kenton
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| posted on 8/1/08 at 01:35 PM |
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speedo calibration for sva pass
Hi all,
My tyres on the toyo website do 831 revs per mile, i am using an electronic speedo so have to set the switches on the back.
Do i need to set them to say 850 or 810 to pass sva.
I can reset to exact reading after sva.
Thanks in advance
kenton
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DaveFJ
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| posted on 8/1/08 at 01:39 PM |
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surely it depends on your diff ratio ?
Dave
"In Support of Help the Heroes" - Always
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Humbug
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| posted on 8/1/08 at 01:44 PM |
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quote:
Originally posted by DaveFJ
surely it depends on your diff ratio ?
...and where you put the sensor. If the sensor magnet is on the wheel or drive shaft, then the tyre diameter is all you need. Otherwise, as Dave says,
the diff will play a part if you have the sensor picking up off the prop.
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BenB
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| posted on 8/1/08 at 01:44 PM |
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What kind of sensor are you using? Normally the speedo is run from a sensor on the propshaft which will obviously (as Dave says) be effected by the
diff. If you run it direct off a wheel just make sure it over-reads not under-reads... Any under-reading is a fail @ SVA. You can over-read by around
10% (exact requirements are in the manual)...
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RazMan
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| posted on 8/1/08 at 01:46 PM |
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Can you have a quick calibration run using a GPS? They are suprisingly accurate.
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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02GF74
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| posted on 8/1/08 at 01:47 PM |
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^^^^ depends on what the sensor is sensing? it could be, like on mine, counintg wheel revs, but unlkley.
to answer the question think of it this way
by taking extrame values, if you set it to say 10 revs, then in one mile you do 800 so speedo will think you are going 8x as fast.
This means that choosing a lower value than actual will show a higher speedo reading, whcih is what SVA want - the speedo must not show less than true
speed; it can be more.
(now waits for someone to say I got it wrong..... again  )
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ditchlewis
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| posted on 8/1/08 at 02:04 PM |
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How many magnets are you using?
if you have the sensor on the engine side of the diff then the calculation should be
nr of magnets x diff ratio x number of revs the wheel turns per mile. this will give you a number to look up on the calibration sheet and you can the
set the dip switches on the speedo.
if the sensor is on a half shaft or after the diff then
nr of magnets x number of revs the wheel turns per mile.
run the calcs on 831 and 850 and choose the calibration number that best fits the answer.
also the GPS is a good way.
i put the sensor on the half shaft and mr SVA said he could not check the accuracy so he just took it for a drive around the car park to check that is
worked!!!!!!
i passed 
the GPS was the way he suggested i check it's accuracy.
hope this helps
Ditch
[Edited on 8/1/08 by ditchlewis]
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kenton
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| posted on 8/1/08 at 05:58 PM |
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Thanks for the replys,
Im using a hall sensor on the rear half shaft, so am not affected by diff ratio.
The speedo needs between 2500 and 135635 pulses per mile so will use four of the bolts where the half shaft bolts on.
From what has been sugested i need to set the speedo to a figure below 831 revs per mile to the display to over read the true speed.
thanks again
kenton
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John Bonnett
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| posted on 8/1/08 at 06:35 PM |
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Kenton, There may not be a problem. Barrie Sharpe told me that the SVA tester allowed him to calibrate his speedo during the test so that it was spot
on. Worth checking with your local SVA station.
John
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