الموضوع: يعني ايه العلامه دي...حد يعرف ؟؟

دة إلي بيقسو عندو الخطأ فالعد أد إيه...

يعني أنا لو عندي سبيد لميت في فرنسا ٥٠ ، لازم يكون ال-error أقل من نسبة معينة ... ودة إلي بيقسو عندو على حسب العربية ديه جاية منين

http://en.wikipedia.org/wiki/Speedometer

[edit] Error
Speedometers are not totally accurate, and most speedometers have tolerances of some 10% plus or minus due to wear on tires as it occurs. Modern speedometers are said to be accurate within 5% but as this is legislated accuracy, this may not be entirely correct. This can make it difficult to accurately stay on the speed limits imposed; most countries allow for this known variance when using RADAR to measure speed, although levels of some 3 km/h or 3% are also used in areas of tough enforcement. This causes many arguments due to motorists complaining that they were not doing the speed as reported. Revenue[3] is being increasingly blamed for these stricter measures. There are strict United Nations standards in place but it seems not being enforced leaving this matter in limbo for many countries. Excessive speedometer error after manufacture can come from several causes but most commonly is due to nonstandard tire diameter, in which case the

percent error = 100x("standard diameter"/"new diameter" - 1).
Nearly all tires now have their size shown as "T/A_W" on the side of the tire (See: Tire code), and the tire's

diameter in inches = TxA/1270 + W.
For example, a standard tire is "185/70R14" with diameter = 185x70/1270 + 14 = 24.196850 in. Another is "195/50R15" with 195x50/1270 + 15 = 22.677165 in. Replacing the first tire (and wheels) with the second (on 15" wheels), a speedometer reads 24.19../22.67..=1.0670139 times the correct speed or 6.7% too high.


[edit] International agreements
In many countries the legislated error in speedometer readings is ultimately governed by the United Nations Economic Commission for Europe (UNECE) Regulation 39[4] which covers those aspects of vehicle type approval which relate to speedometers. The main purpose of the UNECE regulations is to facilitate trade in motor vehicles by agreeing uniform type approval standards rather than requiring a vehicle model to undergo different approval processes in each country in which it is to be sold.

European Union member states must also grant type approval to vehicles meeting similar EU standards. The ones covering speedometers [5] [6][7] are similar to the UNECE regulation in that they specify that:

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.

The UNECE regulation relaxes the requirements for vehicles mass produced following type approval. The upper limit on indicated speed is increased to 110 percent plus 6 km/h for cars, buses, trucks and similar vehicles, and 110 percent plus 8 km/h for two or three wheeled vehicles which have a maximum speed above 50 km/h (or a cylinder capacity, if powered by a heat engine, of more than 50 cc). European Union Directive 2000/7/EC, which relates to two and three wheeled vehicles, provides similar slightly relaxed limits in production.


[edit] Australia
All vehicles manufactured on or after 1 July 2007, and all models of vehicle introduced on or after 1 July 2006, must conform to UNECE Regulation 39.[8]

The speedometers in vehicles manufactured before these dates but after 1 July 1995 (or 1 January 1995 for forward control passenger vehicles and off-road passenger vehicles) must conform to the previous Australian design rule. This specifies that they need only display the speed to an accuracy of +/- 10% at speeds above 40 km/h, and there is no specified accuracy at all for speeds below 40 km/h. There is also the added problem of cars not complying with the United Nations standards, being imported and allowed to be registered, making the situation even more complicated. This needs further investigation.

[9] State assemblies may also set their own requirements but (as of 2004) none specified tighter limits on the accuracy. [10] This has caused some controversy since it would be possible for a driver to be unaware that he is speeding should his vehicle be fitted with an under-reading speedometer. [11]


[edit] United Kingdom
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. [12]

The Motor Vehicles (Approval) Regulations 2001[13] 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 that 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. There is also the added problem of cars not complying with the United Nations standards, being imported and allowed to be registered, making the situation even more complicated. This needs further investigation.


[edit] United States
As of 1997, Federal standards in the United States allowed a maximum 5% error on speedometer readings (per "Auto Tutor", American Automobile Association of California magazine, Oct. 17, 1997). Aftermarket modifications, such as different tire and wheel sizes or different differential gearing, can cause speedometer inaccuracy.

المشاركة الأصلية كتبت بواسطة Ahmad Allawy

مجهود كويس..
بس انا مش شايف غير ان ال50 دي ميل مش كيلو متر..
و ال50 ميل دي تعمل اكتر من 65 كم..
وانا شايف ان الكلام مش منطقي قوي..

أولاً الكلام مش كلامي عشان محدش يزعل مني :D

تاني حاجة هما بيقولو لما الرادار ييجي يمسكهم واحد ماشي على السرعة القانونية مثلاً ٦٠ كم/ساعة الرادار بيقرأ السرعة اكنو ماشي على ٧٢ مثلاً

ف هما بيحددو إيه هي ال-limits المسمح بيها عشان ميبأش كل واحد ماشي على مذاجو.... طبعاً لو ف مصر الظابط حيتكيف ... لكن لو برة عشان في قانون يبئة الموضوع يستاهل حسبة

وخلي بالك إنو كمان لما بيتغير مقاس الكاوتش السرعة بتتغير .... عشان كدة لزم تحسب مقاس العجل قبل متغير أو تشوف الستاندرد بتاع العربية إلي هو محسبلها ....
وال كلام دة بصراحة خلاني أصدق الكلام إن وإنت على الصحراوي قلل من ال-١٠٠ شوية عشان الرادار

لو في علامات كتير (بعدد نقلات الفتيس ) يبقى دي عشان أخر كل غيار ، يعني فرضاً في الميجان في ٤ ذي ما Sharky قال واحدة عند ٣٠ و ٥٠ و ٩٠ و ١٣٠ ، دول بيكونوا أخر النقلات الأولى والتانية والتالته و الرابعة ، و لو وصلت للعلامة دي لزم تعلي النقلة .

أما لو كانت واحدة ف الإحتمالات إلي عندنا كالآتي : يا إما دي علامة أحسن إستهلاك وقود (و هي نفسها إلي بيتحسب عندها قيمة العدم إلي بتتكتب في الكتالوج ) ، يا إما انها نقطة معايرة العداد يعني إلي بيتعمل عندها ضبط للعدد مع السرعة الفعلية ، بمعنى أوضح لو المفروض نسبة الخطأ في قراءة العداد تكون 5% ف دي محسوبة عند العلم دي يعني لو سرعتك ٥٠ ممكن تكون ٥٢٫٥ ، و لم تحب تسلح العداد و تراجعه تاني تزبته عند نفس النقطة دي .
دة باختصار خلاصة إلي طلعنا بيه من كل الحوار إلي فات دة . و شكراً ... سفرووت :)

المشاركة الأصلية كتبت بواسطة farahat

لو في علامات كتير (بعدد نقلات الفتيس ) يبقى دي عشان أخر كل غيار ، يعني فرضاً في الميجان في ٤ ذي ما Sharky قال واحدة عند ٣٠ و ٥٠ و ٩٠ و ١٣٠ ، دول بيكونوا أخر النقلات الأولى والتانية والتالته و الرابعة ، و لو وصلت للعلامة دي لزم تعلي النقلة .

معلومة أخر الأول على ال-megane ٥٠-٦٠ و-٩٠ على التاني !! ف أين تقع ال-٣٠ باءة فال كلام دة :D