新西兰迈速表和GPS 的速度不一样
在新西兰
车跑100时GPS报90，车跑110时GPS报100时速。感觉车的不准。大神们有什么好的建议。
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简单，看到照相机猛加几次油，过后的罚单里就会有公正的速度了
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正常。。。一般的车子都会调底5码左右，这是为了让你在改装车子的时候，换大轮毂不会出现仪表盘高于实际速度的情况。
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另外民用的gps精度还是会造成偏差
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谢谢以上各位，热情帮忙。
但是以前的车就和GPS几乎一样。
遇到这样问题怎么解决。
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很多车厂会把速度表调比真实速度要快的，车速跟轮毂大小是有很大关联的 跟油耗也是有关联的
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http://en.wikipedia.org/wiki/Speedometer
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为什么没有关系。。。轮毂改变轮胎不变了？
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兄弟,这真的是有关的......
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1231321323
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这个说法,没有依据....
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速度表测量速度是靠在波箱的传动速度来测量的，而轮毂变大，轮胎不变薄的情况下，同样的传动，轮子的周长会更长。打个不是很严谨的比方，同样的传动，原来轮子在地上滚一圈，但是换大了以后，同样的传动够原来的小轮子滚一圈半的。
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超一段wiki上的解释你就明白了
Most speedometers have tolerances of some ±10%, mainly due to variations in tire diameter.[citation needed] Sources of error due to tire diameter variations are wear, temperature, pressure, vehicle load, and nominal tire size. Vehicle manufacturers usually calibrate speedometers to read high by an amount equal to the average error, to ensure that their speedometers never indicate a lower speed than the actual speed of the vehicle, to ensure they are not liable for drivers violating speed limits.[citation needed]
Excessive speedometer error after manufacture can come from several causes but most commonly is due to nonstandard tire diameter, in which case the error is
\mbox {Percentage error} = 100\times(1-\mbox{new diameter} / \mbox{standard diameter})
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
\mbox {Diameter in millimetres} = 2 \times T \times A / 100 + W \times 25.4
\mbox {Diameter in inches} = T \times A / 1270 + W
For example, a standard tire is "185/70R14" with diameter = 2*185*(70/100)+(14*25.4) = 614.6 mm (185x70/1270 + 14 = 24.20 in). Another is "195/50R15" with 2*195*(50/100)+(15*25.4) = 576.0 mm (195x50/1270 + 15 = 22.68 in). Replacing the first tire (and wheels) with the second (on 15" = 381 mm wheels), a speedometer reads 100 * (1-(576/614.6)) = 100 * (1 - 22.68/24.20) = 6.28% higher than the actual speed. At an actual speed of 100 km/h (60 mph), the speedometer will indicate 100 x 1.0628 = 106.28 km/h (60 * 1.0628 = 63.77 mph), approximately.
In the case of wear, a new "185/70R14" tyre of 620 mm (24.4 inch) diameter will have ~8 mm tread depth, at legal limit this reduces to 1.6 mm, the difference being 12.8 mm in diameter or 0.5 inches which is 2% in 620 mm (24.4 inches).
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轮胎用错型号了
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我的新车也这样，实际车速要比显示的慢4左右，我是和GPS还有路边的测速比较的。
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我的车最近换了轮子以后这个问题也很明显 估计得去调