Availability of sub-compact chainrings?

[Clancy]

I believe I saw a while back where a company is making sub-compact chainrings that will bolt up to a Shimano compact crank. I believe there was an option of 32/48 and 30/46 and that the company was able to design them to bolt up with I believe some type of different chainring bolts.

Is anyone aware of such a product?

I mounted a White Industries sub-compact crank on my gravel bike and love it. Would like to experiment with different chain rings on the road bike but not at the expense of another crankset.

[nalax]

Absolute black has them

[Mark McM]

Absolute Black makes 30 & 32 tooth chainrings, BUT: They are only available in oval (not round) chainrings, and they are only available in 4 arm 110 mm BCD, not 5 arm 110 BCD.

Praxis Works makes a 32 tooth round chainring for 5 arm 110 BCD, BUT: They only work on Praxis Works compact cranks, which have a proprietary spider.

For geometry reasons, it is impossible to make a round chainring smaller than 33 teeth that fits a Shimano compact (110 BCD) crank.

[Gummee]

Old math: 1 tooth in the back is worth 3 in the front.

IOW a bigger cassette will do more for you than a smaller chainring

HTH

M

[dem]

Just for sake of completeness, T.A. Specialites Zephyr line offers a 33T (yes, 1 whole tooth lower!)

[Mark McM]

Originally Posted by Gummee

Old math: 1 tooth in the back is worth 3 in the front.

IOW a bigger cassette will do more for you than a smaller chainring

HTH

M

That over-simplification only works for large chainrings and small rear sprockets. If you have compact chainrings and a wide range cassette, that rule of thumb definitely does not work. For example, going from a 32 tooth sprocket to a 36 tooth sprocket (2 teeth) is not at all the same as going from the 34 tooth chainring to a 46 tooth chainring (12 teeth).

And if the sprocket is bigger than the chainring (as is often the case for MTBs and gravel grinders), changes in chainring size will have a bigger affect than changes in cassette size.

Instead of "old math", why not use real math? The relative change in gearing is equal to:

Percent change = (new sprocket)/(new chainring) - (original sprocket)/(original chainring)

[SlowPokePete]

GravelCyclist did a very good video review of the Absolute Black sub-compact chainrings...

http://www.gravelcyclist.com/videos/...ltegra-cranks/

SPP

[marciero]

Originally Posted by Mark McM

That over-simplification only works for large chainrings and small rear sprockets. If you have compact chainrings and a wide range cassette, that rule of thumb definitely does not work. For example, going from a 32 tooth sprocket to a 36 tooth sprocket (2 teeth) is not at all the same as going from the 34 tooth chainring to a 46 tooth chainring (12 teeth).

And if the sprocket is bigger than the chainring (as is often the case for MTBs and gravel grinders), changes in chainring size will have a bigger affect than changes in cassette size.

Instead of "old math", why not use real math? The relative change in gearing is equal to:

Percent change = (new sprocket)/(new chainring) - (original sprocket)/(original chainring)

If you put chainring on top, which is common for ratios, you get something like
c2/s2-c1/s1. To get a relative change you could divide by c1/s1 to get

(c2/s2)/(c1/s1)-1.

Another thing is that the amount of change is not constant in both sprocket and chainring teeth. For example, going from 32 to 30 teeth on the chainring produces more of a change than going from 34 to 32.

[pncguy]

I do real math for a living, and here's a preview of a Google Sheet that I'll share later today...

[djg21]

Originally Posted by Clancy

I believe I saw a while back where a company is making sub-compact chainrings that will bolt up to a Shimano compact crank. I believe there was an option of 32/48 and 30/46 and that the company was able to design them to bolt up with I believe some type of different chainring bolts.

Is anyone aware of such a product?

I mounted a White Industries sub-compact crank on my gravel bike and love it. Would like to experiment with different chain rings on the road bike but not at the expense of another crankset.

Try Praxis. I put a subcompact crankset on an old CX bike.

[pncguy]

Bottom line for me, where I never use my 50-11, is that a SRAM 11-36 cassette with 46/30 chain rings eliminates the 4.55 ratio of the 50-11 I never use, makes my largest gear 4.17 - equivalent to my second largest 50-12 - and extends my range all the way down to 0.83 with a 30-36!

To do this I started with Shimano 6800 with a GS RD. Had to turn my b-screw WAY in to get the 36t cog to work nicely. Haven't purchased the chain rings yet, but may ask for them for Christmas. Obviously I'll have to shorten my chain going from 50/34 to 46/30.

No opinions on cosmetics of the silver SRAM cassette or the Absolute Black chain rings, nor their oval nature. You could also do Praxis or Easton cranks to get 46/30 - or White Industries. (And I bet there are other solutions...)

You just need to prioritize what you want: I have no need for tight steps on the cassette. I don't race and my cadence is just my cadence. 13% average jumps are just fine with me. But I really want low range for climbing the steeper hills here in BoCo.