Sorry old bud, but I did consider the lever arms. It is actually fairly
simple analysis.
mayf
Steve Laifman wrote:
> Mayf,
>
> While your numbers seem enlightening, and STATICALLY accurate, there
> are some grievous flaws. Your static weight distribution has nothing
> to do with the peak side loads on the fulcrum pin outer loads. While
> you have static weight distribution, you do not consider the lever, in
> the applied load transfer, that multiplies through the unequal arm
> suspension levers. With an offset teeter totter, you can lift the
> moon with little force, provided you have a place for the fulcrum.
>
> While that is an extreme example, it does illustrate the influence of
> leverage.
>
> Use the existing multiple lever design, and recalculate the maximum
> fulcrum pin bending loads at the thread relief.
>
> Steve
>
> ___
> Steve Laifman
> Editor - TigersUnited.com
>
>
>
> drmayf wrote:
>
>> Steve, I am sorry, but I do not believe that backing loads are the
>> culprit. Here is why. The car has a weight distribution of about
>> 50/50 and it weighs around 2500 pounds. That puts 1250 pounds on the
>> front suspension and about 625 pounds on the indicidual front tires.
>> Even if the coefficient of friction was 1, which it isn't, then the
>> maximum force that the tire can transfer to the spindle is 625
>> pounds: otherwise it just slides. If that force acts perpendicular to
>> the A arm centerline and all the load is on the lower arm then the
>> torque couple at the arm bushings is about 390 ft lbs. on each end of
>> the fulcrum. Remember, that the upper arm also take a significant
>> portion of the side loads and the real force is much lower. Taking
>> the force couple and resolving it into forces, the force near mid
>> point of the bushings on the A arm is about a 1000 pounds. If the car
>> is being backed then the car is going slowly and that is about the
>> max force that can be applied. However, if the car is making a turn
>> around a corner which has a dip in it for drainage (like just about
>> every corner on the planet) then the car is diving into that outer
>> wheel and that adds more down force to the tire. More down force
>> means more friction force that the tire can transfer to the A arm. I
>> suspect that since we go forward more than we go backwards that this
>> is far more likely to add to the failure. I am sure thee any number
>> of other engineers on the list who can sit down and generate a free
>> body diagram and do a far better analysis than my back of the envelope.
>>
>> Never the less, the real issue, is not whether they fail in backing
>> or driving forward, it is that they fail unexpectedly and sometimes
>> catastrophically.
>>
>> mayf, out in pahrump
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