Humbug
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| posted on 20/8/05 at 03:41 PM |
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Help: electronic speedo pulses per mile?
I have a set of ETB instruments and am trying to set up the electronic speedo. I have magnet sensors on the prop flange but since the car is not
roadworthy and I don't have a handy measured mile I am finding it difficult to calibrate. The informaiton with the speedo (and on the ETB
website) says there are 3 ways to calibrate:
1) measured mile (can't do that as described above)
2) set the pulse per mile
3) manual adjust up/down
I want to do 2) but it just says that the factory setting is 41000 pulses per mile. However, I have no clue what wheel/tyre/axle sizes that assumes,
and there is no formula given to work it out mysefl. Does anyone know how these things are calculated, or have I got to wait till Monday and call
ETB?
Thanks in advance
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cerbera
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| posted on 20/8/05 at 03:49 PM |
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If its like my Revotec one, its the number of mangnets x diff ratio x wheel rev/mile. Which will give you the number of pulses/mile.
Best way to calculate revs/mile is, get someone to sit in car, mark a chalk line on tyre at road contact area, push car through 3 wheel rotations.
Measure distance travelled and divide by 3 to give average circumferance. Take the average circumference ( in mm) and divide into 1 609 344mm which is
how many mm there is in a mile.
[Edited on 20/8/05 by cerbera]
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Humbug
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| posted on 20/8/05 at 04:14 PM |
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thanks... based on that, I have:
- tyre circumference of 1814.6mm (185/60/14 tyres - calculated rather than measured, so it is probably a little high give tyre
"flattening" with weight on, but not much)
- 887 wheel revolutions per mile (1609344 divided by 1814.6)
- times axle ratio (3.89) times magnets (2) = 6900
This is way off the 41000. I'm confused...
How many pulses per mile did you end up with (and what tyre circumference, magnets, diff ratio, etc.)?
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cerbera
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| posted on 20/8/05 at 05:25 PM |
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I have mine set at just over 13000 pulses/mile. I have used 4 magnets, my diff is 3.62, and my tyres are the same as yours, so going on that, the 6900
you have seems ok. I would definately find out the role circuference with someone sat in as it does make a difference.
Also, I tried mine with just 2 magnets and the speedo reading was erratic, but its spot on with 4.
HTH
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Humbug
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| posted on 20/8/05 at 06:34 PM |
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cheers - I'll try it
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mookaloid
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| posted on 20/8/05 at 06:44 PM |
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Just call ETB and give them your diff ratio, wheel and tyre size and number of magnets on the prop and they will mgive you the dead accurate magic
number.
Cheers
Mark
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rusty nuts
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| posted on 20/8/05 at 08:23 PM |
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Haven't used ETB instruments myself, but I'm sure that instructions for my Green gauges units recommended using 4 magnets to even out the
signal HTH
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rusty nuts
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| posted on 20/8/05 at 08:25 PM |
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P.S you should be able to get the rolling radius of the tyres from your tyre supplier . If you have problems let me know I may be able to get ot for
you . Someone may be able to help with a link?
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wicket
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| posted on 20/8/05 at 09:09 PM |
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Get the rolling radius from here
http://www.performancetyresdirect.co.uk/converter/converter.html
Having looked at this site
http://www.torquecars.co.uk/Tuning/alloy-wheels.php
I think the Performance Tyres Direct shows the rolling diameter.
[Edited on 20/8/05 by wicket]
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DarrenW
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| posted on 20/8/05 at 11:55 PM |
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Go to ETB website. Download digitools and it has the configuration calculators. You just type in rear whell size and dif ratio and it gives you the
figure you need.
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Humbug
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| posted on 21/8/05 at 07:56 AM |
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quote:
Originally posted by DarrenW
Go to ETB website. Download digitools and it has the configuration calculators. You just type in rear whell size and dif ratio and it gives you the
figure you need.
Thanks - done that and it comes out with 6899, pretty close to my calculation of 6900!!
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wicket
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| posted on 21/8/05 at 09:58 AM |
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Am I going mad or what, but where's the digitools download hiding on the ETB site?
Found it !!!
[Edited on 21/8/05 by wicket]
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Humbug
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| posted on 21/8/05 at 05:50 PM |
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I set the speedo to 6900 and had a little drive - it moved to about 10mph and was steady, so it looks like the magnets and sensor are working ok.
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cerbera
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| posted on 29/8/05 at 05:51 PM |
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If you are only using 2 magnets it works fine at slow speeds, but as soon as you floor it the speedo reading will be all over the place. Well thats
what happened with me
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Humbug
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| posted on 29/8/05 at 06:19 PM |
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quote:
Originally posted by cerbera
If you are only using 2 magnets it works fine at slow speeds, but as soon as you floor it the speedo reading will be all over the place. Well thats
what happened with me
Since I have neither MOT nor SVA I can't really floor it just yet! If I really do need 4 magnets it's a bit annoying of ETB to sell
the sensor and recommend just 2...
Oh well, I'll have to wait and see
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