NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/rec/bicycles/tech/2814

Text File | 1992-12-23 | 10.8 KB | 259 lines

Newsgroups: rec.bicycles.tech
Message-ID: <[e-mail]>
From: [e-mail] (Hans-Joachim Zierke)
Path: sparky!uunet!zaphod.mps.ohio-state.edu!darwin.sura.net!jvnc.net!yale.edu!ira.uka.de!Sirius.dfn.de!mailgzrz.TU-Berlin.DE!math.fu-berlin.de!fub!sisyphos.owl.de!bi-link.owl.de
Subject: B. Rohloff on Rohloff chains
Date: Wed, 23 Dec 92 12:31:00 +0100
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I handed your comments about Rohloff chains over to Mr. Bernhard Rohloff.
As I expected, he likes to reply.  ;-)

I'm posting this text as a christmas present to Jobst, who helped me
understanding bicycle wheels years ago.

Any comments will be forwarded to Mr. Rohloff, who doesn't have access to
email.




Disclaimer: It's Bernie speaking.
------schnippel------------elektronische Abreisskante------------------------

Dear Dick King, Bernd Kischnick and Jobst Brandt,

we have followed your discussion of chain wear in which the
Rohloff chain played a certain role. As we have recognised some
uncertainty with regards to the construction of our chain and
the consequences on overall wear, we would like to submit the
following assignment.

For terminology purposes we start with a description of the
parts of any derailleur chain, which we will refer to during the
article:

1. Roller
2. Roller link plate
   - Inner link plate carrying the rollers on the outside of the
     integral bushings
   - Pins oscillate inside integral bushings
3. Pin (press-fitted in pin link plate)
4. Pin link plate
   -Outer link plate with riveted pins)


Jobst Brand writes:

>I don't believe for a minute that Rohloff bores non round holes
>in his components nor that he has oriented cam ground pins.

We don't know what 'oriented cam ground pins' are but we bet a
box of 20 "Paulaner Dunkles Hefe Weissbier" against a bottle of
original Southern Comfort that all roller plates of all Rohloff
chains do have non round holes! The exact shape of the holes is
called trochoide which you can create by deviding a round gateau
in three parts (of 120 degree) and then moving them a little bit
away from the center and connecting the circle periphery with
three tangent lines.
This form of the integral bushing results in some important
advantages of the Rohloff chain regarding wear of the chain and
the sprockets, flexibility and performance.
In addition, the outside shape of the bushings are of a
trochoide form as well which will be described later.

Jobst Brand writes:

> All this talk about Coulomb and elongation and the rest is
> speculation upon speculation. Let's cut out the pretentious
> jargon. Chains are a relatively well understood mechanical
> element and the machine industry has been using them for a
> century. The auto, aircraft, machine tool, and other
> industrial products use an amount of chains that far exceeds
> the paltry number of bicycle chains in use.

In contrast to the above mentioned uses of chains, the bicycle
chain is an important part of the shifting system. In addition
to performance, strength and low weight a bicycle chain must be
flexible sideways to allow shifting from one sprocket to the
other.
This is normally achieved by increasing the clearance between
the pin and the hole of the roller link plate (that is the
inside of the integral bushings). By this we can achieve 1
degree to 1,5 degree side to side flexibility per link.
However,the problem with increasing the clearance is that
  - the pressure and deformation of the parts increases with the
    concequence of faster wear of the pins
  - The chain can be twisted excessively around its longitudinal
    axis causing bad gear shifting qualities.

This is the first point where the construction of the Rohloff
chain shows substantial advantages.
The inside of the integral bushings, the 'holes', provide a 120
degree segment of the same diameter as the pin increasing the
contact area between pins and integral bushings. Elastic
deformation is therefore very low.
In addition, the force per area is reduced, in turn reducing the
wear of pins and bushings.
The opposite side of the contact area allows more space of
clearance than a conventional chain, with the result that the
chain achieves a side to side flexibility of more than 2 degree
per link. However, the twist around its longitudinal axis is
only 90 degrees per meter (79 links).
The Rohloff chain easily and directly follows the movement of
the derailleur and shifts faster and runs more silently.

However, grit, water and the missing of fresh lubricant do
shorten the life of any chain substantially and our chain is, of
course, not an exception. With a little bit of care the abrasive
wear of a chain can be reduced.


The pitch of the Rohloff chain

Jobst Brand writes:

> There has to be at least the tiniest bit of elongation of the
> side plates of a chain. I conclude this from the fact that the
> side plates of Rohloff chains (...) are purposely produced
> being 1/100mm too short. Rohloff claims this is done to
> prolong the chain's life, and that would be pointless if
> elongation is not a limiting factor to a chain's life at all.
> Indeed without elongation the side plates would never match
> their norm length of 1/2 inch.

Bernd Kischnick writes:

> So I thought, they (Rohloff) use segmented bearings against
> wear in the joints, then the shortened side plates are
> probably to compensate for another effect.
and
> Well, at least Rohloff says the underpitch does not prevent
> the chain to ride in the sprockets in a decent way, and that
> it does not introduce additional wear for the sprockets.

To discuss the quotes we concentrate on two points:

a. The exact pitch of a Rohloff chain
b. The effects of elongation on a chain


a. The exact pitch of a Rohloff chain
The discussion about the pitch of a Rohloff chain can be
summarised as follows:
  - principally, the Rohloff chain is notunderpitched, whether
    1/100mm or more.
  - due to the construction with the trochoide integral bushings
    the Rohloff chain has got different pitches for the roller
    link and the pin link. However, the mean pitch is exactly
    1/2 inch.

The pitch of the pins of the pin link is 12,5mm. Due to the
trochoide holes the pitch of the pins in the roller link is
under load 12,9mm because the pins nestle against the contact
area.

However, for the exact running of the chain only the pitch of
the roller is important because the force is transmitted via the
rollers on the chain wheels.
If the shape of the outside of the internal bushing were exactly
round, the pitch of the rollers would be 1/2 inch. Theis
trochoide shape of the outside results in different roller
pitches of the roller and pin link. The roller pitch of the
roller link adjusts in contact with the sprocket to 12,75mm
(5/100mm oversized), whereas the pin link pitch is 12,65mm
(5/100mm undersized). The mean is again 12,7mm or 1/2 inch.

To understand the advantages of these different pitches we have
to describe the consequences of wear in more detail.
Because of its construction the increase of the pitch due to
wear ONLY effects the roller pitch of the pin link! This means
that the roller pitch of the pin link of a normal chain is 1/2
inch plus 2 times the wear per link. An old chain destroys the
tooth profile of a chain wheel because the too long pin link
creeps up the tooth working face causing wear.

This is the reason why the Rohloff chain offers some advantages
as regards to wear of the whole transmission system. The pin
link, only subject to the consequences of wear, goes from "pitch
too short" through "pitch normal" to "pitch too long". With a
wear of 0,05mm per link the pitches of a normal chain are 12,7mm
and 12,8mm, the pitches of a Rohloff chain are both 12,75mm. And
when a chain is discarded at a wear of 0,1mm per link a
conventional chain measures 12,7mm versus 12,9mm, whereas the
Rohloff chain measures 12,75mm and 12,85mm.

The Rohloff chain starts with a slight difference of the pitches
but this difference is so small that it does not damage the
tooth profiles. However, this construction avoids the big pitch
differences, if the chain is nearly worn out. As this decreases
the damaging creeping up the tooth working face, the Rohloff
chain reduces the wear of the sprockets.

Due to the trochoide outside shape of the internal bushings the
contact area between internal bushings and roller (again a 120
degree segment) is bigger than of conventional chains. Like with
the pins, the result is a reduction of the force per area
decreasing elastic deforming and wear.


b. The effect of elongation on a chain
High performance derailleur chains have to transmit very high
forces of more than 400 kg (track racing, sprints and mountain
biking). Test have shown that normal chains elongate 0,1mm
per link or more under heavy load. Light chains with thin or
asymmetric plates or with hollow pins stretch most.
Again, the elongation mainly increases the pitch of the pin
plate adding to the problem discussed above.
Due to the large areas of contact between pin, integral bushing
and roller, the elongation of the Rohloff chain has been
measured under heavy load with a maximum of 0,05mm per link. The
result is a relatively low wear, especially in the high
performance sector in comparison with conventional chains.


Tim Bradshaw writes:

> However it would seem to be sensible to make chains initially
> slightly too short -- that way you keep inside the acceptable
> roller spacing for longer. I wonder why this isn't done more
> widely?

This reduction of the pitch is actually used by nearly all
manufacturers of derailleur chains to compensate for the
elongation of the running-in of a new chain that happens over
the first miles. Rohloff makes this as well, but it should not
be mixed up with the constructional undersized pin link and
oversized roller link. This is protected by Rohloff patents (EG
patent nr. 396701 of 10.12.92 and USA patent nr 5,140,806 of
25.08.92) and cannot be used by other manufacturers.

They try to optimise the performance by changing the shape of
the plates and by using new materials and coatings.
It must be said that especially the materials and the coatings
do play a very important role in determining the wear of a
chain. After having developed a superior construction of the
joint, we are now concentrating our research on finding more
resistant materials and coatings.

We hope that this article has helped to clarify both the
construction of the Rohloff chain and the effects of wear on a
bicycle chain.
However, we know that a technical discussion without pictures is
limited. We advise everybody who wants to know it exactly to buy
a Rohloff chain and measure the holes and internal bushings. The
best, of course, is to ride with the Rohloff chain and feel the
difference!

Merry Christmas and a Happy New Year to everybody on the
network!




Bernhard Rohloff