SurferRosa

The internet tells me, the down tube.

Was or is there a rule of thumb?

My bikes (55-57cm) measure between 11cm and 13.5cm from shifter to head tube (c-c). I didn't see a real pattern compared to frame size.

I'm switching from barcons on my new '72 Torpado. It's stamped 56cm. There's really no paint scarring on the down tube to use as a guide or to cover.

canklecat

IIRC, when I first put clamp-on downtube shifters on my '76 Motobecane Mirage (it came with stem shifters), I used tape to protect the downtube for the trial rides until I settled on the position that was comfortable for me.

Later braze-on mounts kinda locked us into one spot, although the position seems okay on the bikes I've ridden.

Wish I still had that Motobecane. I'm betting the position I settled on would be exactly where a frame builder would have located the braze-ons if it had 'em.

krakhaus 

My Faggin's braze-on's are exactly 4" down from the head tube. But sometimes I come close to sticking my finger in the wheel, so I wish they were about an inch lower.
It's a 56cm

gugie 

I typically braze them on 10cm off the center of the head tube. I'm pretty sure a centimeter or two off either way wouldn't make much of a difference, at least to me. No one's complained so far.

79pmooney

Is there a braze-on under the downtube tho serve as a stop for a shifter clamp (or housing stop for the barends)?

If you have a bare tube, no braze-on, then you have a blank slate. I'd go for a ride, swing my arm down and note where shifting feel natural. I've had bikes where I liked the location and others I didn't. You get to do it right.

thinktubes 

Here's a pic for reference. The infamous "$1 Trek 400".

thook

there's the shifter clamp stop 79pmooney mentioned. about half way up from your shifters to the head tube..... underside of the downtube. your shifter clamp should go just above that

Fahrenheit531 

Some guy in Japan 40+ years ago says 10cm.

But dude in England says 13. (The height of a typical pint glass, table to rim. Coincidence?)

... so they go right about there. Ish. Maybe a little higher. Or lower. Perfect!

(Both frames pictured are 58st, 56tt.)

scarlson 

Based on my experience with '80s Holdsworth craftsmanship? Nope! Confident the guy still had a pint or several in him or on him when he did my lower head lug. Maybe then went right to the downtube mounts.

daka

The folks in Worksop put them at 13cm. Or close to that. And the stop is centered....kinda, sorta...... With the shifters there I can usually find them without looking or getting my fingers in the spokes.

Lascauxcaveman 

Stick with the barcons.

oneclick 

Interesting. I just went and measured some frames.
Some have a pip on the top of the down-tube, some on the bottom, and some have braze-ons.
For all I measured to the centre-line of the head-tube - either to the centre of the shifter boss or the top edge of the pip.
These are eye-ball measurements - to which I applied a correction for the pip location - -7mm on top, +7mm on bottom, and then -3mm for the band

Frame - seat-tube(cm,c-c) - pip/boss distance(cm) - corrected
Torpado 1 - 51 - 15.25 (pip on top) - 14.0
Peugeot Tour - 53.25 - 12.0 (pip on bottom) - 12.4
Carlton Flyer - 55.25 - 10.0 (boss)
Gardin 400 - 57 - 10.5 (boss)
Guerciotti - 60 - 10.0(boss)
Torpado 2 - 60.25 - 14.0 (pip on top) - 13.0

And beside them was another frame (52cm) that takes a clamp mount; I had put them where I though they looked right and measuring to that boss gives 14.5. Hmmm. Didn't have any wheels on when I did that.

The two Torpados are both bottom end frames - no rear mech hanger, 4-digit serials beginning with 2, so they probably match yours in date of manufacture; but seeing as the smaller has a larger mount distance that's not much help. The Peugeot Tour is what I call a bike I just got, it does not appear in any of the catalogues/brochures, has a Vitus frame with Mafac cantis, date by serial 1983. The Guerciotti I don't know a model or date, except that it is likely late 80s at most.

However, there are more practical considerations. You don't want the shifters to be where if you are using them your pedaling has to change; and of course they should be a comfortable reach. You might want to avoid marring a decal, or fit a water bottle, or carry a pump under the top-tube. I once built a centre-of-the-frame-pack, and narrowed out the place where I thought the shifters would be, after mounting it they of course needed to be moved a bit.

oneclick 

Even so he'll need a clamp for the stops - where to put that?

iab

Where it's best for you?

tiger1964 

This does seem like the logical solution. Not all riders have the same length arms, even for a given frame size.

RobbieTunes

I’m just reading the thread, because I never think about it until I reach down and feel that tire whizzing by my fingers.

At least it’s not government regulated....or is it?

SurferRosa

So, it sounds like, no.

Heard from gugie . Any other builders out here want to weigh in? @bulgie?

gugie 

Or just ask everybody to measure their down tube shifter distance from the centerline of the head tube. The vast majority of bikes have them. Include the bolt around the frame ones if they have a stop brazed on.

I'd bet the Japanese were very consistent, Europeans, not so much. Hmm, I've got a bunch of frames in the Atelier hanging up. Sounds like a quick project...

John E

Bianchi (braze-ons): 10cm back from head tube center

Capo Modell Campagnolo (arbitrarily placed clamp-ons): 11.5 cm back -- looked and felt about right

bulgie 

Where I wanted mine, the pump peg was in the way. I didn't let that stop me:


At least this way I know it won't slide down. Or up! Or rotate for that matter.

As to the original Q, I may have had a measurement that I used when I was actively building (I don't remember), but more likely not, I just put them where the fixture held them on. We did braze-ons on the bare mitered tube before putting the tubes in the frame jig, so the braze-on fixture indexed off the miter, but that's no different than measuring from the head tube on a finished frame. So why am I even mentioning it? I dunno. Of course whoever made the fixture must have had a measurement in mind, but it's pretty arbitrary. Over a wide range, they all work fine.

My '61 Specialissima came with a clamp-on DT shifter that has the pump umbrella integrated. So you position the shifters to where the pump fits best!

One place I worked, we brazed a little pip underneath, and that was done without a jig, completely by eye IIRC. The eye gets pretty good with enough practice though; I bet those pips didn't vary by more than a couple mm. I once glanced at a frame a coworker was making as I walked by, and said to him "check those water bottle bosses, they look too far apart". They were indeed 1 mm too far apart, 65 instead of 64 mm.

Mark B in Seattle

amedias

Don’t forget shifters are different lengths too!

Early cyclo and simplex have very long levers for example, that alone would mean there will be variations over time and between countries.

Wildwood 

Why worry about it?, go Single Speed or Fixie. You need one of those anyway.

SurferRosa

Hey, seadog! Would you rather I worry about the polar icecaps melting or an asteroid collision? This is something I can actually control!

T-Mar

Downtube shift levers should be positioned so that the inevitable paint chip caused by contact from the front brake's cable adjustment knob is obscured when the lever is all the forward and you're cranking along in high gear. ​​​​​​​

madpogue 

^^^^ What happens if an asteroid collides with one of the polar ice caps?