8 Speed with single chainring up front.

Hey all, im build i flatbar roadie for my lady, Its got 8 speed 105 on the back and am thinking of just have a single chainring up front.

I dont need to have a chainguide in place of the front deraileur do I? The chain wont derail off the front will it?

Thanks in advance

It might, leave the front mech on and dial in the limit screws to act a chain guide. Should work a treat.

I’ve done 1x8, 1x9 and 1x10 and never had problems with dropping chains. I think if you do lots of jumps or offroad stuff then the chances of dropping the chain are probaby higher?

I’ve never really understood why a front derailleur should make a good chain keeper - it’s designed to move the chain OFF the chainring, not keep it on. And besides the ugliness, if your gonna have a front derailleur anyway, you might as well have the two chainrings.

Give it a run and just see how it goes and worry about the problems if/when they show up.

FWIW, I’ve had zero trouble with 1x setups using Shimano. I haven’t tried it with anything else.

Keep the front derailleur on- I found it helps a lot,

or you could track down a ss specific 3/32 chainring up front. I use a salsa ring up front on my commuter pig which has seen 1x9 1x8 fixed and ss duty without issue.

So there is more tooth up the front?

I think i’ll do this. and what Snowflake said.


Good point Stu. I think I’ve probably always used bitchin vintage old skool 3/32 rings. You got more tooth for your money back in the day. Maybe that’s the secret?

i think the old school 3/32 rings have ‘more tooth’ but also as they don’t have ramps, shorter teeth etc designed to derail the chain it is more likely to want to stay on

i had a raceface x-type MTB crank running 1x9 on a 29er and it kept dropping the chain at the front. Didn’t change out the rings though - stupid 4 bolt spider.

I’m using a 1x10 on the cross check and they only issue is the chain rubs slightly on the front derailleur when in the highest gear. It doesn’t seem to serve any purpose so I’ll prob ditch it.
Am currently making a chainguard out of an old chainring and might run a chainkeeper/deflector on the inside if there are any problems. I just think you need to keep a bit of tension in the chain. I think I read that somewhere in regards to single ring set ups.

For road a keeper isn’t a big deal, but it may still jump off on big jolts. For CX I’d never run 1x without a keeper/locked out mech/chainguard.

Not all mechs can have the limit screws wound far enough, but a short bit of gear cable anchored at the BB guide can hold it in place.

For a clean solution, I’d go with either a Paul Chain Keeper or put a chainguard (BBG are really well priced, but 52T rings with the teeth cut off are cheaper) on the outside (also keeps grease off pants) and another on the inside, or a chain watcher / jump stop (3rd Eye K-Edge N-Gear (Abbotsford stock the N-Gear))

yep, deeper tooth profile and no ramping/pins etc.

I’m running my 29er 1x9 right now with a ‘normal’ shitmano 32T ring and it’s a PITA dropping chain all the time even with a chain guard. Was thinking about a jump stop type of thing but I think i’d be happier with a ss-specific ring on that one too.

Definitely run some sort of retention device. I ate asphalt quite badly on a 1 x 8 bike, and if your girlfriend does, she’ll hate you and never want to ride a bike again!

SO! Heres an update:

Im totally defeated. The bastard has beaten me. Here are the suspects and the problems
• Shimano 8 speed cassette
• SRAM attack 8 speed shifters
• Shimano 109mm BB
• KMC 8 speed chain
• 44t Cycleunderground Chainring
• RX100 RD

1st and main problem:
Chain instantly drops as soon as i shift to the lowest cog (28T?) Do i need a 107mm?
I know people on here run 1x8-9 without chain tensioners so what the fuck is going on here???

2nd Problem.
Finding it impossible to fine tune the RD, no matter what i do. If i get it smooth as silk down-shifting its stiff and clunky up-shifting . Im not the greatest mechanic but ive setup geared bikes in the past without any issues. When i do get it smooth, If i pedal backward the chain slips gears.

I have never had this many problems setting up a bike before and its pissing me off, What the fuck right?

I think i’ll get a Paul chain keeper if i have to, but id rather fix the main chainline issues first.
Thanks in advance

A few starter questions.

Chain drops off the chainring?

Is the chainring in line with the middle of the cassette?

Is the chain the right length?

Have you set the B-tension on the mech?

Yep its dropping straight off of the chainring.
Yep set the B tension
No the chainring is not in the middle of the cassette, of an 8 speed cassete its half way between the 6 and the 5th (8 being the smallest) i thought it was in the middle but i must have measured wrong.
This would account for the shitty shifting and the derailing.
Chain is normal length but is rubbing on the side of the derailleur cage because of the chainline.

Any suggestion for BB spindel lenght?

Is the derailleur hanger straight?

Does this combo with SRAM shifters work? RX100 was pretty low end back in the day.
A classic cause as Blakey points out it incorrect chain length.
Also if the chainring is very worn this can cause it to fall off too.
Good luck

Bent hanger is definitely worth checking. How new/old are the chainring/chain/cassette?

RX100 wasn’t awful, it was Tiagra level, I had RSX STI (one lower) that performed well until the RHS STI suffered typical shifting failure.

Those SRAM shifters are designed to work with Shimano mechs.

Your chainline could improve fractionally with a 107, but it’s no worse than the inner or outer ring on a double, and they don’t drop chains like you’re experiencing. And if the hard rubbish CX bike I built up with 1x7 and a front mech chain keeper doesn’t drop a chain, then you should be able to fix your setup.

Are you unable to tweak the limit screws on the front mech to eliminate rubbing in all gears? Does it rub on the inner plate? Would moving the mech up the seat tube a little fix this?

RX100 to my knowledge was 105 with a different finish. RSX was the lower end.
its a new Cycleuderground front ring.
Sram shifter should work no problem im pretty sure
I hasd a play around this morning i it shifts a lot better but chain still drops within a turn of being in first gear.

maybe i should just take it to a proper mechaic and let him/her deal with it?

What is the best and easiest way of calculating chain legnth. maybe i should double check that. derailleur hanger is straight.