Wooden Tiger

So, a buddy of mine is piecing together "Frankencycle," basically, a mishmash of all sorts of parts, as the name would suggest.

What strikes me as questionable is that he is using Ultegra derailleurs on this...mountain bike. He claims it doesn't matter what type of derailleurs are used, but if this is the case, why are these companies making "mountain bike" parts like Shimano XT, XTR, etc.?

Would using road bike parts on a mountain bike tend to be reliable, or is he just going to end up breaking perfectly good parts for a task they just aren't made for?

dabac

For rear derailers, the difference between supposedly road and supposedly MBT is how much chain slack they can soak up. MTBs will typically be built to tolerate a bigger speed range, so they need a bigger gearing range.
Road going bikes in need of wide ranges will often use MTB rear derailers. And the MTB DH crowd sometimes use road derailers.
There's very little drawback to using a bigger derailer than actually needed. But road derailers are supposed to shift a little crisper and flop around a little less.
Road fronts are built to be a better fit to bigger chainrings,
And a silly change in actuation ratio to make them incompatible with MTB front shifters.

But a big part is marketing hype and deliberately engineered incompatibility to provide more items for sale.

Wooden Tiger

So basically, one really isn't build "sturdier" than the other, it's just a matter of the dynamics...

Shimagnolo

I once tried an Ultegra FD with an XT crankset with 48T large chainring.
It totally sucked.
The cage was shaped to fit a larger chainring, so even when lowered to fit the 48T ring,
the tail of the cage was too far away to shift onto the large ring.

dabac

Well, whether it's road or MTB, the power source is the same, so not much reason to change things from that perspective. Sometimes though, MTB parts CAN have better seals. And road parts CAN be flimsier as they're usually not expected to deal with the dynamics of drops and jumps.
Although a fair bit of supposedly road kit gets used for Cyclo-Cross, which certainly can be quite rough too.

Rowan

As far as derailleurs go, the Shimano fronts these days are MTB specific. The cable pull on MTB shifters is different from that on STI shifters. That means you won't get the derailleur to move to the correct position with road shifters.

Road rear derailleurs generally come in short and medium cage lengths, because the expectation is that the cassette won't have a bigger sprocket than 28 or 30. The largest MTB sprockets go to 36T, and a long cage is needed to enable the chain slack to be taken up when dropping down to the smallest sprockets.

Rear long-cage MTB derailleurs can be used on road bikes without issue. Many randonneurs use them because of the terrain they often have to ride.

Touring bikes often come specced with road triples which are patently too highly geared for the loads and roads to be encountered, and many owners swap out the crankset to an MTB one. The increased width of the spindle for the MTB crank can present issues with Q and chainline, but it can be done successfully, and the best road derailleur to be matched with STI shifter is the Tiagra triple.

Some of these mismatch issues can be overcome by using bar-end shifters in friction mode.

I built a frankenbike from a GT MTB for Machka to ride in a 200 randonnee after here regular bike was stolen. I had a week or so to put it together from parts I had lying around, and it worked enough for her to finish. But there were tuning issues along the way.

HillRider

If you were using MTB shifters, I can understand why the shifting was poor. In the past, Trek fitted 105/RX-100 road front derailleur intended for a 52T large chainring to bikes with RSX cranks that had a 46T large chainring and the shifting, using road brifters, was just fine.

Wooden Tiger

How'bout if you used an Ultegra FD with an Ultegra RD? Would it have made a difference?

Shimagnolo

No, I was using Ultegra brifters.

Shimagnolo

That has nothing to do with it.
The end of the cage was too far from the chainring.

Wooden Tiger

Well, given all the differences between the parts and what-not, it just sounds like a pain and it's better off to just stick with MTB parts on an MTB unless everything's going to be swapped over to one or the other.

Shimagnolo

I am using an IRD Alpina D with a 48T XT crank & Ultegra brifters, and it works fine.
I have also seen the Tiagra FD recommended for such applications.

RubeRad

"Touring" RD and "Mountain" rd are the same thing; it's just a question of cage length to be able to handle a much larger tooth difference.

Rowan

I referred specifically to road triples, which means cranksets. The RD in this case little to nothing do with what I was talking about. It was in the context of people swapping out a road triple crankset for an MTB crankset to improve the low-gear options depending on terrain and load carried. This was the case with my Fuji Touring way back around 2000, and my subsequent touring bike, a Thorn Club Tour, which was specced the same way, with an MTB triple... and both have the Tiagra triple front derailleur because they both use STI shifters -- the Fuji Tiagra, and the Thorn Ultegra.

krobinson103

All my bikes are franken bikes. I have a SRAM X9/105/deore/slx Soma Double cross, an slx/deore/xt/xtr mtb and a 2300/acera roadie. They all work fine. Just have to watch what FD you use. As long as the cage is long enough the label on the RD matters not. Just don't try to mix SRAM and Shimano. They don't like each other! Soma runs a deore 48/38/26 triple. Fuji runs an SRAM truativiv 48/38/26 and the roadie has a richie compact.

Wooden Tiger

That's one pet peeve of mine; when bicycle manufacturers mix and match component groups. Whether they work in unison and work happily together, I dunno, but I can NOT stand it when companies will mix a Shimano derailleur with a SRAM derailleur, then be running something like Hayes or Magura brakes. Maybe it's just a matter of "OCD," but I prefer to stick with one component group over a "mix and match."

krobinson103

Not companies, me. I use what I have. If it works I don't care what label is on it.

HillRider

+1 I have a Shima-nolo bike with a Campy rear derailleur, cassette and hubs and a Shimano crank, shifters, chain and front derailleur. A Shiftmate keeps peace in the family and everything works happily together.

Shimagnolo

That is sort of the reverse of what I would want.
I have one all-Campy bike, and 3 Shimano-equipped bikes.
I think the best components are:

- Brifters: Campy
- FD: Campy
- RD: Shimano

HillRider

Yes, the "mongrel" I described above started as an all-Campy Chorus 10-speed and I replaced things as they wore out or I needed better gearing.

Wooden Tiger

While I'm not particular about the brand, I just find parts from the same company work together better than parts from two different companies. If some parts are happy working with parts from another company, I don't care too much, I just have to take a longer test ride.

krobinson103

Only ones I found with issues are SRAM and shimano shifters/deraillers. Most of the el cheapo stuff I've played with is all based on Shimano standards so it works with just about anything. Never tried campy or microshift though so I can't comment on cross compatibility with those. Most of my bikes use shimano.

Wooden Tiger

My current MTB is running SRAM X7/X9 derailleurs and Elixer 3 brakes. I'm pretty sure my old MTB ran Shimano Deore all the way around. I liked the Deore component group. While I prefer Shimano to SRAM, I wouldn't discount a bike because it had a SRAM component group.

Retro Grouch 

Rear derailleurs have two functional specifications:
1. biggest rear cog capability.
2. chain slack take up capability.
They are two distinctly different things. You can generally "cheat" on either, to a degree, but there comes a time when they simply won't work.

My general philosophy is, if I already own components in my spares box, I'll bolt them up and see if I can make it work to my satisfaction. If I'm BUYING parts, however, I'll always hold out for components that are designed to work together.

Bottom line, your friends bike might work just fine. On the other hand, he may get frustrated trying to make an workable combination function.

krobinson103

The issue with Sram/shimano is the pull ratio. Same thing with road/mtb front deraillers and shifters from
Shimano. They can work but its not always easy.