RMoudatir

I just got my first road bike last Thursday, I do have some knowledge about road bikes but have been stuck with a single speed for a long time but finally got a road bike. The road bike I'm using is a 2016 Specialized Allez DSW Elite with Shimano Tiagra 4700 group set. It came with a 12-28 cassette but I was wondering what gears I could use for this bike. Would I need to replace the short cage derailleur for a medium/long caged one if I want a bigger cog? What is the limit on how big of a cog I could use? I was thinking of a 11-34 or maybe if possible up to a 11-40, I heard you can use mountain bike rear derailleurs and make it work. I also heard that Tiagra 4700 has compatibility problems, so I'm not sure what to do exactly.

FBinNY 

If you only wanted to go to 30t you might skate by with he short cage RD. But going as wide as you're proposing will definitely call for a long cage RD or mtb derailleur. Don't take me as an authority on this, but I believe that the super big cassettes, like 40t, are going to need a special RD, and a standard mtb won't be adequate.

10 Wheels

I was able to ride up a 22% Hill with just changing the cassette to a 11/32

Craptacular8

Not an expert on this, but with what you've currently got, the easiest/cheapest change to get more gear range without making tons of other changes would be to go with a medium cage version of the Tiagra 4700 rear derailleur and a 11-32 cassette. I know that combo works. I couldn't tell from Specialized's specs whether the rear derailleur that is stock on your bike is the medium cage version or not, it doesn't specify. I would guess that it is, but your LBS that you purchased from should be able to confirm.

If you want a crazy big cassette like you're indicating, trickier, and much more expensive. You'd need to go with a Wolf Tooth Roadlink problem solver. If you want to go up to 11-34 and keep your current front chain rings, you add this one tool, assuming a medium cage derailleur, and you're good to go. For anything larger like you're talking, you can't keep your current front chain rings either, as the wolf tooth fix, which is adjusting derailleur offset maxes out at a 14 tooth difference in the front chain ring set, the medium cage derailleur can't handle the total tooth size of keeping the 50, so have to swap out the front chain ring to a more common 46/36 or 48/34. This would allow you to run an 11-40 behind.

Regarding going with mtb rear derailleurs, they aren't compatible with the STI shift levers you've got, you'd have to lose those, and go with bar end/down tube shifters if you want to go with a long cage mtb derailleur. Since the STIs are a 200+ option, this is certainly not a direction I would want to go on a complete bike.

You'd potentially need a new chain with the above changes as well, depending on total tooth count.

base2 

What chaineings did the bike come with? Stepping down to a 50-34 from a 53-39 or 52-36 that road bikes typically come with would be a pretty reasonable change...and could be cheaper than a cassette/derailleur. I can't speak to Tiagra, but in Ultegra, the gs cage derailleur I think tops out at 28, the sgs derailleur tops out at 32. The difference between an 11 speed 11-28 and an 11 speed 11-32 is the 16 tooth sprocket right in the middle.

For my touring bike, I have an 11 speed XT 8000 11-40 cassette and an XT M9000 Shadow Plus derailleur and a Shiftmate 8 so that I can use Ultegra/105 STI's. The XT rear Derailleur will take up to a 45 tooth capacity, and Ultegra Front has a capacity of 16 so a 50-34 double would work. I did all the math and have a 44-28 and some spacers on an XT crank. It works because I am within everythings capacity limits. The Ultegra cage isn't supposed to like any rings smaller than 32, but in reality the difference in diameter between 28 and 32 isn't enough to make a difference in practice, so long as the max 16 tooth difference between rings isn't exceeded.

So...I guess you can do anything you want. But Swapping the chain rings is a cheap start if you are already at the derailleurs capacity from the get go.

What is the derailleurs capacity, how big is the biggest cog it will take? That will tell you where to start.

RMoudatir

My road bike already came with compact chain rings 50/34 and it comes with a short caged tiagra 4700 rear derailleur

base2 

Then a 11-34 is the most you can go and be within the 39 tooth derailleur total capacity.

The Shimano spec page is a bit confusingly written. 11-28 is the smallest with a front double, 12-34 is the biggest.

Worst case a 12-34 with a 50-34 chainring is a 38 tooth difference.

So, an 11-34 cassette would take you to 39 tooth difference and would be the gs derailleurs (model # RD-4700-SS) absolute limit.

CS-M771 would do the trick.

Maelochs

What kind of mountain-climbing are you foreseeing where you will need a 34x40 gear? And why would you then need the 50x11? I think anyone who could spin out a 50x11 would be able to climb almost anything on Earth with 34x32.

If that is what you want, go for it ... but it is a pretty extreme range.

I would likely look at the kind of riding I planned to do and build a bike that would do it well. If I needed to haul huge loads up mountains (40-tooth cog) i would go for an MTB or CX chainring---46-36, or an MTB triple (42-32-22?)

If you can get that big load to the top of a mountain, .... unless you have a 78-tooth big ring or something, you aren't going to be able to pedal fast enough to keep up with gravity ... and anyway, braking will be your main concern.

If I needed to cruise at 35 mph on the flats or win sprints, I would go for a bigger chainset (53-39?) or stay with the 50-34 and an 11x28 which Ought to giver you a wide range of terrain capability and still silly top end.

I might suggest that you go out and ride your bike a while before you start modifying it ... but if you absolutely know what you want to do ... have at it and have a ball. Lots of folks here have given you the info you should need.

Ride on and enjoy it.

jefnvk

Why this advice isn't given more, I have no clue, but it is the best advice. Once you've ridden something, you'll understand what needs changed, but more importantly WHY. Then, you can either give an in depth description of why something isn't working, and get far more pertinent advice, or just know what you need to change.

RMoudatir

What do you think of this?

Phil_gretz

Only half of this statement is true, and it's not the second half...

Phil_gretz

^ These two thoughts are spot on. First, OP should ride the geared bike and determine what changes might be made later. If he's coming from single speed riding, then having the option of another gear or two should make a world of difference to begin with.


The 11-32T rear with 46/36 or 46/34 front combination would be a sweet and elegant place to wind up. What mountain could not be tackled with that gearing?

CliffordK

I'd say to get out and ride your bike as configured first, then worry about getting the perfect gearing later. You are already riding a single speed or fixie,so you must have some experience climbing hills in high gears.

Keep in mind that a huge rear sprocket comes at the expense of tight gearing. So you won't have the gears if you want to pedal just a little easier, or just a little harder on the flat.

Craptacular8

STI and mtb rd work for 9-speed and below, is this what you're wanting acknowledged? 9-speed M592 Deore shadow rd reportedly will work with 10- speed sti, though this kludge still does not get the OP to the mega range they were requesting.

Phil_gretz

I'm sorry, I was pulling your chain a bit. You're right. 4700 10-speed isn't guaranteed to work with MTB derailleurs. Trying it couldn't hurt, but could cost. I think that Tiagra long cage derailleurs can handle 32 tooth cogs with adjustment. I've done that.

trailangel

I think the fool needs to use Chain-L..... his chain all rusty.

RMoudatir

I was just considering this change because where I live there are a lot of climbs and going up a 5% climb was very tough, I'm not the strongest rider, I only weigh 60kg, I just want gearing that can tackle any steep climb without the need to grind up slowly. A 11-32 or 11-34 would be great and I heard Tiagra 4700 can be done with it without much modifications. I would like a 40t if it were possible but no big deal if it can't be done easily. If I buy a 11-32 or 11-34 M771 10 speed cassette and a 4700 medium/long cage derailleur and swap it for my current set up would it work?

base2 

Your bike has 10 gears in the back and 2 in the front? Is that correct?

Then Yes, as stated in post #7 a CS-M771 will work. As with any cassette change, some minor adjustments *may* be necessary and any decent bike shop will do this as a complimentary service if you bought the cassette from them and have them install it.

Per the spec sheet of the 4700 GS derailleur: Anything beyond 34 tooth big gear, 39 tooth capacity (with a front double) or the bike having a different number of gears on the cassette than 10 invalidates the CS-M771 recommendation.

As far as 9 speed Tiagra, I don't know. As far as mixing mountain/road components, "it depends." Others clearly do know what combinations work, but I don't. But I don't think your bike has 9 in the back.

In any event, if "because a 34 tooth cassette just wasn't low enough for me" I'd look up Jtek Shiftmate if I were to start mixing mountain/road families. But that's just me. As an example of what Shiftmate does: In Shimano 11 speed, the mountain/road cassettes are the same, and interchangeable, save for a spacer needed for the XT on the 11 speed free hub body, and (obviously) the enormous 40 tooth cog the road derailleur won't accomodate...What is different is the "pull ratio." of Each family is designed to a different standard. The ratio between the shifter/derailleur are different between the road and mountain families to move the derailleur the exact same distance on the cassette. The Shiftmate has 2 different sized pullys to correct the ratio to be compatible with the combinations of components of the other family. Thus allowing road shifters with a mountain derailleur, or vice/versa mountain flat bar mountain shifters with a road derailleur. Another example would be the compatibility between Campy v/s Shimano/SRAM. Shiftmate makes it possible.

But given that the Tiagra you already have accommodates a 34 tooth cog...I don't see the need to go mixing & matching.

If your bike has 10 gears on the cassette, Buy the CS-M771, The 10 speed road shifter with the 10 speed road derailleur, with the 10 speed mountain cassette should be fine. Like 11 speed, 10 speed cassettes are interchangeable, it's the pull-ratio standard the shifter/derailleur is designed to that would cause the problem and the Shiftmate would fix if you were mixing shifters/derailleurs.

Retro Grouch 

Also, there is no free lunch. When you install a wide range cassette to gain an easier hill climb gear, you lose the relatively tight spacing between the flat road gears that most riders use most often. A bit of experience will help you to make the best compromise.

RMoudatir

Thank you and yes my road bike is a 2 x 10