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


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189 replies to this topic

#21
Cameron

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Not too long, I'm just waiting to get it on the flat floor at uni so I can measure it accurately. I'll also be finding out the GC height while I'm at it providing my car is below the 880kg limit of the corner weight scales.

I'm not sure you need to rotate the wheel while you're measuring bump steer (I think that's what you meant above). I think an easier way would be to use a variation on the "string box" tracking method, where you jack the car up so the wheels are just touching the floor and support it on stands. Then remove one suspension spring and place a jack under the wishbone. Then you can jack the wheel up from from full droop and measure from the string line to the front and rear edge of the wheel rim, subtracting the front from the rear to find the amount of toe. Jack the wheel up a certain amount and then measure again, then you'll have a simpler 2D line graph that shows your toe change through the whole suspension travel.

I'm not massively convinced that people will need to move to softer springs though, as nobody seems to be running what I'd call excessively high rates. 300-350lbin may seem quite high, but the high spring rate is doing 2 jobs: absorbing bumps and resisting roll. I think as long as your dampers are good enough to cope you'll benefit from rates that high through better body control keeping your camber angles more desirable.

#22
Rippthrough

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As above, 300-350lb isn't too excessive for a track only car (although probably edging to a bit uncomfortable on anything but smooth a-roads).
We run that sort of wheel rate on the rear of the buggy, which is comparable weight wise to the nose of a 205.

#23
kyepan

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Not too long, I'm just waiting to get it on the flat floor at uni so I can measure it accurately. I'll also be finding out the GC height while I'm at it providing my car is below the 880kg limit of the corner weight scales.

I'm not sure you need to rotate the wheel while you're measuring bump steer (I think that's what you meant above).

Well i'm in cast for another 5 weeks, so i won't be doing anything much to the car until then.

About the wheel rotation: mainly because sandy brown told me to on a previous post.

But when i thought about it carefully, bump steer is caused by the track rod pivot points moving in a different arc to the lower arm.
And when you apply lock, you move both the inner and outer pivot points of the track rod, which could induce bump steer relative to the actual amount of lock applied.
So to check bump steer properly it would need to be done at different heights and steering angles, and it would affect both wheels, so you might end up getting toe out on the outer wheel and toe in on the inner wheel or something like that.

Practically speaking, the bump steer suffered on the pulsar was woeful, but only present at 1/4-1/2 a turn of lock, there was very little if any up bump steer from straight line suspension compression. so what Sandy said was exactly what happened in reality.

cheers

J

Edited by kyepan, 26 May 2010 - 12:43 PM.


#24
Cameron

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Ah! I thought you meant the road wheel, not the steering wheel! :rolleyes:

#25
DrSarty

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Yes: fascinating stuff J, and sorry to hear about your leg.

This I think is partly or even mainly why I had Colin Satchell and Sandy Brown do my car, as between them they seem to have a 'firm grip' on this massive, science filled topic.

Colin's held a hill climb record down south since 2004; although he did say they went up that many times that the car could've probably driven itself up in the end.

Their track cars are doing very well too, and each time I look at my car I see and learn of things which like your original post are perhaps contrary to what most people believed was the right way to go.

Ripp likewise seems to be extremely knowledgeable although at the same time I suspect just like with 4-stroke engine development and tuning, no-one really knows it all, and it is a constant trial, test and challenge for those involved.

Such are the joys of motorsport and performance car tuning.

I hope this does become a sticky. :D

#26
Rippthrough

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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.

#27
swordfish210

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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:

#28
Rippthrough

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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

#29
swordfish210

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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:

#30
Rippthrough

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My perfect suspension system is in front of the TV.

#31
swordfish210

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My perfect suspension system is in front of the TV.


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

#32
Rippthrough

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

#33
Cameron

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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. :)

#34
Rippthrough

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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, 26 May 2010 - 10:53 PM.


#35
Cameron

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Yup!

#36
Rippthrough

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It's a fun game.
Multiply that 0.0025% across every component on the car...

#37
EdCherry

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

#38
Rippthrough

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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!

#39
EdCherry

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

#40
Rippthrough

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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