A question of what speed am I doing.

[Allen Kelly]

After mounting my Garmin 396 the other day today was the first opportunity I have had to get out and have a good ride. The GPS worked really well and where I mounted it is perfect for line of sight. BUT I noticed a problem, at 60kmph on the Speedo I was only doing 55kmph on the GPS and the faster I went the larger the discrepancy. At 110kmph on the Speedo I was only doing 100kmph on the GPS. The question is which one is right and which will get me a ticket?   

[r2r]

You will get a ticket for a speed closer to GPS one, but not exactly the speed you measured, because devices used by Police all over the world are not very precise.

[manny]

Yeah Allen, mines the same as yours, speed reads about 10klm to fast, as per my Hema maps phone app. 

[Red n White]

Mine is the same, reads about 10% fast. Our Subaru and Nissan ute also read fast around 5%. !!

 

[r2r]

In EU for example, speedometers cannot show less speed than actual (real), so every producer calibrates speedos to always show a bit more.

Here are some rules of it:

Speedometer - Wikipedia

 

Edited February 18, 2020 by r2r

[WalterT]

10 hours ago, r2r said:

You will get a ticket for a speed closer to GPS one, but not exactly the speed you measured, because devices used by Police all over the world are not very precise.

The police use state of the art speed measuring equipment, which is regularly calibrated (or the tickets would not hold up in a court). Every measurement has an inherent error. To prevent discussions on this, you will only get a ticket when you exceed the maximum speed by at least this error margin. For example, here in The Netherlands that margin is 3 km/h (up to 100 km/h). So if your real (measured) speed is 53 km/h, this is corrected to 50. Add to that the 8-10% of the T7's speedo, you can ride 60 km/h on the speedo without getting a ticket. If you take the speed form a GPS and 53 km/h is your limit.

[r2r]

2 hours ago, WalterT said:

The police use state of the art speed measuring equipment, which is regularly calibrated

You are probably right that there are countries where police uses devices that good  and I would really like it to be true also in my country

Unfortunately it's not. Some time ago journalists found out, that hand-held devices for speed measurement can show speed about 40-50 km/h of standing car with engine running. Vacuum cleaner measured in TV show reached 153 km/h. Police were using those devices many years, not only in Poland and somehow they were passing every year obligatory calibration . . .

Edited February 18, 2020 by r2r

[gofo]

14 hours ago, Allen Kelly said:

After mounting my Garmin 396 the other day today was the first opportunity I have had to get out and have a good ride. The GPS worked really well and where I mounted it is perfect for line of sight. BUT I noticed a problem, at 60kmph on the Speedo I was only doing 55kmph on the GPS and the faster I went the larger the discrepancy. At 110kmph on the Speedo I was only doing 100kmph on the GPS. The question is which one is right and which will get me a ticket?   

Hi Allen, do you run on the pirelli tyres or something else?

 

[WalterT]

2 hours ago, r2r said:

You are probably right that there are countries where police uses devices that good  and I would really like it to be true also in my country

Unfortunately it's not. Some time ago journalists found out, that hand-held devices for speed measurement can show speed about 40-50 km/h of standing car with engine running. Vacuum cleaner measured in TV show reached 153 km/h. Police were using those devices many years, not only in Poland and somehow they were passing every year obligatory calibration . . .

I was planning to go for a ride to Poland this year! Better drive a bit slow after reading this :-).

[Allen Kelly]

5 hours ago, gofo said:

Hi Allen, do you run on the pirelli tyres or something else?

 

Still have the Pirelli tyres on it with no wear as I’ve only done 200km so far.

[r2r]

13 hours ago, WalterT said:

I was planning to go for a ride to Poland this year! Better drive a bit slow after reading this :-).

You don't need to worry much, as the highest ticket costs 125 EUR

After those tests became public police started to retreat from using those devices and now most of them are laser radars, which are much more precise if only someone can properly aim a tiny "red dot" at moving motorcycle from a distance of 200-500 m

 

 

Edited February 19, 2020 by r2r

[gofo]

On 2/19/2020 at 2:46 AM, Allen Kelly said:

Still have the Pirelli tyres on it with no wear as I’ve only done 200km so far.

ok ,the speedometer may show a better result when you change to another tyre, i haven't changed my front tyre yet either.

[Allen Kelly]

1 hour ago, gofo said:

ok ,the speedometer may show a better result when you change to another tyre, i haven't changed my front tyre yet either.

I hear what you are saying but I can’t see them making up 10+ kmph. That I think would require a huge profile difference. I have investigated these phenomena within the motor industry in general and the general consensus is that manufactures are understating the dialled in speed to avoid the legal implications that may arise out of an accurate dialled in speed. This basically arises because us the consumer continually change bits and pieces that alter the original reading. I’m cool with the difference I just wanted to throw it out there so everyone was aware of the difference. Although I still think 10km is a lot. Cheers.