My TT bike currently has a 56T front chainring which I essentially run in 1x mode (I have an inner ring but I never use it). This season I am replacing with a single narrow-wide 58T chainring and removing the front derailleur (although I may fit a chainguard).
My question seems simple but I’ve seen varying advice and usually related to 2x chainrings. Assuming the cassette at the back remains the same, by how many links do I need to increase chain length?
Thanks in advance
I would calculate from scratch rather than using your current chain as a benchmark. That could introduce unnecessary error.
The method I always use is to put the chain on the big (only in this case) front chainring and the big rear cassette cog, without going through the rear mech, and add 1 additional link to this length.
Thanks. Problem is I’ve seen that method for 2x but also comments that say for 1x add 2 or even 4 links so I’m a bit confused!
That method is supposedly the optimum. ie. it gives you a chain that is long enough for cross-chaining but also no longer than is needed. I don’t know why a 1x setup would dictate a longer chain since the chain’s journey doesn’t change just because you’ve removed the small chainring.
It’s not necessarily gospel but I’ve used this method for all my 1x bikes over the years and it’s worked well.
Go round the chainring and the largest sprocket, but not through the derailleur. Add two full links (two outers and two inners). Remember that the quick link is an outer too.
In reality the derailleur can probably handle a link too few or too many. The bikes you need to be careful with are full sus because the rear suspension changes the frame length.
I’ve been riding 1x for about 4 years and I can tell you this: the “add 2 links” or “add 4 links” methods don’t translate to 1x road. I literally used the “add 4 links” method yesterday and ended up with a chain that was about 6 links too short.
For reference, I ride a single 50t with an 11-40 cassette and I needed the entire 114 link chain to make it work. I’ve yet to find a reliable quick-and-easy measurement method for 1x road, but I’d start with at least 114 links if I were you.
Precisely the reason for this thread is that there is a lot of different advice so very much appreciate all the contributors. My TT bike doesn’t have any rear suspension and it is 58T with 11-25 at the back. Currently 56T with 11-25. I suppose I can use the methods above and compare to the existing chain and see what “looks” best. Equally I could probably use the existing chain to start with using the quick link to get another view?
For my 1x CX bike I’ve always used the add 2 links and it’s always worked perfectly for me. This is a 36t with an 11-32 cassette.
I’m planning to change my road bike to 1x (50t 11-32) this spring, so I guess I’ll see if it still works for that
Get a complete new chain, ultra sonic clean, and wax. I wouldn’t use a old chain on a new chain ring or block. IN a TT when every watt counts. If you don’t have access to a ultra sonic, use mineral turps, in a jar. Let is soak. Shake it around. Then strain it out. And then wax. If you don’t wax, then buy Smoove Lube, a little expensive but will last a long while and Zerofriction rates it as the best in bottle wax lubrication.
Yes I meant use the old chain to assess the sizing and then replace with a new chain. Cheers
It depends on the frame length, and maybe also on the derailleur. The “add two full links” rule is for sram.
If you know your frame dimensions, you can also calculate the chain length in inches.
Chain = 2 x chainstay + front teeth/4 + rear teeth/4 +1
Front and rear teeth are the amount of teeth on you largest chainring and largest sprocket. Chainstay length is in inches.
There is a good article on the parktool website,
I ride TT’s, but what has put me off going with a single chainring is that I think the chain line, from the new big single chainring at the front, to the bigger cogs at the back will now be more angled.
I would have thought this makes the drivechain less efficient.
Is there a way to minimise this?
Yep as stated, 2 full links if using a road derailleur, 3 if you use a clutched derailleur 
It’s not as dramatic as you think because the 1x ring isn’t as far outboard as it is on a dual setup. I don’t think it’s any less efficient than using a 2x setup, though I have absolutely no data to back that up. If there’s a difference, I’m sure it’s beyond marginal.
Thanks.
Does the new single chain ring just bolt onto the crank in the same place as the old larger one of the twin chainring set up?
What makes the new single chain ring less outboard than the original ?
The single chainring mounts the same way on the crank, yes. But you have to look to the chainring design itself—it’s specifically designed to set slightly further inward than a 2x big ring would.
You also have to considering the design of the teeth and 1x derailleurs themselves, both of which are designed to optimize the 1x system overall and reduce drag. Pairing a 1x chainring with a standard derailleur will still work, but likely not be quite as optimized as a full 1x system.
If it’s a sram or similar chainring, you might need new chainring bolts or spacers for your old bolts.
The 1x chainring sits in the middle of where the other two would have been.
Oh, and +1 for switching out the derailleur. A clutch one is helpful for stopping the chain from dropping (in addition to the narrow-wide chainring design).
I’m thinking of doing a quick 1x road conversion for the last few hill climbs of this season, are there any more insights on chain sizing from anyone since Feb 2020? @adehughes Hopefully you’ve actually had a chance to race that bike this year rather than last! Cheers.
@Dylan_van_Green I’d forgotten about this thread. I managed 3 races in March 2020 and then nothing until May this year. So yes I have raced it. I can’t remember quite what I did but luckily I keep a blog for exactly that reason (it’s here if you are interested) Basically I used the park tools chain sizing on their website and then added a link or two! Looking back now in hindsight I think I didn’t need to add the extra links because I never use the 25 cog anyway. Hope this helps
That’s good to hear! Thanks, I’ll check out the blog 