Why are front forks all upside down??

Stephen Greenwood wrote:
On Sep 24, 12:56 pm, "Leo Lichtman"
wrote:
"Jon_C" wrote: Can anyone tell me why all MTB forks (all the ones I've

seen) have the stanchions (chrome inner part) at the top and the sliders (cast outer
part) at the bottom? (clip)
^^^^^^^^^^^^^^^^
Several years ago a friend of mine installed a set that are right-side-up
according to your standards. )I have forgotten the brand.) They used
elastomer inserts of various "constants" to adjust the springiness--he
carried an assortment in his pocket, but seldom found a need to change them.

I agree with you that the tubes should be on top. As I recall, though, this
involves complications in mounting caliper brakes, since you can't attach
them to the lower stantion. (I'm really fuzzy on this part.)


There are various forks like the OP describes, and I think I know
which fork Leo's friend had: the Halson Inversion. I've never seen it
myself, but I do recall seeing magazine ads for it in the early- and
mid-1990's, years before disc brakes were generally available for
MTBs. I don't know if Halson is still in business, but I on Ventana's
website I found this snippet describing the way that this fork solved
the brakes-must-move-with-wheel problem:

"An inverted suspension fork is a great idea on paper. The strongest
part of a fork needs to be at the top, next to the crown. It makes
good engineering sense to use the large-diameter alloy part on the
top, and put the smaller-diameter, moving part on the bottom. Not only
is this a better use of materials, supporting the bearings and sealing
its moving parts is made easier with an inverted arrangement. Known as
"upside-down forks," the idea has been borrowed from motorcycles (even
though professional motorcycle racers are returning to right-side-up
forks).

The fly in the ointment of upside-down forks is the brakes. They must
be close to the rim, and that means ten inches above the front axle.
Since the upper part closest to the rim of upside-down forks doesn't
move, it's hard to get the brakes to follow the rim. This problem has
sidetracked most inverted fork concepts into the waste can. Halson
Inversion forks solved this problem by slotting the upper alloy
section of its fork. The cantilever bosses move up and down inside the
vertical slots without having to depend on a disc brake. You get
superb bearing overlap, increased rigidity and less unsprung weight
(the part of the suspension that follows the ground on upside-down
forks)."

The link below has the full article from the April 1995 issue of
Mountain Bike Action:

http://www.ventanausa.com/mba0495.html

Stephen Greenwood



Good link, thanks. Another bunch of user reviews:
http://www.mtbr.com/reviews/Front_Sh...ct_21662.shtml

People seemed to find it nice and stiff.

Jon_C wrote:
Hi,
Can anyone tell me why all MTB forks (all the ones I've seen) have the
stanchions (chrome inner part) at the top and the sliders (cast outer
part) at the bottom?

Two reasons why this is backwards:
-The max stress occurs at the top of the fork so this would be the
logical place to put the larger dia, stiffer slider.
-The bottom half of the fork is unsprung weight, which needs to be
minimized to help the suspension work well, so this is the ideal place
for the lighter stanchion.

I know it's a bit easier to manufacture them with the stanchions at
the top but that should only concern low-end manufacturers.

It's been done the other way too, but I think stiffness becomes the problem.

On Wed, 26 Sep 2007 21:50:45 +0100, Zog The Undeniable
wrote:

Jon_C wrote:
Hi,
Can anyone tell me why all MTB forks (all the ones I've seen) have the
stanchions (chrome inner part) at the top and the sliders (cast outer
part) at the bottom?

Two reasons why this is backwards:
-The max stress occurs at the top of the fork so this would be the
logical place to put the larger dia, stiffer slider.
-The bottom half of the fork is unsprung weight, which needs to be
minimized to help the suspension work well, so this is the ideal place
for the lighter stanchion.

I know it's a bit easier to manufacture them with the stanchions at
the top but that should only concern low-end manufacturers.

It's been done the other way too, but I think stiffness becomes the problem.


Most high end forks I've had apart have the spring on one side and the
shock on the other. Some have the piston acting INSIDE the upper tube
making it "rightside up" even though it looks "upside down".The large
lower "outer" needs to be stiffly connected side to side when the
spring is only on one side and the damper only on the other.

--
Posted via a free Usenet account from http://www.teranews.com

clare at snyder.on.ca wrote in message
...

Most high end forks I've had apart have the spring on one side and the
shock on the other. Some have the piston acting INSIDE the upper tube
making it "rightside up" even though it looks "upside down".The large
lower "outer" needs to be stiffly connected side to side when the
spring is only on one side and the damper only on the other.

Which is why Maverick use a 24mm axle front wheel for their forks.

cheers,
clive

Cannondale Lefty?
Upside down fork, no issue with left-right connection (spring/damper),
sealing and brakes (disk only). Pretty smart if you look at it this
way (I never did)

wrote:

Cannondale Lefty?
Upside down fork, no issue with left-right connection (spring/damper),
sealing and brakes (disk only). Pretty smart if you look at it this
way (I never did)

It still has to have a funny axle and hub. And brake, if you consider
disc brakes funny.

Chalo

wrote:
Cannondale Lefty?
Upside down fork, no issue with left-right connection (spring/damper),
sealing and brakes (disk only). Pretty smart if you look at it this
way (I never did)

How can something with only one leg be a fork?

--
Tom Sherman - Holstein-Friesland Bovinia
A Real Cyclist [TM] keeps at least one bicycle in the bedroom.

--
Posted via a free Usenet account from http://www.teranews.com

Chalo Colina wrote:
wrote:
Cannondale Lefty?
Upside down fork, no issue with left-right connection (spring/damper),
sealing and brakes (disk only). Pretty smart if you look at it this
way (I never did)

It still has to have a funny axle and hub.

Are you calling the four (4) single-sided Phil Wood hubs I have funny?

And brake, if you consider disc brakes funny.

Quite a few tadpole trikes have single-side mounted drum brakes.

--
Tom Sherman - Holstein-Friesland Bovinia
A Real Cyclist [TM] keeps at least one bicycle in the bedroom.

--
Posted via a free Usenet account from http://www.teranews.com

Tom "Johnny Sunset" Sherman wrote:
wrote:
Cannondale Lefty?
Upside down fork, no issue with left-right connection (spring/damper),
sealing and brakes (disk only). Pretty smart if you look at it this
way (I never did)

How can something with only one leg be a fork?


there's hope for you yet!

wrote:
Cannondale Lefty?
Upside down fork, no issue with left-right connection (spring/damper),
sealing and brakes (disk only). Pretty smart if you look at it this
way (I never did)

Tom "Johnny Sunset" Sherman wrote:
How can something with only one leg be a fork?

In the olden days, a bicycle had 'forks'. The term became singular at
some point, obviously more singular with that thing.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971