Suspension And How It Works

[Guest Batfink]

Adi on my quest for rear coilover suspension I have found yet another company. This place makes a custom double wishbone setup for the rear. What is that and why is it good??? Dont the Ford Focus's have this?

[Adi 0]

This place makes a custom double wishbone setup for the rear. What is that and why is it good??? Dont the Ford Focus's have this?

 

Is the double wishbone set up......and space frame arrangement......it has to be thinking about it.

I've heard of this done a few times on the rear of the 205. I also mentioned it to Andy Y on here as he too was looking for the "perfect" set up for the track.

 

Quite how everything is made to fit the car I'm not sure.......but some sort of frame arrangement will be fitted to the rear and that frame will have double wishbone rear suspension.

 

Why is it so good???.........without wanting to go deep into the explanation......

the Ford Focus does have sort of a wishbone affair at the rear.....but its not a double wishbone from what I've seen......and it is more like the rear of the old Rover 200 series......which was shared with Honda.

The main reason why the Focus set up is good.....is cos of the rear roll centre.

The roll centre is an invisible imaginary point within the geometry of every suspension set up. So every car has 2 roll centres. One front and one rear.

Ideally for a front engined car......the rear roll centre will be higher than the front.

It has all to do with weight transfer and the speed that weight is transferred on each axle.

Again for good handling on a front engine lay out......the rear weight transfer should be quicker than the front.......and to enable this.....the rear roll centre should be higher than the front.

Now on a Peugeot with a rear beam axle like the 106,205,206,306,307,405....the rear roll centre is on the floor......which is LOWER than the front. So the tendancy will be for understeer. Peugeot got round this to a certain point.....by making the rear axle twist......and passive rear wheel steer.

But with todays technology......manafacturers like BMW on the Mini, Honda with the Civic......and the Focus.....the chassis set up has moved the game on, so cars are steering and handling far superior......mainly cos of the basic rear suspension set up.

Double wishbone set up basically controls the wheel movement a lot better. F1 cars have double wishbone all round. So to check what the set up looks like, have a look at the f1 cars. It will be "similar" to that.

Edited January 2, 2004 by Adi

[Batfink 201]

Cheers for that Adi. To be honest I dont think people will mind you going into detail. I quite enjoy it Its education i enjoy lol

[M3Evo 0]

The focus has a multi link rear end, like a double wishbone except forward and aft movements are taken out by a trailing link. BMWs use the same type of system.

[Adi 0]

The focus has a multi link rear end, like a double wishbone except forward and aft movements are taken out by a trailing link. BMWs use the same type of system

 

Honda/Rover used a similar system to the Focus at the rear on the 214/216 chassis.......but didn't have the same road manners. Just shows how damping etc has moved on.

Honda have changed to a multi link set up on the new Civic and have managed better dynamics with the CTR than the old system on the Rover.

 

BMW use a Z axle at the rear....so called cos the multi link bars look like the shape of a Z. They've used it to good effect along with the excellent damping on all the BMWs and the new Mini.

[DrSeuss 0]

I went to visit a university and was shown one of the research labs. The scientist was researching fluids which changed viscosity at different speeds of application (mainly for dulux). Basically paint is designed so at slow velocities ie as you load your brush it stays on the brush (and prevents runs when on the wall). But when you apply the paint to the wall due to the higher velocities the viscosity reduces.

 

Since the rate of damping is related to piston speed through the strut body. I was wondering whether any variable viscosity fluids where ever used/are being used?

 

And what are the advantages of gas as opposed to oil within a damper.

[Adi 0]

I was wondering whether any variable viscosity fluids where ever used/are being used?

 

Damper technology has improved amazingly since active suspension was outlawed in F1 in '92-'93. Now I've no doubt, that certain companies will have tried all sorts of different practises to get a jump ahead of the competition.

What seems to be norm within the varying technolgies......is to keep the fluid as stable and consistant as possible.......and make any difference/changes to the valving.....whether it be the piston....or shaft etc. This is why in motorsports where the damper fluid can overheat, external reservoirs are used to maintain the cooling and viscosity of the oil.

 

what are the advantages of gas as opposed to oil within a damper

 

All dampers use oil. It is a misconception that gas pressure dampers don't use oil, they do. A volume of nitrogen gas is added to keep the oil under pressure......so when the damper does become warm/hot.....the viscosity is maintained and the oil doesn't aerate.....meaning the damping effect is reduced.

[DrSeuss 0]

Any chance you could point me in the direction of some info about shock absorber design. I've had a look online but no where really explains how they work. I think i can work out most of it, just how the valving works.

 

I still reckon a variable viscosity fluid is the way forwards btw.

[Adi 0]

Any chance you could point me in the direction of some info about shock absorber design

 

Have a look on www.ohlins.com and www.penskeshocks.com and search for tech manuals......it will give you a good idea.

 

I still reckon a variable viscosity fluid is the way forwards btw

 

You may get a better idea once you see exactly how the valving works etc. With the more complex valving systems and how they work.....it is easier/better to adjust the way the oil flows (valving etc) to control the damping effect......rather than change the flow rate of the oil itself.

But heh.....who I am to stand in the way of progress. You may have a formula to revolutionise the hydraulic damper. :o

[puginfo 0]

>>> hi Adi, i have a 405 which has 25mm thick steel wheel adapters fitted on all 4 not to widen track width but to have them run on the most common pcd available here...114.3mm. The original pcd 108 is so rare here let alone getting a design you would want. This is a hub centric, 8 bolt design which had run pretty good but with EXACTLY the symptoms you had mentioned ie. torque steer and bump steer.

 

The rims are 17ins and i noticed that the 205mm width tyres are wearing out on the outer edge which pretty much says that the top of the wheel is slanting outwards. Why is this so as the camber reading goes like 0deg 30mins? All bushes and mounts on the suspension are new.

 

As far as setup is concern, the camber and castor seems to be fixed and the only thing needs a tune is the toe in/out. Would i be able to rid off the bump steer by resetting the toe in/out? With the pas, it seems to be a bit better but overall it would still need plenty of correction while you drive, pls help. Thks.

 

cheers

[Adi 0]

Why is this so as the camber reading goes like 0deg 30mins?

 

Hi M8,

 

The problem with tyre wear occurs when you are cornering not travelling in a straight line. As the car is cornering, the tyre will tuck under the rim and run more on the outside edge of the tyre. This is a side effect of the McPherson strut design. It doesn't allow the wheel/tyre to change angle enough and gain -ve camber as the car rolls. With double wishbone set up......the tyre angle changes as the car rolls......allowing the tyre to stay far more upright......and the tyre to be more square to the ground.

The only way to make the tyre angle better when cornering......is to add static -ve camber. So when travelling down in a straight line the front tyre will be leaning in at the top slightly. When the car rolls.....the tyre will then be flat.

Another way would be to add some more +ve castor. So as the steering is turned, the outside wheel will again add -ve camber. This is in theory the better way, as the tyres aren't angled when travelling in a straight line......and causing a drag effect.

 

The problem occurs when trying to change the castor/camber angles. As you rightly say, the suspension is not adjustable apart from toe. What you have to do if needs be.....is to either move the top of the strut inwards......or move the bottom outwards. The easiest way would be to get some adjustable lower wishbones. Instead of having the balljoint on the wishbone.....there would be a rose joint. This enable to lower arms to be extended and bottom of the tyre moves outwards and gains some -ve camber. You may have to find a business that competes in motorsport. They will probably be able to rose joint your lower wishbones.

 

Would i be able to rid off the bump steer by resetting the toe in/out?

 

Well in theory....by toeing the wheels in slightly......the steering should become more stable on the straights. But in your case......the tyre wear will be even worse. Toe-in will cause the tyres to run more on the outside edge.

 

The real problem is as you again rightly summise.......the spacers. But also the problem will not be helped at all by the low profile tyres. Mixed in with the torque steer and bump steer......will be tramlining. Cos of the stiffer tyre sidewalls, any ruts or grooves in the road.....will cause the tyres to change its intended path. This again means you having to correct the steering.

 

Unfortunately...the only thing I can advise, is to find some more wheels with the right fitting for the Peugeot. Is it not possible for you to get some wheels shipped in from abroad??

There are a number of wheels here in the UK with the right offset/PCD for the 205/306/405.

 

Sorry I can't be of more help

[puginfo 0]

>>> thks for the reply Adi. I was thinking if both the top mount and the bottom ball joint were to be kept constant, would changing the spring height (say a 1inch drop) give some -ve camber?

 

There are some 108pcd now and then with very ugly designs. I like the M3 design 17ins that's why end up with the adapters. The original pcd was 24 so with 25mm adapter would that make it -1? What impact would be on the wheel bearings? Thks

 

cheers

[Adi 0]

I was thinking if both the top mount and the bottom ball joint were to be kept constant, would changing the spring height (say a 1inch drop) give some -ve camber?

 

A 1 inch drop will probably not give enough camber. You really need about 1.5-2 degrees -ve camber to be effective.

The other problem with lowering is (I don't know the height of your car now), the angle of the lower wishbones and steering arms. The lower wishbone should inclined downwards to the wheel. If the car is lowered too much, the wishbone will become inclined upwards to the wheel. This is when the front geometry is messed up and the steering and front suspension doesn't work together properly and bump steer will be quite bad.

 

The original pcd was 24 so with 25mm adapter would that make it -1? What impact would be on the wheel bearings? Thks

 

I'm guessing you really mean ET (offset) was 24 and not the PCD??

 

I'm pretty sure the 405 offset should be about 16mm. So ideally you should have fit an 8mm spacer rather than a 25mm spacer.

The extra loading on the wheel bearings won't help either.....and will lead to the bearing wearing out a lot quicker than it would without the spacer.

 

I totally understand you wanting the wheels that you like the look of. But is it really worth the hassle when you're driving the car?? After all.....you can't even see the wheels when you are behind the wheel

It took me 2 years to find the right wheel for my car. I just kept looking till I found the right one in the right size/dimensions.

[red 0]

Hello Adi,

 

With respect to the rear beam on the 205 would there be any gain or would it even work to fit somthing like an Avo competition damper say Pro Race unit in place of the current shock? and then add springs to these as they have spring pans fitted, would these work with the torsion bars or is there not enough movment in the shock location? I've always wondered as this would give you some adjustment on the damping and possibly the spring rate at the rear which would mean you could retain the stock set up.

 

Regards Russ.....

[Adi 0]

Hi Russ,

 

This is something I have considered for the rear of my 206. The problem is there is enough room next to the exhaust rear silencer. So it would really be a case of trial and error on the 205.

The main concern I would have is the length of the damper stroke. Normally the little coilover dampers are very short stroke allowing only smaller amounts of suspension travel. So whatever you try will have to allow enough rear travel to not start lifting the rear wheel quicker than at present.

 

Good luck and let me know how you go on.

[cybernck 402 1 Cars]

i think people mention some sort of a "ratio" when it comes to this, i guess

having the lower shock mounting point at the end of the trainling arm is not

the same as with having it nearer to the roation pivot (as we have it).

 

also, should you actually remove the torsion bars as the springs would be

doing they're job now?

 

what do you think adi?

[Adi 0]

i think people mention some sort of a "ratio" when it comes to this

 

Yes the damper moves at a different rate to the wheel. The wheel will move approx 4 times the amount of the damper. This is another reason why the rear end can be unstable at times. By the damper wroking at the same rate as the wheel.......the rear end would be far more stable and better controlled.

 

also, should you actually remove the torsion bars as the springs would be

doing they're job now?

 

Don't remove the torsion bars......as they provide bracing for the rear arms. If the rear arms didn't have any sideways protection.....all the load would be on the am bearings. The rear anti roll bars also provides stability for the rear arms.

[red 0]

With respect to the rear arms they don't look very strong at all for lateral strength, I 'm wondering if you'd get any problems by strengthening them with a plate welded across the middle, or even make them into abox by welding plates across bothe sides at the top and bottom? or is a little bit of flex required/

 

Regards Russ.....

[pug_ham 244 3 Cars]

Didn't C&CC do this to a 205 a few years ago & replaced the rear shocks etc with a coilover setup? I seem to remember someone posting the pictures of how they had done it on a previous version of the forum.

 

Graham.

[cybernck 402 1 Cars]

graham> yeah i intended to post that pic, but had to go. here it is now though .

[Adi 0]

With respect to the rear arms they don't look very strong at all for lateral strength

 

It's not the rear arms themselves that need strengthening. It is the rear arm bearings where any extra load is placed. The rear arms must be kept stable laterally to protect the bearings. This one of the reasons why Peugeot have fitted stabaliser bars on the rear of the new 206SW and GTI180. It is simply to reduce sideways movement of the rear arms.

 

Didn't C&CC do this to a 205 a few years ago & replaced the rear shocks etc with a coilover setup?

 

If its the one I'm thinking of.......it was on a 205 track car. The main object of the exercise was to create more damper movement. To get that all important ratio of wheel/damper movement closer together. That way the rear end was far more stable.

[twowheelterror 0]

I'm currently converting a 205 rallye into a track car.. now with me keeping the engine the same size as standard I'm concentrating on the handling so I can make up ground on the corners.

 

now.. weight being a priority I should have cut that down to about 650kgs by the time I make my debut on track. A roll cage will stiffen up the chassis nicely then I'll turn my attention to the suspension..

 

now the 205 rallye has got a 55.1 inch front track and with the 309 rear beam I'll have a 54.5in rear track. is this a good front / rear difference???

 

from what I've read so far it I shouldn't fit hubcentric spacers to the front to widen that - is that correct.. but.. the question is should I fit them to the back to make it wider?

 

with some leda coilovers on the front and some adjustable topmounts I should be able to tweak the handling..

 

But what else can I do????

 

 

edit... tire wise i'm keeping the 13 inch steelies to keep the weight down.. unless you convince me otherwise I can't see any benifit in alloys..

Edited February 19, 2004 by twowheelterror

[Ahl 4]

You could always get 14 or 15" steelies from a 406. I don't know what the offset would be like, but they'd be cheap and light.

Might not get the same brake cooling as from alloys mind.

[Adi 0]

TWT,

 

You'll have to give me a bit of time to reply to your quiery. At the moment I'm trying to sell my car.......which hasn't been helped by my ads being deleted by certain forums

[DrSeuss 0]

With the secondary shocks/springs won't you get an odd oscillatory system. With a fundamental and several harmonics suffering from interference.

 

In one of the programmes i designed it consisted of two different rate springs linked together oscillating with a mass and damper attached. Either way i'm an electronics person.

 

Supposing one got round to making up trailing arm braces would this help tighten the rear end? Also what kind of joint is required to connect the brackets to the bracing bars?