Imperial converts the headline figures and comparisons. Detailed tables and tube sizes stay metric for now.
Orientation If the frame shows on its side, upside down or the wrong way round, turn it here.
Suspension Pickups
Reset
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Torsional stiffness axle to axle, Nm/deg (estimate)
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Frame Mass
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Nm/deg per kg
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Bending stiffness, N/mm
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Of target weight
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Gussets resolved
Torsional stiffness, front and rear
Real-world stiffness estimate
Calibrate to your FEA or rig test
Have an FEA result or a rig test for this frame? Enter it and FrameScore scales every stiffness estimate on this device to match it, for this frame and the next ones you design. For a fair match, the FEA should hold the rear suspension pickups and twist the front pickups, using the same pickups as Edit Pickups.
Biggest gains
Gussets
Joints are checked for tight angles, offset centrelines, weak pickups, crossed tubes and unbraced corners, against FIA Appendix J Art. 253-8 and structural welding guidance. Tap a joint to see the gusset on the model.
Where It Sits Nm/deg
Bare frames and complete cars aren't directly comparable: panels, glass and subframes add a lot of stiffness to a finished car.
Your reference frames
Save frames you know work. Each new design is compared against them, and any measured stiffness you enter calibrates the estimates. Saved on this device.
Notes
Use your own frame
Upload the frame as a STEP file (.step or .stp) exported from SolidWorks, Fusion, Rhino, Alias or CATIA. FrameScore finds every round tube from its cylindrical faces, reads diameter and wall, follows bends, and rebuilds the nodes where coped tubes meet. Brackets, plates and holes are ignored.
After loading, use Edit pickups and tap the nodes where the wishbones, pushrods and dampers mount. FrameScore sorts them into front and rear, left and right, and remembers them for this frame on this device. A 3D DXF of tube centrelines, or the frame file below, also works.
Not sure how to set up your STEP file? Download the example, open it in your CAD to see how it's built, then set your frame up the same way.
Download example STEP fileSample roadster frame: 79 round tubes including a bent roll hoop, in millimetres (11.8 MB).
Bare chassis only: every tube as its own solid body. Leave out suspension parts, panels and the engine; brackets, tabs and gussets are ignored anyway.
Real round tube: hollow tube with the true outer diameter and wall, so FrameScore can read both. Square and rectangular tube aren't read yet.
Ends: coped (fish-mouthed) or square-cut both work; FrameScore extends the centrelines to find each joint. Bent tubes are read as one tube.
Units and axes: millimetres, Z up and X along the car, as in the example. If yours differ, change Units in file and Orientation above before uploading.
Export: STEP AP214 or AP242 (.step or .stp).
To check it works, upload the example first: it should read 75 tubes and 48 nodes.
No CAD? You can describe the frame in a spreadsheet instead. Number every joint (node). With the frame on a level floor, measure each node's X along the car, Y across it (left negative, right positive) and Z up from the floor; a tape, a plumb bob and a string line along the centreline are enough. Then list each tube by the two nodes it joins, with its outer diameter and wall. Save it as a .csv and upload it, one row per line:
The box below shows the current frame in this format: copy it into a spreadsheet as a starting point.
Suspension pickups
How the score works
The design score checks the frame against the layout rules that proven space frames follow. Each check looks at geometry only:
Torsional stiffness (25%): 70% from the whole-chassis stiffness, axle to axle, against published figures for the class you pick (Seward recommends at least 1,000 Nm/deg for any racing car), and 30% from the balance between the front and rear halves.
Triangulation (20%): share of flat bays braced by a diagonal. Bays you keep open for the driver, engine or drivetrain don't count against you.
Suspension load paths (15%): every pickup you designate should sit on a node with tubes running in three directions.
Chassis weight (10%): frame mass as a share of your target vehicle weight. For steel space-frame kit and track cars, 12–17% is the desired range; under 9% is underweight and over 20% unnecessarily heavy. For cars under 450 kg the range is 10–20%.
Clean nodes (10%): from the STEP geometry, how many coped joints have centrelines meeting at one point.
Joint angles and gussets (10%): joints still needing a gusset or a decision from you.
Diagonal angles (5%): triangles with an angle under 20°.
Unbraced tube lengths (5%): tubes longer than 35× their diameter between nodes.
Real-world stiffness. The beam model assumes perfectly rigid joints, so it reads high. Real welds, fish-mouth gaps and joint flex typically cost 15–30% of torsional stiffness. FrameScore shows the theoretical value and an estimated real-world value, using either a fixed reduction you choose (15–30%) or a node-by-node assessment of every joint: wall slenderness, tube size ratio, joint angle, number of tubes and, from STEP files, centreline offsets, weighted by the twist load through each joint. The design score is shown both ways. A measured frame saved as a reference replaces the correction.
Front and rear stiffness. One twist test is run: rear pickups held, front pickups twisted. FrameScore measures the twist at every cross-section along the frame, takes the frame between the innermost front pickup and the innermost rear pickup, splits it at the middle, and divides the torque by the twist across each half. The loaded and held pickup regions are left out because they are forced rather than free; if the split can't be measured reliably (for example when pickups reach far along the car), only the whole-chassis value is scored. The two halves act like springs in series, so the whole chassis is always softer than either half and the weaker end sets it; that's why the average of the halves is shown but never scored. The balance score is 100 up to a 1.5:1 ratio, 70 at 2:1, 30 at 3:1 and 0 at 4:1 or worse. A ratio of 2:1 or more is flagged as a significant imbalance. These limits are working rules of thumb.
Gusset rules. A gusset is suggested where two tubes meet at under 30° (AWS D1.1 and AISC Design Guide 24 treat 30° as the minimum branch angle for a full-strength weld), where centrelines miss by more than a quarter of the tube diameter, where a pickup node is braced in one plane, where two tubes cross (FIA Art. 253-8.3.2.1.5 requires at least two gussets where cage diagonals or door bars cross), and at corners where only two tubes meet. Suggested sizes follow FIA Art. 253-8.2.14: U-shaped sheet at least 1.0 mm thick, with legs 2–4× the largest tube diameter from the corner. FIA rules apply to safety cages; elsewhere treat them as good practice.
Weight benchmarks. A GT40-replica builder's 150 kg frame for a 1,000 kg car is 15%; another builder's 375 lb frame for a sub-2,400 lb car is about 16%. Formula Student steel frames run from about 11% to 15% of wet car weight. Mass shown is tube mass plus gussets you mark as added; brackets, tabs and weld are extra.
Bent tubes are kept as one continuous tube. Bends are checked against the FIA minimum centreline radius of 3× the tube diameter (Art. 253-8.3.3).
The stiffness figure is a quick estimate, worked out automatically with no meshing, loads or setup. It treats every tube as a beam and every joint as fully welded, so it reads higher than a rig test. Save one of your measured frames as a reference with its measured value and every estimate is calibrated from then on. It's a screening number for comparing designs, not a replacement for your FEA.
The rule thresholds (20°, 30°, 35× diameter, a quarter-diameter offset), the weight bands and the kit car stiffness bands above the 2,000 Nm/deg minimum are working rules of thumb, to be tuned with your own experience.
Biggest gains tries a 19.05 × 1.6 mm diagonal across every open, flat bay, recalculates each one, and ranks them by stiffness added.
FrameScore scores a space frame chassis and its suspension geometry in seconds, explains what the numbers mean and shows where to improve, so you can make better decisions before you spend on tubes, welding or FEA.
Why we built it
FrameScore started in our own garage. We're building a project car ourselves and kept running into the same problem: the information we needed was scattered across forums, textbooks, racing regulations and the knowledge of experienced engineers.
We wanted one place to bring it all together, a tool that helps you make better decisions before committing to a design. So we started building FrameScore, and we're putting it to use on our own car.
Our mission
To serve the project car community: home builders, students and anyone curious about how cars are built. Clear numbers, plain explanations and honest limits, with a way to compare your chassis against established examples and get a better idea of where it stands.
What you can do
Space FrameUpload a STEP file and get a score for stiffness, triangulation, joints and weight.
Frame BuilderBuild a frame node by node, mark bays and pickups, auto-triangulate and export STEP.
SuspensionCheck camber, roll centre, bump steer and more from your pickup points.
What's coming
FrameScore grows every month. This is the plan, in phases; each phase arrives sooner the more people join.
Phase 1, nowSpace Frame scoring, the Frame Builder with auto-triangulation and STEP export, and suspension geometry. New reference frames and benchmarks added monthly.
Phase 2, more vehicle typesOff-road: trophy trucks, side-by-sides and rock crawlers. Then cross-karts and other classes, each with its own targets and benchmarks.
Phase 3, the Project Car PlannerStart a project, choose the drivetrain and layout, and FrameScore fills in what comes with it: cooling, oil system, gearbox, weight, space claim and estimated cost. See every major part as a 3D block with a driver dummy from small to large, seating, sight lines and the centre of gravity. Save the parts and links you find, keep a checklist and shopping list, and export the package as STEP for your CAD, then build the frame and suspension around it.
Free members can try an early preview of Phase 3 now. Planned, not promised: the order and timing may change with what members ask for.
Thank you
Every frame you test and every note you send helps. Your support is greatly appreciated.
Important disclaimer
FrameScore is designed as a preliminary optimisation and educational tool to support your space frame design workflow before Finite Element Analysis (FEA). It does not replace FEA, professional engineering judgement, or sign-off by a qualified engineer.
All results are estimates intended for guidance and learning purposes only. They must be independently verified by qualified engineering professionals before being used to inform real-world designs, manufacturing, or safety-critical applications.
Using FrameScore means you accept these limits and the Terms of Use.
Suspension geometry with your own coordinates: scores, graphs and fixes
Auto-triangulation: FrameScore designs the tubes for your nodes
STEP export: download your frame as solid tubes for CAD
Everything in the free tools: frame scoring, gussets and the frame builder
Payments are processed by Paystack. Cancel any time from your profile menu and you keep Pro until the end of the period you paid for. Tokens don't expire.
Have a preview access code?
Tap a pickup point or a link line to edit or lock it
You're exploring the sample suspension. Scores, graphs and suggestions are all live. Entering your own geometry is part of FrameScore Pro.
Suspension setup
Enter 3D coordinates in millimetres. X is forward from the middle of the wheelbase, Y is to the right of the centreline, Z is up from the ground. Left-hand points have negative Y; the right side mirrors them unless you enter it separately.
The spreadsheet has a Front sheet and a Rear sheet with every pickup point and its X, Y, Z, plus a Vehicle sheet. Fill it in, then upload it to fill these fields.
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Vehicle parameters
Coordinates
Geometry at ride height
Through travel
Graphs
My suspension vs reference
Not calculated
How it's calculated
The upright is solved as a rigid body held by five fixed-length links: for a double wishbone, the two legs of each wishbone and the tie rod or toe link. For each wheel-centre height the solver finds the upright position that keeps every link at its design length, using Newton iteration on the actual 3D coordinates you enter. Nothing is assumed beyond them.
Camber and toe come from the spin axis (spindle point to wheel centre). The contact patch is the lowest point of a tyre of the diameter you enter, in the wheel plane. Kingpin inclination, caster, scrub radius and mechanical trail come from the line through the ball joints, extended to the ground. Scrub radius is always calculated, never entered: it is the sideways distance at the ground between that steering axis and the centre of the contact patch. With the tyre width entered, the tool also shows whether the steering axis meets the ground inside the tyre tread. Enter the wheel centre on the middle of the tyre tread, so wheel offset is already included.
Instant centres come from the motion of the ball joints (for multi-link, the highest and lowest link joints): each moves at right angles to the line joining it to the instant centre, in front view and in side view. Roll centre: the line from each contact patch through that side's front-view instant centre; where the left and right lines cross is the roll centre. Anti-dive, anti-lift and anti-squat use the side-view path of the contact patch (outboard brakes) or wheel centre (drive torque reacted at the hub), with the CG height, wheelbase, brake balance and drive layout you enter: anti % = tan θ × wheelbase ÷ CG height × force share.
Roll is checked at 1° and 2° by moving the outer wheel into bump and the inner into rebound by half the track times tan(roll). Camber recovery is the share of body roll cancelled by camber gain. Motion ratio is the change in spring/damper length per millimetre of wheel travel; wheel rate = spring rate × motion ratio².
Reference profiles are typical design ranges for each class, drawn together from race car design guidance: roll-centre movement under about 100 mm laterally and 50 mm vertically, anti geometry limited to about 20–30%, and lateral tyre scrub of about 5 mm (Seward, Race Car Design, ch. 3). The other ranges are working rules of thumb. They are not measurements of specific cars: save a measured car as a reference to compare against it directly.
No CAD? Measure your car
You don't need a CAD model. A tape measure, a plumb bob, string line and a level floor give coordinates good enough for most results.
Park on a flat, level floor at ride height, with ballast for the driver and tyres at pressure.
Run a string line along the car's centreline between plumb bobs hung from the middle of the front and rear of the frame. The origin is on that line, halfway between the front and rear hub centres.
For each pickup, hang a plumb bob from the centre of the bolt, rod end or ball joint and mark the floor. X is the distance along the centreline to the mark (forward positive), Y is the square distance from the centreline (right positive, left negative), Z is the height of the point above the floor.
Wheel centre is the hub centre. For the spindle point, hold a straight edge flat against the hub face and mark a point on the axle line about 100 mm inboard.
Measure each point twice. About ±2 mm is enough for camber, roll centre and anti values; bump steer is sensitive to the tie rod points, so measure those carefully.
Enter the numbers here, or fill in the spreadsheet table below in Excel or Google Sheets and paste it back.
Spreadsheet table (CSV)
Every coordinate and vehicle parameter as rows of section, side, point, X, Y, Z. Copy it into a spreadsheet, fill it in, then paste it back and apply. You can also save it as a .csv file and use Import file.
Import and export format (JSON)
Export JSON saves every coordinate and vehicle parameter so you can share a design or reload it later. The same format imports.
Validation and sources
Each method and convention was checked against Derek Seward, Race Car Design (ch. 3 and 6) and published definitions:
Anti-dive = front brake share × wheelbase × tan θ ÷ CG height, with θ the slope from the contact patch to the side-view instant centre (Seward eq. 3.1–3.2). Matches the app.
Anti-squat, independent rear uses the slope from the wheel centre, because drive torque is reacted at the hub bearings (Seward eq. 3.3). Rear anti-lift under braking uses the contact patch. Matches the app.
Roll centre is where the lines from each contact patch through its front-view instant centre cross (Seward 3.3.2). Checked against the textbook construction (each wishbone plane cut at the contact patch): the same within 0.5 mm on the sample front and rear.
Anti geometry checked against the textbook pivot-axis construction (lines through each ball joint parallel to its wishbone pivot axis, meeting at the side-view instant centre): identical on the sample front (38.4% anti-dive) and rear (25.4% anti-squat), and on steep and pro-dive test layouts.
Roll-centre movement: under about 100 mm sideways and 50 mm vertically is acceptable (Seward 3.3.2). Anti geometry: most designers limit it to about 20–30% (Seward 3.4). Lateral tyre scrub: about 5 mm maximum (Seward 3.5).
Scrub radius is positive when the steering axis meets the ground inboard of the contact patch centre, negative when outboard (SAE convention, as on Wikipedia). Seward recommends keeping it below about 40 mm.
Kingpin inclination is positive with the top of the axis toward the car's centre; caster is positive with the top tilted rearward; caster (mechanical) trail is the distance at the ground between the axis and the wheel centreline, positive ahead. Seward suggests at least about 15 mm of trail, without going much larger; the reference ranges now start at 15 mm.
Camber is negative with the top of the wheel tilted inboard; toe-in is positive with the front of the wheel pointing inboard. Camber recovery is the share of body roll cancelled by camber gain; Seward's Formula Student example reaches about 115%.
Solver check: equal-length parallel wishbones give zero camber change through travel, as theory predicts (Seward 3.3.1).
Ranges not covered by these sources are working rules of thumb and are labelled as typical ranges.
New bay
Frame builder
Build a frame from nodes and tubes. X runs along the car (front positive), Y across it (left negative, right positive), Z up from the floor. All dimensions in millimetres.
Nodes from a spreadsheet
Download the template, fill in your node coordinates in Excel or Google Sheets, then upload it. The nodes appear in the workspace and you connect them with tubes.
Columns: Node name, X, Y, Z (mm), Suspension pickup (yes or no). An optional Tubes sheet (From, To, Outer diameter, Wall) adds tubes too.
Add node
Tip: in Add node mode, click the floor grid to fill in X and Y.
Tube size for new tubes
Pick two nodes and choose Add tube, or choose Connect and click the first node and the second node in the workspace. Keep clicking to chain tubes; press Esc or Select to stop.
Auto-triangulate Pro
Enter your nodes, then let FrameScore choose the tubes: it joins every node, braces each suspension pickup in three directions, keeps your bays clear and adds the diagonals that add the most stiffness per kilogram, until the frame reaches the target for its class or its weight budget.
Mark pickups by selecting a node and ticking Suspension pickup point. Mark bays with Mark bay in the toolbar (or Add bay under Bays). Each bay is the box around its nodes; no tube passes through it or across its top opening.
Properties
Select a node or tube in the workspace or the lists below.
Nodes
Tubes
Bays
A bay is the space kept clear for the engine, gearbox, driver and so on: the box around at least 4 nodes, with at least one at a different height. Auto-triangulate keeps tubes out of it.
Import or export
FrameScore frame file: NODE name x y z, TUBE from to outer_diameter wall, PICKUP name, BAY type name node node node node. Paste one here (or CSV with the same columns) and apply, or copy this frame out.
STEP file for CAD Pro
Every tube as a hollow solid at its outer diameter and wall, running centre to centre between its nodes (ends overlap at the nodes; trim or merge them in your CAD). Millimetres, same X, Y, Z as here. Opens in SolidWorks, Fusion, Rhino, CATIA, Onshape and FreeCAD.
Preview. Blocks are approximate space claims: check every size and weight against the maker's drawing.
Coming soon · Project Car Planner
Your whole build, in one place.
Every build starts with decisions that shape everything after: the engine, where it sits, how it's cooled, where you sit. The Planner turns those choices into a package you can see, weigh and take into CAD, and keeps every part you find with your project.
Start from the drivetrainPick an engine and layout. It fills in the cooling, oil system, gearbox, weight and space each part needs.
One sound recommendationThe part that works, from builders who've done it, with the alternatives a click away. No more fifty tabs.
Your build, savedEvery part, link, price and note in one project, with price alerts and a shopping list.
Straight into CADExport the package with the driver and sight lines as STEP, then build the frame and suspension around it.
Help decide what we build first:
Try the preview below: change the layout, engine and driver, and watch the package, balance and sight lines update.
Project Planner Preview
Plan the package before the frame. Pick the layout, engine and driver, and FrameScore blocks out the space each part claims, estimates weight and balance, and lists what else you'll need. Then build the frame around it.
Project and targets
Front axle at X = 0, rear axle at X = minus the wheelbase, Z up from the ground; the same axes as the Frame Builder.
Drivetrain
Also plan for
Cooling and systems
Driver and visibility
Weight and balance
–Front / rear weight
–Centre of gravity height
–Estimated weight with driver
Parts, links and shopping list
Save the parts you find, with the link, the price and a note. They stay with this project on this device.
Add your own part
Saving parts, links and the shopping list arrive with the full Planner.
Next steps
Take the package into your CAD, then build the frame and suspension around it.
STEP export of the package arrives with the full Planner.
Before you use this tool
FrameScore's suspension and triangulation outputs are design aids. Real-world performance depends on materials, fabrication quality, welding and testing that FrameScore cannot check. You remain fully responsible for your build.
