Mini 0803 KPH Speed issue (4-5kph difference)

[acrowau]

Howdy,

I have just checked my recordings on the mini 0803 and see that the speed on the unit is stating 4-5 kph less than what my vehicle speedo shows.

I was using the vehicle cruise control at :-

80 kph (unit hovers at 75-76 kph)
90 kph (unit hovers at 85-86 kph)
100 kph (unit hovers at 95-96 kph)
(all for a couple of kilometres for each set speed.)

I have firmware 20140826 which was on the unit when purchased and has been changed.

Any thoughts on how this can be rectified?
Thanks

 

[jokiin]

what vehicle do you have?

most speedos are not accurate but some are adjustable in service, have you compared to any other GPS devices?

 

[reverend]

That sounds about right - a lot of speedos over read by up to 10% - it's the manufacturers trying to ensure you don't get a ticket in a 40 when you think you're doing 40 but in reality you're doing say 37. If you were doing 45 and the speedo showed 40 it opens them up to lawsuits. Also aftermarket wheels with different tyre profiles can throw the speedo out even more

 

[Nigel]

In most countries it is actually a legal requirement on the car manufacturers that the speedometer over reads by up to 10%, most are around 4kph over depending a bit on which wheel/tyre option you choose since they don't bother correcting it for different width/circumference tyres and the different options due to car spec or engine size will have different circumference tyres.

You could correct it by 1 or 2 kph by adding some extra air to the tyres.

The 0803 on average will be exactly correct on a straight road, although individual readings can easily be 5kph out if the satellites are in unfavourable positions. On a bendy road it is possible that it's measurements will cut some corners and be slightly high.

 

[jokiin]

No such rule in Australia, up to 10% more than actual is permissible, any fraction under is not allowable, vehicles that have different wheel options that have different circumferences have different settings for each but 5% or more error is pretty common, some of our cars can be calibrated in service very accurately but it needs to be done on a rolling road (dyno) a lot of good workshops have them, dealerships not so much

 

[Nigel]

No such rule in Australia, up to 10% more than actual is permissible, any fraction under is not allowable,

Since the rule is written for an analogue display, that amounts to the same thing!

vehicles that have different wheel options that have different circumferences have different settings for each but 5% or more error is pretty common, some of our cars can be calibrated in service very accurately but it needs to be done on a rolling road (dyno) a lot of good workshops have them, dealerships not so much

It's not the circumference of the wheel that matters, the larger diameter wheels, once fitted with low profile tyres normally have about the same, or quite often have a smaller rolling circumference which effectively gives them lower gearing and thus more acceleration. Normally the available sizes are within the 10% allowance so there is no need to recalibrate the speedo.

Even if your car is calibrated, the actual circumference and thus speedo accuracy is still affected by the amount of air in the tyre, the air temperature, the road temperature, the amount of tread left on the tyres, the current speed (rolling circumference expands with centrifugal force), tyre brand/model (sidewall stiffness), etc.

 

[jokiin]

Even in the days of analogue speedos they were still adjusted to suit different model variants

In regard to wheel differences we have vehicles where different models have different size options that vary the rolling diamater and the settings are different for each, these days that's something that is set in the ECU and it is adjustable to keep the speedo within permissible limits, some can be adjusted quite accurately, not a job for the consumer though

 

[acrowau]

Just got back from work and see all these replies - thank you.

My vehicle is a 2013 Holden Cruze sedan 1.8lt.

Some have said that the speedo could be inaccurate, which can be true, but around 5% is too much. (1-2 kph maybe). But in Australia, I believe, that speedo's must be extremely accurate, but there is an allowance.

It maybe best if I get a test with the local automobile association (in Adelaide - RAA).

It just seemed to much of a variance especially on a straight road and fine weather conditions, proper tyre pressure and not over loaded weight.

 

[jokiin]

Just got back from work and see all these replies - thank you.

My vehicle is a 2013 Holden Cruze sedan 1.8lt.

Some have said that the speedo could be inaccurate, which can be true, but around 5% is too much. (1-2 kph maybe). But in Australia, I believe, that speedo's must be extremely accurate, but there is an allowance.

It maybe best if I get a test with the local automobile association (in Adelaide - RAA).

It just seemed to much of a variance especially on a straight road and fine weather conditions, proper tyre pressure and not over loaded weight.

ADR for your vehicle allows up to 10% over variation, 5% is better than many

I used to work in a Ford dealership when I was an apprentice mechanic and we used to service the cop cars, back then the highway patrol cars were fitted with two speedos, the original Ford speedo was a digital unit made by VDO, it would generally read around 71km/h when the calibrated police speedo was on 60km/h, they were way off back then, these days the factory speedos can be calibrated and even adjusted for different wheel/tyre combos in the ECU

 

[Nigel]

Some have said that the speedo could be inaccurate, which can be true, but around 5% is too much. (1-2 kph maybe).

It's not actually a %, your figures show a constant 4 kph which is probably the value programmed in for the computer to add just to ensure it never falls below the real value thus leaving the manufacturer open to prosecution. If you have a diagnostics reader for the car (OBD) then check the digital value, that is normally a lot closer.

 

[acrowau]

I will get my car checked, but, just to get this in my head.....

If the car computer is programmed to a 'value' (say my 4 kph), does that mean when the speedo is showing 100 kph (forgetting all variances - tyre pressure etc) then am I actually travelling at 96 kph or 104 kph.

Or.....if after a vehicle test it shows my car (for argument sake) is perfect at 100 kph, then the 0803 is not accurate or can't keep up with satellite 'stuff' when showing 96 kph - so therefore a little useless when needed.

And if 0803 is inaccurate, surely this would not prove positive in a court of law (on a speeding charge say) even though it shows 4 kph less. I'm sure, either way, a court would say 'bad luck', our radars are far more accurate than your $100 unit!

 

[jokiin]

when your speedo shows 100 you'd be doing 96, not 104, ADR allows it to read over, not under

the difference is very typical though