de Dion axle

[Cherian Thomas]

I'm new to this FSAE business, and I'm trying to compare a de Dion rear end with the usual double wishbone setup. I was wondering if anyone could offer their opinions.

Ignoring unsprung weight and packaging concerns, on a smooth track (and how smooth is an FSAE track?) it seems to me that the lack of camber compromise with a de Dion makes it superior to the traditional IRS. Am I missing something? And if it is better, don't the same arguments apply at the front end as well? How much of an issue is the increase in US weight?

Would love to hear from Paul Clausen and anyone involved with Brown's de Dion cars.

Regards,
Cherian Thomas

PS: Just read Z's post where he reckons a solid rear is a performance advantage. I guess what I'm really wondering is why more teams don't go for this setup?

[Cherian Thomas]

I'm new to this FSAE business, and I'm trying to compare a de Dion rear end with the usual double wishbone setup. I was wondering if anyone could offer their opinions.

Ignoring unsprung weight and packaging concerns, on a smooth track (and how smooth is an FSAE track?) it seems to me that the lack of camber compromise with a de Dion makes it superior to the traditional IRS. Am I missing something? And if it is better, don't the same arguments apply at the front end as well? How much of an issue is the increase in US weight?

Would love to hear from Paul Clausen and anyone involved with Brown's de Dion cars.

Regards,
Cherian Thomas

PS: Just read Z's post where he reckons a solid rear is a performance advantage. I guess what I'm really wondering is why more teams don't go for this setup?

[Z]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Cherian Thomas:
Would love to hear from Paul Clausen and anyone involved with Brown's de Dion cars.
Just read Z's post... </div></BLOCKQUOTE>
Cherian,

I've rambled on about it quite a bit, and there are pics of Clausen's car on one of the threads. Use the "Find" button with appropriate keywords/names/etc...

Z (sounding like Denny)

[clausen]

Hi Cherian,

Unsprung weight isn't too much of a concern. our car had almost exactly the same rear US weight as the 03 car, and the axle was a little bit overweight still. Packaging is a bit more "entertaining" but not too terrible.

The one downside is the lack of independance and it's effect on single wheel bumps. There is obviously going to be some interference to the left hand contact patch if the right hand contact patch encounters a bump. There's no doubt that this problem exists, but I couldn't think of a decent way to quantify it, which I should have been able to do if i was going to be able to claim that the benefits outweigh this.

A big benefit with regard to bumpy tracks is that you can run a much more compliant suspension because you don't have to worry as much about losing camber due to roll.

[Z]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by clausen:
The one downside is the lack of independance and it's effect on single wheel bumps. There is obviously going to be some interference to the left hand contact patch if the right hand contact patch encounters a bump. There's no doubt that this problem exists, but I couldn't think of a decent way to quantify it... </div></BLOCKQUOTE>
Since I am going on about this subject on several other threads, I may as well add some more here http://fsae.com/groupee_common/emoticons/icon_smile.gif.

So how can the bump at the right wheelprint effect the left wheelprint? I reckon two main ways (neglecting steer effects, etc.) - change in camber angle, and change in vertical load.

A beam-axle (eg. De-Dion) will definitely change the left wheel's camber angle when the right wheel hits a bump. If the beam has a stiff axle-bounce mode and softer axle-roll mode (as is normal) then a bump at the right wheelprint will INCREASE the left wheelprint's vertical load.

An independent suspension will only change the left wheel's camber angle if the bump at the right wheel changes the body's roll angle. If the "independent" wheel pair have a soft axle-bounce mode and stiffer axle-roll mode (because of a stiff ARB), then a bump at the right wheelprint will DECREASE the left wheelprint's vertical load.

So which is worse - change in camber angle, or change (+/-?) in vertical load?

I figure that momentary change in camber angle has a smaller effect on grip than momentary change in vertical load, and decreasing vertical load is worse than increasing load ('cos of tyre "relaxation" time).

So possible advantage to beam... But bigger advantage to independent system with stiff axle-bounce, softer axle-roll (see posts re: Z-bars).

Z