anthonym Posted July 27, 2015 Share Posted July 27, 2015 Original R500 K Stack dash. It's quite a bit out even at 30mph. I am wondering about fiddling with the wheel circumference parametr in the Stack setttings.Anthony Link to comment Share on other sites More sharing options...
SM25T Posted July 27, 2015 Share Posted July 27, 2015 Has it always been like it ? Link to comment Share on other sites More sharing options...
anthonym Posted July 27, 2015 Author Share Posted July 27, 2015 I was wondering that, yes I think so. Wonder if anyone knows the circumference of a 13" CR500 tyre? ah yes, I have a spare somewhere I will go measure it. Link to comment Share on other sites More sharing options...
SM25T Posted July 27, 2015 Share Posted July 27, 2015 Gearbox speedo sender or hall effect proximity switch on rear wheel ? Link to comment Share on other sites More sharing options...
anthonym Posted July 27, 2015 Author Share Posted July 27, 2015 edit: front wheel sensor. Not that.. ahI can guess what hall effect is. yes.Rear 168cmFront 166 cmStack reading: 1705mm now changed to 1660mmSeems to be a big change does that. It has always been like that since I bought the car. 1705-1660=45 45/1660 = 2.7108 % (45/1705=2.63% looks suspiciously like an attempt at 2.5% induced error to be prudent.)hmm.. the difference seemed to be more than that. This was a sat nav comparison which is always difficult given the need for a constant speed while the sat nav makes its mind up. I was also comparing to road side "radar smileys". Link to comment Share on other sites More sharing options...
SM25T Posted July 27, 2015 Share Posted July 27, 2015 If a wheel sensor ... is it seeing all the teeth ? Link to comment Share on other sites More sharing options...
anthonym Posted July 27, 2015 Author Share Posted July 27, 2015 teeth?here what the book doth say:Wheel Pulses and CircumferencesCalculations for the Standard ST670 Wheel SensorYou must supply a value for the wheel circumference that you obtain from one of the following calculations:If the sensor is mounted on a wheel, set this value to the circumference of the wheel and set the number of pulses per revolution to the number of targets on the wheel. Istr there is only one target on the wheel. edit: I feel the need for a measured kilometre. Link to comment Share on other sites More sharing options...
SM25T Posted July 27, 2015 Share Posted July 27, 2015 Can't be missing that then !Tread depth wear would have a fair impact then ... difference in circumference between a new and a worn tyre ? Link to comment Share on other sites More sharing options...
anthonym Posted July 27, 2015 Author Share Posted July 27, 2015 yes the tyres on wheels I just measured are new/unused whereas the ones in use are.. in use, so they will only get smaller presumably. Ugh, altitude affects pressure affects circumference?I suppose an inspection of the sensor and whatever ferrous thing it is sensing may be wise. Must be something on the rear of the hub. I do vaguely recall checking it out some time ago. Need a proper jack, one not meant for lorries. Link to comment Share on other sites More sharing options...
sjmmarsh Posted July 27, 2015 Share Posted July 27, 2015 SM25TThe circumference is pi * diameter, so the change is easy to calculate. In the example above, the wheel circumference is 1660mm. If this is with a full 6mm tread depth, then by the time the tyres are down to the wear bars, this will have reduced by (4mm+4mm)*pi = 25mm to 1635mm, a reduction of 1.5% i.e. an increase in recorded speed. Steve Link to comment Share on other sites More sharing options...
SM25T Posted July 28, 2015 Share Posted July 28, 2015 You need a jack to get the car on that monster jack of yours ! Link to comment Share on other sites More sharing options...
anthonym Posted July 28, 2015 Author Share Posted July 28, 2015 zackly Link to comment Share on other sites More sharing options...
Ray Pearce Posted July 28, 2015 Share Posted July 28, 2015 Did you just wrap a tape around a new tyre to get the circumference?The weight of the car squashes the tyre a bit and thus reduces the radius.Best way to measure is to make a chalk mark on the tyre and the road and then push the car for a known number of revolutions - the more revolutions the better but you will need a longer tape.Also note that (during the IVA test) speedometers are allowed to overread by up to 10% but must NOT underread. Link to comment Share on other sites More sharing options...
sjmmarsh Posted July 28, 2015 Share Posted July 28, 2015 SM25T - that is the circumference, not the diameter!Steve Link to comment Share on other sites More sharing options...
SM25T Posted July 28, 2015 Share Posted July 28, 2015 What ??????? Link to comment Share on other sites More sharing options...
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