When the brakes are applied, the car pitches nose-down and load shifts from the rear axle onto the front. Adjust vehicle mass, wheelbase, CG height and deceleration to see the dynamic front and rear axle loads, the front-load fraction and the deceleration at which the rear wheels lift, all in real time.
Parameters
Vehicle mass m
kg
Actual running mass including occupants and cargo
Wheelbase L
m
Distance between the front and rear axles
CG height h
m
Height of the vehicle centre of gravity above the road
Static front-axle load split
%
Fraction of weight on the front axle at rest
Deceleration G
g
Braking strength. 1.0g equals gravity
Results
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Weight transfer ΔW (N)
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Front-axle load (braking) (N)
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Rear-axle load (braking) (N)
—
Front-load fraction (braking) (%)
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Rear-lift deceleration (g)
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Verdict
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Brake dive under braking — side view
Under braking the body pitches nose-down, the front suspension compresses and the rear extends. The downward arrows are the dynamic axle loads; their length tracks the load magnitude.
Longitudinal weight transfer ΔW under braking. a is the deceleration (a = g·n, with n the deceleration in g), h the CG height and L the wheelbase. A low CG and a long wheelbase reduce the transfer.
Dynamic front-axle load W_f and rear-axle load W_r. W_f0 and W_r0 are the static axle loads. The rear load is clamped at 0 (it cannot go negative).
$$n_{\text{lift}}=\frac{W_{r0}\,L}{m\,g\,h}$$
Deceleration n_lift at which the rear wheels just lift off the road (solving W_r = 0). Beyond it the vehicle risks pitching over its front axle.
What is Braking Weight Transfer?
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When you slam on the brakes the car dips forward hard. Does that mean the car is about to tip over forward?
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Good question. That dip is a phenomenon called "weight transfer". The braking force acts at the road surface — at the tyre contact patch. But the car's mass is concentrated at the centre of gravity, which sits well above the road. That height difference creates a "pitching moment" that wants to rotate the body forward. As a result, part of the load that rested on the rear tyres actually shifts onto the front. The "nose dive", where the front suspension compresses and the rear extends, is exactly that.
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When you say the load "transfers", is real weight actually moving, or is it just a feeling? When I raise the deceleration on the left, the front-axle load keeps climbing.
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It is real, measurable load. The amount is ΔW = m·a·h / L — proportional to mass m, deceleration a and CG height h, and inversely proportional to wheelbase L. With the default settings the front-axle load climbs from 8093 N at rest to over 10,000 N under braking, and the front-load fraction jumps from 55% to almost 72%. Since tyre grip is roughly proportional to the load pressing it onto the road, the now heavily-loaded front tyres can produce a strong braking force. That is why a car's front brakes are built larger than the rear.
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So the rear wheels lose load, then. Do the rear brakes stop working well?
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Exactly. The unloaded rear tyres lose grip, and pressed hard they lock up easily. A locked rear axle makes the car unstable and prone to spinning — that is far more dangerous than locking the front. So the brake-force distribution is always biased forward. A proportioning valve, or electronic brake-force distribution (EBD), exists precisely to "stop the rear locking first". Preventing the unloaded rear wheels from locking is also one of the main jobs of ABS.
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There's a number called "rear-lift deceleration". Does that mean the rear wheels actually leave the ground?
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Yes — in the extreme case. As you keep raising the deceleration, at some point the dynamic rear-axle load reaches zero. That deceleration is n_lift = W_r0·L / (m·g·h). For a passenger car the default works out to about 2.1g — real tyres cannot decelerate that hard, so an ordinary car will not pitch over. But for a tall, short-wheelbase vehicle, especially a motorcycle or a tractor, n_lift drops sharply. A motorcycle whose rider grabs too much front brake, lifts the rear wheel and pitches forward — a "stoppie" — is exactly this. A lower CG and a longer wheelbase both push you toward the safe side.
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I see. So a sports car sitting low isn't just about looks.
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That is exactly it. Lowering the car drops the CG height h, which makes the weight transfer ΔW smaller. The front and rear tyres can then share the load more evenly, so the car keeps its composure under hard braking. Racing cars use long wheelbases for the same reason. Conversely, loading heavy items on the roof or fitting a roof box raises the CG, so the rear unloads more easily at the same deceleration. Move the slider on the "ΔW vs CG height" chart below and you will see at a glance how strong that effect is.
Frequently Asked Questions
The longitudinal weight transfer is ΔW = m·a·h / L, where m is the vehicle mass, a is the deceleration (the deceleration in g multiplied by gravity, a = g·n), h is the CG height and L is the wheelbase. The braking force acts at the road surface, below the centre of gravity. That height offset creates a pitching moment that rotates the car nose-down, and this moment appears as the load ΔW shifted from the rear tyres onto the front. A low CG and a long wheelbase both make ΔW smaller.
Under braking, the load ΔW shifts from the rear axle onto the front, so the front axle carries far more load than at rest. The braking force a tyre can produce is roughly proportional to the load pressing it onto the road, so the now heavily-loaded front tyres can generate a large braking force while the lightly-loaded rear tyres can generate far less. In a typical car the front wheels do 60-70% of the braking. That is why the front discs and calipers are larger and why the brake-force distribution (proportioning valve, EBD) is biased forward.
The rear wheels lift when the dynamic rear-axle load reaches zero. Setting rearDynamic = rearStatic − ΔW = 0 and solving gives a_lift = rearStatic·L / (m·g·h), in g. The taller the CG, the shorter the wheelbase and the smaller the static rear load, the lower this value, so even moderate braking moves the vehicle toward pitching over its front axle. Motorcycles, tractors and tall, short vehicles need particular care.
Since the weight transfer is ΔW = m·a·h / L, it is proportional to CG height h and inversely proportional to wheelbase L. A lower CG or a longer wheelbase makes ΔW smaller, so the rear tyres keep more load and the car stays stable under heavy braking. That is why sports cars run low and racing cars use long wheelbases. Conversely, loading heavy items on the roof raises the CG, so the rear wheels unload more easily at the same deceleration.
Real-World Applications
Brake system design: The split of braking capacity between front and rear is decided directly from this weight-transfer calculation. Because the front axle gains load under braking, it gets large discs and multi-piston calipers, while the rear gets smaller brakes. On top of that, a proportioning valve or electronically controlled EBD throttles the hydraulic pressure to the rear as deceleration rises, dynamically adjusting the split so the rear does not lock before the front. The basic goal is to keep the rear with a margin against the ideal distribution curve, where front and rear would lock simultaneously.
Suspension and anti-dive geometry: The amount of nose dive is set by the suspension spring rates and geometry. Designers use "anti-dive geometry", clever suspension link angles, to mechanically resist the forward pitch under braking. The weight transfer itself cannot be removed by physics, but the body attitude change (pitch angle) can be suppressed, which keeps the driver's sight line and the headlight beam steady and reduces occupant discomfort.
Motorsport setup: In racing cars, braking weight transfer is used as a weapon. "Trail braking" — carrying brake pressure into a corner while turning — loads the front tyres, raises front grip and sharpens turn-in. Engineers adjust CG height, front-rear weight distribution and brake bias to build a weight-transfer behaviour the driver can exploit confidently.
Commercial-vehicle and motorcycle safety: Trucks, whose CG is high and varies greatly with cargo, and motorcycles, with their short wheelbase and high CG, face a higher risk of rear-wheel lift and pitch-over than passenger cars. A motorcycle "stoppie", where grabbing too much front brake lifts the rear wheel, is exactly the state of exceeding n_lift. Linked braking systems and cornering ABS are technologies that secure the braking stability of such vehicles.
Common Misconceptions and Pitfalls
The most common misconception is that "weight transfer changes the total weight of the car". Weight transfer only redistributes load between the front and rear axles; the total vehicle weight — the sum of all four contact loads — does not change during braking. If the front axle gains ΔW, the rear axle loses exactly ΔW. In this tool's calculation, the front-axle load plus the rear-axle load always equals the total weight. The car does not become "lighter or heavier under braking"; the place the weight sits simply moves forward.
Next, the assumption that "CG height is just the height of the car". CG height h is not the height of the roof; it is how far above the road the centre of gravity of the whole mass — engine, occupants, fuel and cargo — sits. For the same body height, packing heavy cargo low under the floor lowers h, while loading it on a roof rack raises h significantly. The h you enter in this tool should be the actual CG height reflecting the loaded state, not the visible body height. On a real car, accurate measurement of h (for example by the tilt method) governs the accuracy of any weight-transfer prediction.
Finally, the misconception that "an ordinary car can decelerate all the way to its rear-lift deceleration". The n_lift this tool shows is around 2g for a passenger car, but that is only a geometric limit — the car cannot actually reach that deceleration. The tyre-road friction coefficient μ is roughly 0.8-1.0 even on dry asphalt, and the deceleration is capped by μ. So an ordinary passenger car will essentially never pitch over. For a tall, short-wheelbase motorcycle or small vehicle, however, n_lift drops into the range of deceleration that is actually achievable, so the pitch-over risk becomes real. Read n_lift as a measure of "how resistant the vehicle's geometry is to pitching over", not as a deceleration to aim for.
How to Use
Enter vehicle mass (kg), wheelbase (mm), and centre-of-gravity height (mm) using the numeric inputs or sliders.
Set the front-axle static load percentage under no-braking conditions (typically 50–65% for passenger cars).
Adjust braking deceleration (g) to simulate real-world scenarios: light city braking (~0.4 g), highway emergency (~0.7 g), or track-limit stopping (~1.0 g).
Read the outputs: weight transfer magnitude (ΔW in N), redistributed front and rear axle loads, and rear-lift risk indicator.
Worked Example
Mid-size sedan: mass 1500 kg, wheelbase 2700 mm, CG height 550 mm, front static load 55% (825 N front, 675 N rear at rest). Under 0.75 g emergency braking: weight transfer ΔW = 407 N, front-axle load becomes 1232 N, rear-axle load drops to 268 N. Front-load fraction reaches 82.1%. Rear-lift deceleration threshold (when rear axle unloads completely) occurs at 0.91 g, flagged in verdict as "liftoff risk."
Practical Notes
Higher CG and shorter wheelbase amplify weight transfer; SUVs (CG ~650 mm) transfer more aggressively than sports cars (CG ~400 mm).
Rear-axle load approaching zero indicates potential wheelie or loss of rear braking grip; anti-lock braking systems adjust pressures to prevent this.
Front-load fraction exceeding 85% on light vehicles may cause front tyre saturation before rear tyres engage fully—critical for ABS tuning.
Real brake bias must account for this transfer or front wheels lock prematurely.