Speedometer inaccurate

[Steve Whits]

I know it’s illegal for speedometers to under read and have a tolerance of 10% over but I’ve never had a car (to my knowledge) that has been anywhere near the 10% mark.......until now.

i started to notice a problem when I was being tailgated and flashed in 30 zones but as I don’t do many long journeys it was difficult to verify until I used my tomtom which seemed to confirm my feelings. 

Anyway ive also used an app while going up to Scotland last week and this confirmed my suspicion showing 53mph when the car was showing 60.

Its in for service atm and I’ve asked them to look at it. I understand I can adjust my driving by increasing my speed but my issue is that if the speedometer is out then so will the mileage be. Current mileage is 19000 so in effect the car has only actually done 17100.

Has anyone else had a similar issue?

my wife’s Yaris is pretty much spot on

Forgot to add garage have confirmed its doing 27 whilst showing 30 but going to check it at 60 today.

 

[FROSTYBALLS]

In the UK the legal tolerance for speedometers is up to 110% of the true speed, and additionally for speeds between 25mph and 70mph, plus 6.25mph. The service intervals of any car will be based on either time or recorded mileage, whichever measure is reached first - the manufacturers cannot realistically adopt a system where one assumes the mileage is X when the odometer reads Y.

Don't see that the garage will be able to do anything as the speedometer meets legal requirements.

 

[Notoyboy]

Presumably you've got the standard fit wheels & tyres?

[Steve Whits]

8 minutes ago, Notoyboy said:

Presumably you've got the standard fit wheels & tyres?

Yes it has. 

If I was being pedantic 110% of 27 is 29.7 so reading 30 is outside tolerance. But as the speedo doesn’t read tenths I suppose it’ll be difficult to prove unless it’s more noticeable at higher speeds. It’s just really annoying.

[Jonmartin]

Mine’s the same. TomTom shows 67 when the speedo is at 70. Mine also disagrees with itself. The digital speedo is always about 1 to 2 mph different to the analog needle. Still better to be below the speed limit, far less chance of a fine and points. 

On a separate point, if I’m doing the speed limit, according to my speedo and someone behind starts flashing. I tend to slow down, if they want to overtake them that is their choice.

[FROSTYBALLS]

35 minutes ago, Steve Whits said:

Yes it has. 

If I was being pedantic 110% of 27 is 29.7 so reading 30 is outside tolerance. But as the speedo doesn’t read tenths I suppose it’ll be difficult to prove unless it’s more noticeable at higher speeds. It’s just really annoying.

No it isn't - as I stated previously, in the UK in addition to the percentage, for speeds between 25mph and 70mph a speedometer can read up to 110% of the true speed plus 6.25mph. So for a true speed of 27mph, the speedometer can read up to 35.9mph (27 + 2.7 + 6.25) and still be legal.

[Steve Whits]

22 minutes ago, FROSTYBALLS said:

No it isn't - as I stated previously, in the UK in addition to the percentage, for speeds between 25mph and 70mph a speedometer can read up to 110% of the true speed plus 6.25mph. So for a true speed of 27mph, the speedometer can read up to 35.9mph (27 + 2.7 + 6.25) and still be legal.

Ah ok thanks. But that’s ridiculous imho :). 

Oh and yes I also do tend to slow down if tailgated but in this day and age I’d expect my speedo to be more accurate. I can live with a 3mph discrepancy at 70 but not 8 to 10. 

[Heidfirst]

2 hours ago, Steve Whits said:

Its in for service atm and I’ve asked them to look at it. I understand I can adjust my driving by increasing my speed but my issue is that if the speedometer is out then so will the mileage be. Current mileage is 19000 so in effect the car has only actually done 17100.

the speedo will have an error programmed in, the odo is likely to be pretty accurate.

My 3 Avensis have all overread by ~6-7% (depending upon wheel/tyre sizes, tyre pressure/wear etc.) so it surprises me that yours is so far out.

At constant speed I also reset & use the average speed feature of the trip computer to compare against the speedometer - they read differently.

[Mike J.]

If you install the Toyota Touch and Go app called a glass of water, then you can see the speed that the car's computer has worked out. It is always lower than the speedo, usually by around 2-3 mph at any speed - it is not a percentage.

[ziauris]

18 hours ago, Jonmartin said:

Mine’s the same. TomTom shows 67 when the speedo is at 70. Mine also disagrees with itself. The digital speedo is always about 1 to 2 mph different to the analog needle. Still better to be below the speed limit, far less chance of a fine and points. 

On a separate point, if I’m doing the speed limit, according to my speedo and someone behind starts flashing. I tend to slow down, if they want to overtake them that is their choice.

When I used the GPS to display speed, it always showed ~3 mph less than the speed shown on the speedo. This was a few years ago but it is probably still the case. You don't have military grade GPS so it will not be accurate and the GPS will under-read. 

I use one of these to display the speed "on screen" as I find it really difficult to look at the speedo when on the "smart" motorway and I find the Auris' speedo difficult to "work out"  (due to the poor increments as it goes from 20 to 40  to 60 - they really show go up in 10's) so I find it difficult to work out my speed unless I think about it and that's not what I want to be doing when driving! For this reason I wish I had bought a Civic with the digital display. I've "calibrated" on screen display to the speedo and  they both show the same speed at 30mph but at higher speeds like 60mph the on screen display under reads by ~3mph but I don't know WHY this is. This is good on the motorway as it means I know I am under when on screen shows 60mph. The on screen display gets its data from the OBD port.

Frostyballs: I'm really surprised that the speedo can over-read by so much, I wonder if that's why I also get people flashing at me on the motorway!!!!!! I too slow down and let them pass.

 

[nielshm]

My speedometer is rubbish too. My wifes Aygo is much more accurate. How ever, the ODO-meter is - 2%, so a 100 mile trip only reads 98 miles in the car. 

[FROSTYBALLS]

The speedometer requirement quoted is for the UK, which is different to that in the rest of the EU (which just adheres to the +110% requirement).

GPS gives an average speed over a given number of points, rather than the true speed, but is probably more accurate.

Our i20 has both an analogue speedometer and a digital speed readout, and when compared to GPS, over reads by approx 2 mph at an indicated 70mph.