30 =27 - Page 2

davo69 · 09-05-2007, 21:45

right so if we have identicale cars but i le t some air presure out of my tyers and both cars say 30 miles hr you would beat me

MikeSz · 10-05-2007, 05:25

There is some truth in that - you only need to pay any attention to speeding cases that go to court etc. Often, independent reports carried out on Police cases (particularly when assessing accuracy of equipment) will point to the margins of error - like those affected by pressure and the amount of tread. This is not just for a possible speeding vehicle, but also for the equipment say in a police land rover. You imagine if it hasn't been calibrated correctly (and land rover's have pretty big wheels) - at 100mph for instance you can be traveling X meters per second (cant remember what it is off the top of my head now) and have a certain number of revolutions per meter traveled, but this can vary with pressure or tread and the police have to account for it in their margin of error. A friend of mine is a former traffic Sergeant, and he now does expert evidence for court cases so I've had the geek lesson a few times now...

davo69 · 10-05-2007, 06:47

well they say you learn something new every day and i have

steeljack · 10-05-2007, 07:07

I once got fined 10 shillings for exceding the 30 mph speed limit between Sparth Rd. and the Hyndburn bridge on my Lambretta LI 150 , (a lot of money for a 4 pound a week apprentice) still have the little red driving license, (with endorsment) stashed away with the family documents

Neil · 10-05-2007, 07:09

Quote:

Originally Posted by davo69

right so if we have identicale cars but i le t some air presure out of my tyers and both cars say 30 miles hr you would beat me

I could not say because you don't know how accurate the speedo is in each car.

If anyone drives a Ford Focus, Mondeo and probably others with the digital milage reading under the speedo you could try this - With the ignition key off press and hold the trip meter reset button, turn the ignition to position 2 while still pressing the trip reset, after a couple of seconds the milage reading will say gauge and all the gauges (temp fuel speed revs) will move to the max value and back. Let go of the reset. This puts the dash in test mode. Keep pressing the reset button and it will change the test. You will find one that shows speed in mph. I thing is shows spd and a number, another press shows it in kmh. Go for a drive and you will see the speedo will read different to the digital reading. My Mondeo does and so does the works Focus. Both were a couple of mph out at 60mph. When you turn of the ignition the dash resets to normal. Another useful thing it shows is battery voltage, you can see how well your battery is charging, it should be over 14 volts with the engine running and all your lights, heater fan etc on. ( Don't be surprised if it drops lower when you switch on the heated quick clear windscreen, that pulls a lot of current ).

Neil · 10-05-2007, 07:24

If your worried about soft tyres or punctures then you need Michelin Tweels

Taken from here http://www.carbibles.com/tyre_bible.html

Also useful if you plan a bank job and need to avoid police stingers