Plus sizing tires

Plus sizing means fitting a bigger wheel with a lower-profile tire so the overall diameter stays about the same. Each inch of wheel is "plus one".^{[1 · Oct 29, 2026]}

A young man and his grandfather crouch beside a red hatchback on a coastal pull-off, comparing a loose wheel and tire with the one on the car (AI-generated image)

The rule of thumb

For each inch you add to the wheel, Tire Rack's rule of thumb is to add about 10 mm of tire width and drop the aspect ratio by 5 to 10 points.^{[1 · Oct 29, 2026]} Here is their example, with our diameter math:

Step	Size	Overall diameter	vs original	Sidewall
Original	205/55R16	24.88 in	+0.0%	4.44 in
Plus 1	215/45R17	24.62 in	-1.0%	3.81 in
Plus 2	225/40R18	25.09 in	+0.8%	3.54 in
Plus 3	235/35R19	25.48 in	+2.4%	3.24 in

Tire Rack pairs these with 16x7, 17x7, 18x8 and 19x9 wheels.^{[1 · Oct 29, 2026]} All three stay inside the 3% guideline from BFGoodrich and Continental.^{[2 · Oct 29, 2026]}^{[3 · Oct 29, 2026]} The decoder suggests calculated plus-one and plus-two sizes for any size you type.

The math (our own arithmetic): sidewall height = width × aspect ratio ÷ 100; overall diameter = rim × 25.4 + 2 × sidewall (mm), ÷ 25.4 for inches; revs per mile = 63,360 ÷ (π × diameter in inches); true speed = indicated speed × new diameter ÷ original diameter. These are nominal figures from the size code. Tire Rack notes that real tires differ from the formula, so use the tire maker's published spec when clearance is tight.^{[4 · Oct 29, 2026]}

Six checks before you upsize

Continental's plus-sizing bulletin lists six things to match or confirm:^{[3 · Oct 29, 2026]}

Load capacity equal to or greater than the original tire.
Inflation pressure never below the vehicle maker's figure, keeping the same front-to-rear difference.
Speed rating equal to or greater than the original.
Rolling circumference as close to the original as possible.
Rim width approved for the tire size by the industry standards.
Body and chassis clearance in every condition.

On all-wheel and four-wheel drive vehicles, Continental says to replace all four tires together.^{[3 · Oct 29, 2026]}

The trade-offs

Shorter sidewalls leave less cushion against potholes and curbs, so wheels and tires can be damaged more easily.^{[1 · Oct 29, 2026]}
Wider tires can be worse in snow and more prone to hydroplaning in heavy rain.^{[1 · Oct 29, 2026]}
Bigger, heavier wheel and tire combinations on trucks can lengthen stopping distances and add wear.^{[1 · Oct 29, 2026]}
If you keep the diameter close, Tire Rack says speedometer change is negligible, around ±0.4 mph.^{[1 · Oct 29, 2026]}

Going taller instead, for lift kits or off-road looks? See tire size comparison and tire size by vehicle type.

Sources: 1. Tire Rack, What are plus size wheels and tires?. 2. BFGoodrich, Changing tire size. 3. Continental Tire, PSIB 06-03: Tire plus-sizing for passenger and light truck vehicles (PDF, 2006). 4. Tire Rack, How do I calculate tire dimensions?. Checked Oct 29, 2026. Size dimensions, revolutions per mile and speedometer figures are our own arithmetic from the size code. Trademarks belong to their owners; figures are restated in our own words and tables, not reproduced.