Since 2016 I have been using a Sugino OX601D “compact-plus” crank on my Elephant Bikes National Forest Explorer. A compact-plus crank offers lower gearing than conventional 50/34 “compact” or 52/36 “mid-compact” cranks. I use 42/26 rings. Another popular combination is 46/30.
These smaller tooth counts allow for lower gears, making hilly courses more accessible to many cyclists of different abilities. This used to be the purpose of triple cranks until they were largely abandoned by Shimano, Campagnolo and SRAM a couple of years ago. In 2013 Shimano dropped triples on Ultegra when it moved from 6700 to 6800. The following year it did the same to 105 with the switch from 5700 to 5800. So-called compact and mid-compact double cranks were supposed to be a replacement for triples, but in truth their gearing never went low enough for many cyclists on all kinds of terrain.
Most road triple cranks used a bolt circle of 130/74 mm or 110/74. That meant the middle could be no smaller than 38T (130 BCD) or 33T (110 BCD), though in practice 39T and 34T were more common. The 74 BCD allows rings of 32T and smaller, down to 24T. Shimano compacts give you only 110 BCD, excluding any inner rings smaller than 34T.
Into this void stepped Sugino with its compact-plus cranks that combined the more flexible gearing of triples with compatibility with double front derailleurs and shifters. They do that with a 110/74 BCD combination with 5 bolts, just like an old touring triple (typical configuration: 48/36/26).
Effectively, a compact plus crank is a triple in which the middle and large rings are replaced by one in-between ring that can do both jobs. So for example, instead of a 50/39/30 you would have a 46/30. You just give up some very tall gears, but those typically see very little actual use outside of road racing.
Eventually Shimano also jumped on the compact-plus bandwagon: It is now offering 48/31 and 46/30 cranks in its GRX group set for gravel bikes, using a proprietary 110/80 BCD setup with 4 bolts.
I’ve been very happy with my Sugino OX601D. The 42T large ring and the 26T small ring in combination with a 11-32 cassette (11 speed) provide just the right gear range for my kind of riding. I ride a lot of mountain routes with grades of 10 percent and more and 160 km or more in a day where I really appreciate being able to spin up a mountain in a low gear. If I push heavy gears, I end up paying for it with knee pain.
Recently I replaced my bicycle chain as it had worn and stretched and noticed in the process that the teeth of the large ring were quite worn too. I had put over 30,000 km on that crank already and should have replaced the most recent chain a long time ago. In any case, I realized that I now needed a new chain ring and it turned out that Sugino no longer makes it. That’s because the OX601D and OX801D cranks have been discontinued, along with the PE110S rings that were used on them.
Sugino only ever sold these cranks with ring combinations of 44T to 50T for the large ring and 30T or more for the small ring. The 40T and 42T versions of the PE110S were made specifically for use with the ZX801D, a Mountain Bike equivalent of the OX801D but Soma/Merry Sales in the US sold them as a combination with the OX601D. That’s where I had bought mine.
Sugino’s current compact-plus offering is the OX2-901D, the successor to the OX901D which in turn was the 10/11-speed version of the 9/10-speed OX801D. My OX601D is a cheaper but functionally identical version of the OX801D – basically just not as shiny. I had no problems running the OX601D in an 11-speed configuration, with an 11-speed chain, cassette and rear derailleur, but I guess there are some subtle differences with the latest versions, such as maybe the spacing between the two rings to optimize it for the narrower 11-speed chain.
The OX2-901D uses CP110S chain rings with the same 110 BCD bolt circle as the PE110S, but they’re for 11 speed. The large rings are offered in even steps from 44T to 52T and small rings (CP74S, CP110s) in even numbers from 30T to 36T. There is no 40T or 42T for the large ring or 24, 26 or 28 for the small ring as there was for the PE110S for the ZX801D because there’s no MTB equivalent of the OX2-901D. Sugono’s only concession to people needing lower gearing is the “Super Hill Climb” CY5-SHC, a 27T 74 BCD inner ring.
One option would have been to buy a CP110S 44T chain ring. Given the close family relationship between the OX2-901D, OX901D and OX801D/OX601D, I am pretty sure it would have worked worked just fine on my older crank. It would have raised the gearing on the large ring by about 5 percent though (44/42). On top of that, the difference in tooth count between the two rings would have increased from 16T (42-26) to 18T (44-28). The specification for my FD-CX70 says its maximum capacity is 16T, but it would probably would have still worked. However, 44/26 at the front with 11-32 at the rear would on paper have required a total rear derailleur capacity of 39, one more than the specification of my RD-6800-GS. That can get tricky.
Exceeding the total rear derailleur capacity theoretically creates problems during cross chaining, as the rear derailleur arm can not take up all the chain slack from switching between the two extreme positions. If the installed chain is kept short enough to not go slack when running on the the small ring at the front with the smallest sprocket at the rear, it risks the derailleur pulley making contact with the spinning cassette when running on the big ring at the front and the largest sprocket at the rear. That could be disastrous. The safer way is to keep the chain long enough for the big/big combination, which I quite often use. At worst your chain will slip in the small/small combination which should be avoided anyway (and which is easy to avoid, you just switch back to the big ring after the first couple of upshifts when you have reached the top of a steep climb).
Sugino rings are not the only choice for compact-plus cranks. French bicycle parts maker Spécialités T.A. also offers a wide variety of high quality chain rings that can be used on many different cranks. Specifically, the TA Zephyr rings are also ramped and pinned for Shimano STI and will work with 10 and 11 speed groups. When you are looking for a large ring for a Sugino OX crank, it is best to use a 110 BCD ring meant for a use as a middle in a triple. That’s because these rings are mounted on the inside of the OX crank spider, not the outside. This matters because some rings have bolt holes that are countersunk for mounting on a particular side, to match bolts with conical heads. So it makes a difference if the bolt enters the bolt hole from the left or the right. In any case, there’s a TA Zephyr 110 BCD middle in either 40T or 42T, making them suitable replacements for the PE110S 40T and 42T formerly made for the ZX801D that are no longer available (EDIT: for the 74 BCD inner replacement I used a TA Zelito, which are available in 24T, 26T, 28T, 30T and 32T).
It’s a pity that Sugino no longer offers chain ring combinations below 44/30, such as 44/28, 42/26, 40/26 or 40/24 which would all be possible with the dual bolt circle of 110/74 mm on OX and OX2 cranks. As long as TA offers the rings we can still create and maintain such combinations though.
Another great option are Rene Herse cranks, which are available in a wide range of chain ring sizes, supporting speeds from 9 to 12 speed. That may be my fall-back position a couple of years down the road.
EDIT: I bought a 110 BCD TA Zephyr 40T as the large ring and a 74 BCD TA Zelito 24T as the small ring replacement (www.bike-components.de/en). The shift quality with the Spécialités T.A. rings is fantastic. The OX601D now shifts better than with the Sugino rings, arguably as well as any mechanical shifting (non-Di2) setup of any brand or model I have ever used. I am extremely happy with it. Dropping the chain ring sizes by two teeth from 42/26 to 40/24 has not been any drawback on the flat or descents but has helped me on climbs.