Bolt Hole Circles

"!Jones" wrote:

When you're talking about a bolt hole pattern on a chain
ring, you specify the radius and # of teeth, correct?

Normally the bolt circle _diameter_ and number of teeth.

The tandem timing ring has 32 teeth. The 5 holes measure about
29mm on center. Solving for the radius of the bolt hole circle, I get
24.67mm; however, I see nothing like that in any of the catalogs.
Am I on the right sheet of music here?

Is it a TA Cyclotourist (Pro 5 vis), Stronglight 49D, or one of many older
cranks that used a 50mm primary bolt circle? If so, TA rings are still
available. In the USA, try Peter White Cycles or Harris Cyclery (Google
will find you their web sites).

James Thomson

"!Jones" wrote:

Peter White just said in an e-mail that he has never heard of
a 50mm BC!

If you'd said TA pro 5 vis tandem timing rings, he would have understood
right away. But in any case, my advice was bad. Peter White says:

"I haven't stocked any Pro 5 Vis arms, chainrings or bottom brackets in
years."

http://www.peterwhitecycles.com/zephyr.asp

Oh, well. I have a mill so I suppose I can drill out a blank.

No need. Harris Cyclery can still help:

http://www.sheldonbrown.com/harris/f...ml#chainwheels

so can these guys:

http://www.tandemseast.com/chain.html

James Thomson

!Jones wrote:
-snip-
Peter White just said in an e-mail that he has never heard of a 50mm
BC! Oh, well. I have a mill so I suppose I can drill out a blank.

Perhaps a different approach? If Peter White says he's
never heard of a 50mm ring ( me neither) it probably is
_not_ a 50mm ring!

Why don't you just come right out and tell us what bike it
is, year and model , and any markings on the cranks or
chainrings? It would be so much quicker.

Earlier you asked about brakes on your Suntour-equipped
tandem, than a half-hour later said they were Mafac. It
doesn't help to be cryptic!

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

jones- you
specify the radius and # of teeth, correct? BRBR

Nope. BCD or bolthole chainring diameter is taken from a straight line of two
adjacent holes and a line perpendicular to that line to the opposite bolt hole.

Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"

On 27 Dec 2004 14:04:44 GMT, (Qui si parla
Campagnolo ) wrote:

jones- you
specify the radius and # of teeth, correct? BRBR

Nope. BCD or bolthole chainring diameter is taken from a straight line of two
adjacent holes and a line perpendicular to that line to the opposite bolt hole.


Peter, Peter, Peter...wrong! I've never actually measured a chainring
before, but your posting had me reaching for a chainring (Shimano SG
42), and a ruler. Turns out your method measures 118mm, but the true
bolthole diameter measures 130mm.


jeverett3ATearthlinkDOTnet http://home.earthlink.net/~jeverett3

Peter Chisholm wrote:

Nope. BCD or bolthole chainring diameter is taken from a straight
line of two
adjacent holes and a line perpendicular to that line to the opposite
bolt hole.

That method doesn't give the bolt circle diameter.


Tom Ace

A usually-reliable source wrote:

BCD or bolthole chainring diameter is taken from a straight line of two
adjacent holes and a line perpendicular to that line to the opposite bolt hole.

Nope, that's not correct. It is "measured" the cirucular arc, not from
a straignt line.

The easiest way to calculate this is to measure between two adjacent
bolts, then multiply that dimension by 1.7. and round up.

I've got a chart on a couple of different places on my Website that
lists this information:

http://sheldonbrown.com/gloss_bo-z.html#bcd

and:

http://harriscyclery.com/chainrings

Sheldon "Insert Nickname Here" Brown
+----------------------------------------------------+
| A little inaccuracy sometimes saves tons of |
| explanation. --H.H.Munro ("Saki")(1870-1916) |
+----------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

!Jones wrote:

On Sun, 26 Dec 2004 21:05:04 -0600 in

A Muzi said this:


Why don't you just come right out and tell us what bike it
is, year and model , and any markings on the cranks or
chainrings? It would be so much quicker.


It's an old Santana I picked up in a garage sale. I suspect it's an
'84 model or thereabouts. It's a chromoly frame, so it can't be any
older and, with the components it has, it's not any younger. It has
Suntour shifters and Mafac brakes. It also has a "child stoker kit"
installed which I'm going to remove and toss; however, this kit
introduced some spacing issues on the stoker timing ring... i.e., it's
a longer spindle.

You know, you're not under any *obligation* to help; I will manage to
muddle through somehow. OTOH, your advice is valued and appreciated.
I wasn't trying to obfuscate; I just didn't think anyone would really
want to hear the details of the junker I found.

(BTW, if anyone out there in Usenet-land happens to have their heart
set on a 50mm set up child stoker kit for an old tandem that uses TA
cranks, then now is the time to ask... it's incomplete.)

Jones

Such a nice bike! Everyone has an opinon.Here's mine.

I'd redo those brakes with modern cables and Kool Stop shoes
and ride it.

If you _and your companion_ find the fit, handling and the
concept of tandeming all to your taste, redo the gear system
later to something modern. That shouldn't keep you from
riding. There are some technical issues that make it
expensive because it's hard to do a partial gear system upgrade.

Everything you own is of good quality, assuming it isn't
worn out. So don't obsess over the details. Just ride for a
season and then worry about upgrades.

http://www.yellowjersey.org/photosfr...t/SGSANTAN.JPG


--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

John Everett writes:

specify the radius and # of teeth, correct?

Nope. BCD or bolthole chainring diameter is taken from a straight
line of two adjacent holes and a line perpendicular to that line to
the opposite bolt hole.

Peter, Peter, Peter... wrong! I've never actually measured a
chainring before, but your posting had me reaching for a chainring
(Shimano SG 42), and a ruler. Turns out your method measures 118mm,
but the true bolthole diameter measures 130mm.

I think this works better:

http://tinyurl.com/699er

Jobst Brandt

writes:

From:
Subject: Bolt Hole Circles
Date: Mon, 27 Dec 2004 19:52:38 GMT

John Everett writes:

specify the radius and # of teeth, correct?

Nope. BCD or bolthole chainring diameter is taken from a straight
line of two adjacent holes and a line perpendicular to that line to
the opposite bolt hole.

Peter, Peter, Peter... wrong! I've never actually measured a
chainring before, but your posting had me reaching for a chainring
(Shimano SG 42), and a ruler. Turns out your method measures 118mm,
but the true bolthole diameter measures 130mm.

I think this works better:

http://tinyurl.com/699er

It does, but I think that it's less error prone to skip one
hole by 1.05 (1/cos(18 degrees)).

Joe