From: jwgst2+@pitt.edu (James W Gourgoutis)
Newsgroups: rec.bicycles.tech
Subject: suspension questions
Date: 7 Jan 93 20:41:40 GMT
Organization: University of Pittsburgh

Hi!
	I'm an engineering student (now in grad school 8*)) and I have the
intense desire to work for a bicycle company.  After sending out a few resumes
to a few companies, and getting the typical "we'll keep your resume on file"
response (if any!), I've decided that I need to do something to prove my
worth to a potential bike company employer.  Therefore, I've decided to 
design my own bike.  Understand, that this is probably something that will
never be built, it will only serve as a design exercise.
	I've come to the conclusion that "designing" bikes is kind of a 
misnomer, because I THINK (stress that!) that it is just a matter of deciding
on what kind of tubeset you want to use.  There is no real "engineering" 
involved.  In other words, you don't really need to do any analysis on the 
frame, since the materials you will ultimately use are pretty much 
predetermined.  Am I right?  Please correct me if I'm wrong!!!!
	Therefore, I've decided that the best type of bike for me to design
that would showcase my design skills is a full-suspension mountainbike, since
this will take some "real engineering".
	What I would like to try to do is incorporate a rising-rate suspension
in my design.  Basically what this means is that the bigger the bump, the 
stiffer the suspension gets.   MX motorcycles and snowmobiles use this type of
technology, and it works.  It allows you to use a relatively soft spring, to
give a cushy ride over small bumps, and still provide a lot of spring for big
pounders.
	I have done some very simple graphical analysis on two rear 
suspensions:  the Specialized and the Diamond Back, and these APPEAR to be 
rising rate.  However, I'm not yet absolutely certain.  Basically what I've
done is checked the wheel travel vs. the spring compression, to see if a 
linear or non-linear relationship exists.  If it is non-linear, then it is 
rising-rate.  I'm pretty sure that the Specialized is rising-rate, since it
uses a four-bar linkage, which is the key to rising-rate.  A bellcrank is 
used to give a nonlinear relationship between wheel travel and spring travel.
	I was wondering if anyone knew anything about this type of suspension
and its use on bicycles.  If rising-rate suspensions exist on bikes, I would
like to find some other "hook" to use in my design, since it probably won't
have much impact if it already exists.  I would eagerly like to discuss this
with anyone if anyone knows anything about it.   Thanks.
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James Gourgoutis       				   
Mechanical Engineering                                O   
University of Pittsburgh                           _ /__,     
e-mail me at:  JWGST2@unixd.cis.pitt.edu          (_) /(_) 
	       or JWGST2@vms.cis.pitt.edu
Thanks!           			   "Why am I so late?  It took me 
					    25 minutes to decide which bike
					    to ride!"--me. 
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Newsgroups: rec.bicycles.tech