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setting up suspension droop

Suspension Tuning & Optimization

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hi all just wondering

as my car is very light in the rear as its FWD in short if i put a strong spring in the struts i get no droop. but as weight is barely 150kgs on a wheel.

if i go to a softer spring to get droop. the spring is that light a get alot of body roll.

would a helper spring be used in this situation to get some droop but maintain a stronger spring??

or antiroll bar on the rear with softer springs be better??

cheers mic

It's not clear if you understand what the "droop" is and/or the relationship with roll resistance?

You don't say what you're using the car for, and what you're trying to achieve?

For the most part, I'd be inclined to run a little softer on the spring and look att he ARB for balance, as stiffer springs can be a bit 'skippy' over bumps, partly because the tyre becomes more of the spring and it's undamped.

However, there are some very experienced folks on the FWD platforms who can better comment.

Sorry start again

It's a little fiat 127 for track use.

Rear end modified suspension to McPherson struts no antiroll bar.

And first setup it had was so stiff it had no droop at rest.

I put the lightest spring I had in still no droop (have been watching your lessons and have to do some cals)

Local suspension joint suggested helper springs to get the droop with out going too soft a spring.

So was wondering why this would be a option and if viable

Car is always lifting inside rear

To the point nearly put the car over at one event.

Can upload video if like.

And does not take much to upset over kerbs on the rear.

Perhaps your strut is too short. The droop limit on my sports racers is controlled by the uncompressed length of the damper. We adjust this by putting spacers in the damper to limit the uncompressed length.

Perhaps something similar can be done with your McPherson strut inserts.

Or maybe you have some binding that is limiting the droop (Just make sure it's not the brake lines or similar!)

hi guys thanks for comments so far think before i get into this too much might sit down and work out spring rate with the cals from tutorials see what numbers come up with as a starting point.

You may need to go back to fundamentals, such as -

As soon as an inner tyre lifts you are at 100% load transfer on that axle - going stiffer makes no difference.

Droop is the suspension extending from the normal ride position - if you don't have any droop is is because something is preventing the spring extending within the suspension - usually it's because too much preload is used because the wrong spring rate and/or length is being used. Other issues is if there is a binding problem, restricted damper travel - to be considered with spring selection, or something else suck as cables or hoses being stressed.

The tyre is part of the springing, if the rear is lightened the tyre pressure should be reduced to reduce it's spring rate. Most have a minimum pressure of 1.8-2.2 bar. This will also increase the slip angle.

If understeer and/or excessive body roll is a problem, increasing the roll resistance at the front will reduce the camber gain - if the inner rear is already lifting this is the only remedy for it.

Yeah agree

When spring is out can move wheel full travel up down. once spring back in put car on ground shock doesn't compress

I do like your bit on tyre pressure needs to be lower had not considered weight on it compared to fronts as a Fwd.

So hopefully will look at the maths for spring rates next week or so.

And see if close or not on paper to what's in car.

And may have more questions From there

Cheers mic

thanks all so far

sorry i have changed cars to my khana car that i modified adjustable struts to the rear for now.

and as want to lower the ride height for this weekend. so as have to work on it thought

just to get used to working the cals i would do this car.

and has

following info.

unsprung mass m=222 ratio = 1.1 undamper freq=2

the cals come out to need a 4.5 spring

i currently have a 7 kg spring in as that was what i had available and still get body roll

hopefully an see attached footage of its first time out last week. what would the lower spring rate do for it? and currently does not have sway bar on the rear. was thinking of putting it in?

Attached Files

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