Austin 7 Special

Got springs today. $25 for a pair. I hope to use them as front quarter-ellipticals. Each leaf is 45mm wide and 6mm thick.

I ground off the retainers and pulled the 3 leaves apart ... and figured I'd used a ~400mm long section of the middle leaf.

So I set up a test rig, clamped one spring to the bench and carefully measured the deflection at the point where my axle will be, for a given load at that point. One spring sagged exactly 6mm for 5kg load.

So with 2 springs it will sag half of that: or 3mm for 5kg. If my Kart weighs, say, 240kg all up (excluding the unsprung front wheels and axle) and if say 1/3 of this carried by the front axle, that's 80kg on the front axle or 16 x 5kg, so the springs (and body) will drop 16 x 3mm or ~48mm from its unweighted position when at rest, and drop a further 48 mm from a 1G "bump". Putting it another way - if someone about 80kg leant down hard on the front of the kart, they'd lower the front by about two inches.

So I think I'll run with that and not chop the leaves in half lengthways. It seems to me that, using a spring as a cantilevered quarter-elliptical effectively halves its effective stiffness, compared to using it as a full semi-elliptical, supported at both ends. Makes sense because only half the spring is present and working.