OneUp 45 Tooth Cog
For most the initial reaction to the idea of a 45 tooth cog for the rear cassette is one of mocking disbelief. Sure, wide range rear cassettes make single ring drivetrains viable for a broader range of riders and trails, but why would anyone ever need a cog so big? ‘If you need a gear that low then get yourself a double or a triple chainring’, is one common retort.
Well the appeal of a single chainring is strong; I for one love having fewer gear cables and some extra free space for a dropper post remote. With no front derailleur to clatter against, they are also comparatively quiet. Locally I have some long and steep hills to contend with, so a wide range single ring drivetrain certainly appeals to me—the wider the better as far as I’m concerned as I always prefer to pedal rather than push.
With these thoughts in mind, I was keen to try this new 45 tooth cog from US manufacturer OneUp. It may seem crazy to have a cassette that’s larger than the big ring on a triple crankset but if it adds range and flexibility to a one-by drivetrain then why not?
It’s only available directly from the manufacturer and sells for $90. This kit is made specifically for Shimano 11-speed systems—either XT or XTR. It is designed to run in conjunction with their 11-40 cassette (not the 11-42 option). The kit includes the massive machined 7075 alloy cog as well as a supplementary 18-tooth steel cog that slips in mid-way down the cog stack.
The 45 cog goes onto the hub first, followed by the regular Shimano cassette. Three quarters of the way down, you leave out the stock 17 and 19 cogs, replacing them with the single 18 tooth OneUp cog. You still finish up with 11 gears but have a wider 11-45 spread. As you can see on the gear chart below, this provides a 409% variation in ratios; it’s a good deal wider than the 363% range offered by the 11-40 cassette and even Shimano’s 11-42 option only provides a 381% range. For those who think the 45 cog is taking thinks too far, the total gear range is actually narrower than what you get from a SRAM 1x11 system; their 10-42 cassette offers a 420% gear range.
Weight wise the OneUp conversion added 57g to our 11-speed XT donor cassette, taking it from 412g up to 469g. It’s a relatively minimal increase if you’re already a Shimano user, although it’s quite hefty when compared to SRAM’s expensive one-piece machined XX1 and XO1 cassettes. They’re around the 265g mark but require a dedicated XD Driver freehub body. This 11-45 setup still offers an impressive gear spread whilst fitting on any regular 10-speed rear hub.
Range extending cogs are nothing new for 10-speed systems; we’ve tried a multitude of them on both Shimano and SRAM drivetrains. Plenty of people use them and are happy with the result but more often than not, mounting a 40 or 42 tooth cog to a 10-speed system compromises the shift quality. If you’re fussy about the accuracy of your gear shifting, these add-on cogs probably aren’t for you.
Surprise Shifting
We’re happy to report that we got a far better result when adding the 45 cog to our 1X11 Shimano XT drivetrain. Once fitted we made a minor adjustment to the B-tension screw, tweaked the cable tension a bit and we were off. Occasionally there was some slight hesitation when shifting from the 15 cog up to the OneUp 18 cog but it really wasn’t bad. The new generation Shimano 11-speed derailleur was more than up to the task when it came to shifting into the 45 cog.
Having such a big cog on the back allowed us to run a bigger chainring without compromising the climbing gears. Where I’d normally want a 30-tooth chainring with a 42 cog on the back, I was now able to get the same low gear by using a 34-tooth chainring, and this in turn provides better top-end gearing. Of course you can retain a smaller chainring if you wish and proceed to climb the nearest tree!
Using the 18 cog in lieu of the stock 17 and 19 keeps the jumps between gears relatively normal but there’s still a substantial gap is between the 15 and 18 cogs; this produces a 20% jump in the gear ratio. The biggest variation on a regular Shimano 11-40 cassette is 18%. OneUp’s marketing material promotes this bigger gap as being beneficial, saying it splits the cassette into distinct climbing and descending zones. I think it really depends on what you’re doing at the time. It can be handy to skip to a much bigger gear just as you begin a descent but the sizable jump can also be annoying on flatter terrain where you may have one gear that’s too hard and the next cog being too easy. To pitch this as a ‘feature’ is marketing at its best!
Overall I felt that the compromises were pretty minimal with this conversion. If you’re after a wider gear spread out of your new 1X11 Shimano drivetrain, the OneUp 45 cog certainly delivers, and it does so whilst retaining 90% of the stock gearshift quality. Combine it with a bigger chainring and you get more top-end speed without cutting back on your climbing gears.
OneUp XT & XTR Chainrings
Unless you’re chasing super low gearing, the benefits of the 45 cog are best realised by fitting a bigger chainring up front. Shimano offers chainrings up to 34T in XT and 36 for XTR cranks but OneUp also has aftermarket rings that will fit the new XT and XTR drivetrains. Selling for $90, the OneUp rings are made from 7075-T6 alloy, use a wide narrow tooth profile and come in 30, 32 and 34 tooth sizes.
We’ve found the chain retention to be very good with the stock Shimano 1x11 drivetrain. Thankfully the aftermarket ring didn’t mess this up and we didn’t lose the chain once.
While we only used this chainring for two months, we’d expect the alloy teeth to wear faster than the steel or titanium teeth found on the original Shimano items. On the positive side, the OneUp ring sits a little further inboard a, creating a 49mm chainline. The stock Shimano chainring produces a 50.4mm chainline and in our review (MBA Aug/Sept/Oct 15) we found this to be excessive; it made the chain derail off the top of the cassette if you backpedalled whilst in the lowest gear. This was far less likely with the OneUp chainring fitted and it pretty much fixed the problem.
Aside from the improved chainline, the OneUp chainrings also save around 35g in weight when compared to the original setup. With XTR the weight is saved by eliminating the bulky chainring nuts, as the bolts thread directly into the chainring. On XT the weight savings come from the all-alloy construction versus the steel and composite materials used in the stock ring.
