I'm having some troubles with the stock FSA chainring on my Thron 6.9. I think Focus is using non-optimal parts on this bike (also noticed they use the same chainring on Shimano drivetrain Jam²)
On my new Thron2, with a FSA G4 34t megatooth chainring, When pedelling uphill mainly off-road(especially on grass), and putting pressure on the pedals, it makes a noise from the chainring and a sensation through the pedals. After closer inspection it appears the chainring isn't letting go of the chain properly causing a bit of 'chainsuck'. The problem comes and goes a bit, the video below demonstrates it at its absolute worst:
Focus sent me another FSA chainring this time instead of a direct mount it was a 104bcd attached to a spider. Same tooth profile, same issue straight away. The chain was also replaced at that time.
I believe that focus isn't using the optimal chainrings on the Thron/jam for the Hyperglide+ chain. FSA megatooth chainrings are made for 1x11, not 1x12, and Hyperglide+ chains are especially picky about the chainring tooth profile.
So I purchased an Ethirteen e*spec Bosch direct mount chainring that Trek uses on the Rail 7 with the same 12 speed SLX cassette and chain. On ethirteens website it specifically says it's compatible with 12 speed shimano. My bike is with my lbs now getting it fitted.
Wolftooth components has a good writeup on the difference between chainrings / chain engagement for Hyperglide + chainrings and what happens if you use the wrong one is exactly what's happening with me on my Thron with both the FSA megatooth chainrings:
www.wolftoothcomponents.com
As per the above link, it appears that the FSA chainring uses the first "drop stop A" style of tooth, where as the new Ethirteen uses the third "drop stop ST".
So I have high hopes that when I pick up my bike this week that the issue will be resolved and the pedaling will be a lot smoother. You can see in this picture the wear on the wide teeth. This is the spot where the Hyperglide + chain inner link comes in a bit.
After emailing FSA they informed me that only the megatooth chainrings with 'SH12' designation printed on it are compatible with Shimano 12 speed chain. So the plain FSA megatooth chainrings are not optimal and may cause extra chain wear/chain suck.
I'll let you all know how my bike is when I get it back from the lbs with the E*thirteen chainring.
*edit* few months later, i can confirm that the bikes are now shipping with the correct SH12 chainrings. However still the models i see in my local store have the old chainring. So might want to double check what you've got.
This is a screenshot from a youtube video of a 2021 Thron with the new update chainring. Check out how different the teeth profile are! And clearly you can see why the existing chainring was a problem..
On my new Thron2, with a FSA G4 34t megatooth chainring, When pedelling uphill mainly off-road(especially on grass), and putting pressure on the pedals, it makes a noise from the chainring and a sensation through the pedals. After closer inspection it appears the chainring isn't letting go of the chain properly causing a bit of 'chainsuck'. The problem comes and goes a bit, the video below demonstrates it at its absolute worst:
Focus sent me another FSA chainring this time instead of a direct mount it was a 104bcd attached to a spider. Same tooth profile, same issue straight away. The chain was also replaced at that time.
I believe that focus isn't using the optimal chainrings on the Thron/jam for the Hyperglide+ chain. FSA megatooth chainrings are made for 1x11, not 1x12, and Hyperglide+ chains are especially picky about the chainring tooth profile.
So I purchased an Ethirteen e*spec Bosch direct mount chainring that Trek uses on the Rail 7 with the same 12 speed SLX cassette and chain. On ethirteens website it specifically says it's compatible with 12 speed shimano. My bike is with my lbs now getting it fitted.
Wolftooth components has a good writeup on the difference between chainrings / chain engagement for Hyperglide + chainrings and what happens if you use the wrong one is exactly what's happening with me on my Thron with both the FSA megatooth chainrings:
Chain Compatibility by Chainring Tooth Profile
Wolf Tooth patented wide-narrow chainring tooth profiles are compatible with all 9-speed, 10-speed, 11-speed, and 12-speed mountain bike and road bike chains from SRAM, Shimano, KMC, Campagnolo, Connex, and Wipperman.
www.wolftoothcomponents.com
As per the above link, it appears that the FSA chainring uses the first "drop stop A" style of tooth, where as the new Ethirteen uses the third "drop stop ST".
So I have high hopes that when I pick up my bike this week that the issue will be resolved and the pedaling will be a lot smoother. You can see in this picture the wear on the wide teeth. This is the spot where the Hyperglide + chain inner link comes in a bit.
After emailing FSA they informed me that only the megatooth chainrings with 'SH12' designation printed on it are compatible with Shimano 12 speed chain. So the plain FSA megatooth chainrings are not optimal and may cause extra chain wear/chain suck.
I'll let you all know how my bike is when I get it back from the lbs with the E*thirteen chainring.
*edit* few months later, i can confirm that the bikes are now shipping with the correct SH12 chainrings. However still the models i see in my local store have the old chainring. So might want to double check what you've got.
This is a screenshot from a youtube video of a 2021 Thron with the new update chainring. Check out how different the teeth profile are! And clearly you can see why the existing chainring was a problem..
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