Donuts Dual Purpose?

[type26owner]

I've been thinking through the ramifications of replacing the rubber
donuts halfshafts with a constant velocity joint axles system before
proceeding. It seems that the compliance of the donuts have a centering
effect which in essence is somewhat over-constraining the coil over
springs on the Chapman struts. To put it another way the donuts act as a
quasi-swaybar for the rear suspension. Has anyone noted an additional
bit of body roll when the conversion was completed?

After viewing the photos taken of my car at speed cornering at the GGLC
trackday it's obvious that sticker tires for cornering purposes are
going to be useless until I reduce the body roll substantially. I could
benefit from someone posting a picture of their rear sway bar setup that
you're happy with.
--
Keith Franck

Martinez, California

[rodney]

Keith

I have still got donuts so I cannot say whether putting CV joints on has
your explained consequences, but I cannot see how the donuts act as a
quasi-sway bar.
They may add to the spring rate of each side of the car individually, but a
sway bar transfers pressure from one side of the car to the other using the
body/chassis as a pivot point.

I suppose one of the main problems with the donuts is that their effect on
the spring rate varies depending on where they are in their rotational
position.

Rod

Rodney Stevens
CSIRO Minerals
http://www.minerals.csiro.au

Ph. 61 2 97106701
Fax 61 2 97106789

Personal Home Page
http://mywebpage.netscape.com/rodjohnst ... mePage.htm


-----Original Message-----
From: keith franck [mailto:***@***.***
Sent: Thursday, 21 March 2002 5:06 PM
To: ***@***.***
Subject: [LotusElan.net] Donuts Dual Purpose?


I've been thinking through the ramifications of replacing the rubber
donuts halfshafts with a constant velocity joint axles system before
proceeding. It seems that the compliance of the donuts have a centering
effect which in essence is somewhat over-constraining the coil over
springs on the Chapman struts. To put it another way the donuts act as a
quasi-swaybar for the rear suspension. Has anyone noted an additional
bit of body roll when the conversion was completed?

After viewing the photos taken of my car at speed cornering at the GGLC
trackday it's obvious that sticker tires for cornering purposes are
going to be useless until I reduce the body roll substantially. I could
benefit from someone posting a picture of their rear sway bar setup that
you're happy with.
--
Keith Franck

Martinez, California

[motocicletta at aol.com]

I use my 65 S2 strictly as a street car so have not driven it hard enough to
see any such effect personally. What you are describing sounds like spline
lock. At the time that Elans were current the most common way of allowing
for the necessary change of length of the half shafts of IRS was a double U
jointed shaft with sliding splines. (If memory serves Datsun Z cars had
these). The problem was that under hard acceleration the driving forces on
the splines would keep them from sliding which would tend to lock the
suspension, not unlike the way it is hard to move a standard shift
transmission into neutral when you are accelerating This would have the same
effect as the spring rate suddenly going up very high. Among the reasons put
forth for Chapmans use of the donuts ( aside from weight and price) is that
they did not exhibt this locking tendency when the suspension worked under
acceleration. These donuts were used on the race cars as wellas the street
cars. If you are seeing something like this I would guess there is more
going on than just the donuts.
Jeff Manuel

[type26owner]

When a vehicle has no lateral force acting upon it and the body is level
a sway bar is stress free and generally so are the halfshaft donuts if
the car is aligned properly. Body roll caused by cornering bends a sway
bar and stresses it, which it resists by exerting a force to straighten
it's self back out. It's a restoring force which tries to cancel the
body's roll. Entropy! <bg> The donuts are distorted and therefore
stressed in a similar way when the body rolls. The sprint type donut are
very stiff and I'm guessing when stressed by cornering they resist with
at least 100 pounds force. Wouldn't be surprised if that value is low by
a factor of two or three.

Removing this restoring force contribution is going to make the car roll
at a faster rate. I can imagine it degrading the cornering ability from
the stock setup significantly.
--
Keith Franck

Martinez, California

[motocicletta at aol.com]

Certainly there is no free lunch and the donuts do absorb energy and will
have some effect on roll stiffness. When I compared these to a splined
u-joint shaft it was to point out that at the time these were the best option
open to Chapman. The only other commonly used (in racing cars) option would
have been the pot type U-joint which would have been heavier and more
expensive. Plunging CV joints did not become commonly available until the
mass introduction of front wheel drive cars in the 80's. The problem with
sliding splines is that when they lock or get tight the response is
non-linear whereas as the donuts will be much more so. The amount of energy
absorbed by the donut will be proportional to both the angle between the two
shafts and the power transmitted. In a light car like the Elan with a low
CG, and especially one set up for the track with stiffer springs and dampers,
the amount of roll is relatively small hence the angularity of the drive
shafts will be equally so. While I have no data to prove or disprove the
point my guess is that the impact of the donut in roll control is minimal as
compared with roll bars, springs and dampers and in any event it is
untuneable background 'noise' unless you want to put something like plunging
CV joints to work around it.

I will be interested to see what you have done with boring cylinders as I
have never been able to get closer than .004 to.005 due to chatter wihich
has to be honed out to get a good finish.
Jeff Manuel

[type26owner]

Hi Jeff,
Point taken on the torsional lock-up effect of a spline. If I'm not
mistaken the cv axles have four of them. With my 104hp though I'm hoping
it's not as annoying as the donuts' lurching. My point is if one
installs the cv axles then along with that a rear swaybar should be
added to not degrade the handling. Isn't Lotus ownership all about
pushing the envelope on occasion?

I too got tool chatter that looked like a washboard initially.
Remembered that way back it was not a problem and I just had to figure
out the solution again. Did it. I'll spend some time explaining how
later. Going off now to spend a play day spectating at the CSRG vintage
races today.

Here's why I'm thinking of tuning my suspension a bit more. Exiting turn
four at Laguna Seca in third gear at about 5k rpm in a 4-wheel drift
right to the edge.
<http://www.headonphotos.net/Galleries/2002/LOTUS-0304/Black%20Elan/pages/IMG_8289.htm>
--
Keith Franck

Martinez, California

[simonknee]

Cool pics!
The only time I've ever driven those corners in an Elan (or any other car)
is in GranTourismo 2!!!!

Simon

Here's why I'm thinking of tuning my suspension a bit more. Exiting turn
four at Laguna Seca in third gear at about 5k rpm in a 4-wheel drift
right to the edge.
<
http://www.headonphotos.net/Galleries/2 ... /pages/IMG
_8289.htm
<http://www.headonphotos.net/Galleries/2002/LOTUS-0304/Black%20Elan/pages/IM
G_8289.htm> >
--
Keith Franck

Martinez, California

[garyeanderson]

Hi Keith

I am not too sure of what you mean by "the cv axles have four of them"
unless your talking about 4 cv joints. I have them in my 65 Elan with
150 plus hp at the flywheel and I don't experiance any lookup. I have
Dave beans recomended fast road springs in front 115lb x 12inch with
adjustable platform spax shocks and a 7/8 inch front sway bar, in the
rear I had to use 140lb x 10inch x 2.5inch diameter with the
adjustable platforms to get the back of the elan to sit level (not
much weight in the back of a 1280 lb. elan). the elan rides on 175/50
x 13 Pirelli P7's, I uploaded a picture in the photos section
called "side view of lowered S2"

Gary

--- In lotuselan@y..., keith franck <kdfranck@p...> wrote:

[lotocone]

Keith,

I've uploaded a photo of an authentic (original, real, etc.) 26R chassis to our yahoo files collection. You will notice a pin or threaded stud protruding from the lower corner of the rear tower. I believe this is a factory mounting point for a rear sway (anti-roll) bar. That's about all I know about it (and that ain't much!).


--
Ken Claiborne
26/4396
50/0118N
So California



__________________________________________________________________

[Brian Walton]

I can't find the photo. Where did you put it?

Brian

[type26owner]

Thanks Ken,
Does that boss happen to extend through to the forward side of the box
section and have a weld there too? I assume the sway bar ends then point
forward. Could you show me the attachment point on the suspension.

Has anyone loosening the body and tilting it up in the rear to work on
the rear end? I'd like to do some gas welding on the chassis without
catching the bodywork on fire. I'll need access to drill some holes in
the chassis box section for attachment points too.
--
Keith Franck

Martinez, California

[lotocone]

keith wrote:


I created a folder called 26R chassis and moved that photo plus added an additional photo. It shows that the boss does not extend through to the front. If I were to add one, I think I would drill all the way through and weld both sides.


All I know is what you can see in the photos. As I said, that ain't much. I'm not 100% positive this really is the sway bar mounting, but what else could it be? I know who is now restoring this car and could probably find out.


I can't figure that out. Maybe someone else on the list knows.

I wish I could be more help.

--
Ken Claiborne
26/4396
50/0118N
So California



__________________________________________________________________

[kstrutt1]

Keith,

When I modified the backbone of My +2 to accept a sierra 5 speed
gearbox I simply cut a section of the body away using a fine toothed
saw and then re-bonded it back in when I had finished, this was both
quick and neat.

Kevin
73 _+2S130

[bigvalvehead]

Hi
Sorry i used your folder I'm new to this
I'll get my son to show me how to thumbnail pics and set up new folder
Dave
---- Original Message -----
From: ***@***.***
To: ***@***.***
Cc: ***@***.***
Sent: Wednesday, March 27, 2002 6:51 PM
Subject: RE: [LotusElan.net] Donuts Dual Purpose?


keith wrote:


I created a folder called 26R chassis and moved that photo plus added an additional photo. It shows that the boss does not extend through to the front. If I were to add one, I think I would drill all the way through and weld both sides.


All I know is what you can see in the photos. As I said, that ain't much.I'm not 100% positive this really is the sway bar mounting, but what else could it be? I know who is now restoring this car and could probably find out.


I can't figure that out. Maybe someone else on the list knows.

I wish I could be more help.

--
Ken Claiborne
26/4396
50/0118N
So California



__________________________________________________________________