babymerc Posted May 30, 2018 Share Posted May 30, 2018 Hi all,Hope someone can help. I need to recalibrate my Speedo but unsure of the calc formula. The car is 2015 with the 43 tooth ring, tyres are toyo r88r 185/60/14 with a rolling circumference of 71 1/4 inches. If anyone can help. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 30, 2018 Member Share Posted May 30, 2018 Is that electronic off a wheel? Caerbont or Stack or some other instrument? Calibration by button on the front or switches on the back?And what factor does it want as an input?This might be the most useful single thread. Full search of the archives....How about doing it with GPS instead, eg using a smart 'phone? Find a road where you can run at steady speed... compare the indicated speed and the GPS speed, tweak the calibration, and repeat... Jonathan Link to comment Share on other sites More sharing options...
babymerc Posted May 30, 2018 Author Share Posted May 30, 2018 Hi Jonathan,It's a Caerbont with wheel sensor. Single button on the front. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 30, 2018 Member Share Posted May 30, 2018 The first thread linked from #2 has a link to the Caerbont instructions. They tell you how to get the "Calibration Number" in pulses per mile. And also how to "Drive to Set" using a measured mile, which is a lot more awkward than using GPS!Jonathan Link to comment Share on other sites More sharing options...
babymerc Posted May 30, 2018 Author Share Posted May 30, 2018 Am I right in thinking it's 63360 ÷ 71 1/4 x 43 = 37840 or is this complete rubbish Link to comment Share on other sites More sharing options...
babymerc Posted May 30, 2018 Author Share Posted May 30, 2018 Am I right in thinking it's 63360 ÷ 71 1/4 x 43 = 37840 or is this complete rubbish Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 30, 2018 Member Share Posted May 30, 2018 Jonathan Link to comment Share on other sites More sharing options...
John Vine Posted May 31, 2018 Share Posted May 31, 2018 Am I right in thinking it's 63360 ÷ 71 1/4 x 43 = 37840 or is this complete rubbishNo, that's exactly how to do it. Be sure to include a leading zero when you enter the (six-digit) code.Here's a table with the codes for some of the more common tyres: And if you compare the tripmeter with a GPS device, you can fine-tune the code to a very close tolerance.JV Link to comment Share on other sites More sharing options...
John Vine Posted June 1, 2018 Share Posted June 1, 2018 I omitted to add that your value of 37840 equates to a rolling circumference of 72.00". For 71.25, the code would be 038238.JV Link to comment Share on other sites More sharing options...
babymerc Posted June 13, 2018 Author Share Posted June 13, 2018 Hi John,Many thanks for that. I did get to the root of the problem. The light on the sensor on the drive shaft was staying on for about ten teeth effectively reducing the ring from 43 to 33 teeth. A small adjustment and all was good. Link to comment Share on other sites More sharing options...
John Vine Posted June 13, 2018 Share Posted June 13, 2018 Good news!JV Link to comment Share on other sites More sharing options...
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