Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Knackered AVOs

UPDATE!

Yesterday, and as an experiment, I lowered Monty's Mulfab front wishbone conversion front end by 23mm on the new Protech coil overs.

I brought the front end down to more or less where it was with the AVOs largely to test if the improvements I've experienced with the Protechs are only coming from their superior damping, or as I suspect, roll axis is also at play?

In theory the effects of lowering the front will be:

A 23mm reduction in ground clearance over the initial higher setting I’ve been running for the first few days with the Protechs

Pretty obvious really, however the car isn’t sitting much lower now than it was on the knackered AVOs, the Protech have much better damping & control, so I do not see that this one causing any issues


An increase in forward bias rake

Typically should improve high speed stability, this worked really well on my TVR


A reduction in the preload on the springs

The effect will be nominal as the 275 lb spring rate remains the same


A decrease in compression travel

Only an issue if I find the bump stops, the Protechs have far greater travel than the AVOs so I do not anticipate any issues here


An increase the rebound travel

Again, the Protechs have far greater travel than the AVOs so I doubt I need the additional articulation at full droop


A lowering of the centre of gravity (front end only)

Should improve turn in and cornering speeds


A decrease in the front roll centre

Should improve turn in, but may increase roll


A change the relationship between the front and rear roll centres (roll axis)

This is the big one, while a lower roll centre is better for handling, what's more important is the relationship between the front and rear roll centres, i.e. the roll axis


On a live axle the roll centre is the nose of the diff, this gives vehicles with this ancient arrangement a very high roll centre, typically a live axle is slung under the chassis but Morgan fitted it above the chassis, this was a trick used in the 1930's to make a car look lower and more sporty but it actually makes the roll centre even higher which is never a good thing for handling. Unlike Monty's adjustable wishbone front end, the roll centre at the rear its largely fixed. Excluding the lowing blocks, changing the roll centre front to rear (roll axis) can only really be achieved with the Protechs on the front, but I can definitely use them to change how Monty handles during cornering, his overall weight distribution and rake.

Changing the roll centre will transfer weight front to rear, more weight on the flawed rear suspension will make it work even harder, while more weight at the front will improve front-end grip and by taking some load of the rear may also improve overall ride quality. It all needs testing, for example lowering the front may have a negative impact on Monty's front end ride quality because as his tires move up and down relative to the body, the height of the roll centre causes a side-to-side motion of the tire contact patch which is clearly undesirable for smooth suspension articulation.

For many reasons the 23mm front end drop I dialled in yesterday has the potential to have a negative impact on Monty's handling and ride quality. However, changing the relationship between the front and rear roll centres is a real science and the results could easily go either way, ultimately the only way to find out is test it, so I'll report back here with my findings. Essentially what I'm looking to study and understand with this experiment is how the front end effects the rear, I've already proven a more compliant and well damped front end noticeably improves the behaviour of the rear suspension.

What I now need to study are the effects of altering the roll axis, i.e. the line drawn from the rear roll centre to the front roll centre?



Every car is different, to achieve better handling and go faster one must properly understand what the car likes and doesn’t like, and the best way to achieve this is to experiment with different setups until the Goldilocks settings are found.

After that, it’s back to accepting the limitations of the system, managing one’s expectations of what it can ultimately achieve, and of course being guided our old friend and mentor Wabi-sabi