CornCrake wrote:I assume that is the weight of everything excluding the un-sprung weight, eg weight excluding wheels & bearings?
Yes in theory but they don't weigh enough to make a significant difference
So far I have got an approximate minimum weight for the coach of 166gms, but I can easily add more, even if it is in the form of passengers!
Also I have since noticed that where I annotated 9mm for both the outside fulcrum measurement it is actually currently 9.5mm. I can reduce it, but not make it any wider. Are wider springs better than narrower springs?
Based on a 9.5 mm end overhang
If your vehicle ends up weighing 166gm the you want 11 thou wire.
If you weight it weighs above 210 gm you will need 12 thou wire
if you weight it weighs above 290 gm you will need 13 thou wire
If it gets much more than that its probably too heavy!!
Personally I think the 9 mm at the ends would be fine and it's worth leaving yourself a little room.
Based on a 9 end overhang, 11 thou is still right but add 10 grams to the limits above. I.e. it doesn't make a big difference.
Russ Elliot is keen on a longer spring but, while there is nothing wrong with his theoretical argument, I'm not convinced it makes a significant difference within the limits we work to. There's a lot to read on this
on the CLAG website.
That said very short end overhangs should be avoided as the calculation becomes less certain as the axle fulcrum moves too close to one end. I would suggest that a good rule of thumb which doesn't require complex calculations would be that we should avoid anything less than
the total wheel base/
no of wheels in your case that would be 8mm so you're OK.
While we are here it is also true that too long an overhang is equally undesirable and leads to unstable solutions which magify the effect of any minor inaccuracies, such as the actual location of fixed fulcrums or the location of the Centre of Gravity. Again a reasonable rule of thumb which should leave us in the methods sweet spot would be nothing greater than half the distance between the adjacent wheel sets.