JohnFol
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 posted on 11/8/02 at 01:05 PM |
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Loads of suspension questions
Here's the deal. Front suspension is going on. Fitted brackets and wishbones. Set castor and camber to be as correct as I can make it. However I have
a few questions I can't get clear direction from
What limits the vertical movement of the suspension? It seems to be the top suspension joint.
When the car is complete, should the lower suspension arm be horizontal?
Top wishbone is angled up on some cars (ie wheel end is highest), and parallel to the lower wishbone on others. Since the vertical movement is limited
by the top ball joint, surely having it angled to start with limits the movement even more?
Should the shock absorber be the limiting factor for vertical movement? ie if the suspension moves up from 0cm to 10 cm, should I make sure the bottom
extent of the shock travel is 0.5 cm with the upper limit being 9.5cm?
Is there any problem mounting the top shock absorber mount inboard? It is currently positioned upside down, on a welded plate in the triangle you get
both sides at the front (sorry, can't remember length names). Particularly interested if this is permitted for the 750 formulae.
Sorry for so many questions, but I guess suspension setup is quite key to a good drive. . .
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Alan B
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| posted on 11/8/02 at 04:03 PM |
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John,
My build is somewhat different so I can't/won't answer all your questions.
However, suspension travel should be limited by shock absorber travel and NOT anything else. You should be able to remove the shock and manually move
the suspension beyond both limits before it binds up on anything (not having your bushing bolts tightened helps when you move the suspension)
Hope that helps a bit.
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JohnFol
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| posted on 11/8/02 at 04:10 PM |
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Alan, thanks for the response. Are your lower wishbones horizontal?
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Alan B
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| posted on 11/8/02 at 04:21 PM |
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Yes, pretty much John.
Check out the front end of my rolling chassis in my picture folder in the archives.
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interestedparty
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| posted on 11/8/02 at 04:31 PM |
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The correct setup for a car with twin wishbone suspension is for the lower wb to be horizontal and the upper to be angled downward from wheel to
chassis. This gives more desirable camber change when that wheel is pushed up during hard cornering, the negative camber will be increased more than
if the upper wb was horizontal.
John
As some day it may happen that a victim must be found,
I've got a little list-- I've got a little list
Of society offenders who might well be underground,
And who never would be missed-- who never would be missed!
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philgregson
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| posted on 11/8/02 at 07:19 PM |
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This is (yet) something else that causes me concern (This user group has been utterly invaluable in my build but I sometimes wonder If I would have
been happier in my ignorance just unquestioningly following the book!).
I am about to build my front suspension and I have heard mutterings about the book layout (roll centres etc), which also seemed to be a cause of
concern in an article in the recent CCC.
Is the standard book layout crap? or is it just the way some people have built it? Could it be a problem with people increasing wheel and tyre size
(I'm planning to stgick with 13x185x60)? does anyone have a better alternative?
Answers on a postcard please.
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theconrodkid
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| posted on 11/8/02 at 08:07 PM |
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My suspenders are all by the book and it handles like a go kart,i put 185 tyres on and it was crap,im using 155,s again.hth
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stephen_gusterson
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| posted on 11/8/02 at 10:27 PM |
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as far as my car is concerned, you are bang on right that the top joint is the limiting factor.
although the transit joint is in common use, it actually has quite a small angle of movement as was never a suspension part.
I found that in order to stop it having a problem, I had to angle it. But then I am using sierra type hubs with a 'strut adaptor' in it.
Look at a pic of an MK indy - you will see they had the same problem cos their top joint is also angled.
I was also concerned that a big bump would snap or stress the top joint. however, it seems that people dont do anything to limit suspension travel.
I would think some kinda rubber bump stop on the shocker shaft (if its possible to get one on) would be the way.
atb
steve
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philgregson
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| posted on 12/8/02 at 07:43 AM |
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I'm glad to hear that the go-cart style handling is present and correct and, to be honest, this is what I hear from most people.
My concern is that some people are quite obviously getting it wrong and I would like to know quite how so that I don't.
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interestedparty
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| posted on 12/8/02 at 07:55 AM |
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Although the Locost suspension can appear to have problems at full travel, in normal road use the suspension only moves a short distance so it really
doesn't matter. The springs are too stiff to allow full suspension movement by such a low weight car.
The springs have to be that stiff because the ride height of a car (assuming you have no way of easily altering its weight)is set by the unfitted
length of the spring and its poundage. There isn't room for a really long spring so the springs that are used to set the ride height will also be
very stiff.
John
As some day it may happen that a victim must be found,
I've got a little list-- I've got a little list
Of society offenders who might well be underground,
And who never would be missed-- who never would be missed!
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stephen_gusterson
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| posted on 12/8/02 at 08:00 AM |
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It seems on my car that there is a degree of adjustment of ride height by altering the spring preload on the shock. Obviously if you use too much
preload the shock will be at its bottom stop at rest, which would be a bad thing as there will be no rebound movement.
atb
steve
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interestedparty
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| posted on 12/8/02 at 01:00 PM |
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quote:
It seems on my car that there is a degree of adjustment of ride height by altering the spring preload on the shock. Obviously if you use too much
preload the shock will be at its bottom stop at rest, which would be a bad thing as there will be no rebound movement.
atb
steve
Ideally the correct ride height would be achieved by changing the spring itself to one of the required free length and poundage. Naturally the ideal
setting would be one where the lower wishbone is horizontal and the suspension in mid-travel. That would leave the spring seat adjustment available
for fine adjustments, and more particularly, for setting up the cornerweights
John
As some day it may happen that a victim must be found,
I've got a little list-- I've got a little list
Of society offenders who might well be underground,
And who never would be missed-- who never would be missed!
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Dick Axtell
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| posted on 12/8/02 at 05:04 PM |
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Quote:
"The correct setup for a car with twin wishbone suspension is for the lower wb to be horizontal and the upper to be angled downward from wheel to
chassis. This gives more desirable camber change when that wheel is pushed up during hard cornering, the negative camber will be increased more than
if the upper wb was horizontal." End quote
It also fixes the front roll centre position lower than would be the case with upper w/b angled upwards from upright to chassis mounting. You
definitely DON'T want a relatively high roll centre, which would amplify any understeer tendency.
Dick
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johnston
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| posted on 12/8/02 at 07:55 PM |
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goto amazon and get "compition car suspension" by alan stainforth names spelt wrong but not far away i think!!!!!
got it same time as i got THE book its a good read and explains a lot of previous styles and their pro's and cons
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JohnFol
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| posted on 13/8/02 at 03:49 PM |
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Thanks for all the comments. I have 1 last question.
The race regs state I cannot change the suspension pickup points. Would these be the points at which the wishbones attach? Does it also include the
mounting points for the dampers?
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Alan B
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| posted on 13/8/02 at 04:31 PM |
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quote:
Thanks for all the comments. I have 1 last question.
The race regs state I cannot change the suspension pickup points. Would these be the points at which the wishbones attach? Does it also include the
mounting points for the dampers?
IMO wishbones definitely, and dampers quite likely too.
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