Converting Tiagra to single gear (at crank)

[DeafFatalBruno]

Hi

While i have been fiddling with bikes for some years, this is something i have not done before and I just learning about my own ignorance.
I have flat bar road bike with a Tiagra FC-RS400 crankset ( 5 mounting points for the gears,.. 2018 model)
I would like to convert this into a single speed on the crank and keep the 10 gears on the back wheel.
I just learned that if I just removed the front derailleur and lower gear, then chain would likely come off very quickly on rear wheel gear changes.

So, i would need something like narrow wider (alternating) gear for the front.
I found over the year that it is very confusing what in bike world is compatible and what is not.
So - if possible i would appreciate some advice on what the best path here is.

- are there any 50t ( or 48) gear i can buy that fit a Tiagra FC-RS400 ( i.e. 5 mounting points crank) that are narrow wide, that I can just replace. Type/name/model/brand would be extremely helpful. Anything available in Australia at all?

Or is it the only option to replace the whole crankset? I Can get any 50t( ish) gears or I am I stuck with MTB gear ratios.
This i for a road bike after all.

Any advice on where I can or should source parts in Australia would be highly appreciated.

Thank you and kind regards

[Andy01]

I have no idea as to your specific question, but I would ask (and almost certainly showing my ignorance here);

I currently have a Giant Roam 1 with a 2 x 10 Deore drivetrain. I only use the larger front ring about 99.9% of the time - the only time I use the smaller ring (in the 2½ months I have had the bike) is for crossing a muddy "creek" after recent heavy rains in Brisbane. So probably used the big ring for about 619.8km of the 620km I have done on the bike. In that time, I have never had the chain jump off when shifting exclusively with the rear gears (when on the big ring up front).

So, the questions are;

1. Why bother removing the small front ring & derailleur ? Why not leave it there and just not use the front shifter ? Is it a weight thing ?

2. Does a 50T front ring and your 10 speed cassette give you adequate gearing for any hills / terrain that you might encounter ? My Roam has 44T front big and 42T (ie. larger than most road bikes I think) rear big, and as mentioned I still go to the small 32T front ring for real slow riding. I generally never use the rear big gear with the front big ring (although it rides well with no noise or noticeable rubbing, unlike a big front & big rear on a 3x system) - that is where the small front ring comes in.

3. If you did remove it, why would you expect the chain to jump off when changing the rear ? Why would it be different to just using the big ring on a 2x system like I do ? My understanding was that the narrow-wide front rings for 1x systems were mostly for off-road MTBs where the chain is bouncing around madly because of the terrain (that is why they have clutches on the rear derailleurs as well) - but I may be completely wrong in my assumptions.

As I said, I am probably showing my ignorance here

[Duck!]

You're chasing a unicorn. N/W rings, as mentioned previously are primarily designed for MTB use, so won't fit on your crankset, and are too small, typically maxing out at 36 or 38T. There are some cycloross-oriented ones that may fit, but still only go up to 44T, maybe 46.

You don't need a N/W ring on a road bike unless you're really pushing the definition of "road" and hitting really rough stuff. There are 1x specific chainrings which are the same thickness for all teeth, however I think the largest you'll get is 48T. The difference from a multi-gear ring is the tooth shaping; on a 1x ring the teeth are taller and all the same height and shape because they don't have to allow for front shifting, thus hold the chain better. What you need to look out for is the difference between a 1x and a true single-speed (SS) ring; 1x is 3/32" tooth thickness to fit narrower multi-gear chains, while SS is thicker at 1/8", which the narrow chain won't fit on.

2x & 3x rings have very finely shaped teeth of differing heights to allow shifting. This shaping makes them prone to chain drop at extreme angles and need some kind of guide to keep the chain on; the front derailleur serves as a chain guide/retainer as well as moving from one ring to another.

The final piece of the puzzle is the correct Bolt Circle Diameter (BCD), which logically enough is the diameter of the ring and crank at the mounting bolts. You're looking for a 5-bolt, 110mm BCD.

[bychosis]

For ease of discussion, if you refer to your conversion as a 1x (1-by) conversion you’ll get a little less confusion.

No actual idea on chainrings, but I’m running a 2x on my flat bar roadie and find it useful on occasions. I ghetto converted mine from 3x by grinding out the rivers on the granny ring (smallest) and took it off. If I converted to a 1x I’d probably want a chainring that fits in between the big and small at present to maintain some of the lower gearing.

You could remove the shift cable and wind the limit screws in on the derailleur to use as a chain guide. You should also aim to mount any 1x chainring in the position that gets you best chain line for your range of gears.

[10speedsemiracer]

Sorry, am also not a fan of 1x for a roadie. Why limit the bike and exaggerate the jumps between sprockets ? Makes no sense. If you don't like the triple, swap out the shift lever and the crankset and go 2x.

Do the whole swap for about $250-ish with new parts. There's a 50-34 in Tiagra (fc-4700) and a shift lever (sl-4700-l or whatever).

Will need a new shift cable and the chain resized, but that's minimal stuff.

I'm assuming you want to do this as you don't like the triple crankset .. If you already have a 2x then I'm lost as to why anyone would want to do this. Tiagra shifts quite nicely, especially with Shimano flat bar shift levers. One of the better-shifting bikes I own is a Tiagra 4600 (prior series) 10sp

[MattyK]

There are plenty of larger (50t) 1x narrow wide chainrings on eBay, by all accounts they are fine.

You will probably need one with a 110 bolt circle diameter (BCD) to suit your cranks. And you will probably need some 1x chainring bolts.

[warthog1]

Sorry, am also not a fan of 1x for a roadie. Why limit the bike and exaggerate the jumps between sprockets ? Makes no sense.

Well said.
Makes no sense to me either.
Even on my gravel bike I am glad I don't have 1x.

[rkelsen]

Sorry, am also not a fan of 1x for a roadie. Why limit the bike and exaggerate the jumps between sprockets ?

The OP said it's a flat bar, so he's clearly not racing on it.

IME, there's nothing wrong with a 1x, as long as it covers your needs. A lot of people carry an 11 tooth sprocket around... but how many actually use it?

With a 1x, you will.

[baabaa]

Before you mess about going x1 and all things like lousy chainlines (for any single 48 tooth plus with greater chain wear), suggest you try a set of 46/36 chainrings - Is light on the maintenance, wear and tear and the tears for big $$ on parts. Seems to work for most things people do on flatbar bikes.
If you do go x1, a 42 tooth chainring is quite like the 2x 46/ 36 which is used in CX = is easy to live with.

[Bentnose]

I’m assuming the OP maybe has a 34/50 and doesn’t see much need for the 34T as he lives in a flat area? I used to live in a flat area and had a 42/50 with a 12/25 cassette, worked well, 42T was very useful in the flat area. Of course the OP hasn’t reappeared so it’s only a supposition.

[10speedsemiracer]

Sorry, am also not a fan of 1x for a roadie. Why limit the bike and exaggerate the jumps between sprockets ? Makes no sense.

Well said.
Makes no sense to me either.
Even on my gravel bike I am glad I don't have 1x.

Agree wholeheartedly. It's funny, the 1x gravel bikes I'm selling usually go to people 'new' to gravel. The old hands typically grab the 2x.

Sold two of them today (carbons) and a couple of carbon racey-racey type roadies .. which means I'm really busy tomorrow prepping. Oh well..

[baabaa]

I’m assuming the OP maybe has a 34/50 and doesn’t see much need for the 34T as he lives in a flat area? I used to live in a flat area and had a 42/50 with a 12/25 cassette, worked well, 42T was very useful in the flat area. Of course the OP hasn’t reappeared so it’s only a supposition.

True but they do phoenix like return.... also forgot to mention that with a 42 chainring fitting on the inside you can use a cx chainring guard on the outside ( a 50 tooth just wont work) - then the same 2x chainring bolts will work and no need to try and find a set of single ring bolts - these also stop the chain wanting to jump off outwards and then a cheap chain catcher from going inwards.