Sim Rig Build Guide: Rigidity, Chassis Torsion and Mounting

01Why the rig is part of the control system

Every sim rig build starts with the same principle: the cockpit is part of the control loop. Your hands and feet send inputs through the wheel and pedals; the structure carries the reaction forces back. If the structure moves, part of every input is spent deflecting aluminium instead of reaching the sensor.

That matters most in two places:

• The pedal deck. Under hard braking, a rigid deck turns leg force into a repeatable sensor reading. A flexing deck changes pedal angle and travel mid-stop, so the same leg effort produces a different brake output from one lap to the next.
• The wheel mount. A direct drive motor reacts its torque into the mount. Any flex smears the fine detail in the force feedback and adds a delay between what the car does and what your hands feel.

Consistency is the goal. A rig that does not move lets you build reliable muscle memory, because the only variable left is the driver.

02Aluminium profile rig assembly

Extruded aluminium profile is the standard for serious cockpits: it is stiff, modular and easy to adjust. Profiles are named by their cross-section in millimetres.

Brackets and fasteners

Profiles are joined with angle brackets, T-nuts (or drop-in nuts) and socket-head bolts, usually M8 for 8040 and 8080 systems. Use brackets that span the full face of the profile: wider brackets with two bolts per side resist twisting far better than a single small corner bracket. Gussets at the base of uprights add significant stiffness for little cost.

Squaring the frame

1. Assemble the base frame loosely on a flat floor.
2. Measure both diagonals of each rectangle. Adjust until they are equal, typically within 1–2 mm.
3. Check uprights with a square or level before tightening.
4. Tighten in a cross pattern, the way you would tighten wheel nuts, so the frame is not pulled out of square.

Torque

Follow the profile or bracket supplier’s torque figure. For M8 fasteners in aluminium profile, this is typically around 20–25 Nm. Under-tightened joints slip under load; over-tightened ones can deform the slot or strip the T-nut. Use a torque wrench, and re-check all joints after the first few hours of driving, as joints settle.

03Cockpit rigidity and chassis torsion control

A rig can feel solid when you push on it by hand and still deflect under driving loads. The two load cases to design for are bending (the pedal deck pushed away from the seat) and torsion (the frame twisting around its long axis).

Where torsion comes from

• Braking: the brake sits off-centre, so a hard stop pushes one side of the pedal deck harder than the other, twisting the front of the frame.
• Steering torque: a direct drive wheelbase reacts its torque into the wheel deck and uprights, trying to rotate them in alternating directions.
• Driver movement: pushing against the seat and pedals at the same time loads the base rails in bending.

How to control it

• Close the loop. A frame with the seat and pedal deck tied together by continuous base rails is far stiffer than one where each element is mounted separately.
• Add cross-members. A cross-member directly under the pedal deck and another under the wheel uprights reduces twisting considerably.
• Brace the uprights. Diagonal braces or gussets from the base rails to the uprights stop the wheel deck rocking under torque.
• Shorten unsupported spans. Bending deflection grows rapidly with span length. Support the pedal deck close to where the pedals mount.

Our guide to pedal flex and trail braking explains how small deflections affect brake modulation.

04Mounting high-force pedals

Pneumatic pedals such as the SRP® range produce real braking force. The R-Piston V5 brake compresses air in a sealed aluminium cylinder, so pressure builds progressively: light at the top of the stroke and firmer deeper in, much like a hydraulic race brake. To reach high brake pressure, the driver has to push hard. That force has to go somewhere, and a rigid cockpit is a requirement, not an option.

Pedal deck checklist

• Bolt the pedal set directly to a solid plate or to profile rails, using all the mounting points provided.
• Support the deck from below at the front and back of the pedal footprint.
• Check that the deck does not move when you stand on the brake with full force. Any visible movement means more bracing.
• Use a heel rest so your heel has a fixed pivot point. It improves repeatability and protects the deck surface.

Floor- or top-mounted

GT-style cars typically use floor-hinged pedals, while many single-seaters and some prototypes use hanging (top-mounted) pedals. The SRP® Formula-R can be floor- or top-mounted, and the SRP® inverted pedals kit converts compatible sets to an inverted layout. Inverted mounting needs a strong overhead cross-member, because braking force now pulls the structure forward and downward from above.

Seat-to-pedal distance, heel height and pedal angle are covered in our pedal positioning and ergonomics guide.

05Direct drive wheel mounting and motor torque

A direct drive (DD) wheelbase attaches the steering wheel directly to the motor shaft, with no belts or gears in between. That makes it precise, but it also means every newton-metre of torque is reacted straight into the mount.

Front mount vs side mount

• Front mount: the wheelbase is bolted through its front face to a vertical plate. It is compact and keeps the motor body free, but the whole torque reaction and the motor’s weight sit on one plate. It must be thick and well braced.
• Side mount: the wheelbase is clamped from both sides, usually to two profile uprights or brackets. It spreads the torque reaction over a wider base and is generally stiffer for high-torque motors.
• Bottom mount: the wheelbase sits on a deck plate. It is simple and common, but the deck must not flex under torque.

What motor torque means

Wheelbase torque is quoted in newton-metres (Nm): the turning force at the shaft. Consumer DD bases typically range from about 5 Nm to 25 Nm or more. Higher peak torque is not about running the wheel at full strength all the time; it gives headroom, so the motor reproduces peaks (kerbs, impacts, snap oversteer) without clipping, while normal cornering loads sit comfortably within its range.

Two points matter more than the peak figure:

• Consistency: the motor should deliver the same torque for the same signal throughout a long session, without fading as it warms.
• Mount stiffness: a high-torque motor on a flexing mount loses the fine detail that makes force feedback informative.

06Shifter and handbrake placement

Shifter position affects both comfort and lap-to-lap consistency, because a gear change should require no visual or mental search.

H-shifter

Mount an H-pattern shifter so the knob sits near the height of the wheel’s lower rim and just ahead of the driver’s hip, mirroring a road or historic race car. The hand should reach it without leaning. Pair it with a clutch pedal (for SRP® sets, the SRP® clutch kit) and practise heel and toe downshifts once the pedal spacing allows it.

Sequential shifter

A sequential lever is usually mounted slightly higher and closer to the wheel than an H-shifter, so a short pull or push changes gear with minimal hand travel. Rally-style setups place it high and close to the rim. Many GT and prototype drivers use wheel paddles instead and keep the sequential lever for specific cars.

Handbrake

The SRP® HB pneumatic handbrake mounts vertically or horizontally. For rally and drift, place it close to the wheel rim so the hand travels as little as possible between steering and the lever. The mount needs the same rigidity as the pedal deck, since a hard pull loads the bracket sideways.

07Protecting the structure, the floor and the cables

A rigid rig transmits force into whatever it stands on. Protect both the rig and the floor:

• Floor mat: a dense rubber or composite mat under the whole frame prevents the feet marking wooden or tiled floors, stops the rig creeping under braking, and absorbs some vibration.
• Levelling feet: adjustable feet let you level the frame on an uneven floor. A rig resting on three of its four feet rocks under load, which feels like flex.
• End caps: profile end caps protect skin and cables from sharp extrusion edges.

Cable routing

Route cables through the profile slots using slot covers or clips, and keep them away from moving parts such as pedal arms, the seat slider and motion actuators. Leave a service loop near each device so it can be adjusted without pulling on connectors. Keep motor power cables separated from USB data cables where possible, to reduce interference.

08Motion rig physics

A motion platform moves the driver to simulate the car’s changes in acceleration: pitch under braking and acceleration, roll in corners, and heave over bumps and kerbs. Because the travel is limited, motion systems reproduce the onset of a load (the change), then return slowly to neutral below the threshold the driver notices.

What motion adds

• Earlier perception of weight transfer under braking and turn-in.
• Physical cues for traction loss, kerb strikes and bumps.
• A more natural sense of speed in long sessions.

Load on the structure

Motion makes rigidity more important, not less. The cockpit now accelerates as a whole, so every mass on it (wheelbase, monitor arms, seat, driver) generates inertial loads at each change of direction. A frame that flexes will resonate, adding false cues. On motion rigs:

• Use heavier profile (often 8080) for the base and uprights, and keep total mass within the actuators’ rating.
• Mount monitors off the moving platform where possible, or brace them heavily if they move with the rig.
• Re-check bolt torque more often, since vibration loosens joints faster.

The pedal deck still has to absorb full braking force while the platform pitches, so do not reduce pedal deck stiffness to save weight. Visual alignment matters too: see our FOV guide once the seat and screens are fixed.

FAQFrequently asked questions