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Paul Geithner 01/12/2013 19:51	re : lames arriere
Please pardon my use of English in this reply but I guess something may be getting lost in translation. dyngo: The vertical links do not remain vertical when switching from short to long swing axles. The tops of the vertical links can't move outward any further because the length of the spring is the same, but the vertical link attachments to the hub carriers move outward because the swing axles are each 1 inch longer and so these pivot points each move outward 1 inch. The vertical links have to rotate to accommodate the hub carriers moving outboard. As the vertical links rotate, the top of the vertical links get about 0.2 inches closer to the ground. Because the car is suspended from the spring and the spring is now ~0.2 inches lower, the chassis is now 0.2 inches lower. Because swing axle camber is strictly a function of the height of the u-joint attachments relative to the height of the hub carriers, then the switch from short to long swing axles results in an additional ~0.7 degrees of negative camber. This is what is illustrated by my animation of this effect comparing short and long axles. If you doubt this, directly compare a short-axle Spitfire and and long-axle Spitfire and measure the angles of the vertical links (as well as the distance between spring attach points. the distance between hub carrier pivot points, and the track widths). Alternatively you can build a cardboard model and simply observe what happens. GT676: The rear of the chassis (and hence the rear of the car) does indeed hang from the spring. The differential is sprung mass--it is part of the chassis. The differential is suspended from below the spring--it hangs from it. If you install a shim between the differential and the spring, the car lowers and the camber of the swing axles gets more negative, hence the reason that such a shim when used on the Spitfire is termed a "lowering block." Try detaching the differential from the spring, or detaching the differential from the chassis, while leaving everything else alone--where does the chassis go? Where do the wheels and tires go? Where does the spring go? If you doubt all of this, go take a Spitfire apart and see for yourself. I would also refer you to Standard-Triumph suspension engineer Ralph Wigginton, but unfortunately he died last December. This can be difficult to conceptualize in the mind, so why not just get up from your computer, so to your car, get your hands dirty, take stuff apart, keep and open mind and learn by observing? This is science and engineering after all, subjectable to experimentation, testing and objective observation and is not a matter of opinion or conjecture.

Paul Geithner

01/12/2013
19:51

re : lames arriere

Please pardon my use of English in this reply but I guess something may be getting lost in translation.

dyngo: The vertical links do not remain vertical when switching from short to long swing axles. The tops of the vertical links can't move outward any further because the length of the spring is the same, but the vertical link attachments to the hub carriers move outward because the swing axles are each 1 inch longer and so these pivot points each move outward 1 inch. The vertical links have to rotate to accommodate the hub carriers moving outboard. As the vertical links rotate, the top of the vertical links get about 0.2 inches closer to the ground. Because the car is suspended from the spring and the spring is now ~0.2 inches lower, the chassis is now 0.2 inches lower. Because swing axle camber is strictly a function of the height of the u-joint attachments relative to the height of the hub carriers, then the switch from short to long swing axles results in an additional ~0.7 degrees of negative camber. This is what is illustrated by my animation of this effect comparing short and long axles. If you doubt this, directly compare a short-axle Spitfire and and long-axle Spitfire and measure the angles of the vertical links (as well as the distance between spring attach points. the distance between hub carrier pivot points, and the track widths). Alternatively you can build a cardboard model and simply observe what happens.

GT676: The rear of the chassis (and hence the rear of the car) does indeed hang from the spring. The differential is sprung mass--it is part of the chassis. The differential is suspended from below the spring--it hangs from it. If you install a shim between the differential and the spring, the car lowers and the camber of the swing axles gets more negative, hence the reason that such a shim when used on the Spitfire is termed a "lowering block." Try detaching the differential from the spring, or detaching the differential from the chassis, while leaving everything else alone--where does the chassis go? Where do the wheels and tires go? Where does the spring go?

If you doubt all of this, go take a Spitfire apart and see for yourself. I would also refer you to Standard-Triumph suspension engineer Ralph Wigginton, but unfortunately he died last December.

This can be difficult to conceptualize in the mind, so why not just get up from your computer, so to your car, get your hands dirty, take stuff apart, keep and open mind and learn by observing? This is science and engineering after all, subjectable to experimentation, testing and objective observation and is not a matter of opinion or conjecture.