Chainline question and 1x Drivetrains

[johanpre44]

I still have an older non-boost bike (from 2016, just when the boost spacing started coming out). I bought the bike new with SRAM GX 1x11 (the frame is 1x specific, no mount options for a front deraileur). My crank is nice but still the 104BCD/4-bolt kind and with the 30t 104BCD  (Raceface Turbine just before the 30mm cinch direct mount model was released). I'm looking at getting a direct mount crank (maybe a Raceface Turbine/Aeffect or Sram GX) specifically to have an option to run a 28t chainring if things get really steep. It will also be easier to clean, maybe lighter and look a lot better.

Riding around home (Jhb/West-rand) I use the middle of the casette, but it feels like when things get steep I spend a lot of time on the large cogs. Around home it does not really get that steep except if I search out those really steep hills but when I go on holiday (visiting George a lot) I do spend a lot of time in the granny gear and suffering up the mountains. And this is the question on the chainline (and chain wear).

Is the only reason for the 52mm chainline to give enough frame clearance (this makes sense with large chain rings)? When calculating the centre of the casette I get to about 43mm or 44mm with my non boost frame asuming the 11 speed casetts is about 43 or 44mm thick (smallest to largets cog distances including the lock ring). Is there any benefit of trying to move the chainring closer to the center of the frame (like having a 49mm chainline if possible).

When I bought the bike the mechanic who set it up moved the threaded bb spacer (73mm BSA shell) from the drive side to the non drive side to improve the chainline a bit to try and reduce chain wear somewhat (I'm not too sure about this since it changes the Q-factor).

Any suggestions or comments on this? should I just stick with the standard and get a nice direct mount crankset?

[RobertWhitehead]

I wouldn't go with a 28t at the front, increase the range of the cassette and stick with the 30, heck even go with a 32 oval. In terms of chain lines, it doesn't make too much difference on the 1x, don't over think it, if the chain doesn't make a noise when in the granny and or the rear mech doesn't drop the chain then you're golden 

[DieselnDust]

19 hours ago, johanpre44 said:

I still have an older non-boost bike (from 2016, just when the boost spacing started coming out). I bought the bike new with SRAM GX 1x11 (the frame is 1x specific, no mount options for a front deraileur). My crank is nice but still the 104BCD/4-bolt kind and with the 30t 104BCD  (Raceface Turbine just before the 30mm cinch direct mount model was released). I'm looking at getting a direct mount crank (maybe a Raceface Turbine/Aeffect or Sram GX) specifically to have an option to run a 28t chainring if things get really steep. It will also be easier to clean, maybe lighter and look a lot better.

Riding around home (Jhb/West-rand) I use the middle of the casette, but it feels like when things get steep I spend a lot of time on the large cogs. Around home it does not really get that steep except if I search out those really steep hills but when I go on holiday (visiting George a lot) I do spend a lot of time in the granny gear and suffering up the mountains. And this is the question on the chainline (and chain wear).

Is the only reason for the 52mm chainline to give enough frame clearance (this makes sense with large chain rings)? When calculating the centre of the casette I get to about 43mm or 44mm with my non boost frame asuming the 11 speed casetts is about 43 or 44mm thick (smallest to largets cog distances including the lock ring). Is there any benefit of trying to move the chainring closer to the center of the frame (like having a 49mm chainline if possible).

When I bought the bike the mechanic who set it up moved the threaded bb spacer (73mm BSA shell) from the drive side to the non drive side to improve the chainline a bit to try and reduce chain wear somewhat (I'm not too sure about this since it changes the Q-factor).

Any suggestions or comments on this? should I just stick with the standard and get a nice direct mount crankset?

I prefer a 104 BCD chainring interface as it makes it easier to change the chainring without removing the crank.

chainline is recommendations is designed to centre the chainring on the cassette. The 49mm option for 142mm rear axle and 52mm for 148mm was designed to allow chainrings up to 36t on 1 x 11 speed and 12 bikes respectively. Most new bikes are now 54/55mm chain line to accommodate SRAM t-type rear derailleurs. So if you’re using a SRAM drivetrain you have a wide range to chainline to play with. As Robert says, if the chain isn’t dropping you’re in the right chainline range and the chain can accommodate this.

where you could run into some trouble is if your bike has very short chain stays I.e . A hardtail but most mtbs from even the 2015 era were good on this front.

so experiment and find the limits but I’d suggest rather using a 10-52 cassette and keeping the 30t ring or maybe a 32t to give you a decent spread and the 104 bcd wil allow easy swaps between the two chainrings. 
if you want to go 28T then direct mount is your only option 

Edited October 14 by DieselnDust

[johanpre44]

I was thinking long and hard about this yesterday and realized that with the 104BCD there are some more options and that it will just be better to stick it out with the 30t chainring. Think I will however work on fixing the off-center q factor and see if there are problems running in the big cogs (worst case I can simply add some 2.5mm spacers between the chainring and crank to put it back to where it is now and still having the better q factor).

[dave303e]

honestly, if you live in GP and ride anywhere else, you need a few setups to get the most out of a 1X drivetrain. SRAM AXS app has proven this to me with data.

Mostly gravel around GP I run 36t chainring.

Van Gaalens, Breedts, Buffelsdrift or for longer gravel type rides like Cullinan to Tonteldoos - 34t

Most of your bigger hill areas, clarens, george/knysna, magoesbaskloof, mankele, sabie etc- 32t

Expedition Adventure Races- 30t

This is on a 1x12 setup 10-52 cassette. But you can apply the same logic to any 1x drivetrain

Each front chainring has a chain the right length for it, they get stored together and I swap them for whatever race is happening. 90% of my training rides are from home with the 36t. It can get expensive to have them all, but then your rolling replacements take longer as the mileage is spread between setups. It also means the distribution of wear on your cassette is more evenly distributed.

[DieselnDust]

4 hours ago, johanpre44 said:

I was thinking long and hard about this yesterday and realized that with the 104BCD there are some more options and that it will just be better to stick it out with the 30t chainring. Think I will however work on fixing the off-center q factor and see if there are problems running in the big cogs (worst case I can simply add some 2.5mm spacers between the chainring and crank to put it back to where it is now and still having the better q factor).

Q factor is the distance between the pedal contact centres , not the spacing of the crank. If your crank is offset to one side the q-factor will remain the same as this is set by the crank spindle length and pedal spindle length plus where the pedal engagement is situated from the end of the axle. 
centre the crank so it’s spaced evenly left and right and then space the chainring using Chainring spacers if you need to adjust the chainline. You will also need longer chain ring bolts when doing this …