A rather radical GT6 for your time...

Alas I’ve been caught up making a tractor-driven screw-type log splitter for my dad so I haven’t had the chance to play around with the suspension-o-matic. However, I have been doing as much reading on roll centres and whatnot as I can get away with at work. Here’s what I’ve come up with so far.

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For minimal roll, you want a roll centre that’s quite close to the centre of gravity of the car in order to reduce the moment-arm between the two, minimising roll. However, as the suspension compresses in a turn, the roll centre will move as the suspension arms move. So, the usual practice is to have an upper wishbone angled downwards with the roll centre below the CoG, such that when you’re in a corner the roll centre will raise upwards and get closer to the CoG resulting in a reduction in the moment arm the more the car rolls.

However, on the Spitfire suspension the upper wishbone/leaf spring is as far as I can tell pretty much horizontal, which will bias the roll centre to be higher regardless of the angle of the lower wishbone. That’s not necessarily so bad, although if my internal physics model is up to scratch it would mean that when cornering the roll centre will move upwards rather than downwards (I think that’s right).

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I’ve roughly sketched out where I think the main masses in the car are (mostly quite low actually with chassis, diff and gearbox right down low, most of the engine and GT6 tank (and most of me!) just above it, then a layer of fibreglass above that with a bit more steel up top with the roll hoop and hardtop). So, I think the CoG will be hovering somewhere around the level of the spring, if not a little below.

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So, as the roll centre will probably move downwards (from a place that’s already below the CoG), we probably want it to move as little as possible during cornering.

Next up for the head-physics model to wrap itself around is what sort of angle the wishbones need to be at relative to each other to produce a roll centre that doesn’t move much!

Does any of that make sense?