Conference terri::cars_uk

    Has anybody else got a car with a Panhard rod in the rear suspension?
    
    The car is decidedly odd to drive if you detatch it at one end! :^)
    
    Can anyone describe what the various rear suspension designs are?
    I know there's a De Dion design and multi-link whatsits and everything
    else, but although I can see what suspensions do I can't work out what
    I'm looking at, or imagine what it looks like from the description.
    
    What's a Watts linkage for instance?
    
    As an example, the Marcos has a proper rear axle secured laterally by
    a Panhard Rod (bolted to the chassis one end and the axle at the
    other) and then lots of radius rods holding it in place along
    the length of the car. What's this called? It certainly seems to hold
    the road well.
    
    Mark

The only things I know about corner weight / adjustable suspension are:

front left weight should equal front right weight
rear l.w should equal rear r.w.
Left should be same height as right.

Front/back differences have lots of horribly technical effects on handling...

Told you it wasn't much...

Scott

    From memory....
    
    .... a Panhard Rod is used to stop sideways movement of a solid rear
    end (ie along the axis of the axle centreline). It's fixed to the axle
    near one brake backplate and the opposite end of the rod to the body
    work at or near a point vertically above the other back plate. The axle
    can still bounce up and down so the suspenders still works......
    
    

    re several back.
    
    Is one of the factors that needs to be known the mass bearing down on
    each wheel?
    
    If so, what's wrong with putting the car on a level surface and then
    raising a wheel, putting some kind of industrial scale under it and
    then lowereing the wheel onto the measuring device. Let the car come to
    equilibrium on the scale, note reading, repeat with other wheels. That
    would give the mass distribution acting through the suspension to the
    ground and an indication of what needs to be done to the springs etc.
    
    Or am I off beam (or Panhard Rod.... ;^)....)?

    re: .2

    The radius arms stop axle 'tramp' (or I think it is called tramp).
    When you 'put the power down', the axle 'reacts' by trying to wind itself
    up in opposite direction to the wheels. By having a radius arm above and
    below the axle, the tramp is removed.

    The Mk II Jag had a live rear axle and a panhard rod, but the axle
    was supported by quarter eliptical springs, so the tramp, and the 
    general rear suspension setup left a lot to be desired ... hence the
    later 'S' type with the IRS setup.

  Mark

    
    Scott, 
    
    Doesn't a trailing arm suspension look like this? :-
    
    Front -------O <- Axle 
    
    I had a setup like that on my Triumph. Presumably you could have 2 
    layers of trailing arms.
    
    The Marcos looks like this :-
    
    Front ------ ------
                O <-------- Axle.
          ------ ------
    
    The axle is therefore secured front and rear rather than just relying
    on it being suitably secured from the front and springs (in this case
    coils over shocks). 
    
    The Marcos axle is from a Cortina GT (1960s RS Turbo! :^)), but later
    models use the Capri axle.
    
    Mark

	Sounds like the Marcos has got two trailing and two leading.
	Personally, I can never remember which way round is trailing and
	which way round is leading, at least with the Marcos you will always
	be right, just never try to name a given arm as trailing or 
	leading and no one will ever know.

	The panhard rod is usually there to stop axle tramp and wind up.
	Axle wind up is where the axle tends to spin on an axis drawn 
	through the center of each wheel as you put the power down.  The front 
	end of a Cortina axle can move up to 8" in this case.  Additionally, an
	anti-roll bar is used to stop rolling around an axis drawn through
	the middle of car from front to back.

	Dave

    re: .12


    The panhard rod does not stop axle wind up. It is used to locate
    the axle and prevent it being pushed to one side when cornering.

    If it also stops wind up, it is a radius arm.

   Mark

I thought radius arms were the things that support the back hubs on minis and
metros?

Trailing arm: the arm is fixed to the chassis at its front end, so trails
behind the chassis.  The axle then trails behind the trailing arm.

Axle wind up is prevented by having arms above and below the axis of rotation
of the wheels.

Mark: from your description, the Marcos has 8 arms, four trailing and four
leading.  Seems rather a lot...?

Time to (attempt to) draw some pretty pictures:

NB In the diagrams below, an 'o' denotes a joint free to rotate.

Upper and lower trailing arms, side view:


        o========o|
Axle ->/ \        |      Front of car ====>
       \_/        | <- Part of chassis
        o========o|

        ^        ^
        |        Lower arm secured to chassis here
        |
        Lower arm secured to underside of axle here

The upper and lower arms may be of unequal length, so the diff rotates slightly
as it rises and falls.  This keeps it pointing directly at the back of the
gearbox, reducing the angle in the UJs.


Panhard rod, rear view (the rod is actually behind the axle, not undernetah it
as it might look here; well mine is anyway!):


                   ___
    ______________/   \______________
    ______________     ______________   <- axle
        o=======================o

        ^                       ^
        |                       Panhard rod secured to axle here
        |
        Panhard rod secured to chassis here

The idea is that at neutral ride height, the rod is horizontal.  As the axle
bounces up and down, this then gives minimal left-right movement (about .1 inch
on mine).

Scott

    
    Yes, the Marcos has 8 radius rods (and 16 metallastic bushes!).
    
    I guess the idea is to keep the axle from wandering about and probably
    what gives the car it's "Lotus Elan beating" handling (A quote from a 
    magazine road test of the time before you all scoff! :^)).
    
    The Panhard rod fixing is exactly as you describe (possibly a standard
    Ford fixing on the axle?)
    
    Mark

    <<< Note 1239.15 by CRATE::SAXBY "Time to say something contentious!" >>>
                           -< The more the merrier? >-
    
>>    I guess the idea is to keep the axle from wandering about and probably
>>    what gives the car it's "Lotus Elan beating" handling (A quote from a 
>>    magazine road test of the time before you all scoff! :^)).

	Beano was it?
    

    
	re. Watts link:  this is where the links come in from the two sides,
	either fore/aft or right/left.  It is used right/left in preference 
 	to a panhard rod since a panhard rod will move the axle sideways as
	it swings thru its arc (little when rod is near level, a lot when the
	rod is running at an angle; so, run panhard rods level or adjust the
	pivot points to allow such). The feature of Watts link is no travel
	to/from pivot points, just straight vertical motion.
	
	re. trailing links keeping diff pointed at the tranny: you do NOT
    	want to do this! You want to keep the angles that the front and
    	rear U-joints run at the SAME. To do this, you want to keep the
    	diff at the same angle relative to the car throughout it's travel.
    	You can get big problems with unequal U-joint angles, especially at
    	large deflections!
    
    	re. measuring corner weights: Make sure you do this on level ground 
	support the other wheel at that end at the same height as the scale
	surface. Otherwise you get spring and anti-roll bar effects. 

	Have you done a corner weight check? This can be the first indicator
	of chassis problems. When my Crossle FFord hit the banking at Road
	Atlanta (runnoffs in '70), it still looked good and measured square,
	but a corner weight check showed it to be way off. 16F 69-02 got
	her third chassis as a result.

	As I mentioned in RACERS, you want to be balanced side to side except
	for courses with all the critical turns in one direction. - Chris

Watts linkage is normally used (if at all, it's not common these days) to
locate rear axle laterally. 

Here's a modified version of one of Scott's pictures in .14 to illustrate.
Viewed from rear of car:

                            "a"
                            /
                           o----------------o|[chassis]
                           |          ^      |
                         --|--        |
          ______________/  |  \_______|______
          ______________   o    ______|______
                        \  |  /       |
                         --|--        |
         |                 |<-        |
[chassis]|o----------------o  |       |
                 ^        /   |       |
                 |       "b"  |       |
                 |            |       |
                 |            |       |
                 |            |       |
              (link 1)   (link 2)   (link 3)

Three links in all. Link 2 is much shorter than shown, and is a single link
running from "a" to "b", pivoted at its centre to the rear of the axle
casing (or de dion tube - see 1086.4 for explanation of DD). 

The 3 links form a sort of "Z", and I hope it's clear that with the layout
shown, as axle goes up (bump) so link 2 will rotate clockwise, as it goes
down (rebound) link 2 rotates anticlockwise. Either way the centre of the
axle is constrained to move up and down in a precisely vertical plane, i.e.
better than panhard rod where the axle follows an arc whose radius is the
length of the rod (which is why panhard rods are made long). 


Another method of lateral location is an "A-Bracket". Viewed from above
this time: 

                                         ^
                                         |
                       -chassis-      [front of car (usually)]
   pivot axis =>      -o-     -o-     
                       \\     //      
                        \\---//
          ______________/\\_//\______________
          ______________  \o/   _____________
                        \  -  /
                         -----

The A bracket is jointed at its apex to the top of the axle casing. It's a 
kind of wishbone, usually trailing. It does a more comprehensive job than 
Watts linkage, looking after lateral location completely (as WL does) and
one component of longitudinal location (which WL doesn't). But it's a
compromise: the bracket is generally made short, for strength, and this
means that the axle (at least the top of it) moves up and down in a fairly
tight arc - viewed from the side that is. 

Watts linkage is a purer design, doing only the one job of lateral 
location. The longitudinal location is done separately using one of the
systems mentioned in earlier replies, or some other way. 

Having said this, I think there is at least one car that used Watts linkage
to handle longitudinal location of a live axle. Two complete linkages
running fore and aft, one per side. Original Reliant Scimitar (open 2
seater, 1700cc Ford Consul engine) comes to mind - anyone confirm this? 

Richard

    I am not sure if this is the right place ....
    
    
    I own a Triumph Dolomite 1850HL, the handling on the car is terrible, I
    am sure it is worse than standard. The car is all over the road, it seems
    to float at speed, and roll alot when cornering. 
    
    At first I thought the bushes holding the axle in place were worn,
    although when I inspected these they seemed alright. Once I had got
    them out though I decided to replace them just incase. They were
    replaced by TRIUMPH TUNE bushes, which are slightly harder than
    standard. I put it all back again and tried the car, still the same...
    
    I checked all the usual items, i.e Tracking, tyre pressures etc, but
    these were all o.k.
    
    After talking to the owners club, I was informed that my steering rack
    rubbers might be worn, these were then replaced, but still no
    difference.
    
    My next lead is the suspension, could this possibly be the cause of the
    problem. If so can you recommend any types of shock abshorbers, I have
    thought of fitting Spax, but have heard they are difficult to set
    up....
    
    
    Any views on the above or any suggestions as to what the problem
    could be would be of great interest.
    
    
    Thanks,
    
    
    Graham

    
    Re .16
    
    Hello John,
    
    I wonder why Marcos cars with 1.8 Volvo engines (IE NOT very powerful)
    regularly beat Elans on twisty circuits? :^)
    
    Mark (AKA Gnasher!)

    
    Both running to same regs.
    
    Mark

re .17 I always thought you were supposed to disconnect the anti-roll bar when
measuring corner weights?

re .19 Spax are only difficult to set up because they're adjustable and you
could play around for ever getting the setting you want.  Each shock has 14
positions, so even if you keep left and right the same, just having different
settings front and rear gives you 196 possibilities...

If you get Spax, I'd suggest asking Spax themselves what the "standard" setting
should be on your car.  Start with that, then play around...

Scott

    Re .19
    
    Have you checked out all the shocks? Do they all rebound, these cars
    are certainly prone to odd handling if a shock has packed up.
    
    Do you KNOW it handles worse than normal? Have you driven any other
    similar cars? If it is worse than normal do you have an anti-roll bar
    fitted at the front? Lack of this will lead to a lot of roll (but
    probably not the float at speed), and it is a standard fitting on 
    the 1850.
    
    The problem you have, as I see it, is to identify if the float and 
    the roll are connected or if the car just rolls anyway (Dolomites
    without Anti-roll bars roll a lot, but the front one should definitely
    help matters).
    
    Re Axles.
    
    Can anyone (I'm sure someone can) describe the difference between a De
    Dion axle and a live axle?
    
    Mar

>>    Can anyone (I'm sure someone can) describe the difference between a De
>>    Dion axle and a live axle?
    
    
Mark, see note 1086

    
    Thanks.
    
    The last note in 1086 seems very informative.
    
    Mark

    Why is it important to reduce the unsprung weight?
    
    Mark

    RE .27
    
    Obvious to get a better roadbehaviour of the vehicle.
    
    Hans

	Reducing unsprung weight means that the suspension can react more
	quickly to the road conditions.  Consider the following:

	You're driving along, when the wheel hits a bump.  It will 
	tend to move upwards (slowed by the spring), what stops it moving 
	upwards is the weight of the car (well, actually, the downforce
	generated by the weight of the car plus aerodynamic bits 'n' pieces).
	So, either:

	(1) The unsprung weight, suspension arms, the axle(s), wheels etc is 
	heavy compared to the body.  In this case the whole car tends to 
	rise 'cos the axle rising is generating too much up force. 

	(2) The unsprung weight is very low, so the axle's deflection is
	soaked up by the spring trapped between the body and the moving
	axle.

	Obviously, if the spring gets fully compressed then the whole car
	will rise (same deal if the spring is too hard).  I guess that the
	ideal case is where the body of car remains flat and level whilst the
	wheels merrily bounce up and down.  Of course, make the springs soft
	and the ride in a straight line is wonderful, however it goes around
	corners like a boat.  It's all a compromise.

	Dave

 Another reason that a low unsprung weight is an advantage is that something of
lower mass will accelerate faster than something of a higher mass.
 Thus a low unsprung weight will allow the wheel to follow the contours of the 
road better. (A very neccersary condition with the way the roads are getting 
nowadays !!) 

		 Alan
		~~~~~~

A few questions about springs, with apologies to Europhiles who don't
understand avoirdupois weights and imperial lengths...

Spring ratings are usually quoted as "x lbs", where x is the mass in pounds
required to compress the spring an inch.  Typical figures are 60 to 180.  The
Haynes manual gives the rating of Escort MkII front springs as 520 lb ft (ie 
the work required to move 520 pounds one foot).  How can I convert this figure
to the more usual lbs-per-inch ?

What would be a typical rating for a spring giving a "hard" ride (in a car
weighing, say, 1600 lbs).  And for a soft ride?

Should front and rear ratings be the same (in a front-engined, rwd car)?  Or
should one end have stiffer/softer springs?

Scott

PS 1 lb = 1 pound = 2.2 kg
   1 foot = 12 inches = 0.3 metres

Re .32

Scott,

If you are indeed talking about a MK2 Escort, I can recommend 145lb springs for
the front, and most people reckon 116lb single leafs for the rear, although I 
haven't had a chance to change the rears.

 The 145lb fronts give a firm ride, and decent handling when paired with uprated
shocks (I used Ledas), but at the back I was only able to change the setup to
include a pair of Bilsteins.

	 Alan
	~~~~~~

Alan,

Thanks for the reply.  I'm afraid the only escort bits I have are front springs
and a rear axle; the kit car registry note (1102) details where the rest of the
car comes from!

Are the 145lb springs firmer than standard, (sounds like it from what you
say) and do you know by how much?

Scott

Springs are linear to a first approximation (Hooke's Law), so you should be
able to divide your number by 12 to get the value in pounds per inch.  However,
the unit lb ft is a measure of torque, not spring constant so it's not clear
that Haynes is writing sense.

As an aside, 1kg = 2.2lb.  I'm sure our European colleagues managed to work 
around this slight error!

Mike.

Re 1kg = 2.2 lbs: err, that's what I meant, but the notes server got it wrong...

lb ft is a measure of torque, work done and lots of other things.  Dividing
that figure by 12 doesn't give lbs-per-inch for the spring.  Most of the specs
in Haynes manuals come direct from the manufacturer, and in this case there
are several quoted, from 512 to 539, so I think they're correct.  But I'm as
confused as you about what they mean...

Yeah I know all about Hooke's law, but it doesn't help with the conversion...

Scott

Re: .32
>> What would be a typical rating for a spring giving a "hard" ride (in a car
>> weighing, say, 1600 lbs).  And for a soft ride?

The effect of a spring comes down to the suspension design. The number 
that would be important would be the "wheel rate" which is spring rate 
taken at the wheel. Your suspension is some form of a lever with a 
tire at some point and a spring at some point. Depending where on this 
lever the wheel and spring are determines the spring rate
required to give a certain wheel rate.


               \         __                       \ __
               \        |  |                      \|  |
            o--\--------|  |          o-----------\|  |
                        |__|                       |__|
     pickup ^  ^
     spring----^         ^
     tire ---------------^

The spring in the first picture must be of greater strength to do the 
same work as the one in the second picture.

Yes I know all about lb / lbf, and I agree it would be easier to work in metric.
But not knowing exactly what the lb ft is referring to (and not knowing if it
ought to really be lbf) I can't do the conversion...

Your last paragraph is interesting, I'll do some calculations based on that
(as I know the spring free and compressed lengths and the car weight) and see
if I can get a useful result...

re .38

Not directly relevant to my case.  I have escort springs at the front, and
know which combinations of free length and damping rate give the correct ride
height at the back.  It's now just a case of choosing a damping rate at the
back to match that at the front, given that I know the front springs are
"correct" for the car, but I don't know their damping rate...

Now where did I put that calculator...

Scott

    Mauro Bianchi has designed (and patented) a suspension system using
    2 springs per wheel :
    
    - a relatively soft spring working as usual (car weight)
    - a relatively hard spring working against the above one
    
    Result: better ride comfort, better roadholding (the 2nd spring
    works like an anti roll system allowing NO anti-roll bar).
    
    More details to come when I test drive one of the tests cars equipped
    with his "contractive" system.

	I don't think you've got the hang of it, which isn't surprising
	since you're references simply haven't got a clue.

	When they say 98 lb in they mean 98 lbf/in. It's not necessary
	to multiply by 32.2 to convert lb to lbf. 1 lb in the earths
	gravity exerts 1 lbf.

	When they say 512 lb ft, they either mean 512 lbf/ft which equates
	to 42.67 lbf/in which seems unlikely or that 512 lbf ft of work
	is needed to compress them by 1 ft. Since when fully extended
	the force is zero, this infers that the force compressed by a
	ft is 1024 lbf assuming linear rating. This means that at 5.5
	inches the load is 469 lbf and the rate 85.33 lbf/in which sounds
	plausible.

	Owszat

	-John

John,

Either you did A level maths more recently than me and can still remember it
all, or you did it so long ago they were still using lbf and inches... ;-)

I didn't know that bit about not needing to multiply by 32...  I agree the
spring people and Haynes seem to know as little about it as me!

I'd already thought about your 0 to 1024 idea (ie integration of the force
over distance) but the numbers came out all wrong when I did it, so thinking
it was just another duff idea didn't pursue it.  Thanks for doing it properly;
I think that's probably the right answer.

Now can you come up with an equation that tells me what rate of spring will
give me the most comfortbale ride... ;-)

Scott

the front left shock needs replacement on my car - should the front rhs one
be replaced at the same time too?


thanks,


...Art

    
    RE -1.
    
    Yes.

    Any ideas about this one? The car is a Peugeot 405 estate. Just
    recently, when I go over the speed bumps in the DP2 car park at
    anything greater than 1 mph I get a loud "oink" sound from the front
    suspension. The funny thing is that some days it's ok - one pet theory
    I have is that it's somehow connected with the cold weather.
    
    Dick

    
    Is noisy suspension a quibble that comes with brand new cars for the
    first few months? or is my noisy suspension (my theory is the same as
    Dick's RE-1)caused by cold weather?
    
    The noisy I get is an "oink" but only at low speeds,I don't here it
    above 30-40 mph.
    
    Andy.

    My 405 estate has done this since I took delivery of it. It does seem
    to be worse in cold weather and goes away after a while. Since I've now
    had the car two years and it hasn't actually collapsed on me, I assume
    everything's OK (one of the few advantages left of the car scheme - the
    magic cure-all for funny noises is to turn the stereo up a bit louder).
    
    My previous 405 didn't do this; on the other hand, nor did it have a
    nasty plasticky gear lever. Must be progress of some kind.
    

    Both my MR2 and a Rover 220 I borrowed make/made noises (not oinks more a
    sort of f*rty noise) in situations like what you describe. Always when
    cold.  It's almost certainly caused by cold shock absorbers, the
    acceleration of the damper is very rapid going over speed-bumps. I've
    never noticed it on more softly sprung / less sporty cars.
    
    Steve.

Try veering left or right as the front wheel is about to impact the speed 
ramp, this will throw all the load on the outside wheel's damper.

See if the noise is limited to just one side.

Rob.

Do it right!  Toss the car sideways as you approach the speed bump and power
over it!  :-)

Dave

Gawd preserve us from EX rally drivers ;-)

Don't listen to Burden he's had a lobotomy, I've read some of his exploits of
old!!!!!!!!

Smile please Dave

Mike

    Thanks for the answers (and some of the advice :-). I'm glad I didn't
    imagine the cold weather bit.
    
    Although the note wasn't about speed bumps per se (that was just one
    example of when I heard the noise) I'll be glad if someone develops
    this idea of pop-up bumps. These apparently just raise themselves if
    they detect someone approaching at greater than a certain speed. Even
    though the Peugeot can go conventional ones at 10 or 20 mph I assume
    that something must be wearing out faster than it otherwise would. With
    the Morris it's a different story, it positively does Not Like them. I
    really have to crawl over them at a snail's pace (apologies to anyone
    who gets stuck behind me).
    
    Dick

    I had a creaking/knocking noise coming from the nearside front of my
    205; like your car I only heard the noise going over bumps at very low
    speeds (outside temperature didn't seem to have any affect though).
    
    The reason for this turned out to be a worn tracking arm (part of the
    car's steering for the uninitiated like myself).
    
    As an asside, the part had to be ordered and so in the meantime the 
    mechanic gave the tracking arm a good old spray with WD40 which got 
    rid of the noise... for about an hour.
    
    Stephen
    

    I've never noticed these symptoms in my 405 estate. FWIW.
    
    Laurie.

	My spax's creak going over the speed bumps in DEC park too.
	Maybe I should wind them down a bit.

	Dave