duongrn

Can someone tell me if this is possible for a road bike before I start buying parts?

Shimano Deore XT Rear Derailleur - Short cage
Shimano Deore XT Cassette - 11-34
Compact Crankset - 34/50 (Lose the big ring and just reduce the crank to a 34 teeth)

This way I can get rid of the Front Derailleur.

I know there is going to be questions about my motivation...I am tyring to customize a commute bike to the bare bones.

I've already done a bike analysis of my cadence and the 11-34 gear range and that is perfect for my commmute.

Thanks in advance.

Joony

I'm still new to cycling parts, but I think anything in the Deore line are for MTB...

duongrn

Yeah they are but they are the only ones that have the 11-34 gear range I need.

grolby

MTB/Road is just marketing, for the most part. "Road" derailers tend to have shorter cages, on average, but that's about it.

Anyway, the only problem with that set-up is that a short-cage derailer probably won't clear a 34 tooth cog. Clearance isn't actually a function of the cage length - it has to do with how much swing the derailer has available to it - but the amount of swing and cage length are generally correlated. A medium or long-cage derailer would be more likely to work, but you might be able to use a longer b-tension screw or something. Someone more knowledgeable may be able to answer that question, but the easier solution would be to get a derailer with a wider range.

'nother

Couple of questions/issues:

• Crankset: if you don't already have the 50/34 that you're going to "lose" the 50 from, why not consider a single chainring crankset?webcyclery.com has some stuff that might interest you. Don't forget the appropriate bottom bracket.
  
• Cassette: 11-34 with a 34 chainring . . . Wow! You have some really tough hills on your commute, or carrying really heavy stuff, or what? If not, I'd consider going a little higher on the low-end, (11-27?), so you get some finer increments.
  
• Rear Der: cage length is not the issue; you're fine with short cage and a single front. Just make sure that whatever you select can handle the largest cog of your cassette. Generally "MTB" derailers such as the Deore XT will handle the larger cogs (34), where "road" models tend to top out at about 28 or so, depending. Check the specs for the specific model you have in mind (look for "largest cog" or "max cog" or similar). At any rate, putting a "MTB" derailer (or cassette, or chainrings) on a road bike is no problem. I have a "road" front (52-39) with a "MTB" rear (12-32, Deore RD), with Sora ("road") shifters, it works just fine.
  

Good luck with your build!

Sheldon Brown

I've got a similar setup on my Rambouillet, 11-34 freewheel in back, 42 tooth chainring in front. I like it.

There is some risk of the chain falling off in front if you don't have a front derailer of some sort. Sometimes people leave the derailer, immobilizing it by leaving off the control and setting it with the low-gear limit stop.

https://sheldonbrown.com/rambouillet

Sheldon "1 Shifter Simplifies Things" Brown

Sheldon Brown

That's a marketing hype designation, means nothing in practice.

Sheldon "Don't Believe The Hype" Brown

duongrn

Crankset: I picked up a FSA Energy compact crankset and was hoping to use that. The link you sent me had some good stuff. But I didn't want to spend on a new crank.

I've got a 12% mile climb on my commute, hence the need for the 34 cassette. I have one bike that uses 27 cassette and I can get up the hill...I am just looking for a little more help.

Am I correct in saying that the derailleur length is only an issue for like a triple crank and that the a short cage should be okay then?

Is your Sora shifter a 8 speed or 9 speed shifter out of curiousity?

Thanks.

'nother

Ah, OK, you are already set then, never mind me. Next project, right?


Indeed, 12% for a mile is fairly stiff . . . but still, 34x34 seems awfully low, even for a wuss like me. Nevertheless, you know better than me what you need or not You can always change out cassettes later on if you find you're not using the lowest combination and/or want the finer granularity versus bigger range.


Yes (again, check the specs for the specific model you have in mind to make sure it can handle the largest cog of the cassette you plan to purchase). Cage length alone does not determine large cog capacity.


8 (I don't think there's a Sora 9 . . . though apparently there was a Sora 7 at one time).

duongrn

How much of a risk would it be that the chain fall off the front? Has it happened to you? Would it most likekly drop when I making shifts?

Thank you.

Thor29

Mountain bikers who run a single chainring in front usually have problems with the chain coming off. This shouldn't be a problem on a road bike since you aren't bouncing around so much. I would try to center the front chainring as much as possible. Maybe by moving the chainring to the inside of the "spider" or getting a shorter bottom bracket if needed.

A short cage derailleur should be fine - pretty much any derailleur will have enough capacity for the gears you are planning to run. The only thing you need to make sure of is that it is capable of handling a 34.

I think a 34/34 low gear is a great idea, personally I could give a flying flip flop about having really tight gear spacing. My cyclocross / touring bike has a 24/39/48 by 11-32 drivetrain. When the hill is steep enough, the bike is loaded enough, or I am tired enough, I am thrilled to have a 24/32 low gear.

sydney

Good catch.

same time

It'll probably happen often enough that you'll want it to stop happening.

I tried it once, and my chain fell off 2 or 3 times per mile. This was in Brooklyn, NY, where there are plenty of potholes, and I was riding an old Cannondale, which is the stiffest frame I've ever ridden. I would regularly lose water bottles on that bike, too. So, there are some variables, but I think that even on the smoothest roads you're asking for trouble if you don't have a front derailler, especially with a small chainring that may have different tooth profiles to facilitate shifting.

If you don't want to use a front derailler, maybe you could get a couple of cyclocross-style chainring guards like this:

https://www.peterwhitecycles.com/Cyclo-Cross.htm

You don't have to pay 40 bucks each for them, though - if you can scrounge up a couple of old chainrings and some beer, you can spend an hour filing the teeth off and fitting them to your crank so that the chain doesn't rub them.

Good luck!

giantcfr1

This is exactly the problem I had with my coversion to a single chain ring / flat bar. I ended up putting the front deraileur back on and setting it as above which solved the problem. Runs like a dream now.






Steve.

jimmythefly

If you're really dead-set against any front derailleur, consider getting a single-speed specific front chainring. Because of the fancy ramps and pins and shaped teeth of many chainrings, they actually are designed to let the chain drop, down to another gear. A single speed ring will have a tooth profile that keeps your chain in place better. You could also run a jump-stop or dog-fang style chainwatcher, along with a small bashguard or ring guard.

Sheldon Brown

I wrote:

I've got a similar setup on my Rambouillet, 11-34 freewheel in back, 42 tooth chainring in front. I like it.

There is some risk of the chain falling off in front if you don't have a front derailer of some sort. Sometimes people leave the derailer, immobilizing it by leaving off the control and setting it with the low-gear limit stop.


Depends on the chainring you use, chainline, and the length of the chainstays.

I think it might have happened once on my Rambouillet, can't recall. That bike has a chainring not designed to be upshifted to (it's a 42 tooth Biopace from a double set) so the teeth are reasonably tall. A chainring designed to be used with a smaller ring next to it, for instance the middle ring of a triple crank would likely have shorter teeth to improve upshifting, and these would be less secure.

I can't recall what sort of crankset you've got and this cockamamie message board software won't let me see your original message at the moment, but if it's a 110 BCD setup, you could use a BMX chainring, such as the inexpensive Rocket Rings I sell...these have tall teeth, not designed to make derailment easy. https://harriscyclery.com/110

If the chain does fall off, it will most likely be when you are shifting. If your chainline is poor, it might also derail during backpedaling.

Sheldon "7 x 1" Brown

duongrn

I've got a FSA Energy Compact Crank, 34 as the front. I was also thinking just a normal Shimano HG 73 or something like that for the chain.

duckliondog

Why don't you just get a normal road group with a triple crank and lose the uncertainty? I ran 50-42-30 in the front with a 13-26 cassette for a long time. It was more than enough to get me up some extremely steep hills.

duongrn

I am tyring to customize a commute bike to the bare bones.

Sheldon Brown

See: https://sheldonbrown.com/fixed

Sheldon "Simplicity" Brown

weed eater

i took the front derailer and unused big+small rings off my cargo bike to lose some weight, but ended up putting the derailer itself back on for chainkeeping. There're more elegant ways to do this but they all require buying something else, which I didnt' see the need to do in this particular case.

TallRider

On my commuting bike, I've got a single chainring, a durable steel one from a really old road bike, that has tall teeth. Works great. But the chain does fall off now and then, usually at the most inopportune times, if I don't have a front derailler on there. So I do keep the front derailler on, with limit screws keeping the trim in the correct spot, so that the chain doesn't fall off. Much, much cheaper than chaingards.

Moose

COCKAMAMIE!!!

How dare you! Using such language...tsk tsk.

Maybe you have your view set up differently than I do, but I can view the entire thread from the "Reply to thread" screen. I just scroll down and there it is, newest reply first and a link at the bottom of the page that will take me to the next set of 25 replies (if the thread has over 25)

duckliondog

Wow, sorry, mate, I guess I got too caught up in the hill climbing problem and forgot the reason for it! My friend destroyed his front derailleur one time and didn't replace it for months. He had to stop to shift gears, but you won't have that problem.
If I was making a minimalist commuter I'd go single speed. If I wanted multiple speeds I'd pick the gears I want out of a cassette (34,16,11, for me), shove them on the hub with some spacers, and control it all with an old school style friction shifter.

The Carpenter

According to the Shimano website the max sprocker for that der. is 34 teeth.