XPost: comp.os.linux.misc
From: rich@example.invalid
In comp.os.linux.misc c186282 wrote:
> On 12/9/25 22:05, Rich wrote:
>> In comp.os.linux.misc c186282 wrote:
>>> On 12/9/25 06:53, Daniel70 wrote:
>>>> On 9/12/2025 9:09 pm, The Natural Philosopher wrote:
>>>>> On 09/12/2025 08:35, c186282 wrote:
>>>>>> On 12/8/25 17:41, rbowman wrote:
>>>>>>> On Mon, 8 Dec 2025 14:59:12 +0100, Carlos E.R. wrote:
>>>>>>>
>>>>>>>> No, this is intentional calibration of the car speedometer to 5
>>>>>>>> kilometres low. The reason is that if you see a road limit of 100Km/h
>>>>>>>> and you do drive at 100Km/h sharp, there is no possibility of you
>>>>>>>> driving just a bit above the limit and be fined. You could then sue
>>>>>>>> the
>>>>>>>> car maker for having bad instrumentation that caused you to be fined.
>>>>>>>
>>>>>>> That's the reason I've heard for Japanese bike speedometers being
>>>>>>> off. The
>>>>>>> speedometer in the Toyota is accurate when I'm running the 15" tires
>>>>>>> it's
>>>>>>> calibrated for.
>>>>>>
>>>>>> Yep, tire diameter IS critical.
>>>>>>
>>>>> There is no 'tire diameter'
>>>>>
>>>>> Only circumference.
>>>>
>>>> .... and, as circumference is dependant on diameter/radius ......
>>>
>>> Exactly.
>>>
>>> Pi*D = circumference
>>
>> Yes, for a perfect circle.
>>
>> But a tire under load is no longer a perfect circle,
>
> Familiar with the phrase "Good Enough ..." :-)
>
>> so if you use the
>> loaded "radius" or "diameter" (even though neither really applies to a
>> "non-circular shape") you'll come up short for the "distance around the
>> outside of the tire".
>
> Only a little.
If you plan to use that distance to measure your speed, that little
will amount to a nice error in your final speed number you calculate.
And this subthread got started by discussing speed measurements.
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