Funn RSX Direct Mount Bike Stem 31.8mm - Adjustable 45-50mm

In this review of the Funn RSX Direct Mount Bike Stem, the bottom line is simple: it is built for riders who use dual crown forks and need a rigid, low-weight stem with a small range of adjustable reach. The RSX is clearly aimed at off-road and downhill use, and offers a straightforward, split two-piece design that makes installation and adjustment painless. Riders who value a precision CNC 6061 alloy component with 31.8mm bar compatibility will find this stem delivers solid bar stability and a clean, purposeful look.

Key Features

• Direct mount design: Built specifically for use with a dual crown fork to provide a secure connection for off-road and downhill riding.
• 31.8mm bar clamp: This version fits handlebars with a 31.8mm diameter, ensuring a snug fit when the correct bore is selected.
• Adjustable extension: Offers two effective extension lengths, 45mm and 50mm, which change handling feel and rider position.
• Dual rise options: Provides 20mm and 30mm rise positions via built-in geometry choices for tuning cockpit height.
• 6061 aerospace alloy construction: CNC machined from 6061 alloy to balance rigidity and light weight for aggressive riding.

Who It's For

The RSX Direct Mount Stem is best for mountain bikers who run dual crown forks, including downhill and aggressive trail riders who need a robust stem that keeps the bar stable under heavy loading. It is also a good upgrade for riders who prefer a clean, split two-piece clamp for easier fitment and maintenance.

Riders who should look elsewhere include anyone with a 35mm handlebar bore, since this listing is specifically the 31.8mm version, or casual riders who do not require the direct mount interface and would prefer a standard threadless stem with a wider range of adjustable reach.

Pros & Cons

Pros

• Excellent build quality from CNC 6061 alloy gives a stiff, confidence-inspiring feel.
• Easy to install and adjust thanks to the split two-piece design and direct mount fitment.
• Two extension lengths and rise positions let riders fine tune reach and cockpit height.
• Clean aesthetic and stable clamp keep bars from slipping even under hard use.

Cons

• Limited to the 31.8mm bar bore in this version, so bars with 35mm diameter are incompatible.
• The adjustable range is modest (45mm and 50mm), so riders seeking larger reach changes may need a different stem.

Specifications

Mount type	Direct mount for dual crown forks
Bar clamp diameter	31.8mm
Material	6061 aerospace grade alloy (CNC)
Adjustable extension	45mm and 50mm
Rise options	20mm and 30mm
Design	Two-piece split clamp

Our Verdict

The Funn RSX Direct Mount Stem is a focused, well-made option for downhill and off-road riders running dual crown forks who need a stiff, lightweight stem with small extension adjustments. It represents good value when the 31.8mm bore and the limited 45-50mm extension range match the rider's needs, delivering reliable bar stability and a tidy installation.

Frequently Asked Questions

Will this stem fit my handlebar?
This listing is the 31.8mm bar bore version, so it will fit handlebars with a 31.8mm diameter only.

Can I use this on a single crown fork?
The RSX is designed for direct mount installation on dual crown forks; it is not intended for standard single crown threadless steerers.

How do the adjustable lengths change handling?
Switching between 45mm and 50mm extension alters reach and steering feel modestly, while the 20mm and 30mm rise positions change cockpit height for rider comfort.