# Chainring pairings - 34/46 vs 36/46



## jared_j (Jun 11, 2009)

There is a warning with SRAM 110bcd 46t chainrings to use the ring with a 36 inner for "best shifting performance".

How is it that you can shift well on a compact 34/50, but for some reason a larger inner is needed to go with the 46? 

Anyone run a 34/46?

I'm abstracting from which inner ring size is a more 'optimal' setup for 'cross racing. Just wondering what (if any) mechanical issue there is.


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## kbiker3111 (Nov 7, 2006)

The ramps and pins are designed to work with a 36t ring and won't work quite as well with a 34. In practice, 12 teeth is a pretty small jump and I would imagine it works fine.


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## pretender (Sep 18, 2007)

46/34 is a bigger jump than a standard road double. I'm sure it would work fine mechanically, but for cross racing I'd want a closer ratio, like 42/34 or 44/36 or 46/38.


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## jared_j (Jun 11, 2009)

pretender said:


> 46/34 is a bigger jump than a standard road double. I'm sure it would work fine mechanically, but for cross racing I'd want a closer ratio, like 42/34 or 44/36 or 46/38.


Jump from standard road double = 53 - 39 = 14
Jump from compact road double = 50 - 34 = 14
Jump from 46/34 combo = 46 - 34 = 12

Is there some subtlety to 'jump size' that I'm not getting (e.g. is the linear difference in the number of teeth not the correct metric for sizing 'jump'?)

As I mentioned earlier, I'm asking about compatibility, abstracting from preferences for setup for 'cross racing.


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## redlude97 (Jun 29, 2010)

jared_j said:


> jump from standard road double = 53 - 39 = 14
> jump from compact road double = 50 - 34 = 14
> jump from 46/34 combo = 46 - 34 = 12
> 
> ...


50/34=16


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## kbiker3111 (Nov 7, 2006)

redlude97 said:


> 50/34=16


50/34~=1.470588
50-34=16


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## tsunayoshi (Dec 3, 2009)

Like someone said previously, the ramps and pins are designed with specific ratios in mind, example being the 10spd SRAM mountain groups, their chainrings were designed with a ratio in mind so the shift points lined up (22/33/44, 24/36, 26/39, etc.).

I run a single 38 up front for racing, keeps things really simple


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## pretender (Sep 18, 2007)

Oops yes I was talking about jump in gear ratio, not number of teeth, comparing 52/39 to 46/34.


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## jared_j (Jun 11, 2009)

Thanks all, the ramps/pins design and gear ratio jump arguments make sense.


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## deuxdiesel (May 16, 2007)

On my Apex crank I go from 34/48 to 34/42 regularly, and the shifting performance is fine. I was hoping SRAM wasn't going the Shimano route, telling everyone they HAD to run hyperdrive chains, cranks and cogs together or it wouldn't work (which it does, even when mixed with SRAM stuff).


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