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Suspension And How It Works


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#41
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These posts really are excellent. Thanks adi.
I'll make sure and reference them next time some twerp recommends slamming a 205 by 60mm for the best handling!

I think thats wrong to say to be honest! If it is set up proberly then it will handle well! Well thats what im doing anyway but im gonna use in-situ adjustable track control arms and eccentric top mounts therefore i should have the best of both worlds as this also means that i can apply about 1.5 negative camber at the front and probably 0.8 at the back or 1, depending on how it handles.

Ross

#42
Adi

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I think thats wrong to say to be honest! If it is set up proberly then it will handle well!


Chassis height isn't really the important issue with lowering cars. It is the knock on effect of how much suspension travel remains. That is why WRCs on gravel are set a lot higher than on asphalt.

If you lower a road car a silly amount......you will not get the best out of the suspension....or handling. That is because the tyres & springs need to absorb the bumps. If the spring/tyre doesn't do that......any energy the spring doesn't absorb is passed onto the chassis. The chassis is sent in the upward direction and this leaves the tyre not in full grip with the road surface. If this happens at the wrong time.....whilst cornering for example.....the car can be sent into the hedges or a wall.

Now if you happen to live in a unique place for the UK.....where the roads are smooth and bump free......then the suspension can easily cope with a lot less travel. But it will only be suited to those roads.

People are frequently asking me, why are my dampers leaking after only a few months on the car??? The first question is....is the car lowered a lot. 99% of the time.....the answer is YES. This happens cos the dampers are constantly slamming shut and bottoming out. The hydraulic seals don't last long in this situation.

#43
Swilki

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How much wider is the track on the 309 rear axle? Is it a simple change over from the 205?

#44
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IIRC it is about 2' wider & it is a straight swap over, all you have to change is the rear mounts need turning 180' to match the 205 body, a two minute job.

Try a search, it is quite a common topic.

Graham.

#45
pug_ham

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I was reading through an old Practical Classics today which featured Steve.c's car among with a few others but at the end of the article the author says that he is surprised that a reputable firm offers a coil over set up for the 205, he states 'that a strut must have an offset spring to counter a sideways bending force on the piston rod, otherwise the excess friction will render the ride appalling'

Any thoughts?

Graham.:D

#46
Adi

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offset spring to counter a sideways bending force on the piston rod


One of the disadvantages to the McPherson strut set up is the sideways bending force. There is a high sideways load on the piston and rod guide. This produces friction which not only increases the wear rate.....but can have detrimental effects on ride/handling.
One of the ways engineers have found to reduce this effect is to offset the spring axis on the strut. If you have a look at the standard front strut on most cars, the lower spring pan will be offset to the outside.....so the spring will be closer to the back of the strut.....than the front (transversely).

Now whilst coilovers with 2.25"dia spring, will have a central mounted spring, certain damper manafacturers have changed the design of the damper to counteract this sideways movement.
Rally bred "inverted" struts were used on Subarus and really helped reduce this sideways "bending" force. The inverted strut looks like a conventional strut, but the internals are actually upside down. The piston rod operates in the lower section of the strut with a secondary tube above. This secondary larger diameter piston will then fix to the inner wing as would the piston rod on a convential strut. It is this larger diameter rod that takes the brunt of the bending force instead of the piston rod on a normal strut.
"Inverted" struts can even be found on the front of production road cars such as the Peugeot 307.

I have said many times that coilovers are becoming more like a fashion accessory on cars.....more for the use of excessive lowering........rather than the proper use of fine tuning chassis set up in motorsport. As such, the design of certain aftermarket coilovers are not as critical to detail, and such, can actually make the performance of the suspension worse.

#47
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Adi hes another one to pick your brains:

Im fitting a 309 rear beam to my car. To match the front up I see two options
1. Fit 309 wishbones - this will give me negative camber though and will require more cash and will wear tyres quicker..
or
2. Fit spacers - this will change the offset though. Could mean more torque steer?

Am I best off with 309 wishbones or with spacers

#48
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Am I best off with 309 wishbones or with spacers


Forget spacers......a bad idea.....and will only work for the visual aspect of widening the front track.....otherwise......will create bad steering effects.

Do I remember you getting coilovers for the front of urs??? If you did, you could always try an eccentric top mount. That way you could gain -ve camber without extending the front track. You could gain caster as well.

If not.....the only other way is to use the 309 wishbones.

Ideally you will widen the rear track.....but leave the front track the same. That way the balance will be improved further.

As far as gaining camber and excessive tyre wear..........well that depends on how excessively the outside of the front tyres are wearing at present.
I have just gained some -ve camber on the front of my 206. B4 the front tyres were always wearing heavily on the outer shoulders. Now there is less pronounced wear on the shoulders.......and I haven't noticed any increased wear on the inside.
That is really the idea of camber......to make sure the tyre is used more evenly and you use of the full grip available.

#49
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Ideally you will widen the rear track.....but leave the front track the same. That way the balance will be improved further.

so this will be changing the handling for the better??? Not sure I understand quite what this will do. So are you also saying that there is no point to fitting the 309 wishbones unless you are looking for negative camber on a budget??

#50
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Ideally you will widen the rear track.....but leave the front track the same. That way the balance will be improved further.


so this will be changing the handling for the better??? Not sure I understand quite what this will do.



On fwd production road cars, the front track will be wider than the rear. This is one of the ways (combined with others) that manafacturers make cars understeer.
So, by widening the rear, this helps to reduce the weight transfer....and therefore role. If you then go and widen the front......then this reduces the effect of widening the rear.........as far as balance front to rear is concerned. If this is the only way to gain camber (thru widening front).......then it has to be done. But if there is an alternative.....like thru the top mounts.....then try that first.

#51
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More Brain picking..

How much effect does unsprung weight make?

I've got a pair of 4 pot calipers that I'm fitting but they're a lot heavier than the std caliper and the disc is bigger as well. I'd guestimate about 1.5Kg per side difference.
I've also got to fit 7mm wheel spacers for clearance.

Your thoughts would be appreciated.

Matt

#52
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How much effect does unsprung weight make?


The theory on unsprung weight is a bit of a grey area. There are theories saying for every pound of unsprung weight you add.....it can make upto 10lbs extra in sprung weight. But I think these theories have more to do with rotational mass/inertia.......than static unsprung weight. So some of that theory will be relevant......some won't.

I would say.....any increase in unsprung weight is not good. Usually billett 4 pot calipers should be lighter than the std cast parts. But I suppose a lot will depend on size.
Is it not possible to get the discs with alloy bells as suppose to cast???

I've also got to fit 7mm wheel spacers for clearance


This is deffo a move for the worse. Spacers especially on the front can cause more torque steer......and other effects like tramlining and general pulling/tugging of the steering.
The least you need to do.....is also space the rear track out the same as the front. Cos the handling balance will be altered by the widening of the front track.

#53
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The weight increase is because the calipers are cast iron (from a volvo!) But at 10 ea plus the cost of new seals its worth a go.

I think I'll be looking for a 309 Rear beam to increase the rear track.

Thanks

Matt

#54
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Ok Adi I have another topic for you. How does a wider track affect handling. How does a standard 306 rally car handle compared to its Maxi equivilent. I know the maxi suspension would be more hi-tech but if that was standardised for experimentantion........ What circumstances are each better or worse???

#55
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btw, adi, this is really good info. ive learnt a few of the things ur saying the hard way. like on my fiesta mk4, i fitted zetec-s -20mm springs. these worked great with the 195 50 15 tyres. but i wanted a lower profile so i got some 195 45 15 toyos, and the handling (as the springs were relatively soft and the tyres were hard) was absolutely terrible. it went from very very good to very bad.
if only id read this thread first :)
i knew to corect i shud fit harder suspension, so i saved up over a few months and eventually got a spax vsx kit -40mm (nore like -60mm).
the handling has improved a lot, but now everything is so stif the ride is v harsh, and bumps in the road arent absorbed but passed through the whole car... this isnt the best setup for wet weather driving :( again u have pointed out something very similar
but anyway.......what i wanted to ask is,
how does adding spacers affect the camber?
(ps i know what camber is, just cant work it out)
thanks

#56
jacobs53

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adi can i ask what you do for a living? because i think your either

1) a student studying motor mechcanics or similar

2) you have gone past that stage and have a job in the area

3) learnt by many many mistakes

am i close?

cheers lee

by the way if the rear track of the 309gti beam is 3 inches wider than the 1.9gti item, does it have any problem fitting under the gti arches? its around about 35mm each side wider.

also am I right in saying that negitive camber on the rear increases rear end grip?

#57
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How does a wider track affect handling



The tyre probably has the most effect on handling. After the tyre......weight transfer is a close 2nd. The amount of weight transferred effects the tyres ability to grip......where weight is transferred effects the balance of the car....and the speed of the weight transfer effects the responsiveness.

The 3 ways to reduce weight transfer are 1. lower centre of gravity 2. widen the track 3. reduce the car's weight.

Now with the Peugeot suspension set up.......the basic weight transfer will be quicker at the front than at the rear. This leads to understeer. Now Peugeot's way round this was to introduce the "rear steer" effect. Whilst this can be effective in standard form.......it is far from ideal.
A way to improve the handling is to lessen/speed the weight transfer up at the rear and get rid of the rear steer. This can be achieved by stiffening the rear suspension......which will speed the weight transfer up.......but also by widening the rear track.....which reduces the weight transfer. That way, any understeer is reduced.

#58
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How does a standard 306 rally car handle compared to its Maxi equivilent.


Any road car is a "comprimise" where handling is concerned. Ride is also a main consideration. With a rally car.....ride isn't a consideration as such. If the ride gets too bad......the driver will not cope as well......so certain parts of the ride has to be considered....but not in the same way as a road car.
The main elements of any rally car will be maximum grip and speed. So as such the suspension will be set up accordingly.
To try and compare the 2 cars.....is difficult if not impossible.

#59
Adi

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how does adding spacers affect the camber?


Spacers shouldn't effect camber at all.
The job of a spacer is to widen the track......and as such sits flat against the hub face. So really just extends the hub face out slightly. But it shouldn't change the angle of the hub face.

#60
Adi

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adi can i ask what you do for a living?


2) you have gone past that stage and have a job in the area


I have indeed past the studying stage.......though you are always learning.

I finished studying in the early '90s and worked in suspension engineering and vehicle dynamics.

by the way if the rear track of the 309gti beam is 3 inches wider than the 1.9gti item


Unfortunately....I don't know the precise measurments involved. But I have read that there is 3 inch difference.....with the wider being the 309.

does it have any problem fitting under the gti arches?


Again....cos I've never actually done this conversion myself......I'm not aware of the ins/outs. There will be others on this site that will give you greater detail.
I have read of people that both have/haven't experienced probs with the arches catching the tyres.......that may have more to do with the height of the rear end and as such how close the arches are to the tyres in the first place.

also am I right in saying that negitive camber on the rear increases rear end grip?


Yes and no.

The camber angle should be set so the tyre is flat to the ground when the suspension has the most lateral load........e.g cornering at the limit of grip. But it really depends on the suspension set up and the car's use as to whether increasing rear camber is of any use.
IMO there is more sense to increasing front end camber, than rear. But I could see why someone would increase rear camber to control "rear steer" or "lift off oversteer".....especially if the standard rear axle bushes are still used. I would go about it in a different way though.