Speedo over reading and the effects.

[alhendo1 3,066]

This has got me interested☺..if this has been covered prior to my time on the forum please accept my apologies.......having read DaveM59s post yesterday re the new scooter and the Forza speedo over reading 77mph versus 70 mph I had a look online and it appears from what I can see cars and motorcycles sold in the UK generally overestimate your speed (not legally allowed to underestimate ) ...now I've not ran a Gps app to see if my 2018 CB500x is overestimating but it definately feels as if it does.Quite a number of times I've driven through villages/towns where you get the smiley/sad face sensor thingy clocking your speed and the results suggest the speedo is ambitious....eg yesterday two of them said I was doing 29mph when my speedo said 32mph....so I have a couple of questions. 

 Let's say the speedo is 10% overestimating....does the speedometer work from the same sensor as the odometer? If so does that mean my bikes stated mileage will be showing 10% more than it's actually done.....and if that's the case then when I'm calculating my mpg figures (manually...litres to gallons then divide miles covered by gallons) then the result won't be so generous. I have had a look online and there are some discussions but they tend to fizzle out with no real answer. Please feel free to tell me if I'm overthinking this one...😅....your input would be appreciated. 

 

[Andy m 23,764]

The CB500 generally seems close at city speeds and the full 10% at illegal ones. 

 

Andy

[alhendo1 3,066]

Just now, Andy m said:

The CB500 generally seems close at city speeds and the full 10% at illegal ones. 

 

Andy

Yes I'd agree hence the couple of mph discrepancy in the 30s I find.

[elbee 754]

I found my bike is about 6-7% optimistic when I took the time to ride out and compare the speedometer with GPS.

 

I didn't bother with mileage accuracy but that is easy - find a measured mile*, set a trip meter at the start. There's an excuse for a ride.

 

* Preferably find a measured mile on an OS map first. Finding mile markers on a charity marathon and scattering runners is frowned upon. 

[Andy m 23,764]

To check the odometer why not just compare to Google maps? Probably means riding a fairly known and less interesting route when there is no traffic. A commuter doing the same route ten times would be better. 

 

Personally I don't worry that much. Range is about planning, but you allow safety and when it goes on reserve watch the counter. MPG for me is a case of looking for changes to spot if anything is wrong before it gets serious, so if ten figures are all wrong in the same way it's fine. 

 

Andy

[alhendo1 3,066]

5 minutes ago, Andy m said:

To check the odometer why not just compare to Google maps? Probably means riding a fairly known and less interesting route when there is no traffic. A commuter doing the same route ten times would be better. 

 

Personally I don't worry that much. Range is about planning, but you allow safety and when it goes on reserve watch the counter. MPG for me is a case of looking for changes to spot if anything is wrong before it gets serious, so if ten figures are all wrong in the same way it's fine. 

 

Andy

Mpg is the same for me...I generally do the same....keep an eye out for anything amiss....the bit I can't get my head round is if I adhere to the 8k service interval and the speedo/odometer is 10% over then I'm actually getting it serviced around 700/800 miles early....I am overdoing this aren't I.....😅

[listener 11,322]

49 minutes ago, alhendo1 said:

does the speedometer work from the same sensor as the odometer?

 

It would be interesting to know where the speed and distance signals come from.

 

In the olden days () the speedo and odo were driven, via a cable, from a worm gear at the front wheel.

I once enjoyed the thrill of riding at 0mph (yes zero) on the A90, between Aberdeen and Stonehaven - while the scenery sped by at 'approximately' 70mph!  

[fred_jb 10,269]

There is no reason why the odometer reading should also have any adjustment applied as, when speedo and odometer are both electronically driven, depending on how it is done, the speedo can be made to read high without necessarily affecting the odometer, though from the point of view of services coming around sooner than they should I guess manufacturers would benefit if the odometer also was running fast!  There is probably also some standard about how accurate the odometer should be but I've never come across any information on that.

[Rev Ken 6,348]

uEvery Honda I have owned reads 32mph at a GPS 30, and 64mph at 60. Odometers have always been as accurate as I could assess. (I too remember the days when we had cable driven speedos bit I can't remember the name of the most accurate. All I remember is that it sampled every few revs before changing the reading. In an emergency stop I could apparently still be doing 60mph while sitting with both feet on the ground!

Edited September 6, 2019 by Rev Ken

[alhendo1 3,066]

17 minutes ago, fred_jb said:

There is no reason why the odometer reading should also have any adjustment applied as, when speedo and odometer are both electronically driven, depending on how it is done, the speedo can be made to read high without necessarily affecting the odometer, though from the point of view of services coming around sooner than they should I guess manufacturers would benefit if the odometer also was running fast!  There is probably also some standard about how accurate the odometer should be but I've never come across any information on that.

Thanks Fred jb....I appreciate for me anyway)...the value of having a slightly over reading speedo....I hope you're right re them being able to differentiate on how they're set up..ie the odometer should read accurately as that would definately affect miles covered being read inaccurately /services coming round sooner/innacurate mpg calculations.....I get how it would suit the dealer but not the customer....VWgate anyone.....

The thing is....me being a kind of mechanical numpty does anyone know how speed and mileage is calculated on the CB500x/NC750 as I can only see the abs sensor on the front wheel....is it some kind of magnet that picks up rotations or is it some other kind of electrical sensor reading from somewhere else?.....

[SteveThackery 3,090]

14 minutes ago, alhendo1 said:

The thing is....me being a kind of mechanical numpty does anyone know how speed and mileage is calculated on the CB500x/NC750 as I can only see the abs sensor on the front wheel....is it some kind of magnet that picks up rotations or is it some other kind of electrical sensor reading from somewhere else?.....

 

In a way it doesn't matter where the speed signal comes from.  It's all processed in software to produce the odometer and speedometer readings, and any adjustment from the "true" reading will be implemented in the software.  The only possible sources of inaccuracy in a standard bike are minor differences in rolling radius of the wheels, due to tyre pressure variations and tyre carcass shape.

Having said all that, I recall reading in this forum that changing the rear sprocket to one of the wrong size can cause speedo inaccuracy, which suggests that the speed sensing is from the output shaft of the gearbox.  I might be wrong - someone will be along to say for sure.

 

So, if the gearing is correct, then any inaccuracies (high or low) will be deliberately programmed into the software (notwithstanding that minor issue about tyre pressures).

[alhendo1 3,066]

8 minutes ago, SteveThackery said:

 

In a way it doesn't matter where the speed signal comes from.  It's all processed in software to produce the odometer and speedometer readings, and any adjustment from the "true" reading will be implemented in the software.  The only possible sources of inaccuracy in a standard bike are minor differences in rolling radius of the wheels, due to tyre pressure variations and tyre carcass shape.

Having said all that, I recall reading in this forum that changing the rear sprocket to one of the wrong size can cause speedo inaccuracy, which suggests that the speed sensing is from the output shaft of the gearbox.  I might be wrong - someone will be along to say for sure.

 

So, if the gearing is correct, then any inaccuracies (high or low) will be deliberately programmed into the software (notwithstanding that minor issue about tyre pressures).

Thanks Steve...I think you might be onto something there.....this has kind of jogged my memory a bit....I remember reading somewhere about a fairly common mod for the CB500x come time to change the chain and sprockets is to stick a 16 tooth front sprocket on on instead of a 15 tooth....or vice versa....apparently it drops the revs down a bit at motorway speeds....I seem to remember a couple of posts stating that this mod brings the speedo down to nearer a true reading.....does this make any sense to you.......

Good call with the tyre variations....I realised different tyres would have that effect but didn't think about pressures and carcass shape...

[SteveThackery 3,090]

2 minutes ago, alhendo1 said:

Thanks Steve...I think you might be onto something there.....this has kind of jogged my memory a bit....I remember reading somewhere about a fairly common mod for the CB500x come time to change the chain and sprockets is to stick a 16 tooth front sprocket on on instead of a 15 tooth....or vice versa....apparently it drops the revs down a bit at motorway speeds....I seem to remember a couple of posts stating that this mod brings the speedo down to nearer a true reading.....does this make any sense to you.......

 

It does indeed, yes, and a minor change like that may well cancel out much of the deliberate over-reading built into the speedo.

 

I should point out that the old fashioned mechanical speedos can be very inaccurate - either fast or slow - because many factors can affect their accuracy: the strength of the spinning magnet; the spacing between the magnet and the aluminium cup; the spring rate and preload of the spiral spring which acts to pull the speedo needle back to the rest position; and finally the positioning of the needle on its shaft.

 

Thank goodness all that stuff is behind us with modern bikes.

[alhendo1 3,066]

1 minute ago, SteveThackery said:

 

It does indeed, yes, and a minor change like that may well cancel out much of the deliberate over-reading built into the speedo.

 

I should point out that the old fashioned mechanical speedos can be very inaccurate - either fast or slow - because many factors can affect their accuracy: the strength of the spinning magnet; the spacing between the magnet and the aluminium cup; the spring rate and preload of the spiral spring which acts to pull the speedo needle back to the rest position; and finally the positioning of the needle on its shaft.

 

Thank goodness all that stuff is behind us with modern bikes.

I've just found this on an internet thread re CB500x road speed sensor... "The bike road speed sensor is separate from the ABS system. The ABS uses wheel mounted sensors that are used by the ABS computer to compare front and back wheels speeds, however the bike road speed sensor (VS sensor) is on the top of the gearbox and is the same for ABS and non ABS models. You'll find a picture on page 1-75 of the shop manual. There is a black connector plug with three wires on it. It's hard to see, and even harder to get to, but it has been done."

[SteveThackery 3,090]

1 minute ago, alhendo1 said:

I've just found this on an internet thread re CB500x road speed sensor... "The bike road speed sensor is separate from the ABS system. The ABS uses wheel mounted sensors that are used by the ABS computer to compare front and back wheels speeds, however the bike road speed sensor (VS sensor) is on the top of the gearbox and is the same for ABS and non ABS models. You'll find a picture on page 1-75 of the shop manual. There is a black connector plug with three wires on it. It's hard to see, and even harder to get to, but it has been done."

 

Sorted, then!  

[alhendo1 3,066]

1 minute ago, SteveThackery said:

Sorted, then!  

Assuming UK models software seperates over reading of the speedo and gives accurate reading of the odometer then yes👍Thanks for the posts so far folks.

[SteveThackery 3,090]

Just now, alhendo1 said:

Assuming UK models software seperates over reading of the speedo and gives accurate reading of the odometer then yes👍Thanks for the posts so far folks.

 

Indeed, assuming that.  My concern is that we've probably no way of knowing that without actually doing some road tests under controlled conditions for speed and distance - which would be an awful lot of bother.

[Rev Ken 6,348]

1 hour ago, SteveThackery said:

 

Indeed, assuming that.  My concern is that we've probably no way of knowing that without actually doing some road tests under controlled conditions for speed and distance - which would be an awful lot of bother.

Within reason any satnav can give you a reference point and will be more accurate than your speedo and even your odometer.

[SteveThackery 3,090]

2 hours ago, Rev Ken said:

Within reason any satnav can give you a reference point and will be more accurate than your speedo and even your odometer.

 

I agree, it should be able to in theory.  I've noticed that sometimes the speed readout on my GPS can be a bit "splashy", presumably due to minor jitter in the received signal and varying reception conditions.  I think (but correct me if I'm wrong) that the GPS velocity data from the GPS receiver chip is updated once per second, which implies that it is probably calculated once per second, so you don't need much positioning error for the calculated speed to be off by a noticeable amount.

 

Having said that, I used GPS to calibrate the speedo on my Bullet, but I used a dead straight, dead flat dual carriageway late at night, so I could maintain the most constant possible speed.

[SteveThackery 3,090]

2 hours ago, Rev Ken said:

......and even your odometer.

 

By the way, one of my uni lecturers told me that the GPS distance calculation only uses the two horizontal planes (X and Y) and not the altitude plane (Z).  In other words, it measures your distance by looking down on you from above to see how far you've gone, so to speak.  Thus it doesn't take into account the extra distance due to going up and down hills, so in hilly country it will underestimate the distance that a "true" odometer would have recorded.

 

I don't know if that's true - it's just what the lecturer said.  In any case I reckon the error would be trivial.

[fred_jb 10,269]

6 minutes ago, SteveThackery said:

 

By the way, one of my uni lecturers told me that the GPS distance calculation only uses the two horizontal planes (X and Y) and not the altitude plane (Z).  In other words, it measures your distance by looking down on you from above to see how far you've gone, so to speak.  Thus it doesn't take into account the extra distance due to going up and down hills, so in hilly country it will underestimate the distance that a "true" odometer would have recorded.

 

I don't know if that's true - it's just what the lecturer said.  In any case I reckon the error would be trivial.

We had a discussion about that some time ago, I seem to remember applying some schoolboy O level maths to this and finding that you need a pretty steep slope to get a signicant error.

 

 

Edited September 6, 2019 by fred_jb

[SteveThackery 3,090]

2 minutes ago, fred_jb said:

We had a discussion about that some time ago, I seem to remember applying some schoolboy O level maths to this and finding that you need a pretty steep slope to get a signicant error.

 

I went to meet a native American man the other day.  He welcomed me into his wigwam, and in the gloom I saw two young women, each sitting on what looked like a bear hide, and an elegant older woman who was sitting on a very impressive hippopotamus hide which must have been imported from Africa.

 

He said, "Let me introduce my wife and daughters: the squaw on the hippopotamus is the mum of the squaws on the other two hides".

[Hickky 3,131]

I have never yet come across a car or bike with an accurate speedo. Police cars no longer have accurate ones fitted, they use satellite speed recorded on video. Speed limits to nick you are roughly satnav speed plus 10% plus 2mph. So find out how fast this reads on your speedo on the bike at say 30,40,50,60,and 70mph. Once you get this information, ride a bit slower that these absolute maximums when in limits below 40 and keep your eyes peeled when you know your taking a risk! 

Mileage readings don't really matter as getting the plot serviced early can only enhance safety, unless you are a ham fisted owner who doesn't know what he (she's are too sensible) is doing but is too stupid to get in someone who knows. In which case any accident can also improve safety for nearly all other road users.

[Andy m 23,764]

The speedo on the CL is a laugh, 46 year old glycerin must be a bit gloopy as it will still be showing 20 after you've stopped, got it on the stand and opened the garage door. One (of many) ways to start fights with the classic loons is to note the likes of Smiths are really poor against a modern bicycle unit or your phone. 

 

GPS is going to use the old navigation tables. Navigators broke the world into a series of flat surfaces to avoid the worse bits of geometry in world that is shaped like a lemon rotating on a cocktail stick shoved through not quite the shortest axis. The difference in a flat 60 mile wide slice taken off an 8000 mile wide object versus the curve is pretty minimal. The people setting up 1970's computers to do the work would have been daft to do it the hard way. That said, when track testing they add ground beacons to the GPS data for accuracy. Phone based system can also use the mobile cells. Ground navigators would add slopes as simple ratios (hence 1:25 etc. on proper maps) or go by what the last bloke measured. Google maps is your solution in most places. If there are crevasses between you and where you want to be I imagine you do it the old fashioned way. 

 

Andy

 

 

[Tex 36,817]

 

Quote

Odometers have always been as accurate as I could assess. (I too remember the days when we had cable driven speedos bit I can't remember the name of the most accurate. All I remember is that it sampled every few revs before changing the reading. In an emergency stop I could apparently still be doing 60mph while sitting with both feet on the ground!

 

That would be the Smiths ‘Chronmetric’ unit. The needles of both speedo and tachometer moved in a series of ‘ticks’ rather than the smooth sweep of a magnetic unit. 

 

Edit: For our younger viewers, this is them in action..

 

 

Edited September 7, 2019 by Tex