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[GMCnet] Braking performance of the standard system [message #108918] Sat, 18 December 2010 22:30 Go to previous message
Charles Aulgur is currently offline  Charles Aulgur   United States
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Registered: March 2006
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Message: 15
Date: Sat, 18 Dec 2010 17:29:24 -0800
From: Jim Kanomata <jimkanomata@gmail.com>
Subject: Re: [GMCnet] Braking performance of the standard system
To: gmclist@temp.gmcnet.org
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<AANLkTi==Pa+zgzHKt4VSef3fivBBf9oHf8HTPDpA9BcO@mail.gmail.com>
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Gary,
I 'm with you in saying that we can out stop any with the reaction
arm system.


On Sat, Dec 18, 2010 at 12:11 PM, Kosier <gkosier@roadrunner.com> wrote:

>
> ----- Original Message -----
> From: "Hardie Johnson" <hardie.j@gmail.com>
> To: <gmclist@temp.gmcnet.org>
> Sent: Saturday, December 18, 2010 1:03 PM
> Subject: Re: [GMCnet] Braking performance of the standard system
>
>
>
>>
>>
>> Gary Casey wrote on Sat, 18 December 2010 08:32
>>
>>> I've done some calculations related to the braking performance
>>> of the standard braking system using a spreadsheet. ?I the
>>> results are interesting, but not too startling. ?Some of the
>>> assumptions:
>>> 1. ?The braking effort on each wheel is proportional to the
>>> static weight distribution, which I assumed is 36% on the
>>> front and 64% on the rear (32% on each rear wheel).
>>> The rear suspension pivot is 12 inches from the ground and the
>>> swing axles are 18 inches long. ?The front suspension has no
>>> anti-dive geometry.
>>> Here are some of the results: ?At about 0.5 G decceleration
>>> the rears will lock.
>>> <trim the rest>
>>>
>>
>> That is a very interesting analysis and much in line with what
>> I have worked out with basic mechanical statics diagrams. It is
>> why I think no amount of fooling around with the rear
>> suspension will make a big change in braking distance.
>>
>>
>> --
>> Hardie Johnson "Crashj"
>>
>
> You guys can do all your calculating and make your spreadsheets,
> but I have the reaction arm brake set-up and I can out-brake
> you and all your spreadsheets. ?And that's reality.
>
> Gary Kosier
>
Gary, I could not say it any better then you did. I developed the
rear brake reaction arm system over five years ago and have given
numerous seminars on the subject but very few people understand what
I have been talking about. As Steve F has stated to me several times
"when I start talking about rocket science and vector analysis I just
turn people off and everyone goes to sleep."

I just got a call from Jim K. talking about the brake discussion
taking place on the net and he wanted me to help him explain the
reaction arm system so I will try once again. I'm not sure the GM
engineers knew what was going on when they came up with the swing arm
suspension. It was great for providing the smoothest riding RV on
the market and the lowest "step-in" of any other RV but the rear
braking system was not up to par with the rest of the outstanding
design they came up with.

The brakes on a swing arm suspension act totally different then
brakes on most any other vehicle. When the brakes are applied on the
mid-axle of a GMC, all of the restive torque generated by the brakes
has to be reacted thru the backing plate to the outer end of the
suspension arm, which applies an equal and opposite torque trying to
rotate the suspension arm in a CW direction around the wheel axle.
This torque has to be reacted thru the suspension arm rotation pen to
the vehicle frame. The loads on the pen are determined through
vector analysis (I can hear Steve now). The friction between the
tire and the road surface is what determines the loads applied to the
suspension pen which results in a force (vector) pointing from the
center of the tire/road interface upward in a straight line to the
suspension arm pen. The resulting rearward horizontal load on the
support pen is the force that is slowing the vehicle. The almost
equal upward vertical load on the support pen is reacted by lifting
the rear of the vehicle and is not providing any force to help slow
the vehicle and is totally wasted energy.

The rear wheel brakes act just opposite to the mid-axle brakes in
that the force vector from the tire/road contact point is pulling
down in a straight line on the rear suspension arm pen. Same as the
mid wheel, only approximately 1/2 of the forces generated by the
brakes is pushing rearward horizontally and is helping slow the
vehicle. The downward vertical force on the pen is reacting the
nearly opposite vertical force generated by the mid wheel and cancel
each other out during normal braking conditions. Thus, during normal
driving only approximately 1/2 of your braking ability is being
utilized in slowing your vehicle and the other 1/2 is totally wasted.

Things get much worse when you do a panic stop. Within a fraction of
a second after applying full brake pressure, the mid wheel brakes
lifts the rear of the coach until the shock bottoms out, shifting
most all the rear coach weight to the mid wheels and lifting most of
the weight off the rear wheels. That is the screeching that everyone
hears making them think they have good brakes. It is almost
impossible to slide the mid wheels with drum brakes unless you have 2
3/4" wide CM shoes and much larger brake cylinders.

In conclusion, by installing the rear brake reaction arm system that
is available from Jim K, you gain back the 50% you are now wasting
with the OEM brakes during normal driving and the best part you gain
back the 150% you lost with the OEM brakes during a maximum pressure
stop. With the reaction arm system you have full six wheel brakes
with each rear wheel having approximately the same braking capability
as as an OEM front wheel. Your rear brakes will last about twice as
long and you only need to apply about 1/2 the brake petal pressure
during normal driving.

Chuck Aulgur
La Mesa, CA
76 Royale with the same great brakes as Gary Kosier and a few others
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