speed may well be different. You could set your wheel circumference to any size and the assistance will still cut out at 25kph but your true speed will be considerably more or less than this based on whether you increased or decreased wheel circumference.
IMO I don’t think the speed is all that accurate. My wife was in my car recently and I was riding along side her and I asked her what speed she was doing and she said 23kph, my bike was saying 19kph.

 

[Gary]

I was kinda joking about your tyres. I just hate plus tyres.

Car speedos ALL over read speed

 

[pegnose]

My circumference was set wrong from the factory, my bike was always recording more ks than any 3rd party gps program so I reduced it to match. Those people who state that their assistance cutout at exactly 25kph are correct but the motor will use the speedo to do this, the true speed may well be different. You could set your wheel circumference to any size and the assistance will still cut out at 25kph but your true speed will be considerably more or less than this based on whether you increased or decreased wheel circumference.
IMO I don’t think the speed is all that accurate. My wife was in my car recently and I was riding along side her and I asked her what speed she was doing and she said 23kph, my bike was saying 19kph.

Exactly my reasoning, thx.

HOWEVER, today I tested this and found that only up to 5% too many km are recorded by the bike, and the faster I go (the more steady I drive), the lower the km overshoot. My circumference is set to 2300 mm, might be correct afterall, or just ever so slightly too high.

[paragraph removed due to brain fart]

 

[HORSPWR]

Exactly my reasoning, thx.

HOWEVER, today I tested this and found that only up to 5% too many km are recorded by the bike, and the faster I go (the more steady I drive), the lower the km overshoot. My circumference is set to 2300 mm, might be correct afterall, or just ever so slightly too high.

[paragraph removed due to brain fart]

2300 is unless you are running 29" wheels?
I have mine set at 2190 for my 27" wheels.

 

[pegnose]

That would be roughly the 5% difference I observed.

 

[pegnose]

Interesting, the Maxxis support says:

"The outer diameter of 27.5x2.80 Rekon+ is 730 ± 30"

Millimeters, I guess. Yields a circumference of 2293.36 mm, which is nearly exactly what is set for my bike (3300 mm).

 

[lightning]

My Kona E160 came with the wheel
circumference set at 2350mm
lt's on 2.8" Plus tyres.

The speedometer on the bike claimed l had done 30 miles while Strava said it was 27.

That's not too much of a difference, but l checked my tyre with a tape measure and the actual circumference was 2260mm

l reset the wheel circumference to the correct figure, 2260mm

l went out on the same ride and this time Strava said 30.1 miles and the bike's speedometer was showing 29.7.

So the bike is now more accurate and l guess a little bit faster in assisted mode, although it's impossible to notice such a small difference.

l've done another ride today, Strava said 17.6 miles and the bike was 17.1

l think that's as good as it's going to get, the two systems are within 1mph of each other.

l would say it's worth making the adjustment but it does cost U.K. £30 for the premium app license, and if your Shimano FW is the new 4.9 it's necessary to downgrade it to the previous version before you can change the wheel size.

There is a +/- "speed" setting in the Shimano app that you can adjust. l couldn't find out what this does but it may be possible to use that to make the bike more accurate.

On my old Bosch Gen 3 motor you could adjust wheel circumference +/- 5% which was not quite enough but better than nothing.

 

[steve_sordy]

@pegnose With Maxxis Rekons, you have to take into account that the rear wheel may be skidding out and therefore recording more revs than the distance travelled by external sources would suggest.

 

[pegnose]

That might be true, @steve_sordy . I don't actually recall what kind of track I was testing on. But from my notion of going "faster" I guess it was road.

Thank you for reminding me, though. I'll probably get a new rear tire at some point in the near future. Will try something else. Maybe also the front one, which is where skidding always was more of a concern for me. There is an extensive tire thread here, I seem to remember.