Subject: [Tigers] Torque Arm under braking force diagram?

From: "Doornbos, Daniel" <[email-masked]>
Date: Mon, 11 Feb 2013 20:13:05 +0000

I've been thinking about the Torque Arm Impact to breaking.  I am still
planning to order and use a Torque arm but wanted to think out the issue and
the physics of what was happening.  I drew out a simple force diagram to see
if I can understand what's happening under braking vs. under acceleration.
The torque Arm design is to STOP rotation of the rear axle under acceleration
that leads to wheel hope from spring wind up.  In my force diagram I assumed
springs as ridged for transfer of force as spring wind up/release isn't a
common braking problem.

Envision a static diagram of a wheel, leaf spring, leaf spring mounting
points, and the torque arm mounting points it might provide logic to what is
taking place.
-       Assuming fwd motion as a wheel rotating counter clockwise.
-       Brake forces result in an opposite clockwise force
o       This leads to a Clockwise moment of force applied around the axel
o       This leads to forces on the axel mount points to the body
*       Rear Spring point force is down
*       Front spring point force is UP
*       Torque arm mount point force is up

Maybe because the force is UP during braking and the Torque arm is Longer than
the springs it has a great mechanical advantage in acting to LIFT the car and
transferring the center of gravity further forward than it would be without
the torque arm?    The act of braking is adding energy to the system so it's
not a balanced equation and its dynamic with additional loadings beyond what I
have thought out by making it a simple static system.
-       A simple assumption might be that the arm takes up whatever forces are
normally applied due to spring wind up.   But likely it also takes some of the
leaf spring loads as well and then applies it more forward in the car body.
-       Reports that Torque arms decrease braking performance indicate some
kind of lift of the rear or that the center of gravity is shifted forward
under braking because of the upward force causing the rear of the car to
unweight?

Possible improvements for braking while maintaining acceleration performance
would be to allow for only Downward force application of the torque arm at the
spring point.
-       One way Hinged arm that goes open not allowing an upward force to be
applied?
o       Drawback is that a one way hinge would likely be a weak point with
frequent failure
-       Oval shaped dampener (rubber bushing that was shown at the front
transmission mount) that allows for upward travel of the torque arm under
braking but preloaded to always make contact to the bottom for acceleration?
o       Drawback on availability of an oval dampener, also likely to be noisy
rattling from top to bottom under transitions from stopping to going.
-       Mounting point?  Further rearward mount of the torque arm link?
Closer to spring perch?
o       Drawback negative impact to suspension travel/ride quality
-        Stiffer springs?  Less wind up and less load under braking?
o       Drawback negative ride impact.

What's interesting is the opposite force diagram for acceleration shows how
the torque arm shifts weight to the rear of the car allowing for more force on
the rear wheels and better traction at launch.  What are others thoughts?
It's been a long time since I've had static and dynamic classes and I've never
had to use them for work.

dan
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From: [email-masked]
Date: Tue, 12 Feb 2013 22:25:47 +0000 (UTC)

Bob, 

Many thanks for sharing your rather sobering spinout experiences and the technical information. The latter is going to take me more than one read to understand everything, but I am getting the picture! I am thinking that the Tiger's short wheel base is not helping things in our particular application. 

I am inclined to enjoy twisty roads whenever found (and hopefully more autocrossing in the future). A potential unpleasant surprise under heavy emergency braking in a sharp corner is not something I want to risk. If I was just drag racing, or doing stop light burnouts, that would be a much different situation. 

Fellow Listers, 

I, for one, am still looking forward to hearing any experiences with the Caltrac system. It appears to only control axle rotation in the acceleration mode and the axle is otherwise unrestrained in braking. Seems like a good application for the Tiger, in theory at least. 

Gene 

----- Original Message -----
From: "Bob H" <[email-masked]> 
To: "Tigers" <[email-masked]> 
Sent: Tuesday, February 12, 2013 2:31:30 PM 
Subject: Re: [Tigers] Torque Arm under braking force diagram? 

For the more technically oriented in this group: 

http://www.unbalancedengineering.com/Product_Development/Development%20of%20the%20Unbalanced%20Engineering%20Decoupled%20Torque%20Arm.pdf 
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From: " Ron Fraser" <[email-masked]>
Date: Tue, 12 Feb 2013 19:51:29 -0500

It seems to me we might be missing some variables with the setup
since there are variable results.  Possibly different front or rear spring
rates or maybe brake pads and type of tire.

I'm going to throw in another idea.  Anyone look at Air Ride technology for
the Tiger?

Ron Fraser

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
On Behalf Of [email-masked]
Sent: Tuesday, February 12, 2013 5:26 PM
To: Bob H
Cc: Tigers
Subject: Re: [Tigers] Torque Arm under braking force diagram?

Bob,

Many thanks for sharing your rather sobering spinout experiences and the
technical information. The latter is going to take me more than one read to
understand everything, but I am getting the picture! I am thinking that the
Tiger's short wheel base is not helping things in our particular
application.

I am inclined to enjoy twisty roads whenever found (and hopefully more
autocrossing in the future). A potential unpleasant surprise under heavy
emergency braking in a sharp corner is not something I want to risk. If I
was just drag racing, or doing stop light burnouts, that would be a much
different situation.

Fellow Listers,

I, for one, am still looking forward to hearing any experiences with the
Caltrac system. It appears to only control axle rotation in the acceleration
mode and the axle is otherwise unrestrained in braking. Seems like a good
application for the Tiger, in theory at least.

Gene

----- Original Message -----
From: "Bob H" <[email-masked]>
To: "Tigers" <[email-masked]>
Sent: Tuesday, February 12, 2013 2:31:30 PM
Subject: Re: [Tigers] Torque Arm under braking force diagram?

http://www.unbalancedengineering.com/Product_Development/Development%20of%20
the%20Unbalanced%20Engineering%20Decoupled%20Torque%20Arm.pdf
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From: [email-masked]
Date: Thu, 14 Feb 2013 21:33:33 -0500 (EST)

The only observation I'd make is the rubber bushing design does not allow  
for any possible de-coupling of the torque arm under braking. As others have 
 pointed out, there are a number of other variables at play here, including 
wheel  rates f/r, dampers used, brake bias etc, that could either magnify 
or lessen the  effect.
 
The other thing I'm thinking about is the instant center and anti squat, in 
 terms of off corner/on throttle affect.
 
I believe the torque arm brings forces into play which I'd prefer to avoid, 
 if possible. The one thing I do like is the ability to have good forward 
bite  with softer rear spring rates and the lack of bind in roll.

In a message dated 2/12/2013 5:31:40 P.M. Pacific Standard Time,  
[email-masked] writes:

Ron,
I think the main variable is the specific design of the  torque arm
(geometry, construction and mounting techniques). I assume the  production 
GM
F-body design has many compromises due to cost and packaging.  I'd expect a
well engineered aftermarket setup would avoid the performance  related 
concerns
on brake lockup unless it was designed primarily for  straight line
applications.

With this in mind, I'd have little  concern on how Dan's works,
or my Griggs Racing setup. I will admit that I  have yet to risk my Tiger by
pushing hard enough to find the limits,  especially since my Spec Miata is 
so
much ea$ier to replace in a worst case  scenario.

Stephen 
________________________________
From: Ron  Fraser <[email-masked]>
To:
[email-masked]; 'Bob H'  <[email-masked]> 
Cc: 'Tigers'
<[email-masked]>  
Sent: Tuesday, February 12, 2013 6:51 PM
Subject: Re:
[Tigers]  Torque Arm under braking force diagram?

It seems to me we  might
be missing some variables with the setup
since there are variable  results. 
Possibly different front or rear spring
rates or maybe brake  pads and type of
tire.

I'm going to throw in another idea.   Anyone look at Air Ride technology
for
the Tiger?

Ron  Fraser

-----Original  Message-----
From:
[email-masked]  [mailto:[email-masked]]
On Behalf
Of  [email-masked]
Sent: Tuesday, February 12, 2013 5:26 PM
To: Bob  H
Cc: Tigers
Subject: Re: [Tigers] Torque Arm under braking force  diagram?
Bob,

was
just drag racing, or doing stop light  burnouts, that would be a much
different
situation.

Fellow  Listers,

I, for one, am still looking forward to hearing
any  experiences with the
Caltrac system. It appears to only control  axle
rotation in the acceleration
mode and the axle is otherwise  unrestrained in
braking. Seems like a good
application for the Tiger, in  theory at least.
Gene

----- Original Message -----
From:  "Bob H" <[email-masked]>
To:
"Tigers"  <[email-masked]>
Sent: Tuesday, February 12, 2013 2:31:30  PM
Subject: Re: [Tigers] Torque Arm under braking force diagram?

For  the more
technically oriented in this  group:
http://www.unbalancedengineering.com/Product_Development/Development%20of%20
the%20Unbalanced%20Engineering%20Decoupled%20Torque%20Arm.pdf
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/ Virus Database: 2639/6099 - Release Date:  02/12/13
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