Key takeaways
- Plus sizing fits a bigger wheel while keeping overall tire diameter near stock.
- As rim diameter goes up 1″, aspect ratio drops ~10 and width rises ~10 mm.
- Keep the diameter change within ±3% for an accurate speedo and safe clearance.
- Round the target aspect ratio to the nearest 5 to land on a real, buyable size.
What plus sizing actually does
Plus sizing means moving to a larger-diameter wheel while choosing a tire with a shorter sidewall so the overall diameter stays close to your factory size. You get the look and steering response of a bigger wheel and a shorter, wider sidewall — without throwing off your speedometer, odometer, or fender clearance. The trick is solving for the aspect ratio that cancels out the extra rim inches.
The aspect ratio is the lever: a bigger rim eats into the sidewall budget, so the aspect ratio has to fall to hold diameter.
Worked example: 205/55R16 → 17″ wheel
Stock diameter = 16 + 2 × 205 × (55 ÷ 100) ÷ 25.4 = 24.88 in. For a 17″ rim with 215 mm width, target sidewall = (24.88 − 17) ÷ 2 = 3.94 in, so target aspect = 3.94 × 25.4 ÷ 215 × 100 = 46.5, rounded to 45. The recommended 215/45R17 comes out to 24.62 in — a change of just −1.0%, comfortably inside ±3%.
The plus-sizing concept (target ≈ 24.9″ diameter)
| Step | Size | Diameter |
|---|---|---|
| Plus 0 | 215/50R16 | 24.46 in |
| Plus 1 | 215/45R17 | 24.62 in |
| Plus 2 | 225/40R18 | 25.09 in |
Choosing the right step
Each plus step trades sidewall for wheel: up one rim inch, drop the aspect about 10, add roughly 10 mm of width to hold diameter. Always confirm the new section width fits your rim-width range and clears the suspension. To sanity-check the exact dimensions of any size, use the tire size calculator; to line a candidate up against your current tire, use the tire size comparison tool.
Frequently asked questions
What is plus sizing?
Fitting a larger-diameter wheel with a lower-aspect tire so overall diameter stays near stock — bigger wheel, shorter sidewall, same rolling diameter.
Why keep the diameter within 3%?
It keeps the speedometer, odometer, ABS, and traction control accurate and ensures the tire still clears the fender and suspension.
Will a wider tire fit my wheel?
A wider tire usually needs a wider wheel and must clear the suspension and fender. Check the tire's approved rim-width range and your clearance first.
Does plus sizing hurt ride or economy?
A shorter sidewall rides firmer and steers sharper; wider, heavier tires can slightly raise rolling resistance. Holding diameter near stock keeps it minor.
What is "plus zero"?
Same rim diameter, but a wider tire with a lower aspect ratio to hold diameter. Plus one and plus two step the rim up one or two inches.
Do I need to recalibrate the speedo?
If you stay within ~3% of stock diameter, the error is small and recalibration is usually unnecessary. Larger changes should be recalibrated.
Plus-sizing keeps overall diameter constant while stepping up wheel diameter — see Tire Rack's plus-sizing guide. The 25.4 mm-per-inch conversion is exact.
Last reviewed June 2026