"Bigger cars are safer" is one of those claims everyone half-believes and nobody quantifies. It can be quantified. We matched measured kerb weights against the insurance claim indexes for the same models.
| Kerb weight | Injuries to occupants | Injuries caused to others | Damage to others' property |
|---|---|---|---|
| 1,163 kg | 125 | 112 | 91 |
| 1,399 kg | 106 | 103 | 90 |
| 1,627 kg | 94 | 89 | 83 |
| 1,870 kg | 79 | 83 | 88 |
| 2,102 kg | 76 | 84 | 93 |
| 2,399 kg | 66 | 91 | 107 |
| 2,791 kg | 60 | 98 | 118 |
Read the first column top to bottom: 125, 106, 94, 79, 76, 66, 60. Seven weight bands, seven steps down, no reversals. Injury claims to a vehicle's own occupants fall by 52% from the lightest band to the heaviest.
Why the line is so clean
Because it is not really about cars. In a collision between two vehicles, the total momentum is fixed and it gets divided between them in inverse proportion to their masses. The lighter one changes velocity more.
Injury tracks that change in velocity. Not speed at impact, not the size of the dent — how hard the occupant's body has to be decelerated. A vehicle twice the mass of what it hits absorbs roughly a third of the velocity change and hands over the rest.
This is why the relationship holds across brands, classes and decades. It is arithmetic that operates before any engineering gets involved.
Now read the other two columns
They move the opposite way, and that is the part usually left out.
Property damage climbs from 91 at the lightest band to 118 at the heaviest — a 30% increase. Bodily injury caused to other people bottoms out in the middle of the range and rises again at the top, reaching 98 for the heaviest vehicles.
So the protection is not created. It is transferred. The same mass that cuts your occupants' injury claims by half increases what your vehicle does to whatever it collides with, and the collision partner is usually somebody in a lighter car.
What this does not say
It does not say engineering is irrelevant. Crash structures, airbags and restraint systems determine how well a vehicle protects its occupants at a given mass, and they have improved enormously — a 1,400kg car built today is far safer than a 1,400kg car from 1995.
What the weight data captures is the part engineering cannot address: how the energy gets divided between two vehicles. A five-star small car is still the lighter party when it meets a five-star truck, and the barrier test that awarded both those ratings never modelled that encounter.
It also does not say every heavy vehicle is safe. Tall heavy vehicles trade some of the advantage back in rollover resistance, which is a separate failure mode with its own physics.
Choosing with the whole table in view
If the question is purely how to protect the people in your car, the data points one way and it points there firmly.
If the question includes everyone else on the road, the third column is part of the answer, and it deserves stating plainly rather than being left in a spreadsheet. Choosing mass for protection is choosing to shift risk outward.
For most buyers the honest middle is the range around 1,600 to 1,900kg, where occupant injury has already dropped substantially and the property damage index is still at or below average. Beyond that the returns to your own occupants get smaller and the externality grows.
And whatever the vehicle weighs, the safety systems have to be working. A free VIN check lists the open recalls on a specific car, which is where airbag and restraint defects show up.
Frequently asked questions
Does a heavier car protect you better?
Consistently, and the relationship is close to linear. Matching kerb weights against claim data, injury claims run at an index of 125 for vehicles near 1,163kg and 60 for vehicles near 2,791kg — a 52% reduction across the range, or roughly 9% for each 250kg step.
Does driving a heavy car put other people at risk?
The claim data says yes. Over the same weight range where injuries to a vehicle's own occupants halve, the property damage index rises from 91 to 118. Bodily injury caused to others sits near 98 at the heaviest end against 112 at the lightest, so the harm does not vanish — it moves.
Is weight or engineering more important for safety?
Both, and they are not interchangeable. Engineering determines how well a vehicle protects occupants at a given mass, which is what crash tests measure against a fixed barrier. Mass determines how the energy is shared when two vehicles meet, which is what the claim data captures and the barrier test cannot.
Are electric cars safer because they are heavier?
Their occupants benefit from the same physics, yes — battery packs add several hundred kilograms and the injury data follows weight regardless of what causes it. The corollary applies too: that mass increases the energy delivered to whatever the vehicle collides with.
Denis Kataev is a serial solopreneur and the founder of ForCar. With 15+ years in software engineering and 10 years in SEO, he builds data-driven products end to end — backed by a sharp eye for design. At ForCar he mines proprietary vehicle datasets, turning raw numbers into buying advice you can actually trust.
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