Some of the less well designed supension systems in certain sports racers
inthe 60's had short wishbones. Lola T70 if I remember correctly. Clearly
the shorter the wishbone the smaller the radius it will describe as it move
through it's working range. This exacerbates camber change - which is
obviusly not a good thing. The aforementioned Sports racers had seriously
restricted suspension travel in effort to limit camber change. The lesser of
the two evils and all that. This is one of the main reasons why most racing
cars have the wishbones as long as possible - to minimise camber change -
and also leads to the wishbones being extremely slender and very fragile as
a result. A friend of mine had to remake his locost wishbones with
butressing in the design after a mild kerbing bent a wishbone.
Some of the earlier westfields also had extra long trailing arms which had
there forward ends mounted on the outside of the main body tub. Again the
longer arms in this case help to control axle tramp. Same principle really.
P.S. Trust none of this - it's merely my understanding of the subject.
The Locost is really a clone of the early Westie which used a very narrow
Midget/Sprite steering rack the trouble track rod ends are not easily
available to mate these to Cortina or Sierra uprights.
I follow, so far!
> This exacerbates camber change - which is
> obviusly not a good thing.
Why design so the camber changes? - Set the camber, two identical wishbones,
camber doesn't change, why do most seem to have longer bottom wishbones and
the changing camber? This gives more negative camber as the spring goes down
and vice versa if I understand correctly. Does negative cmaber on the
outside and positive on the inside make it ride well, or corner well, or
roll less or ??? I can understand the length of the wishbone makes the
camber 'within limits' over more travel, but what effect do these limits
have?
> P.S. Trust none of this - it's merely my understanding of the subject.
Lol!
I don't think that's right. As Marko pointed out, you can change the
geometry to suit. I think the long wishbones theory is purely one of
aerodynamics. If you shorten the wishbones on a FF Zetec car, then you'd
have to either reduce track, or widen the body. Neither of these are
desirable. The only difference I can think of for long wishbones is that
track wouldn't change so much, but that's negligable.
Andy
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Graeme
"Andy Laurence" <user...@this.is.a.trap.graffl.net> wrote in message
news:a9j948$3k0hb$1...@ID-109625.news.dfncis.de...
Graeme
"marko.cosic" <marko...@ntlworld.com> wrote in message
news:yl9v8.41949$C21.7...@news6-win.server.ntlworld.com...
For anyone intetested the best primer currently available on suspensions is
the Fred Phun book "How to Make Your Car Handle" it was published 25 years
back and is still best book for the beginner. Many other books by such as
those Len Terry, Nicky Lauda, LK Setright and Alan Stanhope are also worth
study.
My head is beginning to hurt... Maybe beam axles aren't such a bad thing
after all!
£11 for the book AWM mentions, and there's a lot more to suspension than I
thought (hey - I own a Series Land-Rover, you can't blame me!), so perhaps
I'd better get the book and have a good read before asking any more
questions...
Cheers guys,
Marko
My response was to a section with no mention of bump steer, just camber. And
everything I said stands. Track change has to do with something. Esp.tyre
wear. I agree that wishbone length has no direct effect on handling, but it
does absolutely minimize camber change for a given wheel movement. And which
Morgan are we talking about, have they made only one model? Are we talking
about those with sliding pillar suspension?
I address the long wishbone/aerodynamic issue in the other part of the
thread.
And isnt it a bit sweeping to say that none of this applies to the kit car
world. Are all kit cars the same? Should we really stay rooted in the 60's?
I love the solution to bump steer 'and make the suspension hard'. Swap bump
steer for over steer, neat. Now you dont dart around on the straights but
you do go straight on at the corners. Or buy my MG midget and do both.
Both Fred Puhn and Allan Staniforth have written excellant books, I'm always
wary of 20 year old books from the USA though, they had some very strange
ideas and a lot of their racing has long history bound rules, leaving them
running obselete suspension types. They make the cars handle despite the
drawbacks(a bit like Porsches) but a lot of what they say is just not
relevent now. Get newer susp. gurus with up to date ideas.
Although, if you are building 7 types with rigid axles then they are way
ahead of us in terms of getting your back end to hook up and resist torque.
Graeme
"AWM" <am...@btinternet.com> wrote in message
news:a9jo4j$guu$1...@knossos.btinternet.com...
Surely the camber change has more to do with relative lengths of upper and
lower wishbones than the overall length. In fact, equal length upper and
lower would have no camber change throughout movement.
Andy
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The big drawback with parallel is track change, dismissed by some, which can
cause horrendous tyre wear. Everytime you brake your wheels move inwards. In
single bump your track changes, in roll it changes. Who would want to narrow
their front track as they roll into a corner?
There you are, roll centre at ground level, nice, then your track narrows as
you brake for the corner, not a huge problem but you are using up some of
your traction allowance, as you turn into the corner the nice big roll
couple caused by your ground level rc and your much higher cog, (and dont
forget your narrower front track) is trying to lift your inside wheel as you
turn. And then the positive camber on the outside wheel and negative on the
inside(dont worry about this too much as the difference in roll centres
front and rear means one of the inside wheels is probably in the air) caused
by your parallel, equal length w/bones adds to the whole sorry mess. So all
your weight has transfered to the outside wheel which is now leaning
outwards. And as you also have stiff springs to compensate for your bump
steer, you now plow on into the car which was going round the outside of
you.
Of course, most of this doesnt really matter on most road cars. Only at the
extremes does it really get bad enough to present a problem. Most light low
kit cars handle well, better than most production cars, even with less than
perfect susp. setup.
And on F1 the fact that its the tyres that do the work and not the
suspension, most of the downsides of parallel disappears, with only tiny
susp. movement, low rc, low cog and minimal roll, any camber change is tiny
anyway. And its made even smaller by having the wishbones longer.
Graeme
Disclaimer: Most of the above may be rubbish.
"Andy Laurence" <user...@this.is.a.trap.graffl.net> wrote in message
news:a9k2vd$3nd1d$1...@ID-109625.news.dfncis.de...
Agreed.
> The big drawback with parallel is track change, dismissed by some, which
can
> cause horrendous tyre wear. Everytime you brake your wheels move inwards.
In
> single bump your track changes, in roll it changes. Who would want to
narrow
> their front track as they roll into a corner?
Agreed, although the difference in track is negligible, unless you're
comparing 3" wishbones with 12" wishbones on a car with over 2" travel!
> There you are, roll centre at ground level, nice, then your track narrows
as
> you brake for the corner, not a huge problem but you are using up some of
<snip>
I see what you're saying - bit exaggerated though ;-)
Graeme
"Andy Laurence" <user...@this.is.a.trap.graffl.net> wrote in message
news:a9k73o$3tl3k$1...@ID-109625.news.dfncis.de...
All Morgans have been sliding pillar since about 1923 (except the freak
super car they are building now).
Camber change is required with wheel movenent to allow for roll, basically
the ammount of camber change is a compromise between the requirements of
cornering and braking. Usually the camber change is about 50% of the roll
angle any more causes excessive negative camber under braking.
> I address the long wishbone/aerodynamic issue in the other part of the
> thread.
> And isnt it a bit sweeping to say that none of this applies to the kit car
> world. Are all kit cars the same? Should we really stay rooted in the
60's?
> I love the solution to bump steer 'and make the suspension hard'. Swap
bump
> steer for over steer, neat. Now you dont dart around on the straights but
Making the suspension hard is the time honoured way way of getting round bad
geometry -- basically it stops the suspension working. To use soft
suspension the geometry must be good through the full range of suspension
travel and the chassis must be stiff enough tgo allow balancing by atering
the roll couple distribution.
A car can be stiffly sprung and neutral it is mainly a question of roll
stiffness distribution front to rear.The big enemy is unsprung mass get the
unsprung weight down and the wheels will stay in contact with the road.
Sorry but I'm not seeing that latter premise which doesn't mean it's wrong
because this is not my area of specialisation. If equal length wishbones cause
no camber change in bump then I don't see how they can cause it in roll. If the
wheel stays parallel to the chassis in bump regardless of suspension movement
then surely it also stays parallel in roll. The amount of roll is not relevant
and is a function of things other than the wishbone length anyway (c.g., roll
centre height etc).
Longer wishbones certainly minimise track width variation but I'd be happy to
see further clarification on the camber change issue.
Dave Baker
Puma Race Engines (www.pumaracing.co.uk)
With equal-length wishbones, then the wheel does stay parallel to the
chassis in roll, but that's not what you want. You want the tyre to
stay at 90 degrees to the road, and as the chassis is leaning in a
curve, you don't want the outer tyre to go positive camber do you?
--
Chris Morriss
Graeme
"Dave Baker" <pumar...@aol.com> wrote in message
news:20020417155509...@mb-fj.aol.com...
Yes I know, that's what I'm saying but I see now what you meant though - that
the absence of camber change in roll is the problem rather than the presence of
it.
"And while equal length upper and lower would have no
> >camber change in bump, in roll they do."
In the same sentence you appear to have used the term "camber change" to mean
relative to the chassis in bump and relative to the road in roll.
When designing race suspension systems we have always stuck to three terms to a
keep this clear.
"Static camber angle".
"Camber change" which is the component caused by movement of the suspension
relative to the chassis.
"Chassis roll angle" which is the same angle whether measured at the wheel or
the chassis.
The three combined give the "dynamic camber angle".
:-)
I dont understand your point. 'absence of camber change in roll is the
problem rather than the presence of it.' There is not an absence of camber
change in roll. There is a very definite camber change in roll.
> "And while equal length upper and lower would have no
> > >camber change in bump, in roll they do."
>
> In the same sentence you appear to have used the term "camber change" to
mean
> relative to the chassis in bump and relative to the road in roll.
>
No, I meant relative to the road in both cases. In bump, with parallel,
equal length w/bones there is no camber change. Relative to road. Or
chassis. The wheels will maintain their static camber setting. (Lets assume
a flat road as in a diagram). In roll, on the same flat road, there is
camber change, relative to the road, the wheels will maintain their static
setting relative to the chassis. So they will adopt the camber attitude that
I described.
By introducing the other 'correct' terms, you are just complicating the
description of a situation that was deliberately kept uncomplicated for
clarity.
Graeme
Dave is using the chassis as a reference point, you are using the road.
Whilst there is no camber change relative to the chassis, there is change
relative to the road.
Hmmm - I honestly didn't drop in on this to nitpick or argue about semantics
but the sentence that started this threw me to the point where I began to
wonder if there was something I was missing about suspension design or not. For
the simple reason that anyone I've ever dealt with when discussing suspension
design would be talking about camber change due to suspension design as being
relative to the chassis and never to the road. However as long as all the
people concerned use the same terms it really doesn't matter. You could call
static camber angle "pink dress" and camber change due to suspension travel
"blue dress" if you liked and then if you asked your mechanic to dial in
another 0.25 degrees of negative pink dress you'd get what you wanted.
But the key is to use the terms consistently or everyone will end up in a
buggers muddle. So I read the thread through from the start to see if a
convention on terms had been established previously and I was the only one
missing the point. In an earlier posting you typed:
"My response was to a section with no mention of bump steer, just camber. And
everything I said stands. Track change has to do with something. Esp.tyre wear.
I agree that wishbone length has no direct effect on handling, but it does
absolutely minimize camber change for a given wheel movement."
So clearly you're using the term camber change to mean relative to the chassis.
And then later:
"And while equal length upper and lower would have no
>camber change in bump, in roll they do."
So now you're using the same term to mean relative to the road which is what
threw me. So please don't try and make out that you were trying to keep the
situation "uncomplicated for clarity" because you aren't. You're using the
terms differently as it suits you which tells me you don't do this for a living
like I have to where clarity and consistency are essential if everyone is to
work together properly.
Camber change is something caused by suspension travel and is always measured
relative to the chassis. Dynamic camber angle is the net result of body roll,
static camber and camber change and is always measured relative to the road.
Get those right and you have a fighting chance of being able to sit round a
table with professional suspension designers and not confuse the the hell out
of everybody.
I apologise if my little joke('Lucky its Puma Race Engines and not Puma Race
Suspension then. :-)') made you feel the need to prove your credentials, it
wasn't intended that way.
Graeme
"Dave Baker" <pumar...@aol.com> wrote in message
news:20020418062904...@mb-cd.aol.com...
Yes a good straightforward guide except they've got the drawings showing
positive and negative camber the wrong way round :)
But whole point is longer wishbone don't give any less camber change than
short ones -- unless they are designed to.
Irespective of length equal length parrallel wishbones give wheel motion
parrallel to the body just like any other suspensions system with a ground
roll centre. The only system in which the wishbone length is really
important is the single wishbone --- more commonly called the swing axle
last seen under the front of Imps with a double wishbone system what really
matters is the roll centre height and the "virtual swing axle" length. If
the wishbones are parrallel and equal length the virtuial swingaxle is
infinitely long resulting in a ground level roll centre.
The sideways tyre scrub argument due short wishbones is also a red herring
as on a double wishbone system the track change caused by the arc of the
wishbones is almost completely cancelled by the change in track at the wheel
contact points due the change in camber. This is why when you jack up the
front axle of a modern road car then release the jack it returns almost
exaclty to the original ride height. Just about the only road car
suspension system this isn't true for is a swing axle -- just ask the owner
of an Imp or Triumph Herald.
I only ever said that "Parallel equal length wishbones give bad track change
in bump and positive
camber in roll, just when you need it the least." Is this not correct then?
I think it is.
And you are correct, "Irespective of length equal length parrallel wishbones
give wheel motion parrallel to the body just like any other suspensions
system with a ground roll centre." So in bump the wheel stays at its static
setting. As I originally said.
And in roll this also applies. The wheel remains parallel to the body. So
its camber, relative to the ground, changes.
Where did I mention "sideways tyre scrub argument due short wishbones". I
only mentioned sideways scrub in relation to parallel, equal length
wishbones(Just as an aside this would be less per unit of wheel movement the
longer the wishbones). And of course, as there is no camber change here, in
bump, the effect is not cancelled out by the "change in track at the wheel
contact points due the change in camber" (Although it is small anyway, I
agree)
So it appears that you are arguing against things I didnt actually say or
you have misread my posts.
And this was all in the context of someone asking why we didn't use
parallel, equal length wishbones.
Graeme
My head hurts and I'm going to bed.
"AWM" <am...@btinternet.com> wrote in message
news:a9n6u2$i1g$1...@helle.btinternet.com...
Hi, any chance of an ISBN for these books so I can order them from the
library?
Cheers,
Marko
"Race and Rally Source Book" by Allan Staniforth (best book by far - IMO)
ISBN 0-85429-984-x
"Chassis Engineering" by Herb Adams (not the musician)
ISBN 1-55788-055-7
Terry
"marko.cosic" <marko...@ntlworld.com> wrote in message
news:SNPv8.213$ML.9...@news2-win.server.ntlworld.com...
If you can find a copy of Alan Staniforth's 'High Speed, Low Cost' book
about designing and then competing in a mid-engined Mini-based single
seater, then buy it. He gives a lot of old, but still relevant design
information about double wishbone suspension, including how to make a
simple 'analogue computer' out of string and hardboard to show you what
is happening to the wheel in roll, and bump.
Chris Morriss
Also at chris....@lakecommunications.com
Shall do.
including how to make a
> simple 'analogue computer' out of string and hardboard to show you what
> is happening to the wheel in roll, and bump.
Lol! Worth it for that alone!
cheers,
Marko
Thank you *very* much people!
Marko
Graeme
"Chris Morriss" <cr...@oroboros.demon.co.uk> wrote in message
news:u+CLuFAk...@oroboros.demon.co.uk...
Graeme
"AWM" <am...@btinternet.com> wrote in message
news:a9n6u2$i1g$1...@helle.btinternet.com...
I've actually got two copies of the 'High Speed, Low Cost' book, a
hardback of the first edition, and a paperback of the second edition,
with some extra information in it.
I'd be quite happy to sell the hardback (good condition!) for 15 pounds
+ postage to someone in the UK, or the useful bits could be scanned and
placed on a suitable website.
BTW, the information on the 'string computer' in the original book is
much more informative than in his 'Race and Rally source book'.
But the wheel should change camber realtive to the body to maintain correct
camber relative to the road durring roll.
With a system with no camber change such as the trailling arms on the rear
of a Mini or Metro the wheel adopts the same roll angle as the body durring
cornering giving less grip -- Issigonnis designed this into the Mini to
reduce the grip at the rear and balance out some of the excess understeer
inherent in the very nose heavy Mini design.
Grip is all about keeping the wheels in full contact with the road, good
handling is mainly about balancing out the grip levels front to rear.
Only 2 suspension system maintain the tyres in contact across the full tread
width durring both roll and dive/squat -- the live axle and the de Dion.
Graeme
"Chris Morriss" <cr...@oroboros.demon.co.uk> wrote in message
news:LqQCLBAs...@oroboros.demon.co.uk...
> In article <a9q0p6$78s$1...@paris.btinternet.com>, Graeme
> <gra...@adaptivedesign.co.uk> writes
> >The string computer is in the Race and Rally Source book too. And Amazon
had
> >a second hand copy of High Speed, Low Cost available a couple of days
ago.
> >
> >Graeme
> >
>
> I've actually got two copies of the 'High Speed, Low Cost' book, a
> hardback of the first edition, and a paperback of the second edition,
> with some extra information in it.
>
>
> Also at chris....@lakecommunications.com
Of these two the de Dion is my choice. All the advantages of the live axle
without the unsprung weight and with better location, although that can be
sorted out on live axle anyway, but only by the addition of more weight.
Plus the possibility of camber adjustment not available to the live axle. If
it werent for its bump issues it would be almost ideal and really the bump
problem is minor in practice. And in most cases it is as good a solution as
wishbones. Ride is also more complient with wishbones but for a race or fast
road car this is not usually an issue. For the road, de Dion is ususlly
messed up by the addition of soft bushes to make the ride nice.
There is a third system that has these traits. The Dax CCAS. And it is
adjustable in almost every way. But complex to build and setup. I believe a
couple of other systems like this have been made in the past, too.
Graeme
"AWM" <am...@btinternet.com> wrote in message
news:a9r4ci$1m0$1...@paris.btinternet.com...
>
> "Graeme" <gra...@adaptivedesign.co.uk> wrote in message
> news:a9neqb$gs6$1...@knossos.btinternet.com...
>
Looks as if the book has found a buyer.
A strut is just a special case of a double wishbone, a strut can be thought
of as a double wishbone setup with a variable length top wishbone. The main
problem with front struts particularly the ones fitted to FWD cars which use
high mounted steering racks is massive bump steer -- with this layout you
can never have zero bumpsteer. This failing aside (as long as the roll
centre isn't too low ) a strut suspension quite closely mimmics a double
wishbone system on bump but is less good on droop.
The movent in any suspension system is modeled as a combination of a
single translation and a single rotation, the translation is relatively
unimportant, but the roatation governs camber so it is a mainly a question
of finding the position of the meta centre of the rotaion, from which you
also work out the roll centre height. Different suspension systems can have
similar locations for the meta centre and roll centre and so with reason
will give similar handling.
I think adding variable length to a double wishbone makes it a very
different animal even if it can be considered a 'special case' in a purely
theoretical situation. And the fact that it acts differently in droop, the
situation that you actually used it in to support your double wishbone
arguement,( "This is why when you jack up the front axle of a modern road
car then release the jack it returns almost exaclty to the original ride
height."), and the fact that you obviously know what you are talking about,
makes me even more sure you were being sneaky.
Regards
Graeme
"AWM" <am...@btinternet.com> wrote in message
news:aa0fop$fqm$1...@helle.btinternet.com...