speedo trueness

[X13OOR]

I have found that at my Sat Nav speed is 10mph less than the speed on the speedo at 100mph.
would the Sat Nav speed be a more true speed than the speedo.  going by this it would seem that the 15000 miles my Vee (1000) has done is more like a true 13500 miles.

my Sat Nav is a Zumo 660

[Piglumps]

I have the Zumo 400 and agree that there is a discrepancy, especially when you get beyond 30mph..There is a thread about replacement dial faces but they don't show km/h just mph which is apparently an MoT failure...

[Firestorm]

If it concerns you enough to part with some cash try a 'Speedohealer'. Programmable, easy fit and sits nicely out of the way under the seat. Will only work on the Vee I think as the speedo pickup is on the gearbox sprocket. Wee has a cable to the front wheel???
I use one on my Vee for over a year as I've changed the gearing and it's still fine.

[X13OOR]

cool idea. shame your not newport south Wales or I'll come and nick the one off your bike  :limp:    

[frez]

Whilst the speedo is off the mileage is pretty accurate.

[Juvecu]

I can confirm what frez said, the odo is accurate, just the actual speed display that's off (that goes for the Wee too.)

[Vstrombandit]

To get a 'genuine' 70 on GPS my GT's speedo was showing around 88 mph when we were riding one of the French toll roads. I've since let the GT go and now have the X model, on this model 70mph shown on GPS gives me a reading of 75 on the bikes speedo. Suzuki need to look at their quality control . Mileage looks to be accurate though.

[mr_diver]

Sat-Nav 70mph
Dash-    77mph

the speedo should be around actual speed + 10%

manufacturers don't want to have law suits if you get caught speeding say at 33mph but your speedo is saying 29mph. so they make them + 10%.
This should also take into account wear, as your tyre tread wears away your wheel will spin faster to cover the same amount of ground it would have when the tyre was new. Marginal but again manufacturers don't want to be blamed.

my millage covered when traveling 100miles or so shows a few (approx. 2-3) miles shorter than the distance covered by the Sat Nav. but the Sat Nav doesn't take into account the fact the wheels will go wider around corners than the satnav, and sat navs don't always count short steep sections, when from above you only travel a short distance but in-fact travel a considerable amount further. I've found the variance is greater if I've been riding in hillier terrain.

but think the manufacturers would program the clocks to calculate actual speed (wheel/sprocket rotations) then add 10% to display the speed but use actual rotations count for the distance travel.

[Juvecu]

If your wheel diametre gets smaller because your tread is wearing down it turns faster and the speed will show higher than what it would show with a fresh tyre that has a larger diametre.

As for the satnav being out on the distance, I don't think it accounts for altitude properly. Riding from point A to point B going over a hill is a longer distance on the road than it would be if the road was flat.

[GrahamT]

There was a thread about this some time ago.
The law states that speedometers can read a percentage plus a fixed value over (e.g. 10% + 6mph) but it is illegal to read under by any amount, so manufacturers always calibrate speedos "fast" to avoid breaking the law.
Tyre wear has very little affect on speedo reading. I did calculate it once and it was less than 1% from new to knackered, and it makes the speedo read faster for a given speed as the tyres wear, so for the manufacturers calibrating with unworn tyres is failsafe.
Note that the Vee and Wee use different methods to drive the speedo as mentioned before, so changing the sprockets or rear wheel size on a Vee will put the speedo way out, and so you need a speedo-healer, whereas it has no effect on a Wee. However if you change the front wheel size on a Wee, it will put the speedo out.
If I wasn't so lazy, I would link to the old thread, but I will leave that as an execise for the reader.

[MARBLE600]

I would go with the '10%' high reading


Another option is to replace the speedo face with a 'corrected' one

There was a bloke in the States making them and they looked pretty good if you could be bothered stripping your clocks to fit it

http://www.vstrom.info/Smf/index.php/topic,2037.0.html

[doebag]

IThere is a thread about replacement dial faces but they don't show km/h just mph which is apparently an MoT failure...

Speedo is not a testable item for an MOT, as the have no way of testing it at an MOT station.
However, dual scale speedo's are a Construction and Use Regs. requirement for vehicles after 1981,

[PHIL FAT]

I have a navman Sat Nav and a road angel in my car both registar the same speed but are both about 4 miles per hour less than the speedo in my car I have read somewhere that satalite speeds are not that accurate as my road angel displayed I was travelling at 372 mph in a 30 mph zone last night on the way home

[GrahamT]

I have a quite good GPS logger that I use when taking photographs to geolocate the pics. I can also link it to my laptop and Google maps to use it like a satnav. With it sat on my window sill, it will happilly tell me I am travelling at 10 KPH, and the log shows it has been flying all over the neighbourhood while I thought it was still in my living room!  
Seriously, civilian GPS is accurate enough to get you from A to B without sending you into too many river/ravines/people's gardens, but I wouldn't trust it to be too accurate with spot speed reading, (average is a different matter) especially if it hasn't got a very strong signal from several satellites.

[Juvecu]

At a steady speed I trust my Garmin much more than I do the speedo on the bike. It consistently shows the same deviation at the same speeds. It's no use at all when you're speeding up and slowing down all the time though.

[Oop North John]

I have a quite good GPS logger that I use when taking photographs to geolocate the pics. I can also link it to my laptop and Google maps to use it like a satnav. With it sat on my window sill, it will happilly tell me I am travelling at 10 KPH, and the log shows it has been flying all over the neighbourhood while I thought it was still in my living room!  
Seriously, civilian GPS is accurate enough to get you from A to B without sending you into too many river/ravines/people's gardens, but I wouldn't trust it to be too accurate with spot speed reading, (average is a different matter) especially if it hasn't got a very strong signal from several satellites.

In their infancy then the processor power was pretty small giving recalculation times of a couple of minutes if you chose to ignore the instructions, now it's in a scond or two with much better aquisition times as well. Comparing steady speed readings on a motorway against the 100m distance sticks showed the even the early GPS to be very accurate, and the speedo in various vehicles to overread. Interestingly, having driven a few cars in the uSA, their speedos seemed to be around 99% accurate.