waggy
|
| posted on 17/1/15 at 01:47 AM |
|
|
I thought the biggest weight factor to be considered when changing from live axle to de-dion was the change in unsprung weight, a disc braked de-dion
setup would have significantly less unsprung weight than a disc converted live axle setup.
Do the right thing, right, first time!
If only it was that simple!
|
|
|
|
|
Sam_68
|
| posted on 17/1/15 at 02:45 AM |
|
|
quote:
Originally posted by waggy
I thought the biggest weight factor to be considered when changing from live axle to de-dion was the change in unsprung weight, a disc braked de-dion
setup would have significantly less unsprung weight than a disc converted live axle setup.
Yes indeed. You'd taking the weight of the diff. and half of the weight of the driveshafts out of the unsprung weight.
Lightweight cars are very sensitive to unsprung weight, so on anything other than very smooth tracks, the slight penalty of a de Dion in
overall weight is usually worth it for the much larger benefits in terms of ride grip and traction.
You need to be careful, though: because it's a structurally inconvenient shape, even a well-designed de Dion tube will weigh more than the tube
of a live axle, so eroding some of the advantage, and a badly designed de Dion can actually end up with little or no advantage even in terms of
unsprung weight, which makes it an almost complete waste of time...
I say almost complete, because the only other thing that a de Dion does is to decouple the axle from the torque reaction of the propshaft (and
from the brakes, if you use inboard discs).
|
|
|
Oddified
|
| posted on 17/1/15 at 09:38 AM |
|
|
I see the dedion axle as a half way house between a live axle and independent. If done right as mentioned above then it's less unsprung weight
but it still connects one wheel to the other so any bump on one wheel still effects the other side.
If i was going to change from a live axle, i'd go full independent as either would be quite a bit of work.
Ian
|
|
|
Sam_68
|
| posted on 17/1/15 at 10:24 AM |
|
|
quote:
Originally posted by Oddified
... but it still connects one wheel to the other so any bump on one wheel still effects the other side.
If it's done right (which admittedly it seldom is) then there are ways of overcoming that in terms of transmission of bump forces.
A bump at one wheel will still affect the camber angle at the other wheel, but then you've got to balance that small disadvantage against
the quite large positive factors that a de Dion will keep the wheels at a perfectly fixed angle to the road under all combinations of heave, squat and
roll, and that there's no jacking effect... neither of which an independent suspension can achieve.
It's also worth remembering that we frequently ruin the main advantage of an independent suspension by bolting on a Beam Axle Conversion Kit
(AKA an anti-roll bar) ...which is necessary to combat the large roll angles generated by the low roll centres you are forced to use on an
independent suspension to avoid large amounts of jacking. With a beam axle, no jacking = no need for low roll centres = no need for an ARB.
I'm playing Devil's Advocate, of course - as much as I like beam axles, I'm forced to admit that you need an exceptionally good de
Dion design to match a merely competent independent design - but surprisingly good things are possible if you are careful enough.
[Edited on 17/1/15 by Sam_68]
|
|
|
Oddified
|
| posted on 17/1/15 at 11:43 AM |
|
|
quote:
Originally posted by Sam_68
quote:
Originally posted by Oddified
... but it still connects one wheel to the other so any bump on one wheel still effects the other side.
If it's done right (which admittedly it seldom is) then there are ways of overcoming that in terms of transmission of bump forces.
A bump at one wheel will still affect the camber angle at the other wheel, but then you've got to balance that small disadvantage against
the quite large positive factors that a de Dion will keep the wheels at a perfectly fixed angle to the road under all combinations of heave, squat and
roll, and that there's no jacking effect... neither of which an independent suspension can achieve.
[Edited on 17/1/15 by Sam_68]
Absolutely, but the same could be said for a live axle 'if it's done right'. A dedion 'should' have less unsprung weight
but otherwise is no different to a live axle if both are done correctly. Independent suspension is a whole different world with pro's and cons
to work into the design. Everything is a compromise.
Ian
|
|
|
Sam_68
|
| posted on 17/1/15 at 12:14 PM |
|
|
quote:
Originally posted by Oddified
Absolutely, but the same could be said for a live axle 'if it's done right'. A dedion 'should' have less unsprung weight
but otherwise is no different to a live axle if both are done correctly.
Well, apart from being decoupled from the propshaft's torque reaction (and brake torque reaction, if you choose to use inboard discs).
Also, it's easier to build in (or add adjustability of) toe and negative camber on a de Dion than it is on a live axle.
But yes, in terms of basic geometry, they're identical.
|
|
|
coozer
|
| posted on 17/1/15 at 02:24 PM |
|
|
Don't forget its inertia that kills diffs and gearboxes, the torque required to move the mass of the vehicle forward is what puts these things
under stress, the less weight, the less inertia required to move the mass, the less stress on the driving parts.
So maybe beefing up the axle checking the spring and damper settings or relocating the mounting points, using a watts linkage? to improve tracking
and bump??
Mate of mine has a 73 mk1 escort with a 550bhp cosworth engine. Its totaly stripped out but he's a big lad, probably wieghs about 600kg, the
thing can lift the front wheels! Standard axle with group 4 half shafts and a plate LSD, single leafs and remote gas dampers.. Goes very well..
Plenty of high horsepower scorts on live axles about..
1972 V8 Jago
1980 Z750
|
|
|
alfas
|
| posted on 18/1/15 at 04:32 PM |
|
|
quote:
Originally posted by alfas
what dampers are installed?
re-newing 1 single damper is a no-go
who re-newed the bushes and dampers? you?
what type bushes have been fitted?
whats the spring rate of your coils?
who setup the suspension? and why it was setup to the actual measurements?
what are the measurements for camber, castor and tracking
was the rear axle ( even its not adjustable) measured to? what are the values?
was corner weighing done with the weight of the driver on the seat?
still no answers......
|
|
|
scootz
|
| posted on 18/1/15 at 05:25 PM |
|
|
Would you not be better off just buying a IRS chassis? There's a fair amount of difference at the back-end of the 2 Striker variants... the
tunnel measurements being the biggest PITA.
It's Evolution Baby!
|
|
|
alfas
|
| posted on 18/1/15 at 07:18 PM |
|
|
wouldnt it be easier to get the basics done correctly first?
like 4 quality dampers, correctly valved for this car. trying with different coil rates. reducing unsprung weight (in case big wheels and /or heavy
alloys are fitted). new metalasitc bushes at the rear trailing arms (instead of poly“s) correctly mounted (bolts tightend when car is back on the
wheels), checking if chassis is straight and the axle is properly located.
all the live-axle sylva“s i have driven (which have been min. 10cars) usually had an IRS feeling compared to other live-axled (sevenish) cars ...e.g.
westfields, tigers, locosts which had a much harsher suspension.
|
|
|
