Howlor
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| posted on 26/2/06 at 03:38 PM |
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Castor Angle - Measuring
Hi,
I have been setting up the suspension geometry today but just need some guidance on the bes way to measure castor angle.
If I place the magnetic angle meter onto the brake disk as though I am measuring camber and then put the car onto full lock. Will the resulting
reading be close to the true caster measurement? I would have presumed it ideally need to be at 90 degrees to the KPI to be accurate?
Is there a better method to use?
Thanks,
Steve
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JoelP
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| posted on 26/2/06 at 04:09 PM |
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doing it like you suggest, on full lock, will reveal no useful results as the KPI will also affect the measurement.
Best approach is to attempt to measure directly from the ball joints. You need to find a way to move the line to one side so you can get the angle
meter on it - maybe some well shaped wood to sit on the ball joints? there must be a better way than that though!
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MrSandMan
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| posted on 26/2/06 at 04:31 PM |
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Obviously your results will only be as good as the method used to produce them. Turning the steering will produce no meaningful data. If you user a
remote method of measuring from the ball joints then reasonably accurate data can be had providing your tool for meauring is accurate. If you use some
kind of stand-off device so that measurements can be taken, it will be essential that the legs to both ball joints are exactly the same length. Any
differences will affect the measurement. If you want both sides the same this will not be critical. Only if you have a target degree measurement will
it matter.
edited to say:-
Just realised, this is my first post after trying to get registered for a while. Hello world!!
[Edited on 26/2/06 by MrSandMan]
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Syd Bridge
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| posted on 26/2/06 at 04:51 PM |
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The old analogue measuring equipment used for steering and tracking setup used the wheel at full lock, measured the lock angle and castor at that
point, and extrapolated it to 90degrees.
eg. set wheels straight, setup castor machine so as to compensate for camber, turn to full lock and measure camber change. If initial camber =1deg;
lock =30deg, camber at lock =3, change =2deg; 90/30=3, x2=6 deg castor.
Or so the old time machines would tell us, Worked out the same as measuring the balljoints.
Syd.
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britishtrident
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| posted on 26/2/06 at 05:11 PM |
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Unless you have calibrated turn tables to turn the wheel 45 in each direction measuring from the wheel or brake disk won't give anything
meaningful.
The try to get reasonable ammount of caster that is as EQUAL as possible on both sides -- if the caster isn't equal the steering will pull and
you will get other strange effects. So it dosen't matter as much as you might think what datums on the uprights you use as long as they are
the same on the left and right sides.
Couple of other ways of doing it --- Measure the trail in mm --- ie measure the distance the upper ball joints are behind the lower and use trig.
or
Make a dummy upright out of round tube that keeps the upper a lower ball joint centres the correct distance apart and do it directly.
[Edited on 26/2/06 by britishtrident]
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nitram38
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| posted on 26/2/06 at 06:32 PM |
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Use an ADA camber/castor gauge. It has all the instructions with it, including the angle to turn the wheels to. I can't remember how to do it
but it involves a pendulum against some figures.
Set your camber first, then your castor. It is pretty simple with the right tools.
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Mark Allanson
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| posted on 26/2/06 at 06:40 PM |
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try this
http://www.locostbuilders.co.uk/viewthread.php?tid=17148
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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britishtrident
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| posted on 26/2/06 at 07:40 PM |
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Good photos Mark -- "a photo paints a 1000 pictures"
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Howlor
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| posted on 26/2/06 at 08:06 PM |
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Many thanks guys I will try the string tomorrow. If it's good enough for F1 then it should be ok for me!
Thanks again.
Steve
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