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Discussion Starter · #1 ·
I wrote this to add to the general knowledge-base of bicycle-mechanics. In the hopes someone may benefit if they plan to upgrade/customize their hybrid bicycle...
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Having installed a Shimano Ultegra Hollowtech II crankset and the corresponding Hollowtech II bottom-bracket on my (former) Trek FX 7.5 hybrid, I ran into a problem. This particular hybrid thinks it's a mountain bike. This due (in this instance) to it's needing a top-pull front-derailleur. A top-pull front derailleur means the cable that operates the derailleur is coming down the seatpost from above. Bottom-pull is where the cable comes from under the bottom-bracket*. Usually. And this presented a problem: Finding a top-pull FD, that could handle the 30-39-52 and the 22T difference, was just about impossible - according to the specs I read in each candidate for a FD.

The derailleurs that could handle this size chainrings were made for road bikes, as was the crankset. It was an attempt to convert a hybrid to, in this situation, behave as a road bike. So a trick I tried was to run a pulley underneath the FD on the seat-tube - to reverse the cable direction. All is fine - until I installed a Shimano Ultegra FD and attached the cables. I could get the Ultegra FD (triple model - FD-6603) to go, with minor difficulty, from the small to the medium chainring. But it didn't like the idea of going to the large. After a substantial period of time, it would. But it then refused to go from large to the medium chainring. Adjusted cable-tension, reset the high - low adjustment-screws. Still it would not, in varying patterns (no large to medium, large to medium - no go to small, etc). So I finally conceded that this thing hates me! LOL. So I started looking for another FD.

As I said - all the front-derailleurs that were top-pull models were made for mountain bikes. This means they had specification for a maximum large ring for between 44 and 48T. The Ultegra was 52T. As I was sorting through specs on every FD out there - nothing met the criteria I had set for the bicycle. But then I remembered something - Shimano also claims the Ultegra rear-derailleurs are given a max-tooth on cassettes as being 27 (28?) teeth on the large cog of a cassette. I was running Ultegra RD's, and heard from people who were doing the same, with cassettes of up to 32T. With zero problems being reported. So...

I had a Shimano FD-M961 XTR front-derailleur living, brand-new, in a box for a rainy day. It is a dual-pull unit. It has a 34.9mm clamp - yay! And it was snowing. The XTR FD-M961 is given, by Shimano, a max of 48T. So what the hey - I put it on. Luckily it had a 34.9mm clamp. As my Trek also is 34.9mm on it's seat-tube it was easy. But would it work? It did and does. Only minor adjustments to the high-low screws and one click on the cable tension adjustment on the shifter itself (SRAM Attack 9spd.). Operates perfectly.

So if you run into a Shimano MAX claim in their ad-copy, disregard same. I can testify that it is working happily, with room to spare, on a 30-39-52T crankset. May this nugget of information come in use to you. With the prevalence of hybrid bikes selling out there, you may well run into people with the same problem. And the Shimano FD-M961 XTR FD will work perfectly.

Anyone have another good FD to suggest? I'm sure the XTR can't be alone regards being low-balled by Shimano. Anyone else have stories/information on attempting this sort of project on a hybrid? What worked for you? People are, by nature, tinkerers. Tinkerer + Hybrid = Innovations & Change.

* not everyone reading this is likely to be a seasoned bike-mechanic :p

Happy Trails!
 

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Max chainring size

Puchnuts said:
So if you run into a Shimano MAX claim in their ad-copy, disregard same.
For rear derailleurs, it is easy to see how there could be an upper limit for cog size, mostly due to clearance between the upper idler pulley and the cog. For a front derailleur, it is much harder to see how there would be a maximum chainring size. there is the issue of curvature of the derailleur cage, but experience with "compact specific" front derailleurs has shown that to be insignificant, at least over 53 to 50 tooth size range. 48 is pretty close to 50, so it is not surprising that a front derailleur with a "max limit" of 48t works just fine with larger rings.
 

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Discussion Starter · #3 ·
Indeed - but Shimano has made a habit of shooting itself in the foot by stating these cast-in-stone limits in their ad copy. And it's not just the Ultegra RD I mentioned. I've heard similar stories regards the 105 and Deore models. One person wanted an Ultegra - but stated he just read a Max 27T. So he kept looking. I asked him his intended set-up. It will work fine.

Me thinks Shimano should put the equivalent of a Surgeon General's Warning on their specs. :D
 
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