Advice please: Converting 3x8 to 1x8

Underscore

I'm going to need to replace my chainring next time I replace my chain, which got me thinking: Currently I'm running 48/36(+ unused granny) on the front with (given it's a MTB chainset) a 50mm chainline. This means that I don't like to use the inside half of my 11-28 cassette with the big ring due to cross chaining. However, once I drop to the 36t ring, I rarely need to use the inside half of the cassette either. Hence, I need to replace the cassette each time I replace the chain (even when I tried changing at 0.75% stretch, the new chain still skipped when really cranking).

Then it occured to me that I would be happy to ditch both 48/11 and 36/28 combos, and - if I were to run a single 44t ring where my middle ring is - the 11-28 cassette would give an equal top gear and only a 5% harder bottom gear to what remains. Hopefully, this would then allow me to use a more robust chainring and spread the wear across the cassette to get better life out of that.

Has anyone done this on their commuter? Has anyone got any advice on any pitfalls that I should consider before going this route? Any onther thoughts?

TIA,

_

wgwarburton

Underscore wrote:

...- if I were to run a single 44t ring where my middle ring is - the 11-28 cassette would give an equal top gear and only a 5% harder bottom gear to what remains. Hopefully, this would then allow me to use a more robust chainring and spread the wear across the cassette to get better life out of that. ...

Good plan. You'll need spacers or single-chainring "stack bolts" to use the current spider with a single chainring.
I'd keep the front mech for a while in case the chain is prone to unshipping, but you shouldn't need it long term.
If you can get a singlespeed style chainring to fit, it should last longer and be less prone to derailing. Check the width, though, some may be too fat to run with an ultra-narrow chain, if you need one of those for your cassette.

Cheers,
W.

nicklouse

depending on the crankset you may need to take a file to the chain ring shoulders.

for example shimano rings have different diameter shoulders for middle and outer rings. they work but can be a pain if going the wrong way.

Underscore

Thanks both for the responses.

WGWarburton wrote:

You'll need spacers or single-chainring "stack bolts" to use the current spider with a single chainring.

Yeah, I figured that I'd probably take a hacksaw and file to the existing outer ring to produce the spacers... though I may just get a set of shorter bolts; they don't seem too pricey.

WGWarburton wrote:

If you can get a singlespeed style chainring to fit, it should last longer and be less prone to derailing. Check the width, though, some may be too fat to run with an ultra-narrow chain, if you need one of those for your cassette.

My plan was to get a Middleburn downhill chain ring:

I figure that it'd probably be harder wearing than a normal outer (which is the same price), it comes in 44t, compatible with 8spd (and 9spd, if I decide I need the extra cog of an 11-32) and is designed for single use with a cassette on the back. Also, I'm guessing that, when it does wearout, you can simply flip it over and start again until the other sides of the teeth have worn out too...

nicklouse wrote:

depending on the crankset you may need to take a file to the chain ring shoulders.

Well, it's a Deore HTII crankset but I'm not afraid of a bit of "fettling" if I'm pretty sure that the outcome will work.

TBH, it's the reference to the chain potentially unshipping that worrys me most. The intent is that this should be a simpler (so more reliable) drivetrain. If it's not more reliable, I might as well stick with what I have - it's worked fine so far...

Thanks,

_

nicklouse

keep the front mech and wind the stop screws in to make sure the chain cant jump off.

wgwarburton

nicklouse wrote:

keep the front mech and wind the stop screws in to make sure the chain cant jump off.

Hmm, I'd leave them where they are, then if the chain does drop off you can shift it back on with the mech.

TBH, I don't think it'll be a problem- it's not like the chain comes off when it has the other rings to go onto, is it? So why would it be any different just 'cos you've taken them off.

It's probably slightly more of a risk while the new parts are bedding in- eg if the chain's a little more worn than your new 'ring it might be prone to riding up the teeth for a bit, or you might take a couple of attempts to get the chain the right length. My thinking is/was to keep the mech on until it's all running sweetly instead of taking it off straight away.

...shimano rings have different diameter shoulders for middle and outer rings. they work but can be a pain if going the wrong way....

Fabulous... Any other company would be standardising the fit, so they don't need to make different rings for in & out. Not Shimano...

Cheers,
W.

jonnyboy77

I hope this isn't considered a hi-jack of the thread - but I am researching the same 'upgrade' for my hybrid commuter too.

Its an older bike - circa 2000, Trek 7500 with a Shimano Nexave triple chainset currently. I removed the front mech when it failed and never needed to use the 2 smaller cogs anyway. Now I would like to tidy it up with a single chainring or chainset but not sure what parts I would need to do this?

The current chainset looks like this:


I am wondering - do I need a whole new assembly, or could I just replace the chainrings with a single chainring?

Any input appreciated.

Thanks

Jon

The Rookie

I'm running 1x9 on my commuter...

Front mech as chain guide locked off on stops

Narrower (108mm) BB fitted to bring the chainline in so that the chainwheel was in line with 5th on the cassette

You could run a SS chainwheel (I am using a Shimano one) but the chain still came off, so if you need to run a guide anyway, you could stick with a wheel from your current cluster, that was with a long cage rear mech, the chain 'waggle seen on my new short cage may mean I can run without a guide - not tested yet, I got a cheap road mech as they are lighter than even top quality MTB parts (Sora one on mine is 127g for £5.20 new off the bay, XT mech 139g for circa £10 used), a 7/8speed chain is more rigid so may not have the same problem.

I used some M12 washers to space the (normal) chainwheel bolts with one side taken off with a grinder so they fitted.

Simon

Underscore

Hi Simon,

Thanks for your comments - it's good to hear from someone who is already doing it! Having had a look over the weekend, I reckon that the stock bolts will be fine for me if I go with a DH chainring as the thickness of the DH ring is about the thickness of two normal rings! I can't take your suggestion re the BB, however, as I'm running and external BB. Mind you, the middle chain ring is close on the middle of the cassette so I reckon that the chainline should be pretty close to ideal anyway.

Having said all that, my BB is starting to feel a little graunchy so maybe I should look to go back to square taper and a dedicated single chainring crankset...

_

The Rookie

OK well best of luck, I did go through a little pain getting mine right, and the reason for the narrow BB is I'm running the wheel in the outer location (neater).

You'll love that nice empty (of shifter and second cable) bit of bar area on the left!

Feel free to pm me if you hit any snags or want to bounce any ideas.

Simon