Speedo innacuracies

[Jon]

i noted my innova's speedo was 10% fast, as many speedo's are. I also noticed the recommended rear tyre is a 80/90, which is quite low profile.

Now, i think the innova's electronic speedo is driven from a sender in the gearbox, it certainly isn't a cable driven one off the front wheel.

This means the diameter of the rear wheel will effect the actual speed of the bike but won't change the gearbox's revs.

Honda would have realised that owners will often fit older type tyres like the generic Cub style 2.25/17. This kind of tyre has a 100% aspect ratio. if that older tyre was taller than the recommended tyre the bike will travel faster for the same speedo reading...

If you fit a taller 120/90/18 onto a Kawasaki W650 in place of the factory 130/80/18, the speedometer gets more accurate...

Maybe Honda are anticipating the same possibility...

[digger06]

maybe its something to do with speed cameras
and manufacturers not wanting to be sued for clocks reading 30mph
but really going fast enough for a speeding ticket

[Jon]

maybe its something to do with speed cameras
and manufacturers not wanting to be sued for clocks reading 30mph
but really going fast enough for a speeding ticket

I'm sure that was the reason initially...Even before cameras Police cars had extremely accurate speed measuring equipment including radar and VASCAR but the older mechanical speedos could be substantially out so a 10% error was understandable, these newer instruments are a lot easier to calibrate and build with closer tolerances, they are in effect the same technology as an electricians analogue multi-meter, accurate to better than a fraction of 1 percent so Honda might have built-in enough leeway to allow for the tallest tyre the bike can have fitted.

Like i say, the electronic speedo on the W650 got as close as just 5% fast with a TT100 4.00/18 on the back. With it's 130/80 it is 10% out, and all the W650's on our forum, 3,000 of them, are out by exactly the same amount!

[digger06]

yup, all will/should be the same, but it only takes one to get you a ticket and they are sued ,,
its not worth building a speedo thats 100%accurate, what if its just 1mph fast ?
thats 31mph in a 30, some areas you get a ticket for that,,,
your safer with a fast speedo, and its cheaper for the makers and you if theres cameras all over
its the reason honda europe (especially) did it,it copes with tyre and speedo error variations

if you want a speedo accurate just move your needle in the clock,,,but its common knowledge they read fast
so who cares? you know what speed your doing, 50mph or 52 and a half? does it matter?

[digger06]

they are in effect the same technology as an electricians analogue multi-meter, accurate to better than a fraction of 1 percent s!

nope, sorry, they are accurate, but no where near that,,,,
iv told you a million times, stop exaggerating

[Jon]

they are in effect the same technology as an electricians analogue multi-meter, accurate to better than a fraction of 1 percent s!

nope, sorry, they are accurate, but no where near that,,,,
iv told you a million times, stop exaggerating

Yeah, you're right...BETTER than a fraction of a percent is totally accurate...Which is a tad extreme!

[Colonel-mustard]

What is the understanding regards the 12v Cubs speedo and over/undereading? (with spec tyre)
Col

[Jon]

What is the understanding regards the 12v Cubs speedo and over/undereading? (with spec tyre)
Col

Tricky one... My 12v Cub's speedo was exactly correct according to my hand held Garmin GPS and remained correct throughout the time I had it. That is however highly unusual and I would usually assume a speedo to over-read by 10% because almost all speedos do. The speedo is driven off the front wheel of course.

in other words, an indicated 55 is a true 50mph.

if you have a battery operated GPS, say a car mounted one, with a facility to record maximum speed, fire it up, reset the max speed record part, pop the unit in your pocket once it's locked up and working and go for a ride where you can safely hold a steady speed. Hold a steady 50 mph (but no more) on the speedo then stop and look at the gps to see what IT says your max speed was. I can hold my little Garmin eTrex in my hand while I compare the two but I used the 'Max Speed' system with my innova (speedo reading was 71mph, GPS said 64mph)

[Colonel-mustard]

Thanks!
I will borrow a GPS thingy and give it a try and report back.
Col

[wightegi]

Of course that is in the asumption that gps is correct. As they are based on a round ball for planet earth with no hills or valleys so not always accurate for a speedo , a measured mile and stop watch is far better .Or the distance markers on a motorway.