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Suspension And How It Works


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123 replies to this topic

#21
Adi

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strut braces, I currently don't run one and was wondering if they are of use on a car with standard bushes etc



Strut braces are useful for keeping the front suspension geometry stable. When the front suspension is under load whilst cornering....the inner wings can flex allowing the tyre angle to change. This will usually mean the outside tyre tucking under more......thus losing grip. A brace is there to increase the torsional rigidity of the shell....and as such, allows the suspension to perform better.
But as always....the benefits depend on the rest of the suspension set up and more importantly....how strong the shell is. The stronger the shell....the less twist there will be. A brace will be less needed or benefitial in this situation.

The best thing to do, is try a brace, or both braces and see how the car feels.

#22
Adi

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I think it would be useful to go through the different aspects of spring and damper rates, eg compression and rebound. How over stiff handles differently to over soft, and front rear balance.



There are many ins and outs on this subject.....so I will try and keep it brief.


Too soft a spring rate will provide a good ride quality. But, the suspension takes too long to absorb the energy, thus the tyre isn't in full contact with the ground for as long as it could be. So not providing the maximum grip.
Also when cornering, especially with a McPherson strut set up, the tyre rolls to a greater angle and doesn't stay square to the ground when under full load. Again, not providing the full grip.

If the spring rate is too high, then when the tyre hits a bump, the spring will not absorb enough of the energy. That is passed onto the chassis. The chassis is sent in the upward direction thus the tyre is not in full contact with the ground. Again not providing full grip. If this happens whilst cornering, it could spell trouble.


Damper rates work hand in hand with spring rates and can give similar effects if the rates are wrong.

In general, the compression side of damping will influence the cars stability and response. The rebound side should influence comfort and traction.
But, for example if the compression side of damping is too high, then the ride will be harsh and crashy. This is why, setting up and diagnosing problems can be very difficult.

Dampers can provide a very useful tool for tuning handling balance especially on aspects of cornering such as entry and exit. This is because the diagonally opposed dampers are usually working in the opposite direction. Working out exactly which direction each damper is moving, at the different stages whilst cornering, you can learn to change the damping accordingly to alter the handling balance.

Anyone looking to improve handling in general, should spend as much as possible on dampers. Modern dampers have improved so much since Active Suspension was outlawed in F1 in the early '90s.
Racing dampers using Digressive technology have so much more control over suspension movements than either progressive or linear dampers.
Can I just point out......that the different types of damping effect the shaft speed in damping, rather than the position of the shaft within the stroke. I have heard people mention that progressive dampers have a higher rate of damping the shorter the shaft becomes. This is not true........it is the speed of the shaft movements that effect the rate of damping.
This is the reason that Digressive dampers are so effective. These dampers can control slow shaft speed movements such as cornering.....where other types of dampers would have little influence. Then when the shaft speed increases on bumps etc.....digressive dampers are more comfortable......where the other dampers are harsh and crashy.

As far as balance is concerned.........in general the end of the car that has the most roll stiffness (provided by springs and roll bars) will have the most lateral movement and will lose grip first.

This is why on cars like Peugeots (that have struts and coils at the front.....and torsion bars a the rear) it is OK to raise the front spring rate to control roll etc, but if the rear rate isn't increased accordingley......then the car's balance will be very much towards the front.......and understeer.

Another "general rule" is that the opposite end of the car to the drive wheels....will have the higher roll resistance. This is so the drive wheels are kept flat and the suspension is more complaint to enable the tyre to follow any undulations.

#23
Adi

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Also ride height and side effects of lower (less travel).



Ride height and centre of gravity height, seem to be the main points that rule general suspension tuning.

Whilst these can be important, suspension travel is also very important, and in certain cases, more important than ride height.
If the chassis is lowered a large amount for general road use, then this is going to leave potentially dangerous problems. When there is a minimal amount of suspension travel, and the wheel/tyre comes into contact with bumps.....if there is too much energy for the short spring (or high rate spring) to absorb, the excess will be passed into the chassis. This will send the chassis in the upward direction and reduce the tyre's grip with the road surface. Again.....if this happens whilst cornering at speed......then a trip to the nearest hedge or wall, will be the usual outcome.
Another major bad point with excessive lowering is, when the spring hasn't enough length to absorb the energy from larger bumps....the damper will constantly be slammed shut at the end of its stroke. This will lead to the internal seals blowing and the oil leaking from inside. It will only be the more expensive dampers that can be rebuilt in this situation. The dampers that can't be rebuilt, will have to be thrown away.

One point that seems to escape most people when altering suspension height, is BUMP STEER and the angle of the lower wishbone.

If the steering arm and lower wishbone aren't working together on similar planes, then when the suspension goes in the bump direction, the wheel will change it's intended path. This means the driver will constantly have to make steering alterations to keep the car travelling in the same direction.
To avoid bump steer.....the lower wishbone should generally be kept inclined downwards to the wheel. That is, the inside mounting point be higher than the outer balljoint.
Bumpsteer and/or the lower wishbone inclination is less of a consideration on smooth surfaces like a track.


There is however a positive reason for lowering Peugeots with beam axles, about 25mm all round.
Every suspension has a roll centre. So a "normal" car will have a front and rear roll centre. For the best ride/handling comprimise, the rear roll centre needs to be HIGHER than the front. This is so the rear weight transfer will be quicker than that of the front......so aiding corner entry and exit. But at the same time having softer rear spring rates to aid comfort.
With the rear beam axle on the Peugeots......the rear roll centre is LOWER than the front. In fact....the rear roll centre is at ground level at all times. This means that if softer springs are used for a smoother ride.....then the rear end of the car will roll more than the front........so producing understeer.
Now if the rear roll centre cannot be raised....the next best thing is to LOWER the front roll centre. So by lowering the car approximately 25mm, the best comprimise will be achieved........again though......remembering the angle of the front wishbones.

#24
NickR

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I have made this into an article on my website:

http://www.lbft.co.u...ticles.asp?id=2

#25
Adi

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how adjusting tyre pressure can make a huge different, infact using s*ite tyres on good suspension can be such a waste of good suspension



Tyre pressures can be a useful tool in changing handling balance.

Generally.......lower tyre pressure will cause a greater slip angle. That is, the tyre will change direction slower and run wider whilst cornering. So as Skip Brown regularly set cars up.......the front tyres would have 28psi and the rears 24psi. This may not be a favourable set up for all......but can be used to fine tune and tweak the balance of the car.


Tyres are the probably the largest single part of a car that can change how the car feels and handles corners.
There is very little or no use in wanting to improve a cars performance and not spending a decent amount of time or money finding a good quality tyre.

A tyre will not only provide grip for a car....but also steering feel and response. By fitting a good quality tyre......the car will not only be safer in more testing conditions......but generally perform/handle better in all conditions.

Even though the general quality of all tyres has improved in recent years, there is still a large gap even between the premium brands.
So it would be a waste of anyones time and money....if money should be spent on improving suspension......and the same time and money isn't spent on fitting good tyres.

#26
NickR

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Damn you !

Just updated my article:

http://www.lbft.co.u...ticles.asp?id=2

#27
TT205

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Fabulous set of articles Adi

Now, how about a recipe book :)

Assuming that someone has ungraded their suspension - dampers/arb's/torsion bars etc and that the front dampers are adjustable.
(i.e. the position I am now in)
What would you say is the best order in which to do your testing to get the best set-up for your individual 205?

eg

1) Ride height
2) Tyres pressures
3) Tyre/rim widths
4) Front damping

etc

Cheers
Dave

Edited by TT205, 06 October 2003 - 02:54 PM.


#28
Ahl

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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!

#29
Adi

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1) Ride height
2) Tyres pressures
3) Tyre/rim widths
4) Front damping



1) Tyre/rim width
2) Ride Height
3) Damping should be adjusted front and rear to tune balance.....and as a general rule.....the rear should be set firmer than the front.
Saying that....you could choose a favourite set of corners and run thru with all dampers set to 0. Then turn the rears upto 2 and try again. If you prefer the balance....then whatever the fronts finally finish on.....just keep the rears firmer than the front.
4) tyre pressures

What spring rates have Leda supplied.......and have you changed the rear torsion or arb??

#30
NickR

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Adi, was just wonder how things change for 4wd and rwd cars

#31
fiji bob

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adj do you think a 309 gti rear set up is a good upgrade on a 205? i think it has thicker anti roll bar torsion bars and is slightly wider but someone will know for sure

#32
TT205

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What spring rates have Leda supplied.......and have you changed the rear torsion or arb??

Springs are - 270's ( Ithink)
Rear ARB now 23mm, and uprated torsion bars

Dave

#33
red

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Thanks for that great section ADI and putting in the time and effort :D , that really gives me somthing to ponder over and look at with respect to testing, as one or two of us sprint I was wondering how seting the car up differs from say a circuit race as we are on cold tyres and normaly get one-two circuits at best at most venues, this is in respect to tyre pressures and the type of compound used, with me it would be a rd tyre from list 1A in the MSA blue book, I use the Bridgestone SO 3's and currently I'm the only one who likes them? do you have any preferences on tyres yourself.
Regards Russ

#34
Adi

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was just wonder how things change for 4wd and rwd cars


RWD cars are generally set up with the frotn end stiffest.....which is why you will see RWD track cars lifting the inside front wheels at extremes. In F1 GP at USA last week.....Mr Schumacher was lifting an inside front wheel in turn 2.

4WD cars are generally set up in a similar way to RWD cars with the front end being the stiffer but not as stiff as say a RWD.

adj do you think a 309 gti rear set up is a good upgrade on a 205?


Yes in theory it is a good upgrade. The major improvement is the increased rear track of the 309 axle. Apart from lowering...increasing the track is the best way of reducing weight transfer.
Because I have never actually driven a car back to back with and without the 309 axle....I can't really comment how the 2 differ in feel.

do you have any preferences on tyres yourself.


I've never tried some of the more exotic Pirelli tyres which are supposed to be very good. But IMO the Goodyear Eagle F1 is very good. Especially in the wet, the Eagle F1 inspired confidence. The Toyo Proxes I have now.....are certainly not as good in the wet.

#35
Doof

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Bloody hell, suspension guru!!

Pitcrew?

#36
Adi

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Pitcrew?


No not at mo.......just studied in the past. :D

#37
Doof

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Muppet :D

#38
Adi

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:blink: :D :huh:

#39
pug_ham

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Bloody hell, suspension guru!!

Pitcrew?

To late Adi, you've had an upgrade! :blink:

This is a fabulous topic to keep up to date with, keeping NickR busy updating the article on his site as well.

Graham.:D

#40
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You certainly know your stuff! Sell your info on Ebay! :P :P