What does 123T mean on a tire?
| Load per tire1,550 kg — index 123 on the ISO scale | 3,417lb |
|---|---|
| All four tiresthe ceiling for vehicle plus everything in it, not a target | 13,668lb |
| Speed rating T190 km/h — the most common rating on sedans and crossovers | 118mph |
| Next index up (124)110 lb more per tire | 3,527lb |
| Next index down (122)110 lb less per tire — do not fit this if your door label says 123 | 3,307lb |
Notes
- **123T means two separate things.** 123 is the load index: this tire carries **3,417 lb** on its own, at the pressure printed on the sidewall. T is the speed rating: the tire is built to hold together at **118 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 123-rated tires carry 13,668 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.** T at 118 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 123T is a 225-wide, 45-series, 17-inch tire rated 3,417 lb and 118 mph.
123T is two answers, not one
123 is the load index: this tire carries 3,417 lb on its own. T is the speed rating: the tire is built to hold together at 118 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 123-rated tires carry 13,668 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
T = 118 mph (190 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 123T is a 225-wide, 45-series, 17-inch tire rated 3,417 lb and 118 mph.
Nearby sizes
Read more
- Recalibrating a Speedometer After a Tire Change: Four Routes, and How to Verify It WorkedOn most modern vehicles the tire size is a stored number, not a mechanical ratio. Where that is true, correcting it takes minutes; where it is not, the options get physical.
- Plus Sizing Chart: Wider Tire, Shorter Sidewall, Same Rolling DiameterPlus sizing trades sidewall for wheel and keeps the overall diameter where it was. Done properly nothing on the vehicle notices — which is the entire point.
- Bigger Tires Change Your Gearing — Here Is How Much, and What to Re-Gear ToA larger tire is a gear change nobody installed. The effect is the same as swapping the differential for a taller one, and the arithmetic is a single ratio.
- Will 33s Fit Without a Lift? Often Yes — the Rubbing Happens Where You Are Not LookingMost stock trucks clear a 33-inch tire driving in a straight line. Fitment is decided at full lock over a bump, which is the one condition nobody tests in the parking lot.