hello folks

I have looked through some threads but did not find answer to my problem.

quite simply I'm looking to obtain a simple approx guide to selection of spring rates for a kit car.

I shall be running coil overs with adjustable damp rates etc but was hoping for a little more informed decision about spring rate selection.

i.e do you guesstimate weight (if have no measuring facility) of front and rear etc and look at unsprung weight etc etc.

any help or advice would be greatly appreciated

all the best
Paul

good book

At £25 per pair, springs are reasonably cheap.
I worked my rates out by weighing each corner and adding weight of people plus allowed for braking (guestimate).
I ended up increasing my spring rates slightly after I had driven the car for a while.
Reselling the old springs on ebay again, helped with the costs.
You won't know your prefered rates until you have driven your car under different conditions.
I knew my front springs were to soft because I got too much dive at the front under heavy braking.
My rears need changing as I fully loaded the car (passenger and tools) and the chassis hit a bump in the road when I gave it a good thrashing.

it's not the cost I worry about.

I have 200lb springs on at moment and when I lower front end of car with jack the springs just keep compressing until I cant get jack out from under chassis.

there is a v6 motor in front with a ford anglia shell over the locost chassis so it is quite a bit heavier than a standard locost.

there is plnty of thread left on body of damper but as I look at springs currently. their is perhaps 1/2" between each coil so almost looks coil bound.

I don't know if I've made a stupid mistake in spring selection or the springs are questionable even though they are new.

I thought I would be ok on 200lbs as I ran a rally car with 180lb with a 4cylinder engine in and it was fine.
just looking to compare with others and how others have gone about it.

Your springs sound too light for me.
At present I have 350lb ones on my rear suspension with a K-series over them and they are too soft. (rear engine)
My fronts are 275lb and I do not have hardly any weight there.
I am running inboard suspension but with a 1:1 ratio so it should be similar to a 7.
I recommend getting hold of a corner weight gauge as this will give you an idea of the spring rated needed.

if you were going to have a punt at it then what would be your choice for a stiff road car setup

the engine is a 300zx TT which is a iron block with alloy heads so is not the heavy old ford or big block engines of historical sense but will be heavier than your k series.
cheers
Paul

I have located this site as a guide but don't know what natural frequency or wheel defelction figures to aim for unless someone knows the answer here.

I would guestimate that my front end is somwhere near 600kilograms 300 each side with approx 30kg in unsprung weight of wheel hub etc but where do I go from here as I'm a bit out of my depth here I'm not too ashamed to admit?

http://www.racingaspirations.com/wheelfrequency.php

I would not be surprised if you end up with a 600lb/in or 800 or even over 1000lbs spring rate. Remember unlike Macpherson struts the angle of mounting of the spring and wishbone leverage ratio has a big effect.

With spring rates that high you will be starting to push the stiffness envelope of the the locost chassis.



[Edited on 21/8/07 by britishtrident]

On a heavy engined locost I would guess 350lb front, 200lb rear would be a good starting point, sound too light at the moment if it's a heavier shell with a v6 iron block engine..

The Viento boys might be nearer your car's weight so might be worth asking luego (or current owners of the range) what they fit as standard?

Ned.

Crunching the numbers and using an educated guess the spring mounting angle and and wishbone design I come up with 430 to 540 lbs/in.

Try and get a more accurate handle on the weights.

My car is fitted with the Ford V6 12 v 2.9i, and my front springs are 350lb's, plus my car is no light weight, being a bit over 900 kilo's. My advise would be to go for the 350lb springs, at the front at least. HTH Ray