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Selected questions, calculated from the same nominal geometry.

24 comparisons

215/55R17225/45R18

668.3 → 659.7 mm

-8.6 mm · -1.29%

This is TireSpan’s reference example. Increasing the rim from 17 to 18 inches contributes 25.4 mm, but the sidewall pair loses 34 mm. The result is an 8.6 mm smaller nominal outside diameter, despite the larger rim and wider marking.

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205/55R16225/45R17

631.9 → 634.3 mm

+2.4 mm · +0.38%

The 17-inch rim adds 25.4 mm to the diameter calculation, but each sidewall loses 11.5 mm. The net outside-diameter increase is only 2.4 mm. The tires still require different nominal rim diameters, so the close outside diameter is not interchangeability on one wheel.

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225/45R17225/40R18

634.3 → 637.2 mm

+2.9 mm · +0.46%

The width stays at 225 mm while the rim grows by 25.4 mm and the two sidewalls together shrink by 22.5 mm. Those opposing changes leave only a 2.9 mm increase in nominal diameter. The close outside diameters do not mean the tires mount on the same rim.

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265/70R17285/70R17

802.8 → 830.8 mm

+28 mm · +3.49%

At a fixed 70-percent aspect ratio, 20 mm more nominal width adds 14 mm to each sidewall. The diameter therefore grows by 28 mm even though both markings use a 17-inch rim. A 14 mm radius change is geometric; it is not a measured lift or a clearance guarantee.

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245/40R18245/45R18

653.2 → 677.7 mm

+24.5 mm · +3.75%

Holding the 245 mm width and 18-inch rim constant makes the five-point aspect-ratio change easy to isolate. Each sidewall grows by 12.25 mm, so nominal outside diameter increases by 24.5 mm. The full-diameter percentage is calculated from 653.2 mm, rather than from the aspect-ratio number.

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225/55R18235/55R18

704.7 → 715.7 mm

+11 mm · +1.56%

The common 55-percent ratio means the wider marking also has a taller sidewall. An extra 10 mm of nominal width adds 5.5 mm per sidewall, giving 11 mm more outside diameter. The nominal radius change is 5.5 mm; it is not an inch of lift or a prediction of loaded ground clearance.

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185/65R15195/65R15

621.5 → 634.5 mm

+13 mm · +2.09%

The 65-percent sidewall ratio turns 10 mm more nominal width into 13 mm more full diameter. The absolute increase matches a 195-to-205 width step at the same ratio and rim, but its percentage is larger here because the original diameter is smaller.

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195/65R15205/65R15

634.5 → 647.5 mm

+13 mm · +2.05%

A 10 mm width step at 65 percent changes sidewall height by 6.5 mm. Doubling that gives 13 mm of diameter change. The fixed 15-inch rim contributes the same 381 mm to both entries, so no part of the difference comes from rim diameter.

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195/65R15205/55R16

634.5 → 631.9 mm

-2.6 mm · -0.41%

A larger rim does not necessarily produce a larger outside diameter. The rim grows by 25.4 mm, while the two nominal sidewalls together shrink by 28 mm. Those changes nearly cancel, leaving 205/55R16 2.6 mm smaller overall.

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205/55R16205/60R16

631.9 → 652.4 mm

+20.5 mm · +3.24%

Keeping width and rim diameter fixed isolates the aspect ratio. The five-point change produces 10.25 mm more nominal sidewall per side and 20.5 mm more diameter. It does not alter the nominal 205 mm width.

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215/60R16215/65R16

664.4 → 685.9 mm

+21.5 mm · +3.24%

Both entries use a 215 mm width and 16-inch rim. Raising the aspect ratio from 60 to 65 adds 10.75 mm per sidewall. The resulting 21.5 mm diameter change is slightly larger than the same five-point step at a 205 mm width.

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265/70R16265/75R16

777.4 → 803.9 mm

+26.5 mm · +3.41%

The same 265 mm width and 16-inch rim isolate the change from 70 to 75 percent. The 26.5 mm diameter increase is numerically the same as the 65-to-70 step on a 17-inch rim, but its percentage is different because the starting diameter differs.

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215/50R17225/50R17

646.8 → 656.8 mm

+10 mm · +1.55%

At a 50-percent aspect ratio, each sidewall is half the nominal width. A 10 mm width increase therefore makes each sidewall 5 mm taller and the full diameter exactly 10 mm larger. The equality between the width and diameter changes is specific to this fixed-rim, 50-percent case.

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215/55R17225/50R17

668.3 → 656.8 mm

-11.5 mm · -1.72%

The wider marking has a lower aspect ratio, and its sidewall is actually 5.75 mm shorter. Since the rim stays at 17 inches, the whole 11.5 mm diameter reduction comes from those two sidewalls. Width alone would predict the wrong direction.

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215/55R17225/55R17

668.3 → 679.3 mm

+11 mm · +1.65%

The aspect ratio and rim diameter stay fixed. The extra 10 mm of nominal width produces 5.5 mm more sidewall height on each side, so overall diameter increases by 11 mm. The resulting radius change is a geometric value, not a prediction of suspension or body clearance.

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225/45R17225/50R17

634.3 → 656.8 mm

+22.5 mm · +3.55%

Only the aspect-ratio input changes. Five percentage points of a 225 mm width add 11.25 mm to each sidewall and 22.5 mm to the full diameter. “Five points” means a change from 45 to 50, not a five-percent increase in overall tire diameter.

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225/60R17225/65R17

701.8 → 724.3 mm

+22.5 mm · +3.21%

The rim and width remain unchanged, so the entire 22.5 mm diameter increase comes from 11.25 mm of added sidewall on each side. The larger diameter also reduces revolutions per unit distance in the circular model.

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255/70R17265/70R17

788.8 → 802.8 mm

+14 mm · +1.77%

A 10 mm width increase at a 70-percent aspect ratio adds 7 mm to each sidewall. The outside diameter grows by 14 mm with the rim held at 17 inches. Nominal section width grows by 10 mm; the page cannot infer the installed outer edge from that alone.

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265/65R17265/70R17

776.3 → 802.8 mm

+26.5 mm · +3.41%

A five-point aspect-ratio step at 265 mm width adds 13.25 mm per sidewall. That is a 26.5 mm increase in full diameter on an unchanged 17-inch rim. The calculation is independent of the specific brands in the discussion.

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265/70R17265/60R18

802.8 → 775.2 mm

-27.6 mm · -3.44%

This pair has the same nominal width but different rims and aspect ratios. The 18-inch rim adds 25.4 mm while its two sidewalls lose 53 mm, so 265/60R18 is 27.6 mm smaller overall. Rim diameter and outside diameter move in opposite directions.

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225/45R18235/45R18

659.7 → 668.7 mm

+9 mm · +1.36%

Both aspect ratios read 45, but their sidewalls are not the same height. A 10 mm wider marking adds 4.5 mm to each sidewall because 45 is a percentage of width. The resulting diameter increase is 9 mm.

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225/45R18245/40R18

659.7 → 653.2 mm

-6.5 mm · -0.99%

The second marking is 20 mm wider, yet its nominal sidewall is 3.25 mm shorter. The smaller 40-percent ratio outweighs the extra width in the height calculation, giving a 6.5 mm reduction in outside diameter on the same 18-inch rim.

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235/55R18235/60R18

715.7 → 739.2 mm

+23.5 mm · +3.28%

At a width of 235 mm, five aspect-ratio points equal 11.75 mm of sidewall. Doubling that gives a 23.5 mm outside-diameter increase. A taller calculated sidewall alone does not quantify ride comfort or impact behavior.

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245/45R19255/40R19

703.1 → 686.6 mm

-16.5 mm · -2.35%

Increasing width by 10 mm does not compensate for reducing the aspect ratio from 45 to 40. Each nominal sidewall becomes 8.25 mm shorter. With the same 19-inch rim, that produces a 16.5 mm smaller diameter.

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Why these pairs are here

The collection follows specific public questions and documented comparison discussions. A source shows that the pair was raised in a public question or comparison discussion; it is not a recommendation, a compatibility verdict or a measure of search volume.

One page for each pair

Each pair has one stable page. Use Swap in the tool to change which size is the original reference. This avoids duplicate pages while keeping both percentage calculations available.

Start with a figure, then ask the right question

Read the width, sidewall, rim and total-diameter changes separately. A pair can have similar total diameters while its rim diameter or sidewall height differs substantially. Use the editable tool for a size that is not in this collection.

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