How much unsprung weight do you really save going Dedion over a live axle? My racing guru calls Dedion "the answer to the question that nobody
asked".
Specifically, I'm comparing the merits of converting a Miata IRS (I think it's called MX-5 in europe) to Dedion, versus using a 1st
generation RX7 live axle. I expect the car to get a lot of track time, so I want a relatively sure thing handling wise versus the difficulty of
sorting out IRS.
A DeDion is basically a live axle without the mass of the diff in the middle. This isn't quite right, since the propshaft willnot contribute to the unsprung mass and the drive shafts contribution to the unsprung mass will be different.
Quite unscientific, but I imagine the numbers will add up somewhat like this...
Live axle:
whole axle (inc diff, tube, and both drive shafts)
+
half propshaft
+
half links (trailing, panhard, etc depending on setup)
De-dion:
de-dion tube
+
half drive shafts
+
half links
That leaves a difference of the diff, one drive shaft and half the prop.
[Edited on 24/10/05 by gutball]
quote:
Originally posted by gutball
Quite unscientific, but I imagine the numbers will add up somewhat like this...
Live axle:
whole axle (inc diff, tube, and both drive shafts)
+
half propshaft
+
half links (trailing, panhard, etc depending on setup)
De-dion:
de-dion tube
+
half drive shafts
+
half links
That leaves a difference of the diff, one drive shaft and half the prop.
i've often wondered this ..........
it always looks to me that the carrier wheel bearings / brakes for the de-dion is huge. Add to this that if you're going over a single axle bump
only half the live axle moves ......
love to see some proper figures.....
could someone with a de-dion weigh all the unsprung parts? (ignore trailing links / panhard rod / drive shaft)
if we get someone with a live axle to do the same (ignore the same bits as well) it would be an interesting exercise.
It no just the large saving in unsprung weight that give the de Dion an advantage other considerations come into it --- torque reactions, coupling
effects on single wheel bumps.
A live axle can give very good road holding on very smooth surfaces but as soon as single wheel bumps are encountered IRS or de Dion will keep better
contact with the road.
One of the troubles with Dedion is that while unsprung weight is lower than a live axle the unsprung weight is mainly concentrated on the outside of the axle, which can lead to the rear end being a little unsettled by larger bumps. With the extra overall weight and complication that comes with a Dedion I'd rather have a live axle.
The weight being concentrated at the ends is actually major advantage of the de Dion --- it reduces the transmision of upward motion from a single wheel bump to the body/chassis and hence disturbance to the wheel that dosen't hit a bump --- all due to coupling effects the late George Bishop wrote a very good article on it in "Car Design" magazine circa 1988/89 in which he covered the physics of a number of obscure dynamic effects on suspension.
It works and thats all I care. Every system has its drawbacks. Unless you have a F1 type budget I would stick with what has gone before....KISS
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don't suppose you could weight that big yellow bit and teh drive shafts (separately) could you?
means when i take my english axle to bits i can do the same and we'll get some comparisons.
quote:
Originally posted by britishtrident
It no just the large saving in unsprung weight that give the de Dion an advantage other considerations come into it --- torque reactions, coupling effects on single wheel bumps.
A live axle can give very good road holding on very smooth surfaces but as soon as single wheel bumps are encountered IRS or de Dion will keep better contact with the road.
Won't a trailing arm system be even lighter. You eliminate the pipe and panhard rod and can do a bit of tweeking.
Always have been conserned about the accuracy of a De Dion built at home. If a flange is welded on ever so slightly scew it is like that for ever.
quote:
Always have been conserned about the accuracy of a De Dion built at home. If a flange is welded on ever so slightly scew it is like that for ever.
A big advantage is that your trans tunnel can be smaller as the prop shaft & diff will no be moving, you can also run uneven axle lengths and have the pinion center-line of the chassis to give more butt room. To make the most you'd use inboard brakes, this will make the axle lighter and will also remove torque reaction on the axle when braking.
quote:
Originally posted by kango
Won't a trailing arm system be even lighter. You eliminate the pipe and panhard rod and can do a bit of tweeking.
Always have been conserned about the accuracy of a De Dion built at home. If a flange is welded on ever so slightly scew it is like that for ever.
quote:
Originally posted by kango
Won't a trailing arm system be even lighter. You eliminate the pipe and panhard rod and can do a bit of tweeking.
Always have been conserned about the accuracy of a De Dion built at home. If a flange is welded on ever so slightly scew it is like that for ever.
How would you set up the jigging to build an accurate de Dion (at home)
With the main carrier at an angle all the way to the flanges, it also needs to be cut very accurately. Then welding on the flanges... then the short
little tubes...
Lost of places to build up mis allignment.
quote:
Originally posted by kango
How would you set up the jigging to build an accurate de Dion (at home)
With the main carrier at an angle all the way to the flanges, it also needs to be cut very accurately. Then welding on the flanges... then the short little tubes...
Lost of places to build up mis allignment.