TrailACT tools:

BASE-Bf v1 (Before Assessment Simulation Engine for Bike features)

A physics-based design tool for rollers, jumps, and drops.

The tool you reach for first — to design and understand a jump, drop, or roller before you move dirt, and before the formal sign-offs. It runs the physics so you walk in knowing what your numbers mean. Call it computational education: the math, in your hands, to learn from.

What it does:

• Physics-based design for jumps, drops, and rollers — takeoff, flight, landing, impact, the whole arc
• Flight solved with real aerodynamic drag, not the drag-free “cannonball” arc — a small correction at trail speeds that grows as you go faster, plus a wind envelope to show you when wind actually matters (and when it doesn’t)
• Chaining for gravity-fed lines
• Clean PDF build sheets, plus DXF and CSV, to take from screen to dirt

A full user guide — roughly 100 pages, with cited sources and educational content alongside the app how-to — ships with every version. The guide alone is worth the price of admission, it’s way beyond anything I ever published at Trailism. BASE-Bf User Guide PDF

Jump Breakdown:

Approach

If you’re not entering a speed directly at the lip/launch, the run-in is an energy model, not a lookup. The rider coasts — no pedaling or braking — down your entered grade and distance, gaining g·sin θ and paying two always-on losses the whole way: rolling resistance against the normal load, and aerodynamic drag charged as work against air-relative speed, ½ρ·CdA·∫v²ds, with CdA scaled from rider height and ρ adjusted for site elevation. Wind, if you set it, enters here as a projection onto the path direction, so a headwind raises air-relative speed and costs you energy before you ever reach the ramp. The climb from ramp base to lip is charged the same way — over the as-built ramp arc, with rolling resistance taken against the full G-profile of the curve, because a 1.5–4 g turn presses the tire into the dirt two to four times harder than straight ground does. Nothing in the chain is lossless, and a run-in that can’t deliver usable speed is refused rather than quietly floored.

Takeoff

Transitions are clothoid–circle–clothoid. The two Euler-spiral bookends ramp curvature linearly from zero up to the arc and back down to zero, so there’s no curvature step anywhere — the rider is released at the lip with near-zero jerk. The arc radius is solved, not chosen: it’s the smallest radius whose normal load (cos θ + v²/(Rg), with speed tracked by energy conservation up the climb) stays under your ramp G limit everywhere along the curve — peak load lands low in the transition, where the rider is fastest, not at the lip, where it falls to cos(lip angle). Two levers reshape it: γ sets how much of the total turn the arc does versus the spirals, and wheelbase floors the exit spiral at one wheelbase so both wheels are on the transition at departure. Enforcing the cap continuously rather than at one design point matters — a single-point radius formula evaluates G at the steepest part of the arc and underestimates the real peak by 5–12%.

Flight

From the lip the rider becomes a point mass integrated through a drag ODE — gravity plus ½ρ·CdA·v² opposing the air-relative velocity vector, same CdA and same elevation-adjusted density as the ground segments, stepped until the path meets the landing surface. Wheelbase is deliberately not in this calculation: for a given lip speed and angle the arc is the arc. Three riders are flown, not one — your design speed, and that speed minus and plus your speed buffer — so what you see is a band of outcomes rather than a single line, and the fast rider is the one that sizes the landing length. An optional pop trajectory adds the vertical velocity to the design speed an active rider generates by extending at the lip.

Landing surface

The landing isn’t a slope you guess at — it’s integrated backward from where the fast rider’s arc crosses the pad, back toward the lip. At every step the solver asks the inverse question: what takeoff speed would land exactly here, and at what impact velocity? It then tilts the surface at that point to the angle that holds the component of impact velocity normal to the dirt at the target — the equivalent fall height, v_n²/2g, which is the height of a flat drop that would hit you equally hard. Hold that target constant all the way down and you get a constant-EFH surface: the same EFH from the lip to the far end, at the cost of a ledge near the lip, where riders are slow and close to the ground anyway. Taper the target instead — from a low value at the lip up to the full target at the far end — and you get a variable-EFH surface: a smooth mound that meets the lip tangent to the trajectory with no ledge like a constant-EFH shape. At a lip target of zero (0.1 minimum setting) the surface literally becomes tangent to the incoming arc; set the lip target equal to the far target and it collapses back to the constant-EFH shape. From there the surface can sit at grade, be raised into a step-up, or be dropped below grade, with an independent control for how far the tie-in blends back toward grade.

What the landing tells you

Because the surface was built against the fast rider, the design and slow riders land closer and shallower on that same dirt and see lower EFH automatically. The tool then re-measures, rather than assuming: it finds each rider’s actual touchdown point on the as-built surface, takes the angle between velocity and the local slope there, and reports peak EFH plus a count of samples over your threshold — so you can see where the landing gets steep relative to the arc hitting it. If the geometry can’t work — a step-up raised above the design rider’s arc entirely, a run-in that stalls, a ramp that can’t be built inside the G limit — it stops and says so rather than producing a drawing that looks fine.

Requirements:

• Windows: Windows 10 or 11, 64-bit. Any modern computer from roughly the last eight years.
• Mac: a Mac with Apple silicon (M1 or newer) running macOS 14 Sonoma or later. Intel Macs are not supported.
• No Linux version.
• 4 GB RAM, 8 GB comfortable.
• About 600 MB of disk space on Windows; about 650 MB on a Mac.
• Computing a feature is single-threaded, so single-core speed matters more than core count. A single small jump is typically a few tens of seconds, or up to a minute; chains, wind scenarios, or fine resolution can take a minute or three depending on the computer.

Installing:

PC

Mac

1. Download BASE-Bf (newest free PC edition) 2. Unzip it anywhere you like — your Desktop or Documents is fine. Don’t extract it into OneDrive, Dropbox or another cloud-synced folder, and don’t run it from inside the zip. 3. Then open the folder and read START HERE.txt. 4. Open the folder and double-click BASE-Bf.bat and it will prompt to create a shortcut. Windows may unpack the zip into a folder named after the zip file. If you open it and find a folder called BASE-Bf, open that one too — BASE-Bf.bat is inside it. 5. It opens in your browser. That is normal — the app runs on your own computer, and your designs stay there. 6. To move it, move the folder. To remove it, delete the folder. Windows may show a blue “Windows protected your PC” box the first time you run it, naming an unknown publisher. That appears for software from small publishers that Windows has not seen enough of yet. Click More info, then Run anyway.

1. Download BASE-Bf (newest free Mac edition) 2. Unzip it (double-click the zip in Downloads), then drag BASE-Bf into your Applications folder. 3. Double-click BASE-Bf in Applications. macOS blocks it and says it could not verify the app. Click Done. 4. Open System Settings → Privacy & Security, scroll down to the Security section, and click Open Anyway next to the BASE-Bf message. Enter your Mac password if asked. 5. Double-click BASE-Bf again and click Open. From then on that version opens normally. 6. It opens in your browser. That is normal: the app runs on your own computer, and your designs stay there. There’s no BASE-Bf icon in the Dock while it runs; the browser tab is the app. You can drag BASE-Bf from Applications to the Dock for a shortcut. 7. To remove it, drag BASE-Bf from Applications to the Trash. macOS blocks each new version of BASE-Bf once, because it comes straight from TrailACT rather than through Apple’s paid approval service. Steps 3–5 get you past it.

Updating from an earlier version:

PC

Mac

1. Download the zip above , or from inside the app — click Check for updates at the bottom of the left sidebar, and a download link appears at the top of the page. — it is the same link, and it is always the current version. 2. Extract it alongside your existing folder, then open the new folder and double-click BASE-Bf.bat. Your desktop shortcut repoints itself automatically. 3. Once the new version runs, delete the old folder. Until you do, whichever copy you opened last owns the desktop icon. 4. Your license key and saved favorites live in Documents\BASE-Bf, not in the app folder, so replacing the app leaves them untouched. There is no second download and no key to re-enter: a 1.x.x license covers every 1.x.x version.

1. Download the new zip above, or click Check for updates at the bottom of the app’s left sidebar. It’s the same link. 2. Close every BASE-Bf browser tab and restart your Mac, so the old version has fully stopped. 3. Unzip the new one and drag BASE-Bf into Applications, choosing Replace. 4. Open it with steps 3–5 above. macOS asks once for each new version. 5. Your license key and favorites live in the BASE-Bf folder inside your Documents folder, so they carry over. A 1.x.x license covers every 1.x.x version.

Buying takes one extra step, because each license is tied to one computer:

1. Install the free edition on the computer you’ll use it on (see Installing above).
2. In BASE-Bf, click License in the sidebar and copy your machine code.
3. Buy below. You’ll be asked for your machine code at checkout.
4. We email your license key. Keys are issued by hand, not automatically: usually quickly, but up to 5 days if I am out of cell range on a trail.
5. In BASE-Bf, click License, paste the key, and press Save. That’s it.

No second download. The same copy you already have becomes the paid edition.

Free edition 1.x.x $0

Design edition 1.x.x $200 · one-time · Everything the app does today

Single jumps, on screen. Design one jump at a time and see the whole picture — the ramp profile, the landing surface, 4 flight paths at 3 speeds, touchdown angle and G-force, and the wind envelope. Everything the physics engine does for a jump, on screen, for nothing. What it doesn’t do: no drops, no rollers, no chaining features together, and no exports — the build sheet, DXF and stakeout CSV are in the paid version. It is free and donating is not required, but if you feel the urge, by all means: donate

One payment. No subscription humbug. Same software, same features, same price. Choose the one that matches how you’re buying (we ask only so the sale is recorded correctly — the software and the price are identical): PERSONAL USE BUSINESS USE License. Keys are issued the old fashioned way, by hand, not automatically. Sometimes I can be out of cell range on a trail for up to 5 days before I can send them, sorry. Jumps, drops, rollers, and multi-feature chains solved as one connected line with speed carried from each feature into the next. And the part you build from: a six-page PDF build sheet — side profile with dimensioned callouts, plan footprint, front view with volume tables, results summary, stakeout table, and a curve-check table for verifying the built curves in the field. Plus DXF with a geometry sidecar, and per-station CSV.

Two more editions follow after R&D field testing — 1. Survey- survey / GNSS world-coordinate export, and 2. Simulate- existing-feature simulation. Owners of these editions pay only the difference if they want them, or full price for all 3 editions when all 3 are available.

Updates to BASE-Bf:

BASE-Bf checks for a newer version when it starts, and tells you if one is available. It also checks whether a version has been superseded. That check sends only your IP address, a timestamp, and your version number. No design file, input, or output is ever transmitted.

Your license does not expire. The paid edition is a one-time purchase for version 1.x.x and it keeps working indefinitely. Updates and patches to 1.x.x are included at no extra charge for at least 18 months from the 1.x.x release. New versions appear on this downloads page; your license key keeps working — it lives in your Documents folder, not inside the app, so replacing the app folder does not disturb it.

Version numbers — 1.0.1 is MAJOR.MINOR.PATCH

• MAJOR, the first number — a distinct product release, 1.x.x -> 2.x.x. Costs an upgrade price, at the edition you hold.
• MINOR, the middle number — new features, 1.0.x -> 1.1.x. Free.
• PATCH, the last number — bug fixes, 1.0.1 -> 1.0.2. Free.

Editions are the other axis. Moving up an edition — Design to Survey or Simulate — costs the difference between them, at any version. New customers always get the current version, and pay full price for the edition they choose.

Version 1.1.6 PC+Mac · released 10-10-26 · BASE-Bf version history · donate

---

BASE-Bf produces physics simulation estimates only. Results are based on idealized mathematical models and simplified assumptions. Real-world conditions — rider technique, terrain variability, material properties, soil conditions, weather, and equipment — are not modeled. These outputs are not guarantees of safety, performance, or suitability for construction. They are planning estimates.

Any feature built using outputs from this tool must be reviewed, approved, and supervised by a qualified professional before construction and before use by any rider.

---

BASE-Bf User Guide · Terms of Service · Privacy Policy · mail support at the url