Popovich - an Essential Derailleur Build

Rear TriangleDerailleur HangerFork Hook


This kit will allow you to build a rear cassette and derailleur Brompton with either a full set of rim brakes or a rear disk/front rim brake combo.

Compatibility and Build Considerations

Rear derailleurs vary in size. It's safe to assume that all short and mid cage derailleurs will provide enough ground clearance. With a conventional rear derailleur, the Brompton fold becomes complicated. One needs to use an extra chain tensioning device or holder. When the bike is folded completely, the stock front fork may or may not clear the derailleur with the stock Brompton hook, this depends on the derailleur used. This is why an adjustible Vostok hook is included, which is compatible with the Vostok fork and the stock fork alike.

Get in Touch

Feel free to message us with any questions about the components and your future build.

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Titanium Finish Options

Blasted matte finish, standard for all Brompton parts.

$619 as a kit

$646 if bought separately


Hand polished titanium, a mirror-like surface resembling chrome.

$0 as a kit

$0 if bought separately


Titanium nitride coating, commonly found on motorcycle forks, drill bits and gun components.

$0 as a kit

$0 if bought separately


Frame Extremities

Rear Triangle

Titanium alloy PT-7M
0.54 kg
O.L.D. spacing
135 mm
Brake mounts
IS Disk and standard caliper
Rohloff TS OEM as well as Shimano non-turn-specific
GOST 19807-91
Superior to Grade-9 alloy

Vostok Rear Triangle replaces the original Brompton bicycle rear frame assembly. It allows hubs like Rohloff Speedhub, Shimano Alfine or any other standard 135mm wide hub to be fitted with or without the disk brake.

The Triangle plays well with Brompton's design: the bicycle folds and rolls as expected. May be paired with a stock front fork as well as the Vostok Fork. When paired with a stock fork, the folding width of the bike does not change considerably.

Considerations: the dropouts will not allow crank arms to rotate 360 degrees when a bike's rear end is folded. Double chainsets may be a problematic fit be it a stock rear triangle or our custom one: choose your BB spacers wisely. Disk brake caliper space is tight and may not fit certain cheaper brands of cable-actuated calipers. There are no issues fitting hydraulic calipers of any kind.

The Triangle is compatible with a standard Brompton rear rack. We feel that our Rear Mini Rack for the Vostok Rear Triangle is the cleanest choice however.

Kit Addons

Derailleur Hanger

0.01 kg

The Derailleur Hanger is designed specifically to interface with the Vostok Triangle's drive-side dropout. It allows you to attach a standard rear derailleur for your cassette build.

Fork Hook

0.01 kg

The Fork Hook comes included with every fork purchased separately and with every kit. If you are purchasing a Rear Triangle separately, makes sense to add the hook to your order. With the rear-only conversion, the hook is optional, but recommended for a rear derailleur build. A rear derailleur, being wide and bulky, might not permit the full fold with the stock plastic hook. The Vostok hook permits modulating the gap between the fork and the rear triangle.

Consider Adding

Rear Mini Rack - Vostok Triangle

The Rear Mini Rack (Vostok Geometry) provides a clean and lightweight alternative to the stock Brompton rack when paired with the Vostok Triangle. The stays of the rack are welded to a 135mm O.L.D. standard. Available in both raw and satin finish.



Front Cargo Rack

A front Brompton rack done right, with a wide base and vertical railings to attach your non-Brompton briefcase of duffel. Will sit firmly on the plastic or titanium carrier block.



Caroline Alexander

Caroline Alexander (born 3 March 1968) is a cross country mountain biker and road cyclist born in Barrow in Furness, Lancashire.

Katie Archibald

Katie Archibald, MBE (born 12 March 1994) is a Scottish racing cyclist, who currently rides on the track for Great Britain and the Scottish Cycling Braveheart.com team.

A member of the Great Britain 2016 Olympic champion team in women's team pursuit, she is a former champion in the same event at both the World (2014) and European (2013, 2014 and 2015) championships. Individually, Archibald has been European champion in the elimination race in 2015, twice in the omnium in 2016 and 2017 and a four time European champion in the individual pursuit between 2014 and 2017.

In 2017 she secured her first individual global title, winning the Omnium at the 2017 UCI Track Cycling World Championships and won a third world championship the following year when partnering Emily Nelson to win the Madison at the 2018 UCI Track Cycling World Championships.