Onboard Speed Cameras - Is it Me?

[Frank Incensed]

It's not the first time I've seen video footage taken from traffic cars and thought this. Does anyone else look at the speed read out, compare it with the apparent speed difference to the other traffic and think, "There's no way the target bike / car is going that fast. You'd have to be crazy to believe they're doing 145 mph and the speed display is accurate."? Maybe it's just that I'm regularly overtaken by cars doing 200 mph, when I'm plodding along at an indicated 80.

[SKS Disco]

I have noticed that as well ! A police interceptor ( think it was one of the Scoobies or an Impressa ) was chasing a Porsche at an indicated speed of well over a ton ( about 125mph or something ).
Well, the 40 ton artic they overtook must have been doing 110mph then !
So was the double decker bus !

Seemed odd at the time !

[zurmac]

After a recent inspection by the Swiss Traffic authorities on my 75 Tourer they found that there was a 10% difference between my Speedo and the actual speed allowed, in my favour. So when I thought I was doing 50KPH, I was actually only doing 45KPH. When you get up to 100KPH, your actually only doing 90KPH and so on. So in a 120KPH traffic zone I can actually do 135KPH without incurring a fine.

[rover54]

Originally Posted by zurmac

After a recent inspection by the Swiss Traffic authorities on my 75 Tourer they found that there was a 10% difference between my Speedo and the actual speed allowed, in my favour. So when I thought I was doing 50KPH, I was actually only doing 45KPH. When you get up to 100KPH, your actually only doing 90KPH and so on. So in a 120KPH traffic zone I can actually do 135KPH without incurring a fine.

All speedos read under, it is designed into them. The speedometer reading in the UK must be within 10% of actual road speed, but not read under actual road speed. i.e a speedometer is legal if it reads within 10% under the actual road speed and nothing above road speed.

When you think you are doing 135kph, your true road speed is 120kph based on your information regarding your speedo.

[berkshirelad]

Originally Posted by rover54

All speedos read under, it is designed into them. The speedometer reading in the UK must be within 10% of actual road speed, but not read under actual road speed. i.e a speedometer is legal if it reads within 10% under the actual road speed and nothing above road speed.

When you think you are doing 135kph, your true road speed is 120kph based on your information regarding your speedo.

Under UK Construction & Use regs, a speedometer must be accurate to +/- 10% at 30 mph.

Subsequent EU regs require that a speedometer must never under read.

So a speedometer that reads 100 mph when the car is travelling at 45 mph is perfectly legal (if otherwise useless!)

[HarryM1BYT]

Originally Posted by berkshirelad

So a speedometer that reads 100 mph when the car is travelling at 45 mph is perfectly legal (if otherwise useless!)

Not quite -

• The indicated speed must never be less than the actual speed, i.e. it should not be possible to inadvertently speed because of an incorrect speedometer reading.
• The indicated speed must not be more than 110 percent of the true speed plus 4 km/h at specified test speeds. For example, at 80 km/h, the indicated speed must be no more than 92 km/h.

The standards specify both the limits on accuracy and many of the details of how it should be measured during the approvals process, for example that the test measurements should be made (for most vehicles) at 40, 80 and 120 km/h, and at a particular ambient temperature. There are slight differences between the different standards, for example in the minimum accuracy of the equipment measuring the true speed of the vehicle.