craig1410
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| posted on 30/5/03 at 08:17 PM |
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Glenn,
A couple of points to clarify:
quote:
correct but KPI is the angle measured as seen from the side
If you look from the side (assuming you mean side of the car) then you won't see the KPI angle at all. KPI is the angle formed between the
vertical wheel axis and a line drawn through the upper and lower balljoints when viewed from the front. (Or from the side if you have 90degree
steering lock  )
quote:
This is genrally reffered to as king-pin offset
My book on suspension design by Des Hammill doesn't even have that term in the glossary, nor does the Race and Rally sourcebook by Alan
Stanniforth. I've always heard it referred to as scrub radius (although the SAE do refer to it as Kingpin offset) and Kingr's description
of it is spot on. Just don't start the argument again over whether zero scrub is optimum or not... By the way, try searching for "Kingpin
offset" on google.com and then try "scrub radius" and see how many hits you get for each 92 v 846 I make it. My point (yes there
is one...) is that it is "generally" referred to as scrub radius as far as I can see.
quote:
No, I dont like the idea of shimming my wishbones, i know it's done but i would rather have my brackets correctly sized i just think it
looks tatty.
That's fine if you have the means by which to accurately position your brackets to achieve the correct castor angle right from the start but
that leaves you with another problem - what is the "correct" angle? Also, if the bodywork is fitted correctly then you can hardly see the
suspension mountings and if you paint the edges of the washers black (or whatever colour your chassis is) then they look fine IMHO.
Cheers,
Craig.
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Glenn
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| posted on 30/5/03 at 11:20 PM |
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quote:
Originally posted by craig1410
If you look from the side (assuming you mean side of the car) then you won't see the KPI angle at all. KPI is the angle formed between the
vertical wheel axis and a line drawn through the upper and lower balljoints when viewed from the front. (Or from the side if you have 90degree
steering lock )
ok ok , no we need a picture here, i meant the side of the wheel
quote:
My book on suspension design by Des Hammill doesn't even have that term in the glossary, nor does the Race and Rally sourcebook by Alan
Stanniforth. I've always heard it referred to as scrub radius (although the SAE do refer to it as Kingpin offset) and Kingr's description
of it is spot on. Just don't start the argument again over whether zero scrub is optimum or not... By the way, try searching for "Kingpin
offset" on google.com and then try "scrub radius" and see how many hits you get for each 92 v 846 I make it. My point (yes there
is one...) is that it is "generally" referred to as scrub radius as far as I can see.
well not meaning to dismiss your comments but goggle is not the most accurate method of determining the naming convention of anything. Having looked
at a suspension book close to me it is referred to as Kingpin offset( Competition Car Suspension by Allan Staniforth). again, we need a picture, I
will draw one when more sober
quote:
That's fine if you have the means by which to accurately position your brackets to achieve the correct castor angle right from the start but
that leaves you with another problem - what is the "correct" angle? Also, if the bodywork is fitted correctly then you can hardly see the
suspension mountings and if you paint the edges of the washers black (or whatever colour your chassis is) then they look fine IMHO.
Cheers,
Craig.
that's fine, personally I still think that a number of washers, painter whatever colour, will look tatty. you will never find washers used to
space a wishbone on a race car and I intend my car to be of the highest standards.
I am not saying that this method is incorrect just that it is "tatty" just MHO.
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craig1410
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| posted on 30/5/03 at 11:59 PM |
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Glenn,
Terminology is a wonderful thing isn't it?
Don't worry about a picture of KPI on my account since I have plenty of pictures in the above mentioned books.
As for Kingpin Offset, try searching on this forum for the term and you will only find your own reference to it. Search for scrub radius and
you'll find over three pages of hits. I'm not saying it isn't a synonym for scrub radius but just that "generally" it
isn't used in the context of this forum. Anyway, 'nuff said.
Finally on the castor adjustment, how do the race cars adjust camber? Surely they don't cut their chassis brackets off and weld them further
along each time they need to change castor angle? The only alternative that I can see is to use spherical bearings to swing the wishbones around as
used on the back of the Tiger Avon. Personally I don't see any problem with using washers, shims or machined spacers since the end result of
being able to set up the suspension correctly will more than make up for any "tatty"ness. I'll try to remember to admire your
non-tatty chassis mounts when I'm driving round the outside of you in the corners... 
Only kidding mate, good luck with your build!
Cheers,
Craig.
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Glenn
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| posted on 31/5/03 at 10:00 AM |
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Well just to clear it up, I have done a little drawing, It's in my photo archive so now weather your from the US, UK or abbojabbi
you'll know what I mean.
"a rose by any other name would still smell as sweet" unless it was called a stench-bush
The strange things is that 2 books by the same guy, Allan Staniforth, use different naming conventions.
[Edited on 31/5/03 by Glenn]
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craig1410
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| posted on 31/5/03 at 10:17 PM |
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Glenn,
At the risk of appearing to be a real pain in the ass I have to say that I think the drawing just adds confusion. It describes KPI and scrub radius
fairly well but what on earth is it trying to show with respect to camber? It shows camber angle as being the angle between the wheel centreline and
some other arbitrary line.
Now if that other line happened to be normal to the road surface then it would make sense but as it is it doesn't make sense.
Here is a very quick diagram made in MS Paint to illustrate my point:
Anyway, I don't know about you but I'm bored with this contest of geometry teaching skills. I know what's what and I expect you do
too but neither of us are very good at describing it. Lets both stick to building cars and leave the teaching to Uncle Ron! 
Cheers,
Craig.
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craig1410
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| posted on 31/5/03 at 10:26 PM |
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Syd,
No, I've not had any revelations on the roll centre front. I did read a good webpage on the subject (
http://web.umr.edu/~formula/library/sae_paper/paper.html )
It talks about the dynamics of Roll and made me think of an interesting scenario. If the roll centre is above the centre of gravity then the car will
lean into the corners
This probably wouldn't be immediately useful since the suspension geometry of most cars would not induce enough dynamic camber on the outside
wheel in this scenario. If the roll centre and CofG coincided though, then theoretically you wouldn't get any roll at all. According to the
above webpage this is what the designers aim for and by getting them close to each other you can use lighter anti-roll bars or none at all.
Anyway, I'm not going to worry about it or I'll never get my car built!
Cheers,
Craig.
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Glenn
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| posted on 1/6/03 at 12:37 AM |
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quote:
Originally posted by craig1410
Glenn,
At the risk of appearing to be a real pain in the ass I have to say that I think the drawing just adds confusion. It describes KPI and scrub radius
fairly well but what on earth is it trying to show with respect to camber? It shows camber angle as being the angle between the wheel centreline and
some other arbitrary line.
the wheel is shown in the upright position with a centreline drawn though the vertical. The arbitrary line is to illustrate the direction that
you would measure camber. I did not draw the wheel at said angle since I was trying to illistrate KIP and scrub rad / king pin offset.
that all do
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craig1410
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| posted on 1/6/03 at 06:39 PM |
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Agreed!
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The One
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| posted on 23/6/03 at 09:10 PM |
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For the record the original MK insert (coloured blue ) was made from EN8 (high carbon steel). They where un-hardened. Ali and steel together do not
mix due to electrolitic action.
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