Re: [CR] 1981 rare motobecane team champion / 22.0 stems


Example: Events:Cirque du Cyclisme:2004

Date: Sat, 29 Jan 2011 15:13:56 -0800
From: verktyg <verktyg@aol.com>
To: Classicrendezvous@bikelist.org
References: <361948.39032.qm@web25901.mail.ukl.yahoo.com> <9636B5B487B44053894692FA8D1AC619@ddddPC>
In-Reply-To: <9636B5B487B44053894692FA8D1AC619@ddddPC>
Subject: Re: [CR] 1981 rare motobecane team champion / 22.0 stems


Loose tolerances plus imaginative dimensions...

You can't put a 22.0mm stem in a 22.0mm hole!

Same thing with inch size 22.2mm (7/8" - .875") stems.

Originally French stems were 21.9mm in diameter to fit into a 22.0mm diameter steerer (metric sized stems also used on Spanish and other countries too). A 22mm bore in a 25mm steerer leaves a wall thickness of 1.5mm per side.

I've measured hundreds of stems over the past 35 years.

While most metric stems were marked 22.0mm they were generally undersize. I found metric cast aluminum "death stems" with quills as small as 21.3mm. Some better quality metric stems that were marked 22.0mm were as large as 22.1mm.

Same kind of results with inch size stems, 22.05mm to 22.3mm.

A few weeks ago I posted a message about Nitto stems that were marked 22.2mm that measured 22.09mm. I checked about 6-7 Nitto stems dating from the late 80s up to factory fresh ones, They all had the same 22.09mm diameter quills.

I found that these 22.09mm Nitto stems will fit in many metric steerers.

I've also found stems with differing diameters up and down the quill plus out of round quills.

It's easier to control the manufacturing dimension on a stem than the bore size on a piece of tubing.

I've seen very few steering tubes that look like they have been reamed to size. One good reason reaming is generally avoided is that the bottom of the reamer can leave a shoulder inside the steerer that could result in a crack forming stress riser.

French bikes from the 70s with Reynolds frames rarely used Reynolds 531 steering tubes.

Gitane used butted steerers made by Nervor while many Peugeots and Motobecanes used a straight piece of seamed tubing with a sleeve brazed into the bottom of the steerer.

As David mentioned, the concern in tubing wall thickness is more in the threaded area than at the bottom. One possibility is that the threads could have been cut off center in relation to the to the tube. The wall thickness can be less on one side of the tube than the other.

If a stem is expanded in the threaded area, it can cause the threads to bulge and possibly crack. That's why the recommendation to insert stems at least 75mm into the steerer so that the expander is below the threaded area.

Before installing a stem I always clean out the steerer with solvent to remove any crud then I run a brake cylinder hone though the stem area to smooth out the bore. I also file a very slight chamfer using a fine round or half round file on the mouth steerer to remove any burrs.

Last suggestion, loosen the headset lock nut before removing or installing a stem. The lock nut can slightly compress the top of the steerer.

Headsets should be adjusted with a tightened stem installed for the same reason.

Chas. Colerich Oakland, CA USA

David Snyder wrote:
> I believe that loose tolerances explain much confusion about this issue.
> I've seen stems labeled 22.2 that were much closer to, or actually were,
> 22.0, and the steerer in my Gitane SuperCorsa is also near to 22.2mm.
> When I decided to replace the Pivo Professional bars/stem on the Gitane
> with Cinelli (since the original bars on this 60cm bike were only 34cm
> wide), I selected a 22.2mm Cinelli stem because it required only
> light/moderate sanding to fit perfectly.
>
> More commonly, a 22.2mm stem will require lengthy, heavy sanding/filing
> to fit into a normal, say Peugeot, steerer, but this time it was a
> breeze, and I recall it was both steerer and stem quill in this case
> that were on the "loose" side of spec.
>
> As for steerer strength, no worries. Only the thickness up where it's
> threaded should be of much concern, as the lower end is heavily butted.
> As long as the stem expands below the threads I'd say it's plenty
> strong, tho many steerers have way more threaded length than is needed.
>
> On a related note, in searching for longer-extension stems for my
> Schwinn Super-sports, I've found several brands of stems that have
> 21.1mm quill diameters but which have the same I.D. (bolt hole size) as
> the similar 22.2mm model (GB, Nitto, SR and Compe) stems. All appeared
> forged, save maybe for the Nitto Young, but still plenty strong.
>
> David Snyder
> Auburn, CA usa
>
> Hugh Thornton wrote:
>
> Some bikes with 25mm French-threaded steerers do take 22.2 mm stems, but
> I have never been sure whether that was because of tolerances in the
> steerer tube or subsequent reaming or by intent from the factory. I have
> one such bike and take comfort from the fact that it has a wooden plug
> up the steerer to reduce the probability of a catastrophic failure. A
> standard French steerer tube has less wall thickness than a 1" one, and
> even less with a 22.2 mm hole down the middle.
>
> 22.0 mm Cinelli stems appear from time to time on French eBay, but you
> need to be a bit cautious - one vendor told me a stem was 22.0, but when
> it arrived I measured it at 22.2. I don't think he was trying to deceive
> because I asked him the non-leading question of whether it was 22.2 or
> 22.0. I think there is more chance that the vendor knows what he is
> talking about if the item description states 22.0.