Plus sizing is the proper way to fit a larger wheel without upsetting how a car drives. It means fitting a larger-diameter wheel with a lower-profile tyre, chosen so the overall diameter stays about the same as the original.
How it works
The idea is a trade. As the wheel grows, the tyre's sidewall profile shrinks by a matching amount, so the total height of wheel plus tyre barely changes. The naming follows the wheel:
- Plus one: one inch larger wheel, with a lower-profile (and often slightly wider) tyre
- Plus two: two inches larger, with the profile dropping further still
As a rough guide, going up two wheel sizes typically drops the aspect ratio by around 20 points and adds about 20mm of width, while holding the overall diameter steady.
Why the diameter is held steady
Keeping the overall diameter close to standard is the whole point. It keeps the speedometer and odometer accurate, keeps the gearing and electronics behaving, and keeps the tyre within the safe size tolerance. Plus sizing is, in effect, a way of changing the wheel and the look without changing the rolling diameter.
The benefits
The appeal is twofold. A shorter, stiffer sidewall flexes less under cornering and braking, which sharpens steering response and gives a more planted feel, and a wider tyre can add grip. Alongside that, larger wheels filling the arches are the look many drivers are after. For someone who values handling and appearance, plus sizing delivers both.
The trade-offs
The same short sidewall that sharpens handling also has less rubber to absorb bumps. The ride becomes firmer, and the wheel is more exposed to pothole and kerb damage, since there is less tyre standing between the rim and the road, a real consideration on poorly surfaced roads. Larger wheels and tyres can also cost more and weigh more, and the extra weight at the wheel can blunt part of the handling gain.
As with any size change, the load and speed rating must remain adequate and the new package has to fit the car without fouling. Done within those limits, plus sizing is a sound way to change a car's wheels; pushed beyond them, it brings the same problems as any oversized fitment. Once the sizing is settled, the larger wheel-and-tyre package can be ordered from an online tyre shop such as Tyres.co.uk and fitted.
From the workshop: plus sizing is fine when the sums are done properly and the diameter is kept in check. Where we see regret is the very low profiles on big wheels meeting British potholes, because there is almost no sidewall left to take the hit, and a cracked alloy soon follows.
Sources and accuracy. The plus-sizing principle and the rough plus-two figures here reflect standard trade guidance at the time of writing. The right wheel and tyre combination for a specific car should be confirmed against its placard and with a fitter. If anything here looks wrong, get in touch and we will check it and put it right.
Common questions
What is plus sizing?+
Plus sizing fits a larger-diameter wheel with a lower-profile, often wider tyre, while keeping the overall diameter of the wheel and tyre roughly the same. Plus one means going up one inch in wheel size, plus two means going up two.
Why keep the overall diameter the same when plus sizing?+
So the speedometer, gearing and electronics stay accurate. Plus sizing trades sidewall height for wheel size: as the wheel gets larger, the tyre profile drops to compensate, leaving the total height almost unchanged and within the safe tolerance.
What are the downsides of plus sizing?+
A lower-profile tyre has less sidewall to absorb bumps, so the ride is firmer and the wheel is more exposed to pothole and kerb damage. Larger wheels and tyres can also cost more and add weight, which can blunt some of the handling gain.
Does plus sizing improve handling?+
It can. A shorter, stiffer sidewall flexes less, which sharpens steering response and cornering feel, and a wider tyre can add grip. The trade-off is comfort, so plus sizing suits drivers who value handling and appearance over a soft ride.