"BiTurbo228 - Dr Frankenstein of Spitfires" (biturbo228)
05/09/2015 at 06:43 • Filed to: Spit6
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"BiTurbo228 - Dr Frankenstein of Spitfires" (biturbo228)
05/09/2015 at 06:43 • Filed to: Spit6 | 2
| 6 |
This is the standard GT6 rear suspension (with CVs instead of a rubber rotoflex joint). The lower wishbone and the radius arm pointing forward form a virtual lower A arm locating the lower end (giving something approximating a high-angle semi-trailing arm suspension). The leaf spring connects to the top of the vertical link and bolts to the top of the diff. The issue is that that makes the upper link far longer than the lower link, meaning you get positive camber as the wheel compresses under load, which is bad for traction out of corners.
Back in the ‘60s, Triumph was developing a GT6 LeMans car to follow in the footsteps of the Spitfire LeMans racers. They had this setup which replaces the lower wishbone and radius arms with two rods that bolt to the chassis and form a virtual A-arm in line with the top link/leaf spring (like a double wishbone setup):
This still has the issue of camber change as the suspension compresses due to having a longer upper link, but it sorts the toe changes when compresses/relaxed that are endemic to a semi-trailing arm-style rear suspension (part of the reason E30s are so tail-happy).
Now, this guy on my Triumph forum (the chap with the !!!error: Indecipherable SUB-paragraph formatting!!! ), has changed the lower rod mounts from the side of the chassis to underneath it, lengthening the lower A-arm and reducing camber change.
However, the top link is still longer than the bottom so what camber change there is is in the wrong direction (positive as it compresses). So, the idea I’ve had is this. A common diff upgrade for these cars is a Subaru/Nissan R160. The guys who do this often switch to coilovers mounting on the shock towers (or inner wing, but that’s not really strong enough), with a long rod running to the diff like this:
My idea is to weld a bracket onto the chassis above the driveshaft (in-line with where the stock inner wishbone mounts on the setup above) and run a short rod from there to the vertical link (about half the length of the upper link above).
And I thought I was done with my chassis modifications :S
E. Julius
> BiTurbo228 - Dr Frankenstein of Spitfires
05/09/2015 at 06:50 |
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Wow this was a really cool read. Suspensions are definitely a weak point in my automotive knowledge. So is the idea behind your proposed modification that the arms would then be equal (or approximately equal) in length, avoiding the camber changes under compression?
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BiTurbo228 - Dr Frankenstein of Spitfires
> E. Julius
05/09/2015 at 07:07 |
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Pretty much yeah :) ideally I want the upper wishbone to be slightly shorter so that when the suspension compresses (like when you’re mid-corner) I get a couple of degrees of negative camber, keeping the wheel flatter to the road as the car rolls.
The negative point that I can see from that is that under braking when the front dips and the rear rises I’ll get positive camber which will reduce grip. However, hopefully because they wishbones will be more equal than in the stock setup that camber change won’t be that much and it’ll be a net positive overall.
So, old suspension setup probably more stable under braking, my suspension setup should be more stable in cornering and under power :)
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E. Julius
> BiTurbo228 - Dr Frankenstein of Spitfires
05/09/2015 at 07:10 |
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Ok, cool. Thanks!
4muddyfeet - bare knuckle with an EZ30
> BiTurbo228 - Dr Frankenstein of Spitfires
05/09/2015 at 07:57 |
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This is turning into a brilliant rebuild. Weight reduction, suspension modification, strengthening... I’m in awe. Are you leaving any room for later adjustment, or just welding and hoping?
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BiTurbo228 - Dr Frankenstein of Spitfires
> 4muddyfeet - bare knuckle with an EZ30
05/09/2015 at 09:46 |
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Thanks :) I’ll have adjustable rods like the above setups, but I can’t think how I’m going to build fore-aft adjustability into the mounts on the chassis. Probably just going to measure out carefully and weld them on with a mockup of the suspension in place :)
Mylowales
> BiTurbo228 - Dr Frankenstein of Spitfires
04/10/2017 at 04:31 |
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Have you got any more info like where get brackets ect as i want one for my self?
that can email me at mylowalesg@gmail.com