XPost: comp.os.linux.misc   
   From: tnp@invalid.invalid   
      
   On 10/12/2025 05:18, c186282 wrote:   
   > On 12/9/25 22:25, Rich wrote:   
   >> 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.   
   >   
   >    It will result in a SLIGHT speed error. IF you plan   
   >    to use speed to estimate arrival at a distant point   
   >    then you will have a problem. If you are only interested   
   >    in not getting a speeding fine then the slight error   
   >    should not be relevant.   
   >   
   No. Do the Sums.   
   Substantial.   
   Which is why they speedometers which count RPM, not 'rollingRadius™' are   
   as accurate as they are.   
      
      
   >    As I plan to drive to the food store, not launch   
   >    500km into Ukraine, I'd say a quick diameter check   
   >    should be "good enough".   
   >   
   >    There are times to get all hung up on the decimal   
   >    points, and times not to.   
   >   
   This is one of them.   
      
   Do the sums. Measure the distance from the top to bottom on an inflated   
   tyre on a vehicle, and then measure its circumference, Deflate the tyre   
   and do the same.   
      
      
   --   
   “Some people like to travel by train because it combines the slowness of   
   a car with the cramped public exposure of 
an airplane.”   
      
   Dennis Miller   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)