SLX seat tube ID

[Derosid]

Did Columbus SLX tubing come with an ID of 27.0mm? I have a De Rosa frame built with Columbus SLX tubing that I bought in 1992. Back then I assumed the it would take a 27.2mm seatpost like my previous SL tube bikes, but it was always super tight. I had to hone it slightly to even get the 27.2 seatpost to insert, and it’s always been difficult to get the seatpost out.

I just tried inserting a 27.2mm carbon fiber seat post and it started scratching up the carbon, so I measured the ID and it is just a hair under 27mm and is not out of round. Have I had the wrong size seat post all these years?

[Doug Fattic]

My 1st guess is that your tubing is SPX and lightly heavier walled than SLX. SP seat tubes (1.0/.7mm wall thickness) required 27.0 seat post. It is also possible that they mixed the 2 different tube sets in your frame. Also when you measure seat posts, you will find they often are not exactly 27.2 or 27.0. This reminds me that tubing specs are not spot on either. Back in the days when I would build frames with Columbus tubing, I would weigh SL chain stays and they would vary between 140 up to 165 grams. And of course brazing on a binder bolt and seat stays can distort a seat tube so they are not perfectly round.

[C40_guy]

My Spiral Conic SLX took a 27.2 seat tube with no issues.

[Derosid]

Originally Posted by Doug Fattic

My 1st guess is that your tubing is SPX and lightly heavier walled than SLX. SP seat tubes (1.0/.7mm wall thickness) required 27.0 seat post. It is also possible that they mixed the 2 different tube sets in your frame. Also when you measure seat posts, you will find they often are not exactly 27.2 or 27.0. This reminds me that tubing specs are not spot on either. Back in the days when I would build frames with Columbus tubing, I would weigh SL chain stays and they would vary between 140 up to 165 grams. And of course brazing on a binder bolt and seat stays can distort a seat tube so they are not perfectly round.

That’s interesting. The frame came with the SLX decal straight from De Rosa so that’s what I always assumed it was made of. I have heard of discrepencies in ID in the old seat tubing depending on which end was connected to the bottom bracket. I can’t accurately tell the wall thickness since the frame is painted, but it measures about 2.1mm with paint. Guess I’ll dig up a 27.0 mm seatpost and see how it fits rather than trying to hone out an additional 0.2mm from the ID.

[Doug Fattic]

Back in the day it wasn't uncommon to mix SL and SP together if a frame was midsize. The tubes going into the BB shell would be heavier than those on top. The biggest frames would probably be all SP. Columbus did not have a decal indicating a mixed set. The importance of the tubing decal was to indicate it was quality tubing. Painters often take liberties with tubing decals.

I'd check closely to see if your seat tube opening is round. Measure in different places with a calipers to see if they are all in agreement. You can also kind of tell by inserting a seat post to see where it rubs or doesn't.

[Derosid]

Originally Posted by Doug Fattic

Back in the day it wasn't uncommon to mix SL and SP together if a frame was midsize. The tubes going into the BB shell would be heavier than those on top. The biggest frames would probably be all SP. Columbus did not have a decal indicating a mixed set. The importance of the tubing decal was to indicate it was quality tubing. Painters often take liberties with tubing decals.

I'd check closely to see if your seat tube opening is round. Measure in different places with a calipers to see if they are all in agreement. You can also kind of tell by inserting a seat post to see where it rubs or doesn't.

It does seem that the older frames were assembled with a bit less “formality” than we all thought. Kind of like vintage Italian cars, where the bodies are actually not symmetrical because they were hand built.

I bought the frame direct from a LBS when I built the frame up and I ordered an SLX frame and it had the SLX decal, so I just assumed that was what it was. We got a decal set from De Rosa for the repaint so I think it was at least supposed to be SLX tubing. Whether it is ALL SLX may be up for debate.

The seat tube does appear to be round, with similar ID when I measure in different orientations. I think I’ll find a 27.0 seatpost and see how that works.

Either way, the frame has been a joy to ride for many years, and much better than anything I had ridden previously.

[Spaghetti Legs]

I have several SLX bikes (including an DeRosa Pro) and all are 27.2. I do however, have a Tommasini in SL that needs a 27.0 post. In addition to mixing in SP, SPX tubes I’ve also heard that sometimes the frames were built with the seat tube reversed and the butting at what would normally be the bottom bracket end results in a smaller seat post diameter.

[Doug Fattic]

Having a mixed SLX/SPX tube set would be an example of a quality build. SL chain stays are pretty light compared to any other .9/.6./.9 mm tube set brand.

It sometimes happens that a seat tube could be turned around and the butted end would be on the top because the builder was a bit careless. It isn't that hard to tell the difference however. It would take an extremely dense builder to turn around an SLX seat tube since the butted end has spirals. Those spirals reinforcements is the difference between a SL and SLX. Going by memory I think I heard somewhere that Columbus started putting the spirals into the bottom of the tubes when braze-on front derailleur became popular.

The most likely tubing placement error is turning around a top tube so the seat tube miter is at the head tube and vice versa. I always have my framebuilding class students mark their tubes clearly so that when their hands and everything else are covered with flux, they get their top tube position right.

[Derosid]

Turns out a 27.0 seatpost fits perfectly. Funny that I crammed a 27.2 in there for all those years. Good thing I didn’t need lots of adjustments.

[Waldo62]

I had a De Rosa Nuovo Classico, which was an excellent riding bike, but the 27.2 post always slipped, so I shimmed it with a piece of a San Pellegrino can. The shim had to be Italian.