Berwyn
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 posted on 6/7/04 at 07:51 PM |
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Smiths Speedo Calibration
Hello, good evening and Aaaargh!
I have read a few threads on this, but still i aint got it sus'd.
Formula is:
TyreRevs/Unit Distance X diff ratio X 4
So I went off to http://www.customautotech.co.uk/
and worked out that my 195x50x15's have a rolling radius of 1.81.
1609.344 metres in a mile /1.81=889.14
889.14 X diff ratio (mine is 3.36)=2987.51
X4 (as thees 4 magnets on prop)=11950
11950 in the chart = 0110011100
Type this in and it recons i'm doing 70mph at tickover in 1st.
Wicked diff Eh!
Anything obviously wrong here guys?
24 hours in a day, 24 beers in a case. Coincidence? I think not
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spunky
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| posted on 6/7/04 at 08:28 PM |
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It had me beat also.
Jack up the back wheels, rig up a cheap cycle computer ans randomly flick the dip switches untill it reads the same....
Worked for me 
John
The reckless man may not live as long......
But the cautious man does not live at all.....
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dmottaway
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| posted on 7/7/04 at 04:00 AM |
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in this line of your calculation
1609.344 metres in a mile /1.81=889.14
you divided by the radius instead of the circumference.
do it again using the circumference (or divide you answer by 2 X 3.14159) and the result is a more reasonable 11mph (or there abouts).
dave
[Edited on 7/7/04 by dmottaway]
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SteveO
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| posted on 9/7/04 at 10:57 AM |
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If its the same as the caerbont which i suspect it is , from the binary numbers you show it dip switches are meant to be set from right to left. ie
10=0.9=1,8=1,7=0 etc.
I also have slight problems with my speedo movement being jumpy between 60 and 70 mph; i double checked the magnets and gap all seems fine, i'm
a bit stuck on this one.
Steve
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zetec
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| posted on 9/7/04 at 03:32 PM |
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I got some help from CAI who are think are Smiths under a different name. contact tel. 01639 732200, bloke in tech helpful. Also check their web site
out at greenguages as it has a setting method and how to work out pulses to speed etc I think.
Might be easier to count the revolutions of the prop or drive shaft you are using for a given number of tyre revolution by pushing in a straight line
then measure the tyre diameter with it on the ground as it will differ to the uncompressed tyre.
If all fails get someone with sat nav to drive with you and use this reading to adjust your own.
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SteveO
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| posted on 16/7/04 at 12:50 PM |
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Hi
The CAI guy said they are fimiliar with the speedo jumping about at high speed; its caused by the prop shaft being magnetized when using 4 magnets, so
he said to reduce the magnets to 2 or 3 which i've done and i've taken it for a blast and its all smooth movement in the range. booked the
retest for monday.
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mad-butcher
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| posted on 17/7/04 at 06:28 PM |
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you can't do the the calculation in metres according to the cai techies the speedo is supplied for the uk therefore MPH even though it also
shows KPH the calculations are for the main use MPH so u need inches per revolution and if your going off the prop shaft you need the dif ratio in the
equation as well
cai tech dept are only to willing to help
tony
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