Going from 16" wheels to 18"? Enter your stock tire size and instantly see the closest equivalent sizes for every wheel diameter — plus exactly how far off your speedometer will read with each one.
Your stock tire size Free
Stock size: 225/60R16 — the numbers on your sidewall, e.g. 225 / 60 R 16
Stock tire specs
Already have a size in mind?
Skip the suggestions below and compare your stock size directly against any specific size you're considering — useful if a tire shop quoted you something not shown in the common-sizes list.
Note: this checks the math for any size, even ones tire makers don't actually produce. The suggestions below only show sizes commonly stocked by major retailers.
Equivalent sizes by wheel diameter
Only shows sizes actually stocked by major tire retailers — not every size that's mathematically close. Tap any size for the speedometer error table and a visual comparison. Rule of thumb: stay within ±3% of stock diameter (within ±1% is ideal).
< 1% — ideal1–2% — fine2–3% — edge of safe
Even within the sizes above, exact stock and pricing vary a lot by brand and by season — a size that's cheap and in stock at one retailer might be back-ordered at another. It pays to check two or three sellers before buying.
Comparison
StockNew size
Speedometer reads
Actual speed
Ready to buy? Availability and price for the same exact size can swing by $30–80 a tire between sellers. Compare a couple options before you check out.
225 is the tread width in millimeters. 60 is the aspect ratio — the sidewall height as a percentage of the width (here, 60% of 225mm = 135mm tall). R16 means it fits a 16-inch wheel. Overall diameter = wheel + two sidewalls.
Why does tire size affect my speedometer?
Your speedometer counts wheel rotations and assumes the stock tire circumference. A larger tire covers more ground per rotation, so your speedometer reads lower than your true speed. A smaller tire does the opposite. Even 2–3% matters: at a true 70 mph that's about 2 mph of error — enough to earn a ticket or fail a state inspection in some places.
What is "plus sizing"?
Going up one inch in wheel diameter while keeping the overall tire diameter nearly the same. The pattern: +1 inch of wheel ≈ +10mm width and −5 to −10 aspect ratio. Example: 225/60R16 → 225/55R17 → 245/45R18 → 245/40R19. Bigger wheel, shorter sidewall, same rollout.
Will a wider tire fit my car?
This calculator matches diameters, but width clearance depends on your specific wheel offset, suspension, and fender room. As a rule, +10 to +20mm over stock is usually fine; beyond that, check a fitment forum for your exact model or measure clearance at full steering lock.
Why don't I see every mathematically close size?
Tire makers don't produce every possible width/aspect-ratio combination — only specific sizes get manufactured and stocked at scale. This tool matches your stock diameter against sizes that are actually common in retailer catalogs, so what you see here is realistically shoppable. Even so, exact in-stock availability and pricing shift often, so it's worth checking a couple of sellers before you commit to a size.
How to use this calculator
The size code on your sidewall contains all three numbers the tool needs, and reading it correctly is the whole task.
Find your current size on the sidewall or the placard on the driver's door jamb. A 205/55R16 reads as 205 millimeters of section width, a sidewall height that is 55% of that width, and a 16 inch wheel.
Enter those three numbers as your stock size. If the placard and the tires disagree, enter the stock size from the placard, because that is what the car was built around.
Pick the wheel diameter you are considering, or use the custom compare card to test one exact size.
Read the percentage difference, not just the diameter. The percent is what your speedometer and odometer care about.
Click a row to see the speedometer table, which shows true speed at each indicated speed.
A worked example: 205/55R16 to 215/45R17
Stock: sidewall is 205 × 0.55, or 112.75 millimeters. Overall diameter is the 16 inch rim in millimeters (406.4) plus two sidewalls (225.5), which is 631.9 millimeters, or 24.88 inches.
The plus-one size: 215 × 0.45 is 96.75 millimeters of sidewall. Diameter is 431.8 plus 193.5, or 625.3 millimeters, which is 24.62 inches. The new tire is 1.04% smaller than stock.
That one percent shows up on the dash. At an indicated 65 mph you are actually doing 64.3 mph, so the speedometer reads slightly high, which is the safe direction for a ticket and the wrong direction for your odometer, which adds a mile roughly every 96 you actually drive. The car also sits marginally lower and the ride is slightly firmer, because the sidewall is thinner even though the wheel is bigger.
For comparison, a 225/65R17 is 28.52 inches and a 235/55R18 is 28.18 inches, so that pairing is about 1.2% apart. Both examples sit inside the 3% band tire shops commonly treat as interchangeable, and neither is a guarantee that the tire clears your strut at full lock.
What your results mean
Diameter is the number the car's computers assume. The speedometer counts wheel rotations and multiplies by a circumference it was programmed with, so a tire that is 1% taller covers 1% more ground per turn, and the dash under-reports speed by 1%. The odometer drifts the same way, which matters at lease return and resale.
The percentage is the actionable number, and the size relative to stock is what you want to minimize. Under 1% is effectively invisible. Around 3% is where you are choosing a new set of compromises, and above that you are changing the gearing the car was designed around.
Diameter is not the only fitment question. Section width has to clear the strut, the spring, and the fender liner at full steering lock, and none of that appears in a diameter comparison. Offset and wheel width change where the tire actually sits.
Two numbers this tool does not compare are load index and speed rating. A tire with the right diameter and a lower load index is the wrong tire. Match the load index on the placard before you care about the percentage.
Frequently asked questions
What does the 205 in 205/55R16 mean?
Section width in millimeters, measured across the widest part of the inflated tire, not the tread. The 55 is the aspect ratio, meaning the sidewall is 55% as tall as the tire is wide, and the 16 is the wheel diameter in inches.
How much does tire size affect my speedometer?
By exactly the percentage change in diameter. A tire 1% taller makes the speedometer read 1% low, so an indicated 65 mph is about 65.7 mph true. Two or three percent is enough to matter on a highway.
Do I need a recalibration after changing size?
If you stay within a fraction of a percent, no. Beyond that, some vehicles can have the tire size reprogrammed through the dealer or a capable scan tool, and vehicles that derive speed from wheel sensors may need it.
Does a bigger wheel hurt fuel economy?
A taller, heavier wheel and tire package takes more energy to accelerate and changes the effective gearing. The effect is usually small compared with driving style, but a much heavier combination is measurable.
How old is too old for a tire?
Tires carry a DOT date code of four digits, week and year, so 3224 means the 32nd week of 2024. Rubber ages regardless of tread depth, and many manufacturers suggest inspecting closely around six years and replacing by ten, which is worth checking before buying used.
Can I change only two tires?
Ideally all four, especially on an all-wheel-drive vehicle, where a significant diameter difference between axles strains the drivetrain. If you are replacing a pair, keep them on the same axle and match the size.
Sources & references
The diameter math is just the size code printed on the sidewall. The safety instruction is NHTSA's.
NHTSA, tires. How to read a passenger tire size, and why the door-jamb placard is the authority rather than a fitment chart.
Last updated: November 2, 2026. Reviewed by David Liu. The 3% band is a trade rule of thumb, not a regulation. The placard is the regulation.