What does a tire size comparison show?

The overall diameter difference (in inches, mm and percent), the section width and sidewall height difference, circumference, revolutions per mile and the speedometer error. The Visual tab draws both tires to scale so you can see how much taller or wider the new size is.

How do I read a tire size like 225/65R17?

Michelin and Bridgestone explain it: 225 is the section width in millimetres, 65 is the aspect ratio (the sidewall height as a percentage of the width), R is radial construction and 17 is the rim diameter in inches. The overall diameter is the rim plus two sidewalls.

How much does the diameter change if I change the aspect ratio but keep the same width?

Each 5 points of aspect ratio on a 225 mm tire changes each sidewall by 0.44 in, so the overall diameter changes by 0.89 in. On a 17 inch rim a 225/45 is 24.97 in tall, a 225/40 is 24.09 in and a 225/50 is 25.86 in. The table on this page lists the full ladder.

What does the to-scale diagram show?

The diameter view draws both tires as circles on the same ground line, scaled to overall diameter. The width view draws each tire at its section width, so the difference in width is visible next to the difference in height.

Can I compare a metric size with an inch size?

Yes. Each panel has its own format, so you can compare 265/70R17 with 33x12.50R17. Both are converted to inches and mm and compared on equal terms. For a flotation size, the first number is read as the nominal overall diameter in inches, the second as the section width in inches.

Does a bigger tire change my speedometer?

Yes. A taller tire travels farther per revolution, so the wheels turn fewer times per mile and the speedometer reads lower than your true speed. The Speedometer tab shows the true speed at common readings, and the speedometer error calculator gives the percentage on its own.

How much change in tire size is acceptable?

Continental says to match the original equipment rolling circumference as closely as possible, and that a deviation greater than 3 percent can affect speedometer accuracy, ABS, stability control and other safety systems. Your vehicle manufacturer's recommended sizes come first.

Does wheel offset change the tire comparison?

No. Offset changes where the wheel and tire sit in relation to the hub, not the tire's diameter or section width. Use the wheel offset calculator for that, and check clearance at all four wheel positions through full suspension travel and steering lock, as the US Tire Manufacturers Association advises.

Is a taller or lower profile tire better?

We have no manufacturer source ranking them. The US Tire Manufacturers Association says lower aspect ratio tires typically aid performance and handling but may give a less comfortable ride, may wear more quickly and be noisier, and are more susceptible to damage from pothole or curb impact. Use the sizes your vehicle manufacturer specifies.

Tire Size Comparison: Side-by-Side Visual Chart in Inches and mm

Quick Answer

A tire size comparison puts two sizes side by side: overall diameter, section width, sidewall height, circumference and revolutions per mile, plus the speedometer error.
Changing the aspect ratio at the same width and rim changes the diameter: on a 225 mm tire and 17 inch rim, 40 series is 24.1 in and 50 series 25.9 in.
Continental says matching the original rolling circumference closely matters: a deviation above 3% can affect speedometer accuracy, ABS and stability control.

Prefer numbers to a drawing? The tire size comparison calculator and the tire size difference tool show the same figures.

Enter Tire Specifications

① Original Tire

Width (mm)

Aspect Ratio (%)

Rim (in)

→ 265/70R17

② Compare Tire

Width (mm)

Aspect Ratio (%)

Rim (in)

→ 285/70R17

🔄

Enter tire specs above and click Calculate to compare

Supports P-metric (225/65R17) and Imperial/flotation (31x10.5R15) formats

Tire Size Comparison Chart: Dimensions in Inches and mm

Overall diameter, width, sidewall and circumference for common sizes, calculated from the size code. Read two rows side by side, or use the tool above for a drawing.

Tire size	Diameter (in)	Diameter (mm)	Width (in)	Sidewall (in)	Circumference (in)	Revs per mile
195/65R15	24.98"	635	7.68"	4.99"	78.5"	807
205/55R16	24.88"	632	8.07"	4.44"	78.2"	811
205/65R16	26.49"	673	8.07"	5.25"	83.2"	761
215/60R16	26.16"	664	8.46"	5.08"	82.2"	771
225/65R17	28.52"	724	8.86"	5.76"	89.6"	707
225/45R17	24.97"	634	8.86"	3.99"	78.5"	808
235/45R18	26.33"	669	9.25"	4.16"	82.7"	766
225/40R18	25.09"	637	8.86"	3.54"	78.8"	804
235/60R18	29.10"	739	9.25"	5.55"	91.4"	693
245/40R18	25.72"	653	9.65"	3.86"	80.8"	784
255/35R19	26.03"	661	10.04"	3.51"	81.8"	775
265/70R17	31.61"	803	10.43"	7.30"	99.3"	638
275/65R18	32.07"	815	10.83"	7.04"	100.8"	629
285/70R17	32.71"	831	11.22"	7.85"	102.8"	617
285/75R17	33.83"	859	11.22"	8.42"	106.3"	596
295/65R18	33.10"	841	11.61"	7.55"	104.0"	609
33x12.50R15	33.00"	838	see size	n/a	103.7"	611
33x12.50R17	33.00"	838	see size	n/a	103.7"	611
35x12.50R17	35.00"	889	see size	n/a	110.0"	576
35x12.50R20	35.00"	889	see size	n/a	110.0"	576

For inch sizes the diameter is the nominal first number, and the metric equivalents are on the metric tire calculator.

Common Tire Size Comparisons at a Glance

What +10 or +20 mm of width, or +5 points of aspect ratio, does to the overall diameter.

Original	Compare	Diameter change	Change %
205/65R16	215/65R16	+0.51"	+1.9%
225/65R17	235/65R17	+0.51"	+1.8%
225/45R18	235/45R18	+0.35"	+1.4%
265/70R17	285/70R17	+1.10"	+3.5%
265/70R17	285/75R17	+2.22"	+7.0%
275/65R18	295/65R18	+1.02"	+3.2%
31x10.50R15	33x12.50R15	+2.00"	+6.5%
245/75R16	265/75R16	+1.18"	+3.9%

Same width and rim, different aspect ratio

225 mm wide tires on a 17 inch rim.

Tire size	Sidewall (in)	Diameter (in)	Change vs 225/45R17
225/30R17	2.66"	22.31"	-2.66" (-10.6%)
225/35R17	3.10"	23.20"	-1.77" (-7.1%)
225/40R17	3.54"	24.09"	-0.89" (-3.5%)
225/45R17	3.99"	24.97"	Base
225/50R17	4.43"	25.86"	+0.89" (+3.5%)
225/55R17	4.87"	26.74"	+1.77" (+7.1%)
225/60R17	5.31"	27.63"	+2.66" (+10.6%)
225/65R17	5.76"	28.52"	+3.54" (+14.2%)

To keep the diameter when you change wheel size, see the plus sizing options calculator, and for sidewall detail the sidewall height calculator.

How to Use the Tire Size Comparison Tool

1Choose a size format for each tire: metric such as 225/65R17 or inch such as 33x12.50R15.
2Enter your current tire in the Original panel and the size you are considering in the Compare panel.
3Click Calculate and Compare, then use the Visual tab to see both tires drawn to scale on the same ground line, in diameter and width views.
4Read the Stats tab for the exact numbers, the Speedometer tab for the error at common speeds and the Graphs tab for bar, radar and speed curve views.

The speedometer effect of one swap is on the speedometer error calculator and the wheel turns behind it on the revolutions per mile calculator.

Frequently Asked Questions

Dimensions are calculated from the nominal size code. Sources: Continental plus-sizing guidance, US Tire Manufacturers Association tire care manual, Michelin and Bridgestone size guides. Check clearance and your manufacturer's recommended sizes before changing tire size.

Tire Size Comparison