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kyepan

How Not To Modify Your 205's Suspension...

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Rippthrough

Yes, it's another of those area's where you the more you know, the more you realise how little you know.

You could do it all your life and still be learning things the day you die.

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swordfish210
Yes, it's another of those area's where you the more you know, the more you realise how little you know.

You could do it all your life and still be learning things the day you die.

 

True, i doubt anyone knows everything there is to know about suspension systems. Theres allways stuff to learn...which is why i love playing about with them :lol:

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Rippthrough

There's so many different, workable solutions to a single problem that I don't think anyone will ever be able to design a perfect suspension system.

Hell, even if we develop anti-gravity some poor buggers'll have to work out how to damp it and control the chassis pitch

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swordfish210
There's so many different, workable solutions to a single problem that I don't think anyone will ever be able to design a perfect suspension system.

Hell, even if we develop anti-gravity some poor buggers'll have to work out how to damp it and control the chassis pitch

 

Good point, what would be your theoretical "perfect" suspension system? Zero unsprung mass, perfect damper control, no body roll with perfect ride quality over bumps :lol:

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Rippthrough

My perfect suspension system is in front of the TV.

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swordfish210
My perfect suspension system is in front of the TV.

 

f*** loads of sprung mass though :lol:

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Rippthrough

It's alright, it only ever encounters two bumps, it's pretty easy to setup for those.

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Cameron
Yes, it's another of those area's where you the more you know, the more you realise how little you know.

 

So true. I wrote a massive part of my dissertation on how chassis stiffness affects handling balance, and in the 50 page limit there was a huge amount of detail I had to leave out or thin down. Say I wrote about 1/4 of the stuff you need to know on that subject, and that's probably about 1/100 of a complete suspension system. So what took me a year to research and write was only 0.0025% of all the info you'd need to learn. :)

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Rippthrough

And by the time you did learn it all you'd be out of date with the new developments and trends in tyre and suspension tech which influences the chassis :)

Edited by Rippthrough

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Rippthrough

It's a fun game.

Multiply that 0.0025% across every component on the car...

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EdCherry

Still trying to get a grip on damper adjustments in practice, bring on the 3 ways testing tomorrow....

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Rippthrough
Still trying to get a grip on damper adjustments in practice, bring on the 3 ways testing tomorrow....

 

At least you've got the adjusters, I have to keep stripping mine down and rebuilding!

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EdCherry

Haha, well ive used 2 ways for the passed year and slightly understand them, but moving onto 3 ways seems like a daunting step...

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Rippthrough
Haha, well ive used 2 ways for the passed year and slightly understand them, but moving onto 3 ways seems like a daunting step...

 

Twiddle the knobs and bits move! :)

 

I could go through it easy enough, but I tend to need a pint and beermat to draw on when I'm explaining :P

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Cameron
It's a fun game.

Multiply that 0.0025% across every component on the car...

 

funny-picture-1127924587.jpg

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TT205

Is that the Total Perspective Vortex?

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Batfink
It's a fun game.

Multiply that 0.0025% across every component on the car...

 

and its then still 0.0025%.. :)

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Rippthrough

Basically, we all know the square root of fook all :)

 

Anyway, swerving back a little more to the topic at hand, on balljoint extenders modifications - this is one of those that sounds great until you realise you generally can only have it a certain size due to getting the balljoint in there, loadings on the joint, etc, etc.

And that size might not be what you want, so then you have to go with what is nearest - which is probably more than you want - so you then end up with a higher roll centre at the front (although it doesn't make as much difference as you think, which is what Cameron was hinting at, the car doesn't actually roll around that, or even the instant centres, but it gives rough idea's of the cars behaviour), as well as more camber gain in roll.

But - you are now rolling less on the chassis....and tending to lift the car on the outside wheel instead - jacking the chassis up, which could well give slightly more lateral force on the tyre and slightly less vertically when the car is rolling to inputs - it can give that feel of the front end washing out on turn in in the wet/low grip situations, so you might now have a situation where you have great turn in and grip on a track with good tyres, yet the car feels horrible in the wet or on road tyres.

Even worse you now need to move either the rack or the track rods as they no longer follow a similar arc to the lower wishbone - the bump steer will likely be much more pronounced when a wheel drops into a pothole or similar - it'll toe in like buggery with the inside wheel on full extension - so now you have a car that's washes out a little on rough surfaces, but feels better at the front on high speed corners, yet never seems to want to turn in properly on tighter tracks....

 

This is all just theoretical without going out an getting measurements - but you can see what I'm getting at, one little change to the geometery can make such a huge difference to everything else, that you better be prepared to alter everything, or nothing.

Lowering, to an extent, isn't bad, because the suspension is designed to cope with that cycle in normal use, you might just want to shim the tie rods/rack slightly to bring the steering curve back to neutral at ride height if feeling adventurous, but you can soon find yourself chasing your tail in circles if you don't treat the geometery as a full package - and that includes considering the effect at the back when altering the front - not too much of a concern with trailing arms, but it does alter the dynamic balance of the car.

Edited by Rippthrough

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Cameron

Amen.

 

There's too much going on to be able to determine exactly how it's going to behave dynamically from a static setup. You either need a really good simulation package like Lotus Shark, although that is still extremely limited, or a whoooole load of trial and error or experience. That's what you're paying for when you go to an expert who's already done all the testing and knows what works.

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B1ack_Mi16

I'm actually working as an analysis engineer at this company now http://www.fedem.com/index.php?option=com_...33&Itemid=5

 

And our software can handle tire models, and dynamic simulation of the complete car.

 

Only issue is that one would need all data on pickup points and such to really be able to make a realistic simulation model.

 

Can then run the car on bumpy surfaces and measure all the angles/responses to any component in the whole car.

Depends on how detailed the modelling is of course.

 

I could really like a FE model of the complete 205 Shell and front subfram, does anyone have this?

The rear beam is easy to make and most of the other parts, it's just the subframe has a bit complicated shape and that's even worse for the complete body..

 

I have been thinking of making a model of a 205 for a long time but have really never got any time for it.

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Cameron

It crossed my mind every now and then, then I remember how much of a ballache it was modelling just the outer skin of the front of an Audi A4 and think yeah, f*** that! :)

Surfacing is very very time consuming!

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kyepan

does anyone know the standard ride height of a 205 1.9? distance from floor to a point... or distance from the wheel to the arch at the front.

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welshpug

I do have a standard 205 I can measure :)

 

I also have the minimum challenge/gp N / gp A ride heights somewhere too :)

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Cameron

The height of the front inner wishbone point would be very nice if you could get it!

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