[xk] Radial tires and intererence with skirts?

Has anyone ever installed a Panhard rod to better locate the rear axle?

Mike Eck
New Jersey, USA
www.jaguarclock.com
'51 XK120 OTS, '62 3.8 MK2 MOD, '72 SIII E-Type 2+2> Has anybody investigated whether this tire contact with the

skirt lock might be, at least in part, due to bad rubber
bushings in the leaf springs, allowing too much side
movement of the axle?

The MK2, which uses parallel leaf springs on a live axle, has a rubber
mounted Panhard rod for laterally locating the rear axle. I just thought I
might be able to bolt a spare one to the XK.

Mike Eck
New Jersey, USA
www.jaguarclock.com
'51 XK120 OTS, '62 3.8 MK2 MOD, '72 SIII E-Type 2+2>

First, they are not a good choice for a street driven vehicle with
a parallel-leaf spring suspension.

In reply to a message from BISHOP13 sent Wed 6 Aug 2008:

The smallest Sixteen Inch Radial tyre we can get
‘‘OTC’’ is a 205/70R16…
To ‘‘translate, the 205mm is the Cross-Section at
it’s widest point… that is 8 3/8’’.
the ‘‘70’’ means the tread of this tyre is 70% of the
Cross-Section, or about 5.75’’

Sorry Charles, that is not my understanding of the meaning
of the /70 in 205/70R16.
As I understand things, the figure after the / is the aspect
ration of the tyre. A /70 tyre will have a height equal to
70% of it’s width. These were initially known as low profile
tyres when they were introduced for the Jaguar XJ. These
days much lower profiles are often used down to /30 and
probably beyond. Where as prior to the introduction of the
low profile /70 tyres, tyres would have about the same
height as width.

Now some of the height is lost inside the wheel. Anyone know
how much?–
The original message included these comments:

The smallest Sixteen Inch Radial tyre we can get ‘‘OTC’’ is a 205/70R16…
To ‘‘translate, the 205mm is the Cross-Section at it’s widest point… that
is 8 3/8’’. the ‘‘70’’ means the tread of this tyre is 70% of the
Cross-Section, or about 5.75’’… not a lot of ‘‘tyre patch’’ improvement over
a late style 600x16, but it is an improvement as every little bit helps.


Ken XK150 FHC S824252, see her on xkdata + X300 3.2 Sport
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Ken G;
Yes, I agree… I’ve been told both ways, supposedly by “those who
know”… I’ve also been told that the “P-Metric” sizing and the “metric”
sizing are two totally different worlds… that is a “205/70” is not the same
size in both listings… Personally, I think the tyre people know less about
this stuff than the average tyre users does… Confusion is the watchword…
On the “new” “30” and “40” profiles, I find it’s easier to just refer to
them as “Rim Rubbers”… one inch of sidewall on a ten inch wide by
twenty-two inch tyre looks plain stupid, to me…
Charles #677556.----- Original Message -----
From: “Ken Green”

Sorry Charles, that is not my understanding of the meaning
of the /70 in 205/70R16.
As I understand things, the figure after the / is the aspect
ration of the tyre. A /70 tyre will have a height equal to
70% of it’s width. These were initially known as low profile
tyres when they were introduced for the Jaguar XJ. These
days much lower profiles are often used down to /30 and
probably beyond. Where as prior to the introduction of the
low profile /70 tyres, tyres would have about the same
height as width.

Now some of the height is lost inside the wheel. Anyone know
how much?

[Original Message]
From: BISHOP13 BISHOP-13@texican.net

On the “new” “30” and “40” profiles, I find it’s easier to just refer
to
them as “Rim Rubbers”… one inch of sidewall on a ten inch wide by
twenty-two inch tyre looks plain stupid, to me…

I agree, Charles!
Also the sidewall does not stick out past the rim hardly at all, and
therefore gives the rim no protection if you get too close to a curb.
And they are typically very expensive rims!
Guess how I found out in a snow covered parking lot, but there again, snow
covered obstacles are not much of a problem in Texas.
New XK’s probably have this problem, but not ours!
Roa

In reply to a message from Roar Sand sent Sun 10 Aug 2008:

Has anybody investigated whether this tire contact with the
skirt lock might be, at least in part, due to bad rubber
bushings in the leaf springs, allowing too much side
movement of the axle?–
XK120 FHC, Mark V saloon, XJ12L Series II
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Mike E;
I’ve looked into the possibility of adding one… the probable “best”
bolt-on item looks to be the Panhard Bars from the MK II Diff.
And, I believe Rob R is correct that worn “Link” bushings will cause the
120’s Diff to “slide” left and right more than good “live” bushings would…
The Spring Eye Bushings on the Leaf Springs just get hard when they go bad,
so I don’t think they would contribute to the diff moving very much… at
least not any more than it moved when new…
Charles #677556.----- Original Message -----
From: “Mike Eck”

Has anyone ever installed a Panhard rod to better locate the rear axle?

Mike Eck
New Jersey, USA
www.jaguarclock.com
'51 XK120 OTS, '62 3.8 MK2 MOD, '72 SIII E-Type 2+2

In reply to a message from Rob Reilly sent Wed 13 Aug 2008:

Could be, but the condition most commonly arises after a change to
radial tires, which are almost always some fraction wider than the
original bias plys. The kicker is that the radial sidewalls are
sooo much more flexible than the bias type, so the tire tread moves
around more under lateral loading.–
The original message included these comments:

Has anybody investigated whether this tire contact with the
skirt lock might be, at least in part, due to bad rubber
bushings in the leaf springs, allowing too much side
movement of the axle?


Mike Spoelker 672027
Louisville, KY, United States
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In reply to a message from Mike Eck sent Thu 14 Aug 2008:

First, they are not a good choice for a street driven vehicle with
a parallel-leaf spring suspension.

The rear axle on a leaf spring car travels in an arc described by
the front spring eye and the axle shaft centerline. Keep in mind
that a simple Panhard rod also swings in an arc, but in a plane 90
degrees out from the spring. This means that as the axle moves up
or down the rod exerts its own lateral force on the axle which may
be either the same or opposite to those of the cornering loads. It
will bind up where the axle arc does not coincide with the
transvers arc of the Panhard rod. They also will transmit lots of
road and suspension noise (maybe not an issue in an OTS with the
hood down) to the frame unless they are rubber bushed, which then
renders them less useful.

They also change the rear suspension roll center, which has a
distinct impact on the handling, adding a jacking effect to the
axle. Note that this won’t be the same for both a left and a right
hand turn. This is why you see the NASCAR boys, who only ever turn
left, save for the two road races they run, running their Panhard
bar frame-end pivot points up or down at each pit stop. Done
skillfully, changing the frame pivot point can cure or create
understeer or oversteer.

There is also not really much room to mount one in a 120 where the
battery boxes and fuel tank are in the way, not to mention that the
frame members behind the front spring eyes are very slender, not
like the beefy Mk-V bridge-beam sections back to that point, so it
would be very tricky to devise a frame mount that would transmit
the forces somewhere where you would not be bending the frame.

If you feel you require more lateral location under load, I think
you would be better served by having four plastic shims (washers)
made that would restrict the lateral movement of the front spring
eye in the mounting pocket. It would fit over the protruding end
of the front bushing sleeve and replace the steel washer which is
already there. Going straight down the road they would do nothing,
even with the usual axle compression and rebound. Under lateral
load they would restrict the lateral deflection of the spring eye
bushing.

Panhard rods are good for live axle oval track sedan racers where
the loads are always in the same direction. I know, I know, plenty
of road racers use them, but most of those cars have coil springs.

Best regards to all,–
The original message included these comments:

Has anyone ever installed a Panhard rod to better locate the rear axle?
Mike Eck

Has anybody investigated whether this tire contact with the
skirt lock might be, at least in part, due to bad rubber
bushings in the leaf springs, allowing too much side
movement of the axle?


Mike Spoelker 672027
Louisville, KY, United States
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Mike S;
Look at a XK’s Unlimited MK II Parts Catalog under Rear Suspension and
see how it’s Panhard Bar is attached. (Items #18 Bracket and #15 Rod
Assembly-- Not to be confused with the anti-wind-up bars #'s 7,8 &9). It
appears the MK-I & II use one bar, but I think two would be better,
especially on an XK120/140. Notice they do not attach 90 degrees to the
Leaf Springs, but mostly “in-line” with the leaf springs. Depending on the
length of the #15 Rod, a #18 “like” Bracket could fitted to the chassis side
rail in the “neighborhood” of the forward Spring Eye Mount.
If I could get my hands on one of these MK I/II Panhard set-ups (rod
assembly & bracket), I don’t think it would be too difficult to fabricate a
pair for an XK.
Done right, this would limit the XK’s rear-end assembly from dancing
around during hard cornering… with or without radial tyres…
Charles #677556.----- Original Message -----
From: “MikeSpoelker”

First, they are not a good choice for a street driven vehicle with
a parallel-leaf spring suspension.

The rear axle on a leaf spring car travels in an arc described by
the front spring eye and the axle shaft centerline. Keep in mind
that a simple Panhard rod also swings in an arc, but in a plane 90
degrees out from the spring. This means that as the axle moves up
or down the rod exerts its own lateral force on the axle which may
be either the same or opposite to those of the cornering loads. It
will bind up where the axle arc does not coincide with the
transvers arc of the Panhard rod. They also will transmit lots of
road and suspension noise (maybe not an issue in an OTS with the
hood down) to the frame unless they are rubber bushed, which then
renders them less useful.

Mike S;
I’m sure you have see it as well, but under some serious side-loading,
the tread of a radial tyre can move far enough to actually be out from under
the rim! I wonder if any street tyre is that “sticky”??
Charles #677556.

The kicker is that the radial sidewalls are----- Original Message -----
From: “MikeSpoelker”

sooo much more flexible than the bias type, so the tire tread moves
around more under lateral loading.

Charles,
When you are talking about two bars, are you talking about a “Watts” linkage?
That would eliminate most of the issues Mike is talking about, - I think, but it would be more challenging to execute.
Roar

In reply to a message from BISHOP13 sent Thu 14 Aug 2008:

Charles,

I have seen the aforementioned photos. I suspect that such
an event may be more a function of inflation and perhaps
sidewall flexibility than stickiness. And then again it
could be the way the suspension tucks under supporting or
enabling the whole process.
I run 205/70/15’s and I am still trying to work out optimum
tire pressures when slaloming the D-Type. Somewhere less
than 36 - there is no tire roll at all using the time
honored chalk on the tire technique and one can happily plow
on straight ahead on full lock with your foot on the load
pedal! 28psi on the road gives a slightly better ride but
don’t give the steering wheel a good wobble as I assume it
is sidewall flex, makes fo a n interesting moment. Note to
self - don’t do that… again.

I am using Kumho’s - light SUV tires so one would expect a
stiffer sidewall and compared to the previous Bridgestone
tires, which the only local equivalent were listed for Dodge
Caravans and the ilk they could be slightly stiffer at the
same pressure.

Anyway the point is that perhaps later radials do not have
as much sidewall flex as earlier designs or then again it
may be a function of the intended use of the tire.

Regards

Keith–
The original message included these comments:

I'm sure you have see it as well, but under some serious side-loading,

the tread of a radial tyre can move far enough to actually be out from under
the rim! I wonder if any street tyre is that ‘‘sticky’’??

sooo much more flexible than the bias type, so the tire tread moves
around more under lateral loading.


Keith Bertenshaw
Rockaway, NJ, United States
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Roar;
No. The Watts Linkage is more of a “Double Link” or “Ladder Bar” type
system… I’m not talking about any fundemental suspension change, just the
addition of a Panhard Bar… actually, two panhard bars… Mike S was talking
about a “Transverse” panhard bar… these are the most commonly seen. a
simple bar mounted on the left rear of the diff anf the right rear of the
body (that’s how my 122S Volvo is set-up)…
But, if we look at a Jaguar MK II Rear End, there is a single Panhard Bar
that goes from the right side of the differential housing (the “banjo” in
the center) over to the right Chassis Rail in the area of the Right Leaf
Spring’s Front Spring Eye Mount. There is just enough of an angle to keep
the rear end from moving left and right… I noted that I believe two (a
left & a right) of the MK II Panhard Bars mounted on an XK120 would be an
improvement.
Charles #677556.

Charles,
When you are talking about two bars, are you talking about a “Watts”
linkage?
That would eliminate most of the issues Mike is talking about, - I think,
but it would be more challenging to execute.----- Original Message -----
From:
Roar

Charles,
I am not sure what you mean by “Ladder Bar”.
What I am talking about is a three piece arrangement that locates the rear axle laterally.
The two longer bars are paralell to the axle (at least ideally when the car is at rest).
Each is attatched to the frame at their outer ends.
In the middle they are connected by vertical link.
This link is attatched to the diff housing in the middle.
This arrangement forces the center of the rear axle to move up and down only, and eliminates all lateral movement.
The outer end of each bar are attatched to the frame at different vertical hights, which is equal to the lenght of the center connecting link.
This link will rotate some back and forth as the rear axle moves up and down relative to the rest of the car.
Wish I could draw a picture.
A Watts linkage is the more elaborate and accurate version of the Panhard rod.
Serves the same purpose, which is to locate a live rear axle horizontally.
The longer the Panhard rod is, the less sideways motion of the axle as it moves up and down reative to the car, so you want to mount one end as far out on the chassis as you can, and the other end as far out to the other side on the axle.-----Original Message-----

From: BISHOP13 BISHOP-13@texican.net
Sent: Aug 14, 2008 5:12 PM
To: xk@jag-lovers.org
Subject: Re: [xk] Radial tires and intererence with skirts?

Roar;
No. The Watts Linkage is more of a “Double Link” or “Ladder Bar” type
system…

In reply to a message from roarsandnorge@earthlink.net sent Fri 15 Aug 2008:

I believe what you are describing is a three link. Several
varieties known to exist. Again, I seriously doubt you need this
on the street with skinny tires.

Regards,–
The original message included these comments:

Each is attatched to the frame at their outer ends.
In the middle they are connected by vertical link.
This link is attatched to the diff housing in the middle.


Mike Spoelker
Louisville,Kentucky, United States
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In reply to a message from BISHOP13 sent Thu 14 Aug 2008:

Yeah, but remember, the rear suspension design under a Mk-II is a
REALLY, REALLY an odd duck.

The front spring eyes mount in a conventional manner, but in the
middle of the spring - where in the rest of the civilized world one
finds the drive axle bolted - you find a reaction pad with the last
of the spring cantilevered out to the rear. There are no rear
spring shackles - that’s where the rear axle is pin-mounted (free
to rotate) unlike the XK axle which is clamped to the center of the
spring. On a Mk-II the parallel arms are required to resist the
torque of acceleration and braking. Otherwise the axle housing
would simply rotate around the mounting pins until the axle tube
crashed in to the springs.

BTW, cantilevered designs - either springs, beams or what not - are
very highly stressed compared to a member supported at both ends.
It would necessarily need to be much beefier to provide an adequate
measure of protection from failure due to fatigue.–
The original message included these comments:

But, if we look at a Jaguar MK II Rear End, there is a single Panhard Bar
that goes from the right side of the differential housing (the ‘‘banjo’’ in
the center) over to the right Chassis Rail in the area of the Right Leaf


Mike Spoelker
Louisville,Kentucky, United States
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Roar;
Here is a URL for the “Watts Linkage”:
http://en.wikipedia.org/wiki/Watt’s_linkage.
It is not a “Four Link” like I thought, although I’ve heard the “Watts”
term applied (incorrectly) to the four link type of drag bars.
Here is a URL for “Ladder Bars” and “Four Link” suspensions:
http://www.magnumforceracing.com/magnumforce_ladderbars_fourlink.htm
“Ladder Bars” and “Four Link” are old '50’s Hot Rod terms (and Drag
Racers)…
Their primary function is to keep the differential perpendicular to the road
throughout the suspension range (up and down)… Becuse of it’s four corner
mounting, there is limited lateral movement, but they aren’t “Panhard Bars”
in the strictist sense.
From looking at the animation in the “Watts” URL, I understand, now, what
you were trying to say… In the strictist sense, the Watts Linkage will
maintain the “Straight & Level” of a differential, providing the up/down
travel is confined within a cetain range… When the “limits” are reached,
the Watts Linkage tries to twist the rear end in an “S” motion.
Charles #677556.

Charles,
I am not sure what you mean by “Ladder Bar”.
What I am talking about is a three piece arrangement that locates the rear
axle laterally.
The two longer bars are paralell to the axle (at least ideally when the
car is at rest).
Each is attatched to the frame at their outer ends.
In the middle they are connected by vertical link.
This link is attatched to the diff housing in the middle.
This arrangement forces the center of the rear axle to move up and down
only, and eliminates all lateral movement.
The outer end of each bar are attatched to the frame at different vertical
hights, which is equal to the lenght of the center connecting link.
This link will rotate some back and forth as the rear axle moves up and
down relative to the rest of the car.
Wish I could draw a picture.
A Watts linkage is the more elaborate and accurate version of the Panhard
rod.
Serves the same purpose, which is to locate a live rear axle horizontally.
The longer the Panhard rod is, the less sideways motion of the axle as it
moves up and down reative to the car, so you want to mount one end as far
out on the chassis as you can, and the other end as far out to the other
side on the axle.----- Original Message -----
From: roarsandnorge@earthlink.net

In reply to a message from BISHOP13 sent Fri 15 Aug 2008:

Exactly. Charles’ keen eye has picked up on a subtle detail that
is unknown to, or ignored, by many - the center of the bellcrank
arm on a Watts link does not move directly up and down. A Watts
link is a better solution than a Panhard bar, but it still changes
the rear roll center in a non-uniform manner. And with three parts
compared to Panhard’s one, it’s more difficult to find the space to
mount the assembly.

Again, coil spring designs and/or big sticky race tires would find
this beneficial, skinny street tires, probably not.

Personally, I really like shimming the front spring eye. It’s
simple, cheap, doesn’t transmit additional loads to a weak part of
the frame, invisible, reversible and it doesn’t change the ride
quality or the fundametal handling characteristics of the car.–
The original message included these comments:

Here is a URL for the ''Watts Linkage'':

you were trying to say… In the strictist sense, the Watts Linkage will
maintain the ‘‘Straight & Level’’ of a differential, providing the up/down
travel is confined within a cetain range… When the ‘‘limits’’ are reached,
the Watts Linkage tries to twist the rear end in an ‘‘S’’ motion.
Charles #677556.


Mike Spoelker 672027
Louisville, KY, United States
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