mjac

What are the differences between a Mountain Bike and a Road Bike Rear Derailleur? I just ordered a Shimano Mountain Bike Derailleur, Acera RD-M360, for a Schwinn Varsity Road Bike because I have an Acera Shifter because it will mount horizontally on the Aero Bars. The Bike Shop said it was fine. Are Mountain Bike Derailleurs and Road Bike Derailleurs interchangeable or you can put a Mountain Bike Dearilleur on a Road Bike but not a Road Bike Derailleur on a Mountain Bike? Like "Jadocs" said in a previous thread when I asked for recommendations for a good Derailleur, if it is a Road Bike, the Shimano 105, if it is a Mountain Bike, the XTR M9100. What is the difference between the 105 and the XTR M9100, two good Derailleurs.



Bike the Shimano

Bill Kapaun

Yes.
No.
Maybe.
Generally Rear is good up through 9 speed. Maybe "some" 10?
That's Shimano. Other brands can have their own "rules".
Road & mountain Fronts use different cable pull ratios.
Than some levels aren't compatible with much other than themselves. Shimano 4700 is NOT compatible with earlier 4x00 versions, for example.
You can look up the rest because life is too short at my age.

mjac

How about components? Are Mountain Bike Rear Derailleurs stronger and more durable? Do they have stronger return springs to eliminate chain bounce? Are Road Bike Derailleurs more precise but more delicate? These are the things I thought might be the differences.

Bill Kapaun

You can think what you want, because it's not all that important.
You seem to have discovered an elephant and are more concerned about what color of hair it has in its' nostrils.
There's more important stuff to concern yourself about.

mjac

Wrong again. If the Mountain Bike Dreailleur was more Durable but stilled delivered pretty crisp shifts, that would important, For some reason I am always dinging up my derailleur and the aluminum derailleur tab. If the Mountain Bike Derailleur could take more abuse that would be a great advantage. And that is not Nostril Hairs.

Bill Kapaun

Ignore list for you since I have a life.

hokiefyd 

Mountain components are generally not any more durable than road components. Traditional mountain derailleurs (like the RD-M360 you just bought) don't have stronger springs to eliminate chain bounce (often called chain slap), but Shadow-style derailleurs do have much stronger springs. Many also have clutches. But this isn't only mountain derailleurs anymore -- many of the road groups are moving to the Shadow-style design, both with and without clutches (this is talking only of Shimano, here). There generally isn't a difference in shift precision between road and mountain derailleurs at the same "quality level" but I imagine that function improves in both lines as you move up in price.

Your bike shop is correct that the M360 will work with your Acera shifter. This is most applicable if you're trying to use indexed shifting. If you're shifting with a friction shifter, then the distinction between "mountain" and "road" pretty much goes away.

Retro Grouch 

Rear derailleurs have 3 significant specifications:
1. What's the biggest cog they will handle.
2. How much chain slack will they take up.
3. The amount of cable pull required to make an indexed shift.
Mountain rear derailleurs will usually handle a bigger rear cog and take up more chain slack. The cable pull thing is kind of a moving target.

Front derailleurs have a BUNCH of specifications and everything has to match. On the front, friction shifting is your friend.

mjac

The more people talk about it the more they say how much the Mountain Bike Derailleiurs and Road Bike Derailleurs are alike. Yet they are designated Mountain Bike Derailleurs and Road Bike Deraailleurs. I thought something had to set them apart. I thought it was sturdiness. But that is not it.

What is the Shadow Design and how does a Clutch work in a Rear Derailleur?

My Acera Shifter is index and the product description from Shimano said the M360 Acera Derailleur shifts quickly and crisply especially with the Acera Shifter. That is why I bought the Acera Derailleur. I understand the Acera is a slight step up from the Tourney and it was only $25 on Amazon. I do not know what the Bike Shop will charge me.

Elvo

Some MTB derailers have stronger springs, clutches, are more narrow to reduce chance of hitting something, and have a higher cassette capacity. Road derailers are typically lighter, can look arguably more aesthetically pleasing, can provide "crisper" shifts due to weaker springs, can have less drag/friction

mjac

So, that is the difference. They are basically the same in shifting speed, precision and durability but a Mountain Bike Derailleur can accommodate an extremely tall first gear and take up the resulting slack when it is shifted up to the conventional gears. If that is the case then you can put a Mountain Bike Dearilleur on just about any Road Bike with the right shifter but you can not put a Road Bike Derailleur on. Mountain Bike with an extremely tall first gear.

squirtdad

Not really there are many road deraillers that have a wide range.

As noted you are trying for a general black/white answer when the answer is: It depends on the exact situation.

you are spinning your wheels trying to get to a general precise statement (note the oxymoron)

again as noted:

rear derailler pull needs to match the pull of the shifts

the rear derailler needs the capacity to handle the largest rear cog

the rear derailler needs to have the chain warp capability to handle (capacity = difference between largest and smallest read cogs + difference between largest and smallest chain ring)

and whet ever you do, make sure it works big/big to avoid bad consequences

mjac

Okay there are no general diffences between Mountain Bike Derailleurs and Road Bike Deraileurs but each individual Deraileur might have some particular features that set it apart from the other group.

mjac

Okay,every Derailleur has its own characteristics and has to be matched to the situation.

hokiefyd 

Besides the differences over the years in cable pull ratio, the distinction between "mountain" and "road" was mostly in marketing and cosmetic differences. Shimano has offered three general cage lengths over the years: short, mid, and long. Many "road" derailleurs traditionally came in short and mid cage lengths, but you could sometimes get them with long cages. And "mountain" derailleurs would traditionally come with mid or long cages, but there are downhill-specific rear derailleurs (such as Shimano Saint) that have very short cages, because you don't need the large wrap capacity on a downhill bike. More recently, "road" derailleurs have taken the Shadow design originally appearing on "mountain" derailleurs, so the visual differences are even less pronounced than before.

For more on Shadow, see . He describes the differences between a traditional derailleur, a Shadow derailleur, and a Shadow Plus derailleur (Plus indicates a clutch). Note that "Shadow" is the design type of the derailleur -- not the model name. He shows two SLX deraillers (both using the Shadow or Shadow Plus design), and a traditional Deore. But the Deore line is also available in the Shadow design.

In many respects, rear derailleurs are very simple devices and, generally, as long as you watch the cable pull ratio (and match it to your shifter) and the specs regarding chain wrap and largest sprocket, you'll be okay. On the other hand, the world of rear derailleurs can seem very overwhelming because there are so many different models and design types available. The bottom line is your shop recommended one that will definitely work with your bike. There are a lot of other models that will also work, both "mountain" and "road" models, but the M360 will work well. It's a good basic derailleur; I have three bikes with them in my household.

mjac

Got it.nI did not know what Shadow referred to and could not picture where a clutch could come in.

There is just such an enormous amount of features and models and most of all no source, even from the companies, explaining what features come with each model and what those features are used for. Throw in marketing and you are lost. I actually picked out the M360. The Old School Shop said they had the 800 and another one in stock and I was going to stop by. But after thinking, I thought, I have an Acera Mountain Bike Shifter let me find an Acera Derailleur . Found one on Amazon and the description said it makes quick, crisp shifts especially with the Acera Shifter. So I called the shop and ordered one since I had talked to them before. Might cost me more. It looked like a solid Derailleur,it was good to hear you have three of them on your own bikes.

hokiefyd 

With your shifter, any 7/8/9 speed derailleur will work. The RD-M360 is a fine choice. It came out 10 or so years ago, and was the mainline Acera derailleur at the time. Although the M360 is still being produced, it's not part of Shimano's "modern" Acera lineup. There are actually two flavors of rear derailleur offered today with the Acera name (besides yours): the RD-M3000 and the RD-T3000. Here again, it's really all marketing, but the M3000 is designed for mountain applications and the T3000 for "trekking" applications. The M3000 is of the Shadow design, and the T3000 is of the traditional design, similar in nature to your M360. Either can be used on any bike with a mountain group flat bar 7/8/9 speed shifter.

The trend with their mountain and road derailleurs seems to be a move toward the Shadow design, and it's proliferating further down into Shimano's portfolio. I think every mountain group now has a Shadow model (even down to Altus: RD-M2000). Will we see this style take over all of the road groups eventually? Perhaps.

dedhed

Not saying this isn't true, but really it's "marketing".
Crisp, quick shifts is really a function of the entire system. If you have a worn cassette, or chain or sticky shifters or bad cables, no derailleur is going to give you Quick & Crisp anything.

mjac

You are right. There were a number of Acera Derailleurs. That just added to the confusion. This one looked more solidly built so I took a shot with it. I could not believe how inexpensive some of these Derailleurs are. You can get a pretty descent Tourney for about $16.

mjac

You are right, but at that point I was ready to grasp at anything. But at least the shifter and the derailleur will have the same shift indexes.One thing one of the guys at the shop said when I told him I was getting inconsistent shifts, is that a lot of times it is the cable housing. I thought of this because when I installed the new housings with the shifter, I blew the first one out with PB Blaster using a straw
and all the factory pre-lube grease blew out of the other end.

tFUnK

The geometry (by design) and weight (moreso as a consequence of other requirements like cage length) differ between road and mountain RDs. You can maybe say that a mountain RD doesn't shift as precisely as a road RD as there may be some trade-off/constraints as mountain RDs need to clear larger cogs, whereas road RDs deal with a narrower range of cogs and can thus be positioned closer (due to its parallelogram geometry) to the cassette and deliver faster, more precise shifts.

mjac

I kept asking what are the differences and it kept coming back they are all more or less the same. So I guess some have features that set them apart and some do not.