Conversion kit

Triumph: Spitfire MK1, MK2 and MK3 (1962-70)

to Swing Spring rear axle

Early Spitfire models featured a rear suspension design known as ‘Swing Axle’ whereby the driveshaft acted as a lower link in the suspension and the transverse leaf spring (bolted on top of the differential) doubled as the upper link. The the handling performance of the axle is somewhat flawed. The now infamous ‘wheel tuck’ results in a sudden loss of rear end grip if the driver ‘lifts-off’ or if a rear wheel hits a bump mid-corner. The solution is known as the ‚Swing Spring’. Rather than having a rigidly-mounted transverse leaf spring, only the lower leaf of the spring is bolted onto the differential. The remaining leaves are mounted in a box with a pivot through it so that the upper leaves are ‘floating’. This means that the roll centre is no longer fixed in a single position and can move slightly as the wheel moves – projecting cornering loads closer to the ground and thus reducing the ‘jacking’ loads. The tyre is therefore less likely to gain extreme positive camber as with swing axle setup. However, as the upper leaves of the spring are no longer clamped in place, the roll resistance is reduced significantly (the ability of the spring to resist the car rolling). To compensate for this, a bigger (and therefore stiffer) front anti-roll bar is fitted to reduce body roll. The result of all of this is that the tendency for sudden oversteer is greatly reduced and the car feels more ‘sure-footed’ when being driven quickly. The biggest improvement will be noticed when hitting bumps midway through a fast corner - instead of a heart stopping sideways ‘hop’ the car will instead feel more balanced.