Fitting a larger chainring to the Apollo

[smorgasbord]

I just fitted a 48 tooth on my Luna Apollo, and it clears! The Apollo comes with 44 tooth chainrings, which is actually a really good compromise if you ride both fast on-road and also steep hills off-road, but I wanted a higher top speed. I already have the 10-50 SRAM GX cassette, so the obvious step was to try a larger chainring. My original was a Wolf Tooth Drop Stop 44T so I ordered from Wolf Tooth a 48T Drop Stop. I did need a longer chain, which meant having to buy two chains since the 126 link chain wasn't longer enough.

Here's a chart of how my speeds have changed:

At a cadence of 90, top speed goes from 34.2 to 37.3. Gear inches at the high gear changes from 127.6 to 139.2. At the low end gear inches changes from 25.5 to 27.8. Should still be low enough, but if not I can try the new SRAM 10-52 cassette.

Here's the 48 toother on the bike in the fully unloaded position (minimum clearance). I didn't measure it, but it looks to be about a ¼" of clearance.

 

[kurt_s]

I have a Luna Apollo and went to the Wolftooth 46T from the 44T. An 126 link chain works fine and maybe even better than with the 44T.

 

[smorgasbord]

Did you measure for the chain length as recommended by SRAM? That is:

1) Lower air pressure in the rear shock until it's at the 30% sag mark.
2) Wrap the chain around the largest cog in the rear and the front chainring.
3) Pull both chain ends towards each other. You want to have an overlap of 1 outer and 1 inner link.
4) Cut the chain so that you have an inner link at each end. That might mean an extra link overlap or one link less overlap.

If you don't have the the two link overlap then getting into the big cog is harder and could be stretching your derailleur more than is goo. If you have too much overlap then the chain will hit itself around the rear derailleur when on the smallest cog.

And then did you adjust the B screw per the SRAM adjustment guide (which Luna didn't provide with the bike in my case)?

 

[kurt_s]

I broke the existing chain and laid it out against a new 126L chain and noted they were same/same. Installed the 46T and the new chain. Then removed the air from shock. Tied the swingarm up to the seat so it stayed at 30% sag an then adjusted the B gap using the latest Sram B gap guage. Then I recharged the shock and tested rider sag again. It is quieter and shifts better with the 46T and 126L KMC DLC chain than it did with the 44T I think.

Your sag and B gap is the critical thing to keep an eye on I believe. That is why I mentioned the latest Sram B gap tool. Makes it easy.

 

[smorgasbord]

Well, if 126 was the right length for a 44T chainring, then it might not be the right length for a 46T chainring.
That said, if it shifts into the large cog without straining the derailleur, and the chain doesn't come back on itself when on the small cog, you're fine.
Clearly, the derailleurs have some range to them - for instance SRAM recently came out with a 10-52 cassette (their max used to be 10-51), and apparently you don't need a new derailleur to use it.