UnAuthorized 45rpm Debut! Chromoly hardtail that excels on trail rides: Its features and how it differs from the 33rpm

The domestic brand "UnAuthorized" has introduced the 45rpm, a hardtail model designed for trails.

It features the unique flexibility of chromoly material and geometry designed with Japanese terrain in mind. This model is perfectly suited for daily mountain biking.

Grumpy has received a shipment, so this time we'll introduce its design philosophy and the differences from the existing 33rpm model.

Features and Design Philosophy of the 45rpm

▸ Head Angle: 64.5°

The head angle is set at 64.5° (with 140mm travel), which is within the standard range for a trail bike.
It offers stability on rough descents and ensures easy handling on tight climbs and quick changes of direction.

With the 33rpm, due to the front travel and center of gravity balance, there were times when the front felt like it was lifting on steep climbs.
In contrast, the 45rpm has a revised geometry balance, improving handling on climbs.

Recommended suspension travel is 130mm ± 10mm.

▸ Rear Center: 410mm

With a very short rear center for a 29er, the bike is easier to maneuver overall and has improved responsiveness when pedaling.
It also provides good traction on climbs, making it easy for the rider to control the bike on tight trails.

▸ Flexibility and Vibration Absorption of Chromoly Material

The double-butted chromoly tubing allows the entire frame to flex appropriately, absorbing impacts from the road surface.

The rear triangle, in particular, uses thinner tubing, providing high flexibility that contributes to rear wheel compliance and traction.

Additionally, the top tube is flattened at the seat tube and transitions to a round tube towards the head, balancing front-end rigidity with overall flexibility.

▸ Responsive Front End

The steering response is also excellent, making it easy to handle in corners and quick transitions between sections.

Compared to a full-suspension bike, the bike's movements are transmitted more directly, which makes choosing lines more enjoyable.

▸ Top Tube Length: Slightly Longer

The top tube is designed to be slightly longer, making it easier to control front and rear load distribution.
It also works well with dropper posts, providing ample space for the rider to move on descents.

What is it suitable for?

The 45rpm is recommended for those who primarily ride trails and occasionally visit bike parks.
This model is particularly worth considering for riders who envision the following uses:

• Primarily trail riding

• Riding well-maintained local trails or mountains with short climbs

• Downhill courses or bike parks only a few times a year

• Prefer the flexible ride quality unique to chromoly

• Love chromoly

Differences and Selection between 33rpm and 45rpm

UnAuthorized's lineup also includes the 33rpm, which is more downhill-oriented.
The differences between the two models, from the perspective of riding style and component configuration, are as follows:

▸ Choose by Usage

Mainly trails, bike parks a few times a year 👉 45rpm

Want to enjoy climbing as well 👉 45rpm

Mainly bike parks/downhill courses 👉 33rpm

Mainly trails, but want to use 150mm+ suspension 👉 33rpm

Specs and Size Range

• Material: Double-butted chromoly tubing
  *Internal cable routing

• Recommended travel: 120mm to 140mm
  

• BB Standard: T47 External

• Headset Standard: ZS44 / ZS44

• Seatpost Diameter: 30.9mm

• Rear End: UDH compatible

• Accessories: Seat clamp, rear axle (Made in USA)
  

• Price: 189,970 yen (tax included)

Size Range (目安)

• XS: ~165cm (limited quantity)

• S: 165~175cm

• M: 170~180cm

• L: 180cm~ (limited quantity)

*Beyond height, we recommend choosing a size that considers reach and dropper post travel, including actual riding position setup. Please consult with us.

*The first batch is limited to 40 frames in CP color. Grumpy has received XS and S sizes. Quantities are very limited, so please inquire soon. For other sizes, please contact us.

The UnAuthorized Brand

UnAuthorized is a brand that doesn't just follow overseas trends, but instead pursues bikes that suit Japanese mountains, rider physiques, terrain, and culture.

Among its offerings, the 45rpm is designed to comfortably and continuously enjoy trail riding as an extension of everyday life.

Summary

The UnAuthorized 45rpm is a hardtail frame that serves as an ideal choice for those who primarily ride trails and occasionally visit bike parks.

Compared to the 33rpm, it is lighter and designed with improved agility and climbing performance. For riders who have a clear vision of "the type of mountain they want to ride," this bike might be an unmistakable choice.

Stock is limited, so please contact us soon if you're interested. You can view the actual frame in our store.
Our staff will also be happy to assist you with size selection and component assembly.