Bicycle Mechanics - So what's the downside of using MTB components on a road bike

I have an XTR rapid rise derailleur on my '98 Fisher Joshua Z0 (yes, thank you, it's a friggin' awesome bike). While out riding today I re-realized that the XTR derailleur on that bike is truly awesome. Are there any good reasons for not considering an MTB derailleur for my TT build?

it's a bit heavier
rapid rise reverses the direction of the shifting, so your levers will do up on a down and down on an up.
it's a bit slower, not that most people would notice it, due to the angle and distance from the top pulley to the cassette. closer and more parallel to the ground gives smoother, faster and crisper shifts.

other than that, there's no real downside.

oh, I think I've heard that the latest generation of XTR rear derailers do not match up to road cable pull ratio. The front derailer never matched up between road and mtb, but barcons in friction mode could fix that.

Aside from the technical things AEO metioned, the only issue might be whether you care if road snobs will laugh at you. Personally, I don't care whether people don't approve of my bike, but some people worry about such things.

I think MTB parts are often seen with touring road bikes like the Deore models. I am thinking they are prolly more "hardy" than the road bike cousins.

A) Rapid-Rise sucks.
B) Real roadies will laugh at you.
C) If you need that much gearing capacity, they have good reason to laugh at you.

Some mountain derailleurs don't have the barrel adjuster on them -- I have an LX that does and an XTR that doesn't. If it doesn't you will have to find a place to insert an in-line adjuster.

A) Rapid-Rise sucks.
B) Real roadies will laugh at you.
C) If you need that much gearing capacity, they have good reason to laugh at you.

A) For road maybe (haven't tried it yet), but MTB, it works great

B) What's a "REAL" roadie and why do you care if someone laughs at you? I've never actually ever witness anyone laughing at others in public. I've also read that "Real roadies" will laugh under any of these other circumstances as well: Wearing a Camelpak; wear MTB shorts; ride without road specific shoes with their mating clipless pedals; and don't meet up at the local StarBucks before every ride.

C) Why would anyone bother to laugh at someone that might need more gearing? At least you're out there riding. Isn't that what matters?

If it works on your bike, use it.

tk

If it works on your bike, use it.

tk

I have an XTR derailleur on my "road bike": http://home.comcast.net/~jeff_wills/jeff-grr/pages/jeff-grr%20006.htm . My low gear is 24/34... 18 gear inches. I used this gear on a long, 10 to 15% climb last summer. I get along fine with "real roadies".

i used to run an XT rear derailleur on my 1x9 road bike (with Ultegra brifters). it would confuse many roadies as i passed them, up hills and down; but mostly up hills. for my riding style, i found that the rapid-rise was less necessary on road riding than MTB, because i could pretty clearly anticipate hills and i never up-shifted more than one gear at a time.

here's to never mashing and happy knees.

I don't understand why you would want a mountain type derailleur on a TT bike unless you plan to use it with a mountain cassette for a mountain time trial.

Mountain type cassettes don't work so well on long flat rides because the ratio jumps are too wide and cause big changes in cadence.
Having said that, if you need it you need it.

It begins to function like a Touring bike, and the guys that can climb in a 39/23 gear will hammer off ahead.

It's about tuning the range of gearing to your needs and to hell with "style". Because I used to live in a location where there's normally heaps of hills I used MTB cassetes and derraileurs on all my bikes so I would have the range of gearing options to deal with all the climbs that came up. However I've recently moved out to where the valley around me is very flat with hills around the edges. I'm finally in a place where I can "safely" set up a bike with a proper road cassete and derraileur. But I think I'll likely keep a triple up front just in case I want to explore the hills around the edges now and then.

It begins to function like a Touring bike, and the guys that can climb in a 39/23 gear will hammer off ahead.

Probably true about guys that can climb, but if the OP needs these gears (like me and others), he would NOT be keeping up with them in any event. I do not really care if 'real road riders' think my gearing is funny. I use what works for me, and they can go 'hammer off ahead' all they want. I have 24/34/52 with 11-34 9spd. The only hill I have had to walk is the VERY steep section at the top of Mt Diablo, but I am not alone there.