Apologies if this has been covered elsewhere. Been wondering how much chainring size impacts suspension performance. maybe not for idler geared bikes, but for most FS designs, would they be optimised for a particular chainring size?

Thinking simply about it for a single pivot bike, if the pivot is positioned above the chainring, then generally the suspension will stiffen under pedal load (due to chain growth). however, if you increase your chainring size, for example moving from a middle chainring to an outer chainring, where the pivot is lower than the outer diameter of the chainring, what happens? if it’s above, does the suspension compress under pedal load?

I know this is all dependent on where the pivot is, if it’s forward of the BB, etc. just interested in how things like anti squat is worked out and what differences it makes. I see most folk may use a 30-32t chainring, but if you’re racing XC for example, you may want a 36T on a wide range cassette.

another thing too, does the angle of the chain make a difference, e.g old school was say 32t chainring to 36t sprocket, whereas now we’ve got 50T+ and a much steeper angle of chain.

I wonder if you may lose something like anti squat if you’re not using the designed chainring size?

hopefully I’m being clear-ish.

🙂

The answer is yes it does. Companies publish charts to show stuff like anti squat in different gears. And design bikes around typical set ups eg bird publish a chart for the aether9 to show that in 32/51 spinny climbing gear there is high enough anti squat to prevent bob .
Whether you or I would notice this is another thing entirely

Edit- see here-
https://www.bird.bike/wp-content/uploads/2020/12/AETHER-9-AL-DATA-SHEET-.pdf

thanks, that is interesting.
I see bird have considered the 51 and the 10 sprockets on the same chainring, so purely differences in approach angle relative to the horst link I guess. I d wonder how that changes if they used a 36T..

you’re right though, would we notice? would it be significant? the difference between how the sprocket sizes seems on paper, to be significant.

I think I remember reading somewhere, that Mojo Rising actually select chainring size for suspension feel rather than gear ratio.

What that means for oval rings is anyone’s guess.

Chainring size has a pretty big effect… depending on the location of the pivot. For our (Bird) bikes dropping a CR size increases anti-squat by a noticeable amount, as increasing the chainring size reduces it the other way. The Mojo approach is correct – we supply 32T as thats a balanced starter. If you change ring size you should ideally do it only for the feel. Anyone thats a real pinner and wants a 34T or 36T for the top end speed should consider a retune on the shock most likely or go for one of the self adjustable options (X2/DHX2/Cane Creeks). The other way, to be honest… a 30/50 or 30/51 is a pretty unnecessarily low gear. Most people can push a 32/51 if they need to and find they settle into it pretty quickly. 30/51 is probably < walking pace in many situations and won’t actually help you out in the long run.

thanks,
I agree a 30T-50T is daft low gear, but would the anti squat be more for a 32t-51t, or a 30t-42t for example? would chainring, or sprocket size make more of a difference?

This question really comes about from watching the XC bods rip around with what looks like 36-40t chainrings and wide range cassettes, and wondering what that does on FS bikes that are mass market items. I guess the shocks are tuned for these racers, but would that not be a compromise?

I recall back in the day, my single pivot 3x cannondale prophet was an OK climber in the middle, dug right in in the small chainring and felt a bit different when churning the 44T on the descents. with 1x being the norm, designers may have less variables, unless of course, the industry makes dinner plate cassettes and people move away from a standard 32T ring?

I love my 30t Oval/52t rear setup, can spin up loads of sustained steep stuff I couldn’t before.

32t might be fine too, but can’t see a reason to change

For our (Bird) bikes dropping a CR size increases anti-squat by a noticeable amount

Even for an average rider?

Thanks for the comments, it’s interesting – I’m swapping to 165mm cranks and got a 30T ring to compensate. Now I’ll probably change one at a time to see how it feels, rather than put both on together.