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Re: [ST] A different brake fluid question



Do you mean John?

 From my original post:

"Now, really, I doubt you will feel it, even though I could instrument 
the hoses and measure it.  The return in ease of bleeding would surely 
offset the extra hose expansion."

And I did say 2%.  The original question was why did a mechanic say you 
might end up with a softer lever with 2 hoses.  Imagine the effect with 
2 rubber hoses that you can see expand!

Rod Brown wrote:

>Steve,
>I here what you say, BUT you are making an assumption that the amount of
>expansion is "significant."  I'm not sure when you already have SS lines
>that the assumption is valid.  Getting that air bubble out of the cross over
>may far outweigh the expansion, IF there is a trapped air bubble.
>Rod
>  
>
>>The effect can happen and is due to "hoop" stress.  Hoop stress is that
>>which splits a tube long-ways.  A large tube has higher hoop stress than
>>a small diameter tube because of the larger inside surface area.  That's
>>why 6" sch 40 has thicker walls than 1/2" sch 40.
>>
>>Higher hoop stress means great tube expansion for the same internal
>>pressure.  A second hose means twice the expansion of one hose at any
>>pressure.  Since the caliper pistons still need, say, 800 psi for 1g
>>deceleration, a second hose doubles the system expansion for that same
>>800 psi (if one hose stretches 2% at 800 psi and needs 2% more fluid,
>>then 2 at 800 will stretch 4%).
>>
>>    
>>
>
>
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- -- 
John Albright
'02 RS
'00 748
Chattanooga
C-RATs


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