What does 120S mean on a tire?
| Load per tire1,400 kg — index 120 on the ISO scale | 3,086lb |
|---|---|
| All four tiresthe ceiling for vehicle plus everything in it, not a target | 12,344lb |
| Speed rating S180 km/h — family sedans and vans | 112mph |
| Next index up (121)111 lb more per tire | 3,197lb |
| Next index down (119)88 lb less per tire — do not fit this if your door label says 120 | 2,998lb |
Notes
- **120S means two separate things.** 120 is the load index: this tire carries **3,086 lb** on its own, at the pressure printed on the sidewall. S is the speed rating: the tire is built to hold together at **112 mph**. The two numbers are unrelated — a high load index says nothing about speed, and vice versa.
- **The load figure is per tire, not per vehicle.** Four 120-rated tires carry 12,344 lb between them, and that has to cover the car, the fuel, the passengers and whatever is in the boot. Compare it against the gross vehicle weight rating on the door jamb, not against the kerb weight in the brochure.
- **Never fit a lower index than the door label.** The placard inside the driver's door gives the minimum load index the manufacturer signed off on. Going below it is the one substitution in tire fitment that has no upside — it saves a few dollars and removes margin from the only four patches of rubber holding the car down.
- **A speed rating is a ceiling, not a recommendation.** S at 112 mph assumes correct pressure, correct load and a tire in good condition. Under-inflation is what actually destroys tires at speed, and it does it well below the rated number.
- Both markings sit at the end of the size, after the diameter: a tire marked 225/45R17 120S is a 225-wide, 45-series, 17-inch tire rated 3,086 lb and 112 mph.
120S is two answers, not one
120 is the load index: this tire carries 3,086 lb on its own. S is the speed rating: the tire is built to hold together at 112 mph.
The two are unrelated. A high load index says nothing about speed, and a fast tire is not automatically a strong one.
The load figure is per tire
Four 120-rated tires carry 12,344 lb between them — and that has to cover the car, the fuel, the passengers and everything in the boot.
Compare it against the gross vehicle weight rating on the door jamb, not the kerb weight in the brochure. The two numbers differ by several hundred pounds on most cars, and the brochure is the one that flatters.
Never fit a lower index than the door label
The placard inside the driver's door gives the minimum load index the manufacturer signed off on.
Going below it is the one substitution in tire fitment with no upside: it saves a few dollars and takes margin out of the only four patches of rubber holding the car on the road.
A speed rating is a ceiling, not a recommendation
S = 112 mph (180 km/h) assumes correct pressure, correct load and a tire in good condition.
Under-inflation is what actually destroys tires at speed, and it does it well below the rated number.
Where to find it on the sidewall
Both markings sit at the end of the size, after the diameter — a tire marked 225/45R17 120S is a 225-wide, 45-series, 17-inch tire rated 3,086 lb and 112 mph.
Nearby sizes
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