agmetal

I have 4 bikes, one of which currently has a relatively upright "city" type handlebar on it, while the others all have drops. I'm planning to convert the 4th to drops soon, and I was doing some comparitive measurements on my bikes the other day. The thing I noticed is what seems to be a strange disparity in the relative positions of BB, stem clamp, and saddle.

The three bikes with drop bars are all relatively modern steel framed sport-touring/cross-commuter style bikes, with fairly typical setback seatposts. Two of them may be getting longer-setback seatposts to account for the position of the rails on the leather saddles. The bike I'll be converting is an early '80s steel road bike, and it has a zero-setback seatpost.

My plan is to use a 60mm stem on the vintage bike to get a more comfortable reach (with the saddle in its current position, it'll give me comparable reach to the other bikes), but it seems like then I'll have to deal with a shorter distance between stem clamp and BB, which I could see being an issue since I stand on the pedals fairly frequently...maybe this can be accounted for with stem height?

Measuring all 4 bikes, the distance from BB center to stem clamp center is approximately the same, and the saddle height is the same...however, even with the ability to set the saddle significantly further forward on the vintage frame, its current position is over an inch further back from the current 80mm stem's clamp than the other bikes. The modern bikes all have 74-74.5º STAs, and the vintage one I'm assuming is about 72º. I know that a 2º difference in STA makes for about a 2cm difference in setback, but shouldn't the zero-setback seatpost on the vintage frame (vs. ~25mm setback seatposts on the other bikes) account for that?

I feel like I'm missing something here, and I'm confused.

agmetal

A little more measuring (of the saddles) has given a little more information that I can share: The bikes are most easily described in pairs. Raleigh is the currently-most-comfortable bike, position-wise. It has one of the Velo riveted classic road saddles, sort of a Selle San Marco Regal copy. Panasonic is the one I plan to convert. It has a Charge Spoon (aka Velo VL-1205). Both of these saddles have rails that have their clamping section close to 5" from the front of the saddle, to about 3.25" from the rear. Raleigh has a typical LaPrade style seatpost, Panasonic has zero setback.

Bianchi has a Gilles Berthoud Aspin, and New Albion has a Gilles Berthoud Soulor. Both of these saddles have the rails starting over 5.5" from the front, and ending less than 2" from the rear. Bianchi has a typical LaPrade style seatpost, New Albion has a different style with comparable setback (Uno SP-248 Seatpost - Seatposts - Components).

All four saddles are about the same length.

I have the Berthoud saddles about as far back as they can get on the current seatposts to get their positions comparable to the Velo saddle on the Raleigh (which, itself, is fairly far back on the rails), and am planning to try the Velo Orange long setback post on at least one of the bikes to make it easier to get the saddle in the right position, without being so close to the adjustability limits.

The Charge saddle on the Panasonic is pretty much in the middle of its rails, on its zero-setback seatpost. Slamming it all the way forward would get closer to my desired position, but it ends up looking a bit odd, and it still wouldn't be quite where I want (I don't think, anyway...?)

tangerineowl

Rather than potentially hitting your knees using a 60mm stem, you could try a shorter-reach bar? (e.g. there are quite a few 70mm reach bars out there).

agmetal

I'm doing that as well

fietsbob

Data: take a plumb, vertical, line at the BB axis.. that is your base ..

setback is the distance behind that line, reach is the distance ahead of that line.

the virtual top tube is a horizontal line compensating for top tube slope , (at a right angle to the vertical line).

if you use the same distance above the BB then the VTT should be useful to judge fit similarities across the various bikes .

Road Fan

@agmetal,

Any luck?

agmetal

The 60mm stem and compact bars, combined with the zero-setback seatpost got me close enough to be mostly comfortable on the bike, and I haven't had any issues with my knees hitting the bars.

Road Fan

That's good!

Are you still interested in getting all four bikes to match, or are you just taking it one step at a time?