My Navman reports my speed as 2 km/h less than the speedo/tacho. The tyres on this vehicle are not new and have covered 300,000 Km, as of Monday of this week, and if you keep a record of these things you will find the distance between two places increases as the tyres wear down, for instance when this vehicle was brand new the distance from our yard to Dover was over a Km less than it is now with the worn tyres. Was 172 km now around 173.4Km, I had to put the price up for the extra Kms.
Another thing is if you run all day with a mate in another truck, follow each other all day along the exact same route, and compare distance travelled at the end of the day you can find as much as 10 Km difference between the two tachos, that is down to tacho calibration and tyre wear.
kalm2kaos:
But didnāt I read on Trucknet somewhere that a tacho on its own couldnāt be used as to wether or not someone had done something wrong,
You canāt be done for speeding by using tacho evidence alone, you can be done for other offences. If you were involved in an accident then the speed trace of the tacho may be used as evidence.
el gordo 78:
M180 coppers last summer worked on a blanket 80mph for cars/bikes to prosecute but I understand that is reducing to 78 this summer.
That makes perfect sense, I went past an M180 roadside camera van at just under 80 and heard nothing, my partner did the same at 82mph and got an SP60,
If truck wheels are about 1 m diameter (which I think is about right), then when you wear off 1 cm of tread (which is realistic, as Iām pretty sure that truck tyre treads are significantly more than 1 cm deep), you get a 2% increase in the speedo reading.
I believe that speedos are allowed to under-read by a small amount (a few %) up to about 30 mph, then over 30 mph they can only over-read, although they can do so by up to about 10%.
The Renault Master minibus I drive regularly shows about 79 mph when the GPS shows 70 mph. My 106 is a bit better - it reads about 74 at 70 mph.
I had my old motor calibrated on `nearlyā bald tyres and got the fitter to calibrate on the best side of the allowable variation - result on new tyres was going about 4 - 5 miles not kilometres faster! and it improved the fuel consumption
Rob
MrReliable:
Does anybody on here with a TomTom sat nav find that the speed on the sat nav is lower than the speed on your tacho?
I operate a Scania which reads 91 km on the tacho but the TomTom says the truck is only doing 54mph.
The truck has been into Scania to be turned up which resulted in a new speed limiter sticker being applied with the set speed now up to 90 kmh.
This means that before it went in it was only doing 53 mph/85kmh as per the old limiter sticker but the tacho still read 90 kmh.
If you sit at speed limits 30/40/50 TomTom still reads 3 mph slower than the tacho.
Does anybody have the same senario or have I done something to me sat nav ?
My english isnāt really the Best
But,your Tyre are Rubber,blowen up whit Air or Liquit.
On Truckās by Air.
The Tacho is celebrated by a empty Truck whit new Tyre.So older the Tyre are,and so more they are pressed down by your Load,so more often they have to turn around to get 56 Miles in one Hour.
So,whit a full Load will you be underway whit 54m/h,as the Computer sayās.
Radiusx2 =x3,14=
40cmx2=80x3.14=251,20
90 km =90000 Meter
1 Hour is 3600secound
90000:251,2=358
the wheal goes 358 times around to get 89,9 km/h
if your Tyres old,and you are loaded will you have 37x2=74cmx3,14=242,36
242,36cmx358rpm=86564,88km/h
You are saying that the circumfrence of the tire changes enough when loaded as to change the speed reading
I find that just a little hard to believe
Just see the Distance bedween middle of Axle and Road by a Tractorunit whitout Trailer and the same by cuppled full Loaded Trailer,and take a look in your Counting
Much more diference will you find bedween new tyres(when the Tacho is celebrated,or how that is called) and old Tyre whit full loaded Trailer
