Evidence Engineering's Adjustable MTB Stem Offers Customization for Length and Stack Height

A revolutionary adjustable stem designed by Michał Piórkowski, a suspension engineer based in Poland, is set to transform mountain bike customization. This innovative component allows riders to fine-tune both the reach and stack height of their handlebars without needing to swap out the entire stem. The product, manufactured by Piórkowski's company, Evidence Engineering, offers a pragmatic solution for cyclists seeking optimal bike fit and performance.

Traditionally, altering a bike's stem length necessitates purchasing a new stem, a process that can be costly and time-consuming if the desired fit is not achieved on the first attempt. Adjusting stack height, while often simpler with spacers, can become problematic if the steerer tube has been cut too short, limiting upward adjustment. Piórkowski's design directly addresses these limitations, providing unparalleled flexibility for riders.

The stem, crafted from CNC-machined 7-series aluminum, provides four length options: 20mm, 30mm, 35mm, and 45mm, alongside two stack height choices: 33mm or 45mm. Laser-etched indicators on the stem clearly display the current configuration. This adaptability is particularly beneficial for making immediate comparisons between different setups during rides, as Piórkowski emphasizes. The stem weighs 187 grams and is compatible with 35mm diameter handlebars.

One of the primary challenges with ultra-short stems is the potential for handlebar-to-steerer contact, often leading riders to shorten their steerer tubes, which then restricts future stack height adjustments. Evidence Engineering's design mitigates this issue by providing inherent adjustability. However, it's important to note that the 20mm and 30mm reach settings are only functional with the higher 45mm stack setting, which might not suit riders who prefer a lower handlebar position.

The stem's construction involves two main parts: a steerer clamp at the bottom and a handlebar clamp on top, secured by M6 bolts tightened to 10Nm. Piórkowski initially explored a direct-mount bolt pattern but developed his own to achieve the desired range of configurations. His calculations indicate that the forces on these bolts are actually less than those found in standard direct-mount setups. Riders can also select between two clamp widths, 58mm or 70mm, influencing the handlebar's feel—a narrower clamp offers more compliance, while a wider one provides greater stiffness.

Piórkowski's engineering background, rooted in motorsport suspension design, heavily influenced his innovative approach. He spent several years working on suspension systems for a Formula Student team and later gained experience in CNC machining and fabricating bike frame components. His extensive knowledge in designing adjustable motorsport suspensions directly inspired the creation of this versatile bike stem. Before tackling the stem, he had conceptualized mountain bike brakes but deemed them too complex for a solo endeavor, choosing a simpler yet highly impactful component.

Rigorous testing underpinned the development of this stem. Piórkowski conducted fatigue tests at Germany's EFBE lab, exceeding standard force requirements. He also developed a custom machine for static testing, revealing that lubricating the bolts significantly reduced displacement by allowing for higher clamping forces at the same torque. Although the stem does not carry an EFBE certificate due to the prohibitive cost of testing every configuration, Piórkowski concentrated on validating the most extreme settings to ensure the design's reliability.

The adjustable stem is available for purchase worldwide, manufactured in Poland. Priced at 199 € (approximately $220), including VAT, the product has garnered significant interest, with a waiting list of over 300 individuals. The initial batch of 40 stems has been produced, and a second batch of 100 units is currently in production, slated for December availability. Piórkowski encourages early registrants to check their emails for order invitations and provides a direct contact for those looking to secure remaining units. The design is patent-pending, and future iterations may include additional spacers for even greater adjustability.