MTB conversion to drop bars - Shifter compatibility - ST-4600

[jaydee]

Hey all, I have an old road bike I want to scavenge from and build a mtb with drop bars. I'm struggling to figure out what components will actually work and which I need to buy new.

So here is my parts list from the old frame:
- Shifters: ST-4600 road, 2x10 speed
- Cranks: FC-6600 Ultegra, 175 mm, 53/39 - yeah, not ideal for mtb
- Bottom bracket: SM-BB52, 68mm
- FD: FD-2300 2spd
- RD: RD-5600 105, 10spd, 11-32 cassette
- Brakes: BR-4500 Tiagra - won't be reusing those

My main question is on the rear derailleur. I'm looking to have a wide range of gears so would like something with 11-40 to 11-43.
What derailleurs will work on here? I saw on another thread that the RD-M592 will work even though it is 9 speed, but it only has a rated max teeth of 36.
Are there alternatives to this RD that would increase the max size while still being compatible with the FD? I found some Deore versions (RD-M5120-SGS and RD-M4120-SGS) and while that would mean new chainrings, that would be OK as long as I get good shifting.

So what rear derailleurs can I use on this build, considering the existing cranks and FD, and a need for large cassetes?
Ask any questions or concerns you guys might have, I'm happy to dive into the details and find what I've missed so far .

As for which bikes I'm considering, I was looking at these: the Orbea Onna, Giant Talon, and the Specialized Rockhopper - this last one comes with a Deore RD-M5120 RD, so if it is compatible with the shifters, I might just stick to that and keep the 1x setup or add the 2x cranks with smaller gearing later on.

If you're curious on the braking side - I was just going to buy a set of road mechanical brakes like the Avid bb5 or bb7 road. In the future I might convert to hybrid mechanical / hydraulic like the TRP HY/RD or, if I do really like the setup, a full hydraulic groupset. The existing hydro brakes will be reinstalled on my wife's electric bike (that has mechanical ones at the moment).

 

[BikeGremlin]

Hi,

That sounds like an interesting, if challenging project.
Curious to see how it pans out.
To answer...

Briefly:
Check out my RD compatibility page to get some idea of what can work with what. For all practical purposes, your existing rear shifter (ST-4600) is compatible with 6 to 9 speeds and old 10-speed road RDs (but not the 10-speed MTB or the new 10-speed road RDs). Relevant articles:

• Compatibility [04] Rear derailleurs
• Compatibility [07] Rear shifters

In more detail, there are several things to consider and note - so I'll give it a go in no particular order:

Frame size​

Consider that drop bars are curved forward (away from the saddle), and that might affect your stem and frame size choice (see here about frame's stack and reach).

MTBs usually have very short stems to begin with, so there is not much room for going shorter, unless you go with a smaller frame (which will make the bars sit a bit lower, usually).

Thinking outside the box​

I love the elegant brake solution idea - for using the road bike disc brakes.
These kinds of adaptations do require some thinking outside the box as they say.

My favourite shifting option - friction shifters - is difficult to mount on a MTB frame. Gevenalle might be a good option, if that price is acceptable and if they are available for sale.

If you are sticking with STIs (no friction shifters), a problem may be to find wide enough gearing. Triples are no longer supported and triple shifting STIs may be more and more difficult to source (I may be wrong, Shimano Claris is still being made, and companies like L-Twoo and Microshift are still making Shimano-compatible shifters of all kinds).

For small doubles, like 24-40 and similar (don't take me for the exact gearing combo), finding a matching front derailleur could be a problem. Such cranks are available for MTBs (though even there, 1x systems are pushing out any doubles).

Shimano GRX makes some 30-46 cranks, that are almost good for off road (though something like 24-40 would be closer to optimal IMO), but they usually require a Shimano GRX front derailleur... which requires compatible shifters (new 10-speed and 11-speed stuff).

This leads us to the next "section:"

Set goals​

Are you looking for the lowest total cost (usually, but not always: the smallest number of parts replaced), or at the lowest cost but without sacrificing the desired gearing (and if so, what is your desired gearing) and so on?

Because, it can get pretty confusing pretty quickly.
I wrote a series of articles about compatibility, and you could (ideally anyone could) see for yourself what works for you and decide:
https://bike.bikegremlin.com/category/technical-part/compatibility/

Of course, i understand that's easier said than done and that it does get overwheliming. But it's also hard to answer the question by covering every possible scenario - it's easier when most things are defined.

On that note: gear ratios explained and discussed (what is good enough, overlapping gears etc.).

Conclusion​

I suppose this is not a small amount of info (especially if you go down the rabbit hole of the provided links). I hope it's more helpful than confusing. But your plan is what I would describe as ambitious/challenging in terms of the number of parts that must be tuned to work together and things that can go wrong or be complicated to match.

The good thing is your bike/frame choice - especially the two models with a front derailleur (which means they have housing guides/stops for the front derailleur - even though the housing is internally routed which sucks).

Relja

 

[jaydee]

Hey Relja, thank you for the great response.
Indeed, my goal is to keep overall cost down. I want to end up with a versatile bike that can take very wide tires, perform acceptably well in the dirt and has road levers for comfort. That's why my focus is on my existing STI levers, since these are usually costly.

The frame size is a good point - I was looking for L or XL frames since I'm 1.88m, but looking at my road bikes and matching that with mtb manufacturer recommendations I'm a bit confused.
My two road bikes have similar geometry: ~400mm of reach as measured according to your instructions and confirmed online. The reach measurement supplied by the manufacturers of mtbs for my size is always higher: around ~440mm.
How worried should I be about matching these measures between road and mtb bikes? My existing handlebar will add 75mm of reach to the above measurements, but it is also a bit narrower than mtb handlebars.

Recap
Rear Derraileur
Assuming any 9 speed derraileur will work with my shifter, these bikes look promising: Orbea Onna, Coluer Pragma. They have 2x9 transmissions and I'm seeing Altus and Alivio RDs (RD-M2000, for example) with cassetes up to 34 or 36 teeth, which paired with the common 22x36 supplied chainrings should be enough given the speed calculator here. If I understood things correctly, that is - meaning this combination of shifter and RD allows me to have 10 speeds, it wasn't clear to me in the documentation if the derraileur will adapt to the shifters or if it's the other way around.

Front Derraileur
I'm assuming the FD won't be an issue, since I'll be using the FD and crank that comes with the bike. And if it turns out to be an issue, would it be too expensive or hard to get one that is compatible with the 22x36 chainrings?

Given all this, I decided to simplify. Get a bike with as much compatible parts as possible, instead of reusing as much as possible.
So new parts list becomes:
- New cassette: 10spd, 11x34 or 11x36 (might even push this a bit, depending on exact derraileur model that shows up)
- 10 speed chain
- Road brake calipers (mechanical)
- Brake cables
- New bike!

Stuff that comes with the bike:
- FD
- Cranks and chainrings 22x36
- RD - Altus or Alivio, 9 speed
- Brake rotors

What I'll reuse:
- Handlebar
- Shifters
- Bar tape?


How's it looking? My main worry just became the frame size all of the sudden

 

[BikeGremlin]

Hey Relja, thank you for the great response.
Indeed, my goal is to keep overall cost down. I want to end up with a versatile bike that can take very wide tires, perform acceptably well in the dirt and has road levers for comfort. That's why my focus is on my existing STI levers, since these are usually costly.

OK, that makes perfect sense.
Note that it might end up costly still. In case it helps, here is my "gravel" bicycle project, converted from a hybrid/trekking bicycle:

https://www.bikegremlin.com/1306/my-road-gravel-bicycle-build/

Costs did add up for that project (it came to around $1,000 in total - or over $500 if I deduct the price of the frame itself and the dynamo lights and the dynamo hub).

The frame size is a good point - I was looking for L or XL frames since I'm 1.88m, but looking at my road bikes and matching that with mtb manufacturer recommendations I'm a bit confused.
My two road bikes have similar geometry: ~400mm of reach as measured according to your instructions and confirmed online. The reach measurement supplied by the manufacturers of mtbs for my size is always higher: around ~440mm.
How worried should I be about matching these measures between road and mtb bikes? My existing handlebar will add 75mm of reach to the above measurements, but it is also a bit narrower than mtb handlebars.

Good question.

For a rider of a given "size" (arms, torso, and leg length), a well-fitting flat bar frame will usually have a shorter reach compared to a well-fitting drop bar frame - because drop bars add some "length" thanks to their curve (unless a very low-aero position is required, in which case things may be a bit different, though that also depends on the rider's torso proportions).

Having said that, compact drop bars usually have a shorter drop-bar reach (your model with 75 mm is among the shorter ones), which can be more easily compensated for (compared to flat bars with basically zero extra reach) using a shorter stem.

However, for off road riding and more technical trails, I prefer to have my bars a bit closer compared to an "on-road" road bike. So there's that (your preferences and experience may differ).

Recap
Rear Derraileur
Assuming any 9 speed derraileur will work with my shifter, these bikes look promising: Orbea Onna, Coluer Pragma. They have 2x9 transmissions and I'm seeing Altus and Alivio RDs (RD-M2000, for example) with cassetes up to 34 or 36 teeth, which paired with the common 22x36 supplied chainrings should be enough given the speed calculator here.

This gear calculator lets you save and share the gearing setup (as that link should show when opened).

Yes, with 22 on the smallest front chainring, you need not worry about having a huge number of teeth on the cassette (even 32 should be more than enough for any terrain).

That lets you use any kind of RD, even decent (long cage) road RDs could work!
* By "any kind" I mean any compatible, of course - in terms of not having to use some newer MTB RD that can handle 40+ teeth.

Also note that there is an option of using a RD hanger extender to handle a huge cassette with a "normal" road RD - video showing that:
https://www.bikegremlin.com/1053/pairing-shimano-11speed-mtb-cassette-with-a-road-groupset/

If I understood things correctly, that is - meaning this combination of shifter and RD allows me to have 10 speeds, it wasn't clear to me in the documentation if the derraileur will adapt to the shifters or if it's the other way around.

Yes - this depends on your use and choice. Shifter generally dictates the number of speeds and both the cassette and the RD must match it. So, depending on what you are swapping, you must change more or fewer things to have it all matched.

See this reply for a bit nicer explanation (it deals with SRAM stuff, but the principle is the same):
https://www.bikegremlin.net/threads/sensah-empire-sram-red-11-speed-compatibility-with-shimano-rear-derailleur.492/#post-2056

Front Derraileur
I'm assuming the FD won't be an issue, since I'll be using the FD and crank that comes with the bike.

Oh... it could be a problem!

FD will need to work nicely with your "old standard" 10-speed front shifter. FDs that work with that kind of shifter cable pull were usually designed for larger chainrings.

More recent MTB double and Shimano GRX ("gravel") FDs require a different cable pull (longer).

And if it turns out to be an issue, would it be too expensive or hard to get one that is compatible with the 22x36 chainrings?

Well, you would most probably need to change the shifters (STIs) along with the front derailleur. And, since STIs are usually sold in pairs, you would need to run them miss-matched, or change also the rear derailleur to match the new rear shifter's cable pull.

As you can see already, things can get complicated and costs do add up.

I just hope I've explained clearly enough what and how exactly is (mis)matched.

Given all this, I decided to simplify. Get a bike with as much compatible parts as possible, instead of reusing as much as possible.

That makes sense.

So new parts list becomes:
- New cassette: 10spd, 11x34 or 11x36 (might even push this a bit, depending on exact derraileur model that shows up)
- 10 speed chain
- Road brake calipers (mechanical)
- Brake cables
- New bike!

Stuff that comes with the bike:
- FD
- Cranks and chainrings 22x36
- RD - Altus or Alivio, 9 speed
- Brake rotors

What I'll reuse:
- Handlebar
- Shifters
- Bar tape?


How's it looking? My main worry just became the frame size all of the sudden

I hope I've explained clearly enough why it may not be a well-working swap with that plan.

It is an interesting project, but if budget is tight, it is usually cheaper to just sell an existing bicyle as used, and get a fitting (try before buying) used bicycle in a decent condition... though that takes time and effort (and may also cost extra).

An important question is: how important are the drop bars? Or, from the opposite perspective: how important is having a front shock absorber on a dop bar bicycle?

Because many modern gravel bikes (despite the modern equipment downsides) can fit 40+ mm wide tyres and be relatively well gripping and comfortable off road.

This is what I chose for myself (my current two bicycles - a commuter, and a gravel/sports/offroad bike):

https://www.bikegremlin.com/2744/robust-and-cheap-to-run-bicycle/

Relja

 

[jaydee]

Good question.

For a rider of a given "size" (arms, torso, and leg length), a well-fitting flat bar frame will usually have a shorter reach compared to a well-fitting drop bar frame - because drop bars add some "length" thanks to their curve (unless a very low-aero position is required, in which case things may be a bit different, though that also depends on the rider's torso proportions).

Having said that, compact drop bars usually have a shorter drop-bar reach (your model with 75 mm is among the shorter ones), which can be more easily compensated for (compared to flat bars with basically zero extra reach) using a shorter stem.

However, for off road riding and more technical trails, I prefer to have my bars a bit closer compared to an "on-road" road bike. So there's that (your preferences and experience may differ).

This is worrying me a bit, I might visit a couple stores around me to get a feel for different models, not having any experience on mtbs my size does not help.

This gear calculator lets you save and share the gearing setup (as that link should show when opened).

Yes, with 22 on the smallest front chainring, you need not worry about having a huge number of teeth on the cassette (even 32 should be more than enough for any terrain).

That lets you use any kind of RD, even decent (long cage) road RDs could work!
* By "any kind" I mean any compatible, of course - in terms of not having to use some newer MTB RD that can handle 40+ teeth.

Also note that there is an option of using a RD hanger extender to handle a huge cassette with a "normal" road RD - video showing that:
https://www.bikegremlin.com/1053/pairing-shimano-11speed-mtb-cassette-with-a-road-groupset/

Thanks for the calculator, I've saved that link. I have seen those adapters, and were considering themas an option. I've been trying to find a decent used frame and was considering just using that adapter with my existing transmission to extend the gearing a bit. That would be another option instead of buying a new bike.

Yes - this depends on your use and choice. Shifter generally dictates the number of speeds and both the cassette and the RD must match it. So, depending on what you are swapping, you must change more or fewer things to have it all matched.

See this reply for a bit nicer explanation (it deals with SRAM stuff, but the principle is the same):
https://www.bikegremlin.net/threads/sensah-empire-sram-red-11-speed-compatibility-with-shimano-rear-derailleur.492/#post-2056

Got it, no problem there

Oh... it could be a problem!

FD will need to work nicely with your "old standard" 10-speed front shifter. FDs that work with that kind of shifter cable pull were usually designed for larger chainrings.

More recent MTB double and Shimano GRX ("gravel") FDs require a different cable pull (longer).

I see.. On the front shifter compatibility page I read this (bold styling is not my addition):

Most double front shifters can be used with most FDs. Mixing different models of shifters from the same brand is no problem. Even mixing one manufacturer’s shifters with another manufacturer’s FDs is not a problem. Mixing road shifters with MTB FDs (and vice versa) works fine as well.

And later on

Road vs MTB front shifters​

Road double shifters can often be combined with MTB FDs and vice versa.

But then I read the "MTB vs road FD" section of the FD compatibility page and while the text there is a bit less encouraging, it still ends on a positive note. I was lulled into a false sense of security
Is there any way to validate if the shifter and FD work together before buying the bike and having physical access to them, or is it a "sure thing" they won't work?

But assuming they don't work, is there no other FD that could work with this shifter? What is the limitation, is it the small size of the chainrings?

Well, you would most probably need to change the shifters (STIs) along with the front derailleur. And, since STIs are usually sold in pairs, you would need to run them miss-matched, or change also the rear derailleur to match the new rear shifter's cable pull.

As you can see already, things can get complicated and costs do add up.

I just hope I've explained clearly enough what and how exactly is (mis)matched.

I see, and in that case the project doesn't really make sense - the point is to use the material I have available. I need to investigate further which FD can work with this shifter, understand the possibilities and work from there.

That makes sense.

I hope I've explained clearly enough why it may not be a well-working swap with that plan.

It is an interesting project, but if budget is tight, it is usually cheaper to just sell an existing bicyle as used, and get a fitting (try before buying) used bicycle in a decent condition... though that takes time and effort (and may also cost extra).

An important question is: how important are the drop bars? Or, from the opposite perspective: how important is having a front shock absorber on a dop bar bicycle?

Because many modern gravel bikes (despite the modern equipment downsides) can fit 40+ mm wide tyres and be relatively well gripping and comfortable off road.

I want to go off-road but like the comfort of drop bars, those are really the main point of the project. The suspension is not that important, if the tires are large enough, I would gladly use a rigid frame bike (I prefer the aesthetics and usability).

I have considered multiple options, like used cyclocross, trekking and hybrid frames. The main issue is the difficulty of striking all points:
- finding a frame in my size
- large enough wheels - either the frame only accepts thin tires or it doesn't have information on maximum tires supported
- appropriate brakes for the shifters - tried looking into mini v-brakes and cantilevers but that got uncertain very fast as well mini-v accepts smaller tires and cantilevers are harder to maintain. Compared to mechanical disk, they're not as simple to match and not as sure to support large tires.

I drafted multiple options, but in the end this option of buying an entry level mtb and replacing some or all of the transmission ended up being the cheapest.

For example, an entry level gravel bike will run you at least 1000€ here, sometimes with triple chainrings and mechanical brakes, and max tire sizes of 32 or 35. Mechanical brakes are good enough for a budget build, but if I'm raising the budget I'd expect more.

On the frame / frameset side I haven't been able to find an option that would keep total costs under ~800€, and that is with some very creative and trusting aliexpress shopping. If I were to spend the 800€, I'd probably be better off buying the gravel bike.

For now, this option of buying an entry level mtb is the best value for money. I get a new frame with new components that I can even salvage and reuse on other bikes (with appropriate warranty!), and it's still very under budget compared to the entry level gravel. Until you pointed out the FD issue, total costs were around ~600/650€. It is still very distant from the 1000€.

I'll continue to search for a cheap frame or bike with rigid frame and large tire capacity, but it hasn't been easy. If you have any recommendations for sites to buy used bikes or frames from in Europe (delivery to Portugal please) I'd be very happy! (Aside from ebay )

This is what I chose for myself (my current two bicycles - a commuter, and a gravel/sports/offroad bike):

https://www.bikegremlin.com/2744/robust-and-cheap-to-run-bicycle/

Relja

Those look great! I do love the simplicity of quality, tested components and the peace of mind they bring. If I were a bit more confident in my mechanic skills I might be a bit more interested in cantilever brakes. Will continue to search though
Thank you so much for the help so far!
José

 

[BikeGremlin]

Regarding the cantilever brakes, there are alternatives:

• Mini V-brakes (a lot simpler to set up).
• Drop bar brake levers with a V-brake compatible pull, like Tektro RL520 for example (Amazon .de affiliate link for the model I bough there a few years ago).
  Such levers will work with normal V-brakes and MTB mechanical disc brakes.
• Using road-compatible disc brakes (as was your original plan), like Avid BB7_ROAD (model DB-BLBG-7R-A1).

Regarding the FD compatibility:

• For not-too-demanding use, old-pull double FDs could be set to work more-less OK (depending on one's criteria of OK).
• For demainding quick shifting, that may not be good enough (and I would expect off-road riding to require reasonably fast shifting).
• Likewise, when discussing the new road (and "gravel") Shimano FDs - their cable pull is significantly different so I could never get one of those to work nicely.

Relja