cjtheman
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| posted on 8/4/09 at 08:52 PM |
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help needed
hi all
had my sva at cardiff speedo problem
speed checks as follows
act speed 41 speedo reads 35
47 40
60 50
71 60
84 70
had the gearbox off and the speedo drive has 25 teeth on it
i also have one that i can put in with 22 teeth on it
is there anybody on here that can work out the maths on this one to make sure that it will come in ok
cheers
colin
wanted
sunny weather
sva pass 12/6/09
taxed 16/6/09
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MautoK
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| posted on 8/4/09 at 10:21 PM |
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If you take the current actual speeds and multiply by 22/25 you should get the actual speeds with the 22-tooth pinion.
The tail shaft does 25(old) or 22(new) revs for 1 rev of the cable. So, for a given speedo reading the tail shaft must rotate at 22/25 (0.88) of its
current rate once the 22tooth pinion is fitted. i.e. the road speed with the 25tooth will become *22/25 (or *0.88) when the 22tooth is fitted
This assumes that the pitch of the teeth and pinion diameters are appropriate to engage the worm.
The three figures per line below are 'Original Actual (25tooth)', Speedo and 'New Actual (22tooth)'
41, 35, 36.1
47, 40, 41.4
60, 50, 52.8
71, 60, 62.5
84, 70, 73.9
Hope that helps. (Hope that's right, too!)
Still not in limit, however, because you'll still be going faster than the speedo says.
[Edited on 8/4/09 by MautoK]
He's whittling on a piece of wood. I got a feeling that when he stops whittling, something's gonna happen. (OUATITW/Cheyenne)
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MikeRJ
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| posted on 8/4/09 at 10:35 PM |
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Going from 25 teeth to 22 teeth should increase indicated speed by 25/22=1.136
This is not enough to bring your speedometer accuracy to SVA standards however, it would still be under-reading by around 5.3% (currently
under-reading by around 16.7%)
You would need 21 teeth on the drive to get you close to zero error, and ideally 20 teeth to get it to safely over-read by 4-5%.
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