Braze on FD = crowding rear tire? Suggest an 'out-of-the-way' option? *Tight* geo...
 

So, a conundrum has arisen in my recent Cyclops build.

The bike has a very tight wheelbase (~97.5cm), with short chainstays (~39.5cm) - tight enough that the rear tire must be deflated to fit the wheel, and to justify a crimp in the rear of the seat tube for clearance. Limited tire clearance, to say the least.

Having just inflated the rear tire to check out how I'm doing there, it seem that the braze-on tricolor FD is actually crowding the rear tire - presenting the main limiting factor re: tire size (not that I could go up much anyways, but I can hardly go skinnier).

In particular, the portion of the FD where the limit screws are located sticks out to the rear/inside, running *very* close to my tire.

I'd hoped to run a hair larger tire (thinking Veloflex Master 25s), if possible...but it won't be like this.

Close of up pics of the problem area:

http://bikeforums.net/attachment.php...hmentid=436882

http://bikeforums.net/attachment.php...hmentid=436883

Tight, eh?

That's with a 23mm Shwalbe Ultremo. If I slide the wheel just a hair forward in the DO, it actually touches...

Wondering if folks have experienced this problem, and what my best bets for an alternate 'out of the way' braze-on FD might be?

Ideally something that will look 'right' with an 8sp Chorus/Record setup and some 7400 Dura Ace cranks on a nice build.

What about 8sp era Campy or 7-8sp Dura Ace (maybe too similar to the tricolor design?) Recommendations?

You could try grinding about 1 mm or 2 from the face of the derailleur where it mounts into the braze on. This will move it forward a bit and might give you the clearance you need.

Very true - I hadn't thought of that, but could work.

This particular FD was NOS 48 hours ago - I took the price sticker off then. So I'm into exploring other options before modifying this one.

I went snooping at the other bikes and noticed that a Shimano 600EX braze-on FD looks a little better.

Wondering about other suggestions that might prove "out-of-the-way" on a bike with little/no clearance between the braze-on FD/seat tube and the rear tire...

My '88 Cannondale Criterium Series (54cm) has a wheelbase of 97cm with adequate space though I run 23's exclusively. They got away with this by having a semi verticle dropout and Shimano braze-on type front derailleur. The FD mounts with rivnuts and is offset to the outside a bit.

Here is a pic of my little Trek 760 with a 96cm WB. This is a Campy clamp-on FD. I think that is what you may be looking for.
http://i62.photobucket.com/albums/h8...1620A7B43A.jpg

Hm. Even a Dura Ace 7400 unit looks as though it doesn't extend to the rear/inside of the FD tab/seat tube the way the tricolor derailleur I have on there now does...in pictures on the internet, at least. The limit screws appear to be more in line with the bolt that attaches to the clamp than offset back/inwards.

A 600EX braze-on FD I have on another bike also looks like it doesn't crowd the same area to the extent that the tricolor does.

Thanks for the info/suggestions thus far - I'm sure I'll figure something out here, hopefully simply an alternative FD (in which case I've got my fingers crossed that I can get it right with one strategic purchase/trade).

The DA would be ideal for this build, if it allows a bit more clearance, as would a Chorus/Record braze on from the 8sp era...assuming they don't present the same issue. I wish I had more spares on hand, but not a single braze-on FD in the bin right now. All clamps!

I may have to stick with 23mm tires, but as is, the tricolor FD on there now is *already* a bit close for comfort - so I think I'll switch out either way.

I don't see a cable hooked up and it looks like the chain is in the inside chainring. Am I missing something?

If this is the case, I can't imagine being able to shift to the outside chainring.

Is the braze-on mount welded on or mechanically fastened?

If it can be removed, you may be able to use a bottom clamp/top swing derailleur. While it may not be something you want to go with, maybe an old XTR.

John

Thanks for your comment.

The cable is not hooked up at the moment - but it does clear the 23mm Schwalbe tire when it is. Not by much, though - good observation, as the rest would be pretty much moot if there were not room for the cable to run up to the FD.

Even with another RD, this probably keeps me on 23mm tires, if I'm being realistic. The exact location/configuration of the cable clamp on different FDs would induce some slight variation in the line the cable travels past (or through) the circumference of the tire, I guess, but probably not much.

The arm where the cable anchor point is located is well clear of the tire when it swings in to shift to the outer ring, BTW.

I was initially most iffy, really, about how close the part of the tricolor FD where the limit screws are located is to the tire - and am noticing other derailleurs don't seem to project back towards the tire in this fashion. Thus trying to settle on a suitable alternative to see if I can solve this, at least. Though I may still have an absurdly tight clearance with the FD cable anyways!

The braze-on FD mount is an integral part of the frame - the tab was brazed on to the frame 25 years ago by the builder, and isn't going anywhere.

So a top-swing unit, or any clamp-on FD, is a no-go.

Hoping I can *at least* get more comfortable clearance there with the 23s; I'd have been ectastic if I could, as I'd alluded to above, fit Veloflex Master 25s.

Those tires do run a bit narrow - but looking at things more closely today I'm not hopeful about that possibility.

I'll likely source a 7400 FD or a suitable Campy unit to try it out and see - though I suppose if the cable is going to leave me stuck with the 23s, maybe I shouldn't worry about the minimal clearance between the rear-protruding part of the tricolor FD and the tire. Still, making just a bit of room there would make me a little more comfortable.

I don't understand the OP. He buys a bike with ultra short chain stays so he can go Fast Fast Fast and lane change if a flea sneezes, and then he wants to put FAT tires on it. The OP should be putting 20's or 18's or even 16's if they make them so he can be faster then everyone else. Trade it in on a different type of bike if you want fat tires but don't try putting them on a racing bike.

I think this discussion is getting over complicated. Just get a tricolor FD that isn't so NOS and take a grinder to the protruding corner. The screw is just the limit screw, there isn't much load on it, you don't need that much metal around the threads. Seems you can get a few mm more clearance easily.

25's are "FAT" and 16/18/20's are faster? I think you might need to tell all the pros who are riding on 23's and 25's since they seem to be missing out on a competitive advantage.

Yep, old school was real skinny. My 89 racing bike had 20 on the front, 23 on the rear. Current thinking is wider is faster and handles better - and is more comfortable.

How about a Superbe Pro?

Suntour made some of the best derailleurs and the Superbe was probably as high end as your Chorus.

I use their Cyclones in a lot of wider range applications where their Shimano counterparts are not happy. I'm running one on the front with STI.

Here is a pic...

http://bikeforums.net/attachment.php...hmentid=437088

John

That's one of those briefly-made Shimano FDs that moves diagonally -- seems like Shimano tried it with 105, RX100, possibly other levels for one generation before resorting back to normal geometry. I'd see if a normal FD gives you more clearance, Clarence. :thumb:

http://www.velobase.com/CompImages/F...837E43648.jpeg

versus

http://www.velobase.com/CompImages/F...A2B92C688.jpeg

(Pics courtesy of Velobase.)

As you have seen, no diagonal movement mechanisms on this bike.
It was designed for tubulars too, in the 21 mm range.

mikemowbz, What is the seat tube angle? Just curious because my Cannondale has practically the same chain stay and wheelbase (39.5 cm / 97.94 cm) and it's not so crowded between the tire and the seat tube despite larger diameter tubing.

I think you are going to need a narrower rim and it's unlikely a tire larger than 23 mm will fit.

Brad

This is C&V, but I can't tell if this is tongue in cheek or just ignorant.

The crux of the problem.

(I tried a similar approach) :)

Looks as if that seat tube/stay length is in conflict of sorts.

PLUS

DING DING DING.

It's actually not complicated, even if the post is wordy.

Looking around since, I've discovered that very few other derailleurs have this design feature - unsuitable for this bike, fine on many others.

So, I try another. Question was: which? Answer: probably lots of good options out there.

I'm more or less resigned to not fitting larger than a 23, but a 23mm will work (so despite others' posts above, I'm neither going to run 19's nor trade in the bike ;)). I will often try to fit roughly as large a tire as I'm comfortable with, clearance-wise, as I'm doing here. I think a lot of us here typically do exactly that. I'm also probably a lot bigger than anyone who's particularly comfortable on a 19mm tire.

That said: the Schwalbe's actual width is currently sitting at about 24mm, so I can probably squeeze a 25mm Master in (they measure small, so maybe .5mm of difference in width, and they might actually *less* tall...as per a measured comparison I just made with another set of wheel that sport the Masters). If not, no biggie.

I've already got a potential alternative RD possibly happening (ISO, FTW), so we'll see how it goes.

Thanks, all, for the many constructive responses.

Not sure about the ST angle. I could try to suss it out...the bike is generally quite steep (though quite a low BB).

Something going on there geo-wise.

20mm rims - not terribly wide.

I suspect you're right that I'm at the limit in terms of tire size - and I'm cool with that. If I can fit the Masters, my preferred tire, I'll be even happier.

As I note in my post just above, the Masters should be only .5mm or so wider, and may even be a little *less* tall than the current nominal 23mm tire.

I may, however, go to a Master 22 or similar if I'm not comfortable with the clearances w/an alternate FD, etc.

The Lovell had a band-on Gipiemme FD when it was born but was upgraded to a braze on Super Record at some point. The seller included the Gipiemme in a Bag O Parts. It's also running 22mm tubulars, and there is zero wiggle room back there.

The fact that you're willing to mix-and-match on this bike opens up a lot of options, too. I was going to offer you my NOS braze-on RX100 FD (for cheap), but I just double-checked and it has that diagonal geometry! Rats, I'm never gonna sell that stupid thing.

My vote would be for DA (I can't find any diagonal ones on VeloBase, so you might be safe with any) or 6401 Tricolor (not 6400). :thumb:

Oh, and a further tip -- with a regular FD, you might find that the cable anchor bolt is the next thing to possibly contact the tire. I solved that issue on a previous setup by substituting a different bolt with a much lower-profile head.

Perfect candidate for a 650b conversion. :)

So, I guess Mike Mulholland kept up that tradition!

This will definitely be a fast-but-short-ride bike, sunny days and smooth surfaces - but I'll see what I can squeeze in there.

Yes - I think DA 7400-7403 looks like a potential candidate, and probably top of my list (I might even have a line on one).

And once I've got an FD without that diagonal thing going on, I will definitely need to keep tabs on the cable anchor bolt (as well as the cable itself).

Thanks for the tip!

Back to the drawing board! :lol: