evinX Posted July 20, 2015 Share Posted July 20, 2015 So my speedo isn't accurate, ive used a gps speedo and have learnt whats 30, 40, 70 etc. But I would like it to work properly. Is there a fix for this? im running wider 18"s and wouldn't mind getting it sorted. My speedo wiring has been played with before. How do I go about getting it to work accurately, wouldn't mind getting new speedo faces if need be to. Just fed up now... Quote Link to comment Share on other sites More sharing options...
Ric Posted July 20, 2015 Share Posted July 20, 2015 I think the only way it can be done is to take the needles off, drive at 10mph via GPS speed, pop the needle back on and see how it goes. Usually the same deal once you've took the needles off to fit new dials. Quote Link to comment Share on other sites More sharing options...
evinX Posted July 20, 2015 Author Share Posted July 20, 2015 That dosent work dude, the needles never match up or match the real speed its doing, urghhh Quote Link to comment Share on other sites More sharing options...
Ric Posted July 20, 2015 Share Posted July 20, 2015 But thats why the needles are off, the spindles will still move (be in the position it thinks it is) but you'd position the needle where it actually is. Then it should always be the same Quote Link to comment Share on other sites More sharing options...
Supraleeturbo Posted July 20, 2015 Share Posted July 20, 2015 could be your after market wheels Quote Link to comment Share on other sites More sharing options...
Mike2JZ Posted July 20, 2015 Share Posted July 20, 2015 If your Supra is a Jspec then isn't inaccurate speedo readings normally to do with the KMH -> MPH conversion (black box) being faulty Quote Link to comment Share on other sites More sharing options...
evinX Posted July 20, 2015 Author Share Posted July 20, 2015 If your Supra is a Jspec then isn't inaccurate speedo readings normally to do with the KMH -> MPH conversion (black box) being faulty This could be it, but my speedo has KM and MPH, but I know nothing about this box Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted July 20, 2015 Share Posted July 20, 2015 (edited) Digital speedos basically work on pulses per mile travelled. But you have added a mechanical unknown by removing the speedo needle, which operates against a helical spring. It is preloaded against the minimum speed stop, and now it will have a different preload, and they are very picky about that being bob on. If you'd not fiddled with that it's a (pretty) simple change in how many pulses per mile the speedo sees, despite how many the tailshaft speed sensor is emitting. Modern digital electronics would have sorted that out. But once yo lose the preload on the needle spindle, set in manufacture, if you get the needle right at say 70 MPH it won't be right anywhere else, as it's still getting the wrong pulses per mile. This is because you have presumably changed the rolling circumference of the stock rear tyres by changing sizes? Fiddle with speedo and rev counter needles at your peril.... Getting the PPM right is enough to contend with, without trying to get the preload right, that's an instrument maker's job. Edited July 20, 2015 by Chris Wilson (see edit history) Quote Link to comment Share on other sites More sharing options...
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