Springs

[John L]

Hi all. I am assembling a rolling chassis. I have 2 good sets of springs which I have flattened as I have done for my previous car. One set has heavy leaves  and the other set are a softer leaf.

Which set to people find best for fast road/race type driving?

[Ian Williams]

Tough question to answer John as there are so many variables, you hear very soft springs are good for racing but that is probably only true on a chassis that is a space frame My experience is that if springing is too soft even with a boxed chassis jacking can still be an issue, that said Saloon springs on a light special will be too stiff. Others may have differing opinions but individual cars and driving styles may need individual solutions.

[Alan]

If you drive on any sort of rough road, you will find “softride” springs deflect too much, and you compensate by having stiffer dampers. To me, they are of questionable benefit. I’d give Austin’s the credit for knowing what they were on about and stick with standard rate springs.

[Chris KC]

I can't really speak from practical experience, but I always thought soft springs go with a stiff frame; and if your frame is jelly-esque then stiff springs are the way to go. You don't benefit from 2 layers of compliance.

[Greig Smith]

It also depends on the type of body fitted to the chassis, a heavier saloon body will mean the spring will have to deal with more weight than a light alloy special 2 seater, so with the latter you could go with the lighter springs

Aye
Greig

[Dennis Nicholas]

Spring rates
I can work out the spring rates of a coil spring using a drill press, scales and a ruler to give the pound inch rate.  Can anyone tell me a way to work out the spring rate of a leaf spring?  I have searched thoroughly and seen all sorts of complex formulae involving number of leaves, distance between leaf ends, leaf lengths/thickness but applying my measurements to these does not seem to have come up with anything consistent or believable.
Anyone know of some values for the different springs available?
I have had a new front big 7 spring made but the company were not able to tell me the rate.  It would help to know so I can work out how flat the spring will go when fully loaded with engine (BMC  'A'), body etc and I can get some idea where the ends of the radius arms are going to come in relation to the cross member for mounting the silent block bush housing, without putting a twist on the spring ends/shackles. (wedge will be added between spring and chassis as required) I am just hoping to be able to work things out without endless experimenting...(don't have full engineering machines and skills).

By the way...Land rover used to have heavier grade springs on the driver side than the passenger side to compensate for the driver's weight on the premiss that it was more often driven with no passenger(s).  Just wonder if that would be helpful on A7 in view of relative weight of driver to A7 

Denis

[Paul N-M]

Hi Denis,
To be as helpfull as possible more info is required.
Fast road/race suggests a two seater? Big Seven spring suggests you have a wider Big Seven front axle? 
It is possible to work out spring rates for leaf springs by measuring the lbs force deflection per inch by making up a jig. Adjusting the rate by adding and subtracting leaves. Static height and therefore ride height being determined by the initial set which may need altering depending on final rate selection.
For example are you keeping your rear springs located inside the chassis or moving then on top of the chassis. This design choice will effect the static camber you start out with if using the original Austin axle spring locating lugs.
You give no idea as to weight and % f & r with driver. Or the f & r track depending on final wheel offset. Remember spring rate is one thing but wheel rate another and that is determined by the track to spring eye/sliding block if not using shackles, ratio/leverage.
Also please remember that the castor angle may be fine once the final chassis height, not forgetting the driver, front to rear is established.
If you can give us a bit more info I'm sure lots of good advice will be forthcoming.

Regards,

Paul N-M

[Austin Carr]

Spring calculator:-

https://www.suspensionmaxx.com/tech-supp...alculator/

[Paul N-M]

Calculator for leaf springs way out on actual poundage. Have found this a common problem with these in relation to leaf springs more accurate for coils. Also does not considder quarter eliptics. For one off sets i.e. not production runs to a manufacturers specification most forges wont have a clue what the spring rate is.


Paul N-M

[Tony Griffiths]

This is of absolutely no help with the problem, but it's always struck me as somewhat incongruous that the thick, stiff quarter-elliptic rear springs of an A7 are held in a relatively lightweight housing of pressed steel. That all our chassis have not cracked up long ago possibly shows that the designer knew what he was doing.