Unearthed arcanum: MTB with drop bars
 

I feel like a monk emerging from a dusty corner of the St. Pachomius library with a fresh insight. I found something this weekend in the sacred writings of Sheldon Brown that solved a problem I've been having. Finding something useful in Sheldon's writings is, of course, not at all uncommon. What surprised me is that I discovered something hinted at in passing that I hadn't seen directly discussed before.

I know a lot of people on this forum, myself included, have put drop bars on mountain bikes. When you do that, there are two common problems that need to be solved: (1) the top tube length is usually too long, and (2) MTB front derailleurs aren't index-compatible with road shifters. What I found in Sheldon's writings is a new (yet old) solution to this second problem.

The problem with this incompatibility is two-fold: (1) Shimano MTB shifters and Shimano road shifters pull a different amount of cable, and (2) road front derailleurs are made for large chain rings so the curvature doesn't match MTB cranksets.

There are, of course, a lot of ways around this, mostly involving either using friction shifting or tolerating poor shifting. The solution I discovered in Sheldon's writings this weekend doesn't involve either of these. I found the critical clue in Sheldon's article on "Upgrading Bicycle Gearing". There he says:

(emphasis added)

If Shimano no longer makes a front derailluer that is compatible between drop-bar shifters and smaller chainrings, that would imply that they once did, right?

As fate would have it, I was reading this particular entry because I was upgrading an '89 Rockhopper to modern 9-speed MTB components. I wanted to know in advance whether to expect the old MTB front derailleur to work with the new MTB shifters. It didn't.

So...I pulled the modern MTB front derailleur that had been giving me sub-par service on my 29er drop bar conversion bike and put it on the Rockhopper where, naturally, it performed perfectly. Then, just as I was about to put a Tiagra front derailleur on the 29er, the light bulb came on above my head.

Comparing the old M452 "Mountain LX" front derailleur to the Tiagra front derailleur and seeing that the arm where the cable attaches had a similar geometric relationship to the parallelogram of the derailleur, I decided to give it a try. On the stand, it seemed good. I tried it on the road today, and BINGO! It shifts perfectly.

Now, I realize that like the monk in my opening analogy I may discover that either I'm delusion or nobody cares or both, but I thought I would share, just in case this is useful information.

What shifters are you using on the drop bars with the M452 Front der?

One of the old RSX front mechs was compatible with Shimano brifters and MTB chainrings (26/36/46).

The fix is Bar end shifters
shimano likes to throw 3 times for a triple, then let the cage shape
deal with the different Chain angles coming from the rear
seems cable pull is different on the 2 systems , rears click OK, but the big throws are different in the front.

left bar end shifter lets you trim the cage position, in small amounts .

my preference is non indexing on both ends , saves a lot of derailleur troubles.

but I'm aged past the 18-35 year old target market for everything. :50:

I might be cheating because i run a 50t big ring but i still go triple with a 39 and a 28 with it, and i use microshift brifters and have used them successfully with several derailleurs. But in my opinion the old Falcon i used on my drop bar M-50 worked the best, and now on both my drop bar MTB's im running Suntour XCM fronts, granted on my new build i got bar end shifters.

I am using Microshift 9 speed shifters with an Acera FD and 44-32 (22 removed) MTB rings. It shifts as smooth as my 105's and hasn't come out of adjustment in 1000+ miles.

I'm using Tiagra 4503 shifters.


That would agree with my hypothesis. I'm suggesting that old Shimano MTB front derailleurs (though I don't know which ones) are compatible with new Shimano STI shifters.


Dang retro-grouches.... I'm not giving up my brifters. :D


That fits. If I understand Sheldon correctly, he's saying that ring size is the limiting factor for where a given derailleur will work with a given crankset and cable pull determines the compatibility between derailleur and shifters. So, a big chain ring crankset on a MTB should work with road derailleurs (though it shouldn't work well with new MTB derailleurs).


Natually, everything is easier with a double ring set up.

Ditto ive got about 2k on my micro shifts only problem i have with them is the lack of brake cable pull (using canti)

RSX was a compact-drive road group, though.

Ah, my mistake. It seems that RSX should be added as an addition to my "old MTB derailleur" hypothesis.

Let's qualify this though. It only pertains to the front derailer. Rear works fine. I run LX dual control with an Ultegra rear just fine.

Campy ErgoPower brifters work really well with triples and drop bars (and canti's). I ran them on my commuter with a 9-speed Shimano cassette and SRAM/da Vinci-modified rear mech. Front mech was a vintage Shimano Deore II unit that handled the 24/36/46 chainrings beautifully.

Here's a pic of that da Vinci-modified SRAM mech:

http://farm5.static.flickr.com/4144/...27bb1fa0_z.jpg

^^^^ Traditional Campy ErgoPower shifters work great for front derailleurs of all kinds. A Jtek Shiftmate also allows you to use Campy Shifters with Shimano rear derailleurs.

That's how I eventually got around the problem on my MTB with drops. I liked the Shimagnolo set up on my MTB so much I did the same to my road bike.

So what are you guys doing about problem (1) the top tube length?

Yes, that's true.

I got a really short stem and short reach bars.

I run a pair of Sora brifters on my drop bar MTB. I used a road FD. Solve the problem. Seems to shift nicely with 48/38/28 rings.

That may be just as good as my solution for a 48T ring, since the derailleur is likely made for a 50T ring. It might even work for a 44T ring (which is what I have). In theory, there is a point where the curvature of the chain ring becomes a problem.

...but it is a triple FD...

Using a road derailleur is more complicated if your cables are routed along the top tube like they commonly are on MTBs. All shimano front road derailleurs are bottom pull. You can mount a pulley on the seat tube to get around that problem but it created some clearance issues for me.

I guess i haven't noticed, maybe my arms just got longer:)

Whats even harder and why i went with falcon on my last one is finding top pull in 28.6 dia

1989 Specialized RockCombo (not my bike in picture, but same color, equipment)

I got one of these when I worked at Specialized. The concept didn't work out at the time, so they blew them out for about $250.00 wholesale.

It was in pristine shape..but is now my son's college bike..it's taken a few hits lately..

Just change the way the limits are set. Triple FD will work with a double just fine, it's all about cable pull.

That's what I'm saying. Perhaps I'm reading the OP wrong, but MTB components and standard road levers seem to work fine for me.