Compact gearing has seen smaller combinations in recent years due to the popularity of gravel and adventure riding, and the new AbsoluteBlack micro-compact oval chainrings take it to a new low. We’ve seen 48/32 combinations from Praxis, plus Rotor and FSA (who also have a 30/46), but all of those systems require proprietary spiders, cranks and/or direct mount designs. AbsoluteBlack’s version works on standard Shimano 110/4 cranks, and they’re oval.
AB’s founder says he’s been able to climb a 37% grade on gravel using these with an 11-30 cassette, yet not lose the top end speed needed for regular group rides. His example is that a 53/13T @90rpm gives 46.5km/h(29mph), which is actually slower by 3km/h(2mph) than 48/11T at the same cadence. Yes, you’d be faster in 53/11, but how many of us ever really use that combo? And many more of us wish we had something lower when we’re climbing?
The challenge to making sub-compact chainrings work on standard Shimano cranksets is that the bolt hole for 32 and 30 tooth chainrings would interfere with the teeth. AbsoluteBlack’s solution is a patent-pending “offset chainring” solution that shifts both chainrings inboard by 2.5mm closer to the frame…similar to what they did for their 30-tooth 104BCD mountain bike chainring. They admit this does affect the chainline, but actually improves it when you’re in the top 2/3 of the cassette, which is where you’ll be for climbing and the whole point of this gearing combo.
The 30-tooth uses a smaller M5 bolt on the narrower part of the oval, which lets it clear the chain above. The taller part of the oval, where you’re applying more torque, uses a larger M7 bolt. The 32-tooth ring uses four M7 bolts. All are titanium, and all thread from the front, through the big chainring, into the small one, so you can install them without removing the cranks from the bike. Other than readjusting your front derailleur inboard, too, no other modifications to your drivetrain are required.
As for shifting, they say many road bike frames were not designed with a 46-tooth chainring in mind, so you may end up with up to 5mm of gap between the top of the teeth and the derailleur cage. Normally, you’d want about 1.5mm, but AB designed the tooth profiles and shifting ramps to work with the increased gap.
The 48/32 and 46/30 combos were designed specifically to work in those pairs, so they don’t recommend mixing and matching. The precise tolerances required to make it all work smoothly also means they recommend using only a Dura-Ace CN-9000 or SRAM Eagle chain, both of which they’ve tested to work on on modern 11-speed drivetrains.
Prices for the 46T/48T are €105/95£/124$ and for the 30T/32T 76€/67£/87.5$. Small chainrings include necessary bolts in the price. The 46/30 are in stock and shipping now, the 48/32 should be ready by February 1.