Mountain bike stem. Control centred.

The GCS uses a short 35 mm length, placing the handlebar relatively close to the steering axis. This creates a direct steering response and reduces the distance your hands travel when turning the bar—characteristics commonly preferred on modern trail, enduro, freeride and downhill bikes.

If you are changing from a longer stem, the cockpit will feel shorter and your weight may move slightly rearward. The front wheel can feel easier to lift, but you may need to consciously maintain front-wheel pressure when climbing or entering flatter corners.

Stem length should always be considered alongside your frame’s reach, handlebar sweep and bar rise. A 35 mm stem works particularly well on bikes designed around a long frame reach and short-stem cockpit, but personal preference remains important.

Choose the version that exactly matches the clamp diameter of your handlebar. GCS stems are available for 31.8 mm and 35 mm handlebars, the two principal standards used on modern mountain bikes.

A 35 mm cockpit is often chosen for a solid, direct feel, while a 31.8 mm system may provide a slightly more compliant feel depending on the handlebar’s construction. Clamp diameter alone does not determine performance—the bar’s material, profile and wall thickness are equally important.

The two sizes are not interchangeable. Never fit a 31.8 mm bar into a 35 mm stem without a specifically approved solution, and never attempt to force a 35 mm bar into a 31.8 mm stem.

Check three measurements before purchasing:

• Your handlebar must have a 31.8 mm or 35 mm central clamp diameter matching the chosen stem.
• Your bike’s steerer tube must match the stem’s steerer clamp.
• The GCS Stem has a 40 mm stack height, so there must be sufficient usable steerer tube for the stem to clamp correctly while still allowing the headset to be preloaded.

You should also confirm that the handlebar has a sufficiently wide, straight central clamping area for the GCS’s wide faceplate. If any of these measurements are unclear, a qualified bicycle mechanic can confirm compatibility before installation.

No. The stem can be used with another mountain-bike handlebar provided its clamp diameter, central clamping width, intended use and torque requirements are compatible.

However, the GCS stem and handlebar were developed as parts of the same cockpit system. Their corresponding alignment markings make it easier to centre the bar and reproduce its rotational position accurately. The matching 31.8 mm and 35 mm options also remove uncertainty when building a complete GCS cockpit.

Only if the handlebar manufacturer confirms that the bar is compatible with the stem’s clamp width and required tightening torque.

Carbon handlebars have specific torque limits. If the GCS Stem requires more clamping torque than the handlebar permits, the combination should not be used. Applying additional torque to prevent a bar from slipping can permanently damage a carbon handlebar, even if no damage is immediately visible.

Follow the instructions for both components and never assume that the lower torque figure will be sufficient. If the two requirements are incompatible, choose a different stem-and-handlebar combination.

These measurements describe different aspects of the stem:

• 35 mm length is the effective distance from the steerer clamp to the handlebar clamp. It influences cockpit reach and steering response.
• 40 mm stack is the vertical height occupied by the stem on the steerer tube. It determines how much exposed steerer is required for safe installation.
• 0° rise means the stem does not incorporate an additional upward or downward angle into its design. The final handlebar height will still be influenced by the bike’s head angle, headset spacers and the rise of the handlebar.

These measurements should be considered together when comparing the GCS with your existing stem.

The wide clamping area supports a larger section of the handlebar and provides a substantial contact surface between the bar and stem. This helps resist unwanted bar rotation and contributes to the solid, direct steering feel expected from a gravity-focused cockpit.

A wider clamp also distributes clamping forces across a broader area rather than concentrating them at a narrow point. Correct installation remains essential: the benefits of the design depend on using a compatible handlebar and tightening the hardware evenly to the specified torque.

Machined markings on the stem and faceplate help centre the handlebar and provide a clear reference for bar rotation. When used with the corresponding markings on a GCS handlebar, they make it easier to establish a balanced position and reproduce a preferred setup after maintenance or adjustment.

The markings are setup references rather than substitutes for correct installation. The bar must still be centred, the faceplate positioned correctly and every fastener tightened in the specified sequence with a calibrated torque wrench.

A stem is a safety-critical component, so correct installation matters as much as the strength of the component itself.

The handlebar and clamping surfaces should be clean, compatible and free from damage. Headset preload should be set before the steerer-clamp bolts are tightened. Centre and rotate the handlebar using the machined alignment references, then tighten the fasteners progressively in the specified sequence.

Always follow the torque values marked on the stem or stated in the installation instructions. Do not estimate torque with a multitool, and do not add grease, thread-locking compound or assembly paste unless the relevant instructions specify it. If you are uncertain, have the stem fitted by a qualified bicycle mechanic.

The GCS uses M6 stainless-steel hardware for strength and corrosion resistance in wet, muddy riding conditions. Washers create a controlled interface between the turning bolt head and the aluminium stem.

This helps prevent the bolt head from marking or digging into the aluminium as it is tightened and supports a consistent clamping load. The washers are part of the fastening system and should always be refitted in their correct positions.

GR stands for Gravity, identifying an EFBE test category developed for the demanding loads associated with disciplines such as downhill and freeride.

The “TRI” refers to three principal test modules:

• Fatigue testing applies repeated forces to assess how the component withstands accumulated loading over extended use.
• Maximum-load testing applies defined high static loads and measures whether unacceptable damage or permanent deformation occurs.
• Overload testing examines the component’s reserve strength and behaviour under loads beyond those expected during normal riding.

Passing means the tested GCS Stem design met the specified requirements of EFBE’s Gravity programme. It provides independent laboratory evidence supporting the stem’s intended use, but it does not make the component indestructible or compensate for incorrect installation, crash damage or incompatible components. EFBE explains its TRI-TEST methodology here.

Check that the stem remains aligned with the front wheel and that the handlebar has not rotated within the clamp. Inspect the stem body, faceplate, bolts, washers, handlebar and steerer for cracks, deformation, deep scoring or other damage.

If the bar or stem has slipped, do not simply exceed the stated torque to stop it happening again. Slippage may indicate incorrect installation, incompatible components, contamination or damage.

Stop riding if you find a crack, bent hardware, damaged threads or persistent movement. Because some damage may not be obvious, have the cockpit professionally inspected after a serious crash.

The GCS Stem is designed around a repair-first approach, with replacement hardware and components available separately. This allows a worn or damaged bolt, washer, faceplate or other replaceable part to be renewed without automatically discarding the complete stem.

Only use genuine replacement parts of the correct specification. A generic bolt with the same diameter may have a different strength, head profile, thread treatment or material and should not be assumed suitable.

Supporting repair rather than complete replacement extends the useful life of the stem, reduces unnecessary waste and lowers demand for new materials and manufacturing. It forms an important part of PEMBREE’s environmental approach: making durable products and helping riders keep them safely in service for as long as practical.

The GCS Stem is eligible for the PEMBREE+ lifetime warranty against product defects. Purchases made directly through PEMBREE’s website are enrolled automatically. Products purchased from a retailer must be registered within 30 days of delivery with proof of purchase.

Normal wear, cosmetic changes, unauthorised repairs, incorrect installation and crash damage are not treated as manufacturing defects. Crash damage may instead qualify for the PEMBREE+ Crash Replacement programme. Full conditions are available on the PEMBREE+ programme page.