speed limits

cyclonebri1

scooby75 wrote: »

My speedometer gives the actual speed so if I say I'm doing 70 I am actually doing 70 give or take whatever error the speedo has.

I've got 1 of those too, AKA the wife, whatever she says is good by me:o

cyclonebri1

Nearly_Old wrote: »

If only!

The calibration of speedometers is governed by the Desgin and Construction Use Regulations (DCUR) that every vehicle has to comply with in order to be used on the highway. A speedometer shall not underread the speed; i.e. a reading of 69.5 at a true speed of 70 would mean that it would be illegal for that vehicle (and all others of that type) to be driven on the highway.

The speedometer reading shall not exceed the actual speed + 10% + 6.25; i.e. at a true 70 the maximum permiited reading is therefore
70 + 7 (10%) + (6.25) = 83.25

Your speedometer will overread because no manufacture will ever run the risk of having all the their vehicles failing to comply with the DCUR and so all have some positive "error" built into them. On my 3 cars 70 on the SatNav gives speedometer readings between 61 and 66.

:T:T
Anyone, and Mikey is prime here, that thinks there speedo is accurate is deluding themselves. It isn't/won't be, it will read over by at least 10% for the litigation issues mentioned. The makers aren't totally suicidal.

mikey72

Hammyman wrote: »

There speaks someone who hasn't a clue how modern speedos are calibrated. But then again you've yet to make one factually correct post on this board since you started.

How do you calibrate yours.

Oh hang on, the PS3 doesn't actually go anywhere does it.

shaun_from_Africa

The only speedometers that I've ever seen that tie up to the speed shown by a sat nav are those fitted to cars in the USA.
I've probably driven at least 30 different ones and in every case the speedo and sat nav were always within about 1 or 2 mph of each other when cruising at a constant speed on the interstates.

Every car I've driven and compared in the UK has always had a difference of at least 7 or 8mph at an indicated 70mph.

scheming_gypsy

cyclonebri1 wrote: »

:T:T
Anyone, and Mikey is prime here, that thinks there speedo is accurate is deluding themselves. It isn't/won't be, .

mine is! speedo vs sat nav are identical. Although if i put the original wheels on it'll probably be out again

mikey72

cyclonebri1 wrote: »

:T:T
Anyone, and Mikey is prime here, that thinks there speedo is accurate is deluding themselves. It isn't/won't be, it will read over by at least 10% for the litigation issues mentioned. The makers aren't totally suicidal.

It's a stepper moter driven from the ecu nowadays, off a driveshaft or hub sensor.
It's normally set at -5%, +0%.
The design and construction covers anything on the road, and hasn't been updated since a spinning magnet and a spring loaded needle.

mikey72

Hammyman wrote: »

Really? Post a link to the message.

Hammyman wrote: »

HGV drivers are nowhere near as bad as car drivers for tailgating. They'll typically be 40 or 50ft apart at 56MPH following another vehicle that'll take an equivalent distance to stop being driven by a driver with many hundreds of thousands of miles under their belt too - not to say there aren't muppets who do drive a lot closer. OTOH, L3 is usually full of cars doing 80MPH 15 to 20ft from the one in front being driven by morons who have only rudimentary driver training.

I once took a video from a motorway bridge as proof on a forum once. It shut a lot of people up.

Hammyman wrote: »

My lorry when empty could outbrake pretty much every single car on the road. That is what happens with a vehicle with mandatorily fitted ABS as opposed to optional, where the tyres are twice as wide as a car, you have four times as many of them, the brake discs are bigger than the wheels of most cars, inspected every 6 weeks and they're designed to stop 46 tonnes but only have to stop 16...

Hammyman wrote: »

Whats worse...

A car with basic brakes with a driver with only rudimentary driver training driving a car at 70+ MPH one car length or so from the one in front or...

A speed limited HGV at 56MPH with mandatory ABS braking with a driver with many hundreds of thousands if not millions of miles experience who has had to undergo a medical to apply for a licence, advanced driver training and now periodic training courses following another vehicle with pretty much the same thing at a distance of 50ft?

Chevrons are 130 feet apart.
You admit you drive at 50ft from the vehicle in front, less than half a chevron.
Pity you don't realise when the truck is loaded it won't stop as fast.

If you did actually drive you'd be dangerous.

Idiot.

SHIPSHAPE

Strider590 wrote: »

Yeah, really clever, wind him up and let him go cause a 25 car pile up...... Nice...... What's about the innocent people? I guess they deserve his anger for you being taken out on them!

If he caused a 25 car pile up, guess what?

He would have caused it.

Stupid post.

Nearly_Old

mikey72 wrote: »

It's a stepper moter driven from the ecu nowadays, off a driveshaft or hub sensor.
It's normally set at -5%, +0%.
The design and construction covers anything on the road, and hasn't been updated since a spinning magnet and a spring loaded needle.

Actually the original Road Vehicles (Construction and Use) Regulations 1986 have since been amended to provide European Harmonisation extract below:

The amended Road Vehicles (Construction and Use) Regulations 1986 permits the use of speedometers that meet either the requirements of EC Council Directive 75/443 (as amended by Directive 97/39) or UNECE Regulation 39.[11]
The Motor Vehicles (Approval) Regulations 2001[12] permits single vehicles to be approved. As with the UNECE regulation and the EC Directives, the speedometer must never show an indicated speed less than the actual speed. However it differs slightly from them in specifying that for all actual speeds between 25 mph and 70 mph (or the vehicles' maximum speed if it is lower than this), the indicated speed must not exceed 110% of the actual speed, plus 6.25 mph.
For example, if the vehicle is actually travelling at 50 mph, the speedometer must not show more than 61.25 mph or less than 50 mph.

Two of my cars use sensors on the output shafts from the differential and it is fairly obvious that within the ECU the displayed speed has been set at "actual" plus 5% to ensure that the Directive is always complied with. For one of the cars I have the original wheel/tyre combination plus what was the OEM optional extra with larger wheels and the difference between the two is 0.45% due to a slight change in the rolling circumference.

vaio

A truck out braking a car sounded a bit unlikely to me even if the truck was empty.

A quick goole comes up with a study done by ROSPA at MIRA which shows 30 mph braking distances for a Seat medium saloon and an Iveco artic unloaded and loaded as being 8.5m, 17m and 27m respectively (last three lines of http://www.rospa.com/roadsafety/adviceandinformation/driving/hgv-truck-braking-systems.aspx)

Google also reveals something I hadn't previously thought of which is that truck air brakes have between half a second and a second delay whilst the air pressure decays and before the brakes actually start doing anything.

At 56 mph this means that you will cover between 40 & 80 feet just waiting for the air pressure to decay and the brakes to start working so following something else at a distance of 50 feet is maybe not such a bright idea even if you have perfect brakes and instant reflexes (so none of the "thinking distance" other drivers have to deal with, generally reckoned to be another 50 feet at 50 mph)