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spring setup when do you need a helper spring

Suspension Tuning & Optimization

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hi all just finished watching courses and worked out my spring rate

as follows

ratio =1.1

sprung mass = 222

undamp freq = 2

in kg/mm 4.5 kg spring

so if i have a total damper travel of 103mm ride height should be setup at 1/3 of this 34mm compressed

the part I'm trying to get my head around is

should the spring compress the 34mm under the static weight of the car therefore given up the desired droop?

given that for a 4.5kg spring

with 222 kgs sitting on it should compress 222/4.5= 49.33 which is more than enough

but what do you do, if you feel a stronger spring rate is needed as the lower is giving lots of body roll?

So say we go up to a 7kg spring. this will give 31mm travel with 222kgs on it at rest.

so now very close to not giving the spring preload once i put car at ride height. once i make damper go to full extension.

is this the case where you need a helper spring?????

Attached Files

You've posted that clip a couple of times - it IS a FWD platform, isn't it, as it looks like a RWD conversion with a rear mounted engine?

For that application, lowering the suspension with SMALLER diameter wheels/tyres will help a lot.

Different people may have different interpretations of what a "helper" spring is, in the most basic sense it's a secondary, or auxiliary, spring to aid the main spring. This could be to get an overall spring rate that isn't normally available, to counter 'bottoming out' under full compression or, as I suspect you mean, to prevent a spring becoming unseated under full extension.

TBH, I'm becoming 100% convinced you need to pick up a good book, or two, on basic suspension design and have a good read of it, as you don't seem to quite get the basics of the courses - between them you should be up to speed [sorry, no sorry] very quickly. Looking for a quick fix won't work if you don't have a good understanding of what the problem/s is/are

thanks for the help Gord

yeah to lower the car i have set the foot height to allow the wheel not to rub on the guards, and now trying to lower the body via the spring perch for a lower ride height. but when i lift up body of the car the spring comes loose.

so need helper spring yes???

and was also was hoping for help to check my spring rates maths and the example in the course has very similar weights and ratios but a different outcome

video has a 6 kgs spring mine cals 4.3 spring

Attached Files

Not sure what you mean by "foot height", but if the spring is coming 'loose' on full extension, then the usual remedy is a very light rate clearance, or helper, spring on top of the main spring, to hold some force on the seat. The light rate means it fully compresses under a light load and the main spring does the 'work'.

As I said before, though, I really think you need to go back to basics and work your way though it - and something about vehicle, especially FWD, dynamics certainly seems to be in order.

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