Mountain Bike Action Product Test: Wren Inverted Suspension Fork
The modern innovation of an inverted fork dates back to the early 1980s, when Steve Simmons pioneered the idea to improve the handling of motorcycles. While upside-down forks became the norm on motorcycles, the story of inverted forks in mountain biking has been mixed through the years. An inverted fork design is nothing new, as we’ve seen brands like RockShox and Marzocchi taking a crack at it, but suspension designers keep returning to inverted fork designs because there are benefits to be gained if the design is properly carried out.
Wren’s inverted design sprouted in 2014 when Kevin Wren started to converse with manufacturers he had worked with previously in the industry. Kevin dived in by investigating designs that could be slightly tweaked to supply riders with a better value product. Seeing the potential of an inverted suspension fork, Kevin and his technician, Russ Johnston, put their combined industry knowledge to the test.
Wren’s inverted suspension design is the clever TwinAir system. Essentially, there is a single air chamber that’s split in two by a floating piston. It can be finely tuned using only a shock pump (see diagram for a look inside the technology). This is similar to the token system used in other suspension forks on the market; however, the TwinAir system’s floating piston can be moved as little or as much as a rider would like for infinite adjustability in fine-tuning the suspension. To keep the suspension stable, the beefy 36mm stanchions are keyed, preventing the stanchions from turning and running untrue. The most notable feature is the ability to configure the Wren fork’s hub spacing for 100mm, 110mm, 135mm and 150mm widths.
There are two models that have adjustable travel ranges in 10mm increments. One is 120mm and adjustable up to 150mm of travel, while the other is 70mm and adjustable up to 110mm of travel. A rider can go old school with a straight steerer tube or fit this into a more modern bike with a tapered steerer. The Wren will accept 26-, 27.5- and 29-inch wheels with up to a 2.5-inch width tire with the non-Boost hub spacing and up to 3.0-inch-wide tires with Boost spacing. To test the Wren’s design, we set up the TwinAir system and set off for our local trails.
Field test results:
Why run an inverted fork? One key reason is the stanchions that slide up/down are lighter and can respond to bumps faster. Along with that, the design is stiff—front to back—on a strong chassis, while the inverted fork seals point downward to help prevent trail grime from getting pulled into your fork. It did take a few rides to dial in our preferred feel on the trail. We ended up setting our sag first and only making minor adjustments to the bottom air valve to set our preferred progression. Since there is infinite adjustability, we ended up taking notes and bringing a shock pump with us to test different settings on different trail conditions. Although this is not your typical front fork, we feel that the Wren inverted fork fits a niche for riders who like to spend time tuning their suspension while having the option to configure whatever they require to enjoy their time on the bike.