eno wrote on Oct 8^th, 2007 at 1:09pm:



The legal requirement is as follows:

The Road Vehicles (Construction and Use) Regulations 1986, as amended, allows the use of speedometers that meet the requirements of EC Community Directive 75/443(97/39) or ECE Regulation 39. Both the EC Directive and the ECE Regulation lay down accuracy requirements to be applied at the time of vehicle approval for speedometers. These requirements are that the indicated speed must not be more than 10 per cent of the true speed plus 4 km/h. In production, however, a slightly different tolerance of 5 per cent plus 10 km/h is applied. The requirements are also that the indicated speed must never be less than the true speed. In theory when you think you are doing 30 you could be only doing 24 mph though I don’t think many are that bad.

However, also to take into the whole equation is the effect the tread depth has on speedo accuracy. I found this below after a short search.

Based on a tread depth of 12mm a 205/55 R16 tyre's OD can change by about an inch from new to worn, that would make a difference of 3.14" (about 80mm) per wheel revolution.

OD = 613.9mm
Circumference = 1984.1mm
60mph = 96km/h

At 96km/h wheels turn @ 806rpm = 48360rph
so in an hour the distance you've travelled can vary by...
48360rph x 0.080m (lets say 80mm is the amount the circumference can legally vary by)
= 3868m/hr, so call that +/- 4km/h (2.5mph) variation, and thats just tyre wear.

Matt

eno wrote on Oct 9^th, 2007 at 1:49pm:


Are you training to be an ADI eno? Or is this something in the future?

Rather you than me.... mind you, I suppose there are plenty of 18 year old girls needing lessons out there somewhere...where do I sign up?    

the fastest I have been is 240kmh on the back of a ZZR , the wind almost pulled me off of it , and I am never getting on the back of a bike again!    I did get my worked 'lil Corolla over 200kmh once, but I would hardly brag about that since I should've been locked up.  Now I drive a Holden station wagon....because it transports my 100cc Yamaha Go Kart on Race Day !     woohoo !  ok it only does 120kmh (the Kart) , but it does that with my arse 2" off the ground !   Planning to upgrade to 250cc Superkarts , once our state government upgrades the availability of race trakcs here in New South Wales.  ()read never)

Im yet to find out the top speed of my 3.8L V6 Holden, nor do I really want to know !    as I dont particuarly trust the dynamic of a station wagon !

I drive an Opel Astra 1.7 TD - 68 bhp

I took it to 115 mph ( 180 km/h) once on the German highway, the fastest it would go... yet 120.000 km further I doubt she'd still go that fast. At 294.000 km on the clock, she still does 150 km/h without a hickup... takes some time non the less.

The biggest engine I ever took for a spin was a BMW 530i of the latest model. That engine is a dream! I was a bit sad to hear that my former boss totaled the car a while back. Now he drives a 645i... but I don't work there anymore... darn...