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Suspension And How It Works

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Mattsav

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

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Adi
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.

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Mattsav

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

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Guest Batfink

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???

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Guest ChrisG

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

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jacobs53

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?

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Adi
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.

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Adi
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.

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Adi
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.

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Adi
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.

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Guest Batfink

Adi. I have found a company that have made a few coilover suspension conversions for pug race cars. They use the rear beam but without the torsion bars. Then run turrets into the car to run longer shocks. I would be interested in you opinion on what sort of effects this would have on handing. I guess the balance between front and rear can be tuned more easily. Will the car loose its Lift off oversteer characteristics or would that be determined by spring and damper rates?

 

Also did you ever find out how the 206 180 and 206 sw had had their rear beams strengthened or modified. Have you got pictures at all :(

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Adi
They use the rear beam but without the torsion bars. Then run turrets into the car to run longer shocks. I would be interested in you opinion on what sort of effects this would have on handing.

 

As I think I've mentioned to you before.......the main problem I see with fitting any type of coilover to the rear........is bracing the rear arms against sideways loading.

 

On the new GTI180 and SW, Peugeot have fitted arms from the centre of the rear tube, to the rear of the trailing arms at either side. This helps reduce the sideways movement of the arms.

This helps with 2 aspects........1. stabilises the rear wheel toe angle.....so stops the outer rear wheel toeing out more when loaded in a corner so providing more rear stability. 2. reduces load on the trailing arm bearings.

 

Will the car loose its Lift off oversteer characteristics or would that be determined by spring and damper rates?

 

Lift Over steer is a secondary effect and one that is really a bit of a gimmick. If the rear end was set up better to start off with.......the rear would react when the front end is loaded up. So something that is directly related to the steering at the front end. As it is.......you have to shut off......when cornering......to make the rear end move more.........thats not ideal. Even the designers know that at Peugeot. But thats more to do with packaging and interior space........not dynamics and handling.

 

You can get rid of the lift off oversteer by fitting solid alloy bushes to the rear axle.

 

The firmer the rear end is set up......(in relation to the front) the more the rear will move around when the front end is loaded up. But if the rear end damping is sorted, then the rear stability when shutting off the throttle, will be better as well.

 

"In theory" by turetting the rear end and improving the rear roll stiffness, the above should be somewhere near achieved. But in practise/testing........in rallying terms especially.......the standard rear axle configuration has proved to be quicker and easier.

 

I can't give you a definate yes/no answer on this one. If the rear arms can be braced against sideways movement........then all I can say is give it a go. The damping should be improved.......and it will be easier to change the spring rate and get the right one.

 

By the way.......has anything been mentioned, or have you seen if the rear arb is mounted in a different way????

 

The company you have seen......doesn't happen to be Vic Lee Racing does it????

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Guest Batfink

Nah its not Vic Lee Racing. Can think of the name off the top of my head.

 

I was going to fit solid rear bushes due to the conversation we had b4 where you said there could be a risk of bending the rear coilovers if the beam was allowed to move independantly.

 

So I might need to look into bracing the arms too. Hmm Time to go for a test drive in a 180 methinks! Wonder if get an extended testdrive so I can get it on ramps and photograph the rear :(

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Adi
So I might need to look into bracing the arms too. Hmm Time to go for a test drive in a 180 methinks

 

Have a look on the rear of an SW. The axle is exaclty the same.....and will be easier to get hold of. Less questions asked

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red

Just wondering about how moving weight around in the car can help things,

 

With the battery I'm looking at moving it behind the passenger seat fitted in a proper box, the thinking is the footwell keeps the battery lower down, helps balance my weight on the drivers side and keeps things inside the wheels, + I'm looking at a small fire extinguisher under the front area of the passenger seat, as you kmow I'm getting the car on the scales after Christmas thanks to your help :) , and I'll post all the results when it's finished, as with performance of any car you reach a limit and in sprinting gains of 1/10 of a second can be big gains, are these areas to look at?

 

Regards Russ.....

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Adi
are these areas to look at?

 

Deffo!!!

 

Weight and weight transfer is what hurts the tyre's grip. For a FWD car, it is difficult to get all four tyres performing at a similar level with the same amount of heat. The front tyres will overheat by overloading.....and the rear tyres will not get enough load and heat. So by moving any weighty components from the front end......and placing them from the rear seats backwards......will help balance the cars handling.

F1 cars will actually be made UNDERWEIGHT. Then they add ballast and place it where they want so to create a better handling balance.

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Guest Niklas

Let's say I change to solid bushings in the rear of my 206.

Will this entirely prevent liftoff oversteer?

And will it affect the handling in any other way, for example more understeering etc..?

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Adi

Changing to solid rear axle bushes will not totally prevent lift off oversteer. But it will vastly reduce it.

On FWD cars.....when you shut the throttle whilst cornering....there will always be an element of the rear going light and moving around. That is down to basic physics.

Will solid rear bushes cause more understeer???? It could be perceived as producing more understeer.......as when you lift the throttle.....the rear doesn't move and instantly reduce the understeer. But when the rear axle steer is reduced.....the handling dynamics are more down to how the suspension is tuned.....i.e. spring,roll bar and damper rates.

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Guest Niklas

Is it desireably to limit the liftoff tendency and instead play with the weight transfer in the rear?

Will this be a more "reactive" form of oversteer?

 

And how will this be done then?

Solid bushes and then uprated arb and torsion bars?

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Adi
Is it desireably to limit the liftoff tendency and instead play with the weight transfer in the rear?

Will this be a more "reactive" form of oversteer?

 

This is usually the process of entering a corner with a Peugeot designed with lift off oversteer:

1. first the front end/steering has to load up & the front end starts to run slightly wide.

2. you lift the throttle and the back end reacts and moves out.

 

Now on todays car with multi link/double wishbone rear suspension....... 1 and 2 (above) will happen together without having to lift the throttle. So its a natural flowing process thru turning the steering wheel........as it should be.

 

So in answer to the original question.......first try uprating the rear suspension by way of rear roll/torsion bars.......and see how the lift off oversteer is then. If that is still a problem......then fit the solid bushes.

By uprating the rear suspension......the turn in will be better and far less dependant on the lift off oversteer. The rear dampers will need changing as well.

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fiji bob

so if you used a 309 rear beam on a 205 do you think 309 rear dampers would work?

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Adi
if you used a 309 rear beam on a 205 do you think 309 rear dampers would work?

 

I don't know for sure......but I thought the 205GTI/309GTI rear dampers were the same. In which case.....there'll be no point. If it turns out that the 309GTI rear dampers are more uprated than the 205......then it would be worth swapping.

 

 

Adi: Thanks!

 

<_<:)

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zeolite

Interested in the component moving theme. Now that i have got my 205 running (aaaarrggghh) I am starting the stripping and lightening. I intend to move the battery out of the bay and onto the passenger floor. I thought that it would help balance the weight of the driver. The handheld ext will be there as well.

Does anyone know what the weight of stuff you can strip out of the interior? (I will keep the dash and fit a racing seat and harness)

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pug_ham
I thought the 205GTI/309GTI rear dampers were the same. In which case.....there'll be no point. If it turns out that the 309GTI rear dampers are more uprated than the 205......then it would be worth swapping.

AFAIK the 309 rear shocks are actually softer than the 205.

 

Looking on the parts CD they are definately different part numbers but the 309 GTi ones are listed as heavy duty.

 

Miles on MSN;

They seem to be a bit softer but the damping rate is different.

 

So the jury is still out for a definate answer.

 

Graham.:wacko:

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