Re: [ST] A different brake fluid question

[Colt45 <colt4530@xxxxxxxxxxx>]

It ain't rocket science, but it is tube science. 

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%). 

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. 

As the obsessive engineer that I am, I will not add a second hose.  I 
will unmount the left caliper and elevate it when bleeding.  It saves 
$40, too (what engineers live for).  Anybody know where I can buy just a 
M/C with a 5/8" bore?


Steven Kohlscheen wrote:

>
> I had a discussion recently with a non-Triumph shop manager about 
> this.  He advised against going to dual lines, unless I was reducing 
> inside diameter of the lines.  He said I would get an even softer 
> level replacing the crossover.  There's a hydrodynamics discussion 
> here, but I ain't smurt enough to really understand it fully.  
> Probably something about increasing the amount of fluid being 
> displaced/moved by the same sized cylinder isn't as efficent.  But I 
> have been told by a Triumph shop owner that he did an experiment on an 
> RS using 2 OEM Triumph long hoses, one to each caliper, and the owner 
> of the bike was pleased with the results.  Any thoughts out there? 
>  I've got the parts to do the dual OEM swapover, but now I'm hesitant.
>
- -- 
John Albright
'02 RS
'00 748
Chattanooga
C-RATs


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