How to replace outer cog of SRAM XG-1099 10-speed cassette with up to 39 teeth: review of Ari cog

Summary
SRAM X-DOME cassettes are fantastic. Having to buy a new XD driver is not. The 10-speed X-DOME is the biggest that doesn't require a special driver, but it has limited range (11T-36T). At this writing, familiar makers of cassette expanders don't make anything compatible with the XG-1099 cassette. Ari makes a 39T cog that works.

For those looking to add range to their existing SRAM XG-1099, this is welcome news. Others may wonder why anyone would purchase this cassette in the first place given the bigger options available at a similar price point.

Why pay so much for a 10-speed cassette?
Apart from being lightweight and mud-clearing, the SRAM XG-1099 appealed to me because it's one piece of metal. I own a Niner SIR 9 and waver between single speed and geared, depending on terrain and mood. I grew tired of chasing down the tiny cogs and spacers in the stock SRAM PG-1030 cassette while changing between a cassette and a single cog. The single block of billet steel has proven to be a joy to wrench.

Niner SIR 9, SS

Chasing cogs and spacers of the SRAM PG 1030 cassette

Especially with comparably priced 11- and 12-speed options available
I couldn't justify a new 11-speed or Eagle drivetrain when my 10-speed shifter (X7) and derailleur (X9, long cage) were in perfect working order. On the other hand, the XG-1099 retails for $320 for a 10-speed cassette; if that kind of coin was on the table, why not just upgrade the whole drivetrain? Budget aside, I chose the 10-speed because the 11-speed and Eagle versions of the X-DOME require the XD driver, which would have made single-speed conversion complicated at the time of purchase (that problem has since been solved). The initial driver of this cassette search was the pursuit of simplicity, after all.

Plus, I assumed that I could expand the range of the 10-speed, given the array of aftermarket options to increase the range of popular cassettes (e.g., by Wolf Tooth, OneUp, or First Components). The search proved more difficult than expected. 

The only company I found who would add teeth to the XG-1099 cassette was Ari, an Italian maker of bike components.

So I ordered a 39-tooth in red, by emailing [email protected]. Email correspondence was pleasant and prompt.

Installation and weight
Removing the aluminum outer ring from the steel set of cogs was nerve-wracking, given the value of this precious metal, but not that difficult. I used a flat-head screwdriver to pry it off slowly. Ari has instructions here. 

​Installation was also simple, following the instructional video on Ari's website. Cog first, then spacer, then the rest of the cassette.

The weight of the cassette with the new outer cog is 218 g. With the original, it is 194 g.

With original outer 36T cog

With Ari 39T cog

Cost of cassette, including Ari Cog

• The Ari cog cost €70 EUR plus €26 EUR shipping ($111.59 USD total, June 2017 conversion rate).
• I found the XG-1099 used on ebay for $135 (retail is $320). Buying used was the move, because the steel body is reportedly durable, and the faster-wearing aluminum outer ring was to be replaced anyway.

My total cost: $247 

Durability and performance
That's admittedly a pretty expensive cassette, but it checks my criteria:

• easy to take on and off
• no need for the XD driver
• enough granny (39 teeth)

As for how the cog works, I've really liked it after 3 months. The aluminum outer ring has stayed flush with the steel cassette body, with no sign of movement. The teeth have not noticeably worn. The bright red paint has slowly given way to its metal roots, but I'm alright with the more subdued look.

The cassette itself has already been heavily praised, and for good reason. It's a beautiful piece of metalsmithing that is incredibly lightweight (only 102 grams more than my Surly 20T single cog + spacers), shifts crisply, and completely ignores mud and debris.

Would I recommend?
This cassette build made sense for me, because I already had a working-order SRAM 10-speed shifter and derailleur. I can't say I would recommend this if building a drivetrain from scratch, however. It's just too expensive without providing that much range, especially considering Shimano has a cheaper 11-speed way to avoid an XD driver, and Problem Solvers have devised a way to make XD drivers single-speed convertible.

Still, Ari has made my cassette pretty fly despite not being an Eagle.

All 39 teeth in use to climb the Slate D'huez.

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