All Reeeeet... I'm in...

I've got conformation to Tony Foale's Suspension and Chassis workshop
this weekend at Doc Wong's in Redwood City... who else is going???

I'm so excited... I'm going to give Doc a big hug for putting this on...

Larry L
94 RC45 #2
Have a wheelie NICE day...
Lean & Mean it in every corner of your life...
If it wasn't for us the fast lane would rust...
V4'S are music to the seat of my pants...
1952 De Havilland Chipmunk...
Yank and bank your brains loose...
http://members.ebay.com/aboutme/-xlax-/
http://home.comcast.net/~netters2/
http://www.fox302.com/index.pl?s=vg&user=netters2

 

Congrats Larry! Maybe Tony will shine the light on your riding flaws. I,
for one, am getting really tired of you being the last one at the rest stops
every time we ride. *hehehehehe*

 

Thanks Jason... I know... you're so quick on that old Whale that I'll
never catch up... you'll need to trade it in for the latest wonder bike
with a motor of death... then we'll see about riding together again...

I hoping Tony will shine the light on two areas...

1... why we are not tossing our heavy steel fork springs for free air???
2... will a long and low motorcycle handle as good as a short and high
one???

Larry L
94 RC45 #2
Have a wheelie NICE day...
Lean & Mean it in every corner of your life...
If it wasn't for us the fast lane would rust...
V4'S are music to the seat of my pants...
1952 De Havilland Chipmunk...
Yank and bank your brains loose...
http://members.ebay.com/aboutme/-xlax-/
http://home.comcast.net/~netters2/
http://www.fox302.com/index.pl?s=vg&user=netters2

 

Springs can be built with exponentially arranged rebound and
compression rates... air compresses linearly. So that too much air would be
required to prevent bottoming...and produce too stiff a front end.

But you know that...I think you are just goosing around with Tony.

As you know...within limits. No... long has a wider turning radius so
for back roads its going to be a problem... but not a problem on a soft wide
slab turn...but thats not where we are most concerned with handling... we
care about the tight stuff... and a long wheel base hampers those in the
most usual turns.

Short is an advantage on tight turns but can be a problem in real fast
high speed sweepers...wobbles are easier the shorter the bike is because the
axis of rotation around the steering head in a wobble scenario is shorter.
The tire patches have less leverage on that axis of rotation.

So its a compromise.




Low or not so low is a huge kettle of fish, I'd like to learn more about
that myself,

The worlds best flat tracker frame seats the rider about 4" higher than it
has to. My consideration is that 4" lower would be better...but thats not
whats winning for some reason. You posted a few years ago that when the
japanese tried a frame with the CG below the axles that it wouldnt turn very
well at all... a total disaster.. so these are complex issues that even the
best engineers in the world had not sorted out.

Somehow I think that if the CG is too low you loose or even reverse
gyroscopic leverage on the steering head but thats an opinion with just a
fuzzy gut feel behind it.


Phil Scott

 

to heck with that... BMW is tossing those heavy steel TUBES on a new bike
to be announced later this year... uses a 'Hossack' style front
suspension, which is dual A-arm with dual ball joints, the forks are a u
shaped alloy casting. its supposed to be considerably lighter than
telescoping forks, with less unsprung weight. uses a monoshock similar
to their current Telelever (which is a single A arm + telescoping tubes
system).

 

Actually its the reverse... air is too progressive.
So you can have the right spring rate near full extension
and way too stiff near full compression, or the right spring rate
near full compression and not enough spring rate at full extension.

Yamaha attempted to deal with this problem in their 1976 YZs by
adding a second large air cannister on each fork tube. It had
a piston seperating it from the fork legs. So you could put say
15psi in the fork legs and 25psi in the cannisters. When the fork
compressed far enough to put the pressure up to 25psi, the pistons
in the cannisters would start to move, effectively increasing the air
volume.

It still didn't work very well. The other problem with air "springs"
is that they press against the seals and cause increased seal drag.

Mountain bike suspension has, to a large extent, dealt with
this in the last 5 years.


Eric

 

you are a funny guy... look up the term 'progressive' for
starters. Air pressure in a closed vessel is a direct *linear correlation
to volume...in other words, cut the volume by half and the pressure doubles.

Moving a fork that much against a *progressively wound spring...will get you
vastly more than double the spring pressure (see the chart for the
sprangggg of yer choice).

*that tactic. two separate chambers at different pressures *would create
*progressive air shock.

Yer a little fuzzy in the head there... compression of course reduces
the air volume.


Phil Scott

take some math and science classses....then just think, you too could be
in the 5% catagory of folks in the US who understand basic physics

 

Air is also a lot more sensitive to operating temperature than steel...

M

 

Pressure is INVERSELY proportional to volume: PV = nRT
if we assume cylindrical geometry - the force is proportional to 1/V -
and volume is proportional to (Max_Travel - Travel) ... hence:

F_air ~ 1/(Max_travel - Travel)

for comparison:

F_spring ~ K*Travel (for a non-progressive spring. If it's prog.
we must integrate [K(travel)*dTravel])

The plots of force as a function of suspension travel are quite
different for air and springs. Force from air pressure increases much
more rapidly than linearly for part of the travel.

Advice we can all heed.

 

Oh puhleeese... yes its inverse of course its inverse...but its *LINEAR...
not exponential ..its the *linear nature that is the problem with using air
for suspension without springs...but the dual chamber you mentioned later
would have some progressive characteristics although not as much as is
available with a progressively wound spring and oil damping.

Linear son...can be direct or reverse...but its alway *straight line*
function...and thats the issue.

 

You are joking, right? Are you seriously saying that linear functions
and inverse functions are the same? It's gotta be a joke after you
berated that poor guy about learning physics. [Especially since hook's
law is obviously a linear relation between force and compression and the
gas law produces no such thing].

You have me confused with someone else ...

I am not sure what a linear son is so I cannot comment on how 'direct or
reverse' it may be ... but linear functions are *not* inverse functions.
Try ploting 1/x on a graph - it is not a straight line. (BTW: an
inverse function looks more like an exponential decay than either does a
linear function... maybe that was the cause of that poor guy's confusion.)

More importantly, the curve C/(X0-X) [This is the functional form for
the force of compressed air in this model] is *not* linear - for one
thing it goes to infinity as X-> X0 but linear functions don't approach
infinity over a finite range. Air is *very* progressive (at least at
the end of the travel).

Dude, if you are going to publicly chastise people for ignorance (and
further hurt the reputation of physicists) you gotta cover your tail.

BTW: I know exactly what you meant by "linear": the terms are first
order (in the gas law) - but we are concerned with the restoring force
curve as a function of suspension travel and compressed air pressure
(and hence force) is not linearly proportional to the suspension travel.
In the issue of restoring force of air vs. springs your contention that
the air is linear is either an irrelevance or wrong ... in any case it
is misleading.