Dropbar MTB, pt 2

Continuing from Pt1, I want to put a dropbar on an mtb, but one needs a plan to get around the many pitfalls. The first problem is brakes. Since caliper brakes are not an option with an mtb, that leaves cantilevers, v-brakes, or discs.

tycoon 04.jpg

Once upon a time, mountainbikes had cantilever brakes. With enough fiddling with straddle wire geometry, you can often get acceptable performance with dropbar levers and cantis. But on a bike my size, the rear brake bosses are too close to the seat tube to leave enough room to play with straddle wire height. And of course, who nowadays makes a decent suspension fork with a canti hanger on the fork brace? Scratch cantis.

With V-brake, the geometry of the arms is fixed, and the brake requires a lever with low mechanical advantage and a lot of cable pull to work. And those attributes do not describe dropbar levers. There are some adapters such as Problem Solvers’ Travel Agent that amplify the levers’ cable pull, but they suck. They introduce a lot of friction into the system, are hard to balance the left/right arm spring tension, and require that the pads to be run really close to the rim to get anything near acceptable performance. Plus, I would have issues with the rear cable run on a small bike again because the short housing would over power the spring adjustment. Verdict: not attractive.

Then we have cable-actuated discs. I had tried out the Shimano BR-R505, and I found it’s performance was reasonable. Shop experience suggested that they were more durable than the Avid version, and I like Shimano’s Centerlock rotor fixing system. Okay, we have our brake.

Next is the shifters. Sure, I could put on bar-end shifters for both derailleurs and been done, but where’s the fun in that? Integrated brake/shift levers are too convenient to give up, so bar-end shifters are would be the back-up plan. One derailleur at a time, let’s deal with the rear first.

Full disclosure: it was probably going to be Dura Ace no matter what, but in the end, it made the most sense. I wanted to avoid cable-pull adapters like the J-Tek Shiftmate if possible, so that ruled out Campagnolo. Ergopower shifters work only on Campag cassettes, which don’t fit mtb rear hubs…as in 135mm and disc-compatible. It also ruled out SRAM because SRAM DoubleTaps don’t work with mtb derailleurs and there are no SRAM road triple derailleurs. So it was going to be Shimano, but would it be 9 or 10 speed?

If I went 9sp, I could use an XT 11-34 cassette. There are no Shimano or SRAM 10sp 11-34 cassettes, and anything else out there is crap. On the other hand, I already had a 10sp righthand STI plus an XTR M960 crank that I got on closeout. Since my old mtb had a 2x9 set-up (44/29 and 12-34), I figured that I wouldn’t really need a 22x34 low gear. Besides, in the old days racers used 11-28 cassettes. I’ll run an Ultegra 12-27 cassette with a Tiagra triple rear derailleur.

Okay, the rear shifting is chosen, what about the front? Well, neither SRAM nor Shimano has a solution for running a dropbar integrated brake/shifter with an mtb front derailleur. SRAM DoubleTap is double only, and Shimano road and mtb front derailleurs have a different pull ratio. My bike requires a Shimano E-type mtb front derailleur. In the end, I chose a bar-end shifter for the front shifting duties. It would not be as accessible as an Ergo but it would be simple and guaranteed to work at least. And it would be nearly indestructible. For braking, I would use a Dura Ace BL-7402, the finest aero lever ever made.

What else could I have tried? Well, front shifting leaves you pretty limited if you go with a typical 44/32/22 mtb crank on an external BB. Since the BB spindle is integral to the crank, you can’t do anything to bring the chainline in closer. The chainline is so far outboard that a road front derailleur will be maxed out and swinging upward more than outboard at the end of the stroke. That in turn leaves a big gap underneath the cage to the big ring, which is an invitation for chain drops or at least crappy shifting. Thus, since I’m running an XTR M960 crank, I pretty much have to use some kind of mtb derailleur.

I couldn’t use a road STI like Dura Ace for front shifting duties because the mtb front derailleur needs about 19mm to swing from the granny ring to the big. A road STI triple shifter only pulls about 13mm total.

tycoon 03.jpg

If I were more of a Campagnolo fan, I would have chosen a left-hand Ergopower shifter (non-Escape type) since it pulls round 19-20mm of cable, which is about the same total as required of a Shimano mtb front derailleur. Since the (non-Escape) Ergopower has many indexed increments, there isn’t a problem with trimming the derailleur. However, I’m not a fan of Campagnolo’s ergonomics, since the thumb button upshift is hard to reach from drops with my small hands. Arguably a bar-end shifter would be still be a step down in ergonomics campared to Campagnolo, but I’ve also seen too many Ergopower levers break on a hard impact. On a road bike, I don’t really plan on taking crash damage, but just about every spirited offroad ride I embark on guaranties at least one biff. Yes, you can rebuild the Ergopower on a new lever body, but you won’t be doing that on the trail.

SRAM DoubleTap shifters are completely useless for a mtb triple crank, since they only work for double chainrings. SRAM mtb front derailleurs have the same cable pull needs as Shimano mtb, so they are interchangeable but don’t help us at all with the shifter issue.

I am somewhat intrigued by the notion of a 2x9 system with a dropbar, but I’m not keen on the need for a Jtek to match a 10sp STI to a 9sp cassette. It works fine on a lot of touring bikes, but mtbs get banged up and filthy quite a bit which might compromise the shifting precision. A Jtek system can be sensitive to tuning even on a very clean system, and they won’t fit the newer Shimano Shadow-type rear derailleurs. I could go with a 9sp STI, but I think the newer 10sp models are more durable over all. But maybe the leftside STI would work on a 44/29 double chainring crank. Actually, it might work out well to use a left-side STI on a mtb front derailleur, since the STI’s total pull of 13mm is almost the same as the first pull on a mtb front derailleur. Maybe the triple STI’s index points would be useful trim positions. It would probably also depend on the chainline of the mtb double crank. Typical mtb cranks by Shimano and others have a chainline of about 50-51mm from the center of the seat tube to the middle of the chainrings, whereas the chainline of mtb double cranks (such as FSA or Rotor) have no established standard. Keep in mind that a cross-country double wouldn’t necesarily have the same chainline as an all-mountain double crank, which is essentially a triple crank with a bash guard replacing the big ring.

Perhaps an older style 3-piece, square-taper mtb crank might make things easier. With square-taper, you could cheat the chainline issue with a narrower spindle. Another possibility would be a front derailleur adapter that would place a braze-on type, road front derailleur a bit more outboard than normal, and thus improve the travel profile of the road front derailleur. However, as this option is beyond my means to investigate, we’ll probably not get an answer on this hypothetical question.

In pt3, I’ll detail the rest of the bike and how it rides, and what I would like to change.



5 Comments

Thanks for the write up.  I embarked on a similar project this summer.  I converted my Kona Dew to use drop bars.  This is a commuter, but it’s got a MTB drive train.

I went a bit cheaper and sacrificed some ergonomics and went with Tektro RL520 aero brake levers.  They had the appropriate pull for my MTB mechanical disc brakes (~$20 for the pair). 

For the shifters I got a set of Ultegra 8 speed bar ends.  Due to reasons you mentioned, the front has to be friction.  I briefly considered getting a road triple front derailleur, but with my 26/36/46 crank I had doubts.

The rear indexes beautifully - and as you likely know ultegra bar ends can be switched into friction mode as a contingency.

All this is mounted onto On-One Midge dirt drop bars.  I really like the flarred out drops for stability, and they are the same diameter as MTB flat bars, so I re-used my original stem.

There are some things I’d do differently next time:

1) Add barrel adjusters to brakes.  My original Deore MTB brake/shifter had barrels for brakes and shifting.
Next time I re-tape I’ll run some new cable with nashbar adjusters.

2) shifter cable length.  Another rainy day project is to replace my standard length shimano shifter cables with tandem length, so they may be wrapped under the bar tape.  Not a huge deal, but something I did not consider at the time.

I’m looking forward to p3.
Thanks.

A couple of other shifting options:

1) Paul thumbie adapters. They make them to fit drop bars. Downside is you can only shift from the tops of the bars. Upside is their not as vulnerable as bar-ends or STI.
2) Kelly Take-Off adapters. I used these and they actually work pretty well despite looking really dorky. They do make bar wrapping a pain.
3) Dig up a pair of the WTB shifter adapters from the 80s. These mounted thumbshifters just inside of the brake lever. Pretty much a copy of a French design from the ‘50s.

Since I don’t really ride in the drops that much- neither on my road bike nor my mountain bike- I put poor-man’s cowhorns on my mtn bike.

As the above poster suggested, I used the WTB shift adaptors (since this was over fifteen years ago, I worked in a bike shop where I could easily order the things and I had a Bridgestone with thumbshifters on it).

I still needed to modify things (“needed” as in for fit, not a compelling urge to mess with things for the heck of it, which is still a legitimate “need”). I added a 1-1/2” spacer to the middle of the shift adaptors to move the shifters further inboard so that I could properly wrap my thumb around the bar.

In-line brake levers: I rember Dia-Compe having a funky, cast brake lever years ago- Advantage 292. At the time I was sure I could have made them in-line levers for the flats with no effort given the way the barrel adjuster had a straight shot out of the lever, but they were too expensive and getting them around the bend might have been challenging.

I’d love a report on the BR-505s. I have the Avid BB7-roads now, and it seems like they don’t quite have the cable-pull ratio worked out. What did you mean “Shop experience suggested that they were more durable than the Avid version”. -durable in what way?

Also- consider this another plug for dirt-drops. (or Midge or Gary bars or whatever). I love the feeling in the drops -totally secure. I use a fairly tall stem so that I can ride in the drops all the time. If I wanted to ride on the tops, I’d want to add interrupter levers -as riding on the hoods isn’t really an option.

One more question- you mention thinking the newer 10sp. STI shifters are “more durable overall” than the 9-speed stuff. Is this just for the shifter specifically? I’m asking because I wonder if chain and cog life might need to be part of the equation?

@jimmy

we’ve had a few Avid BB’s come thru the shop with long term issues.  Basically they got kinda sloppy, had a bit of internal friction (not the helpful kind) and tended to howl.  The Shimano R505 seems to hold up a little better and be a little more precise.  As far as cable-pull feel, they aren’t as crisp a normal road brake, but they’re a little less mushy compared to the Avids.

By durable, I’m only talking about the STI internals, and most definitely not the chains and cassettes.  The older 8 and 9sp STI had a tendency of failing after prolonged use, but the newer shifters seem vastly improved.

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