185/60R15 vs 175/60R16: Tyre Size Comparison, Diameter Difference & Speedometer Effect

Comparing 185/60R15 with 175/60R16 comes down to four numbers for each size: diameter, sidewall, circumference and revs per mile. 175/60R16 is the taller tyre: its diameter is 616.4 mm against 603.0 mm, +13.4 mm (+2.2%) larger. The width changes by -10 mm (185 mm to 175 mm) and the sidewall by -6.0 mm. This page puts both sizes side by side, works out the diameter difference in millimetres and percent, shows the speedometer error in both directions at 30, 50 and 70 mph, and explains what the change means for ride, grip and clearance — so you can judge the swap with the actual figures in front of you.

Two things decide whether this swap makes sense: the diameter difference and the physical fit. On diameter, 175/60R16 is +2.2% larger than 185/60R15, which is inside the plus-or-minus 3% guideline. On physical fit, the width change of -10 mm and the rim change from 15 to 16 inches both need checking against the arches, suspension and steering lock. The sections below take each of those in turn, with the numbers worked out rather than asserted.

This is a calculation, not a safety approval. Always check your vehicle's door-jamb placard, load index and speed rating, and confirm fitment with a tyre professional before fitting a different tyre size.

185/60R15 vs 175/60R16 side by side

Measurement 185/60R15 175/60R16 Difference
Overall diameter 603.0 mm (23.7 in) 616.4 mm (24.3 in) +13.4 mm (+2.2%)
Sidewall height 111.0 mm 105.0 mm -6.0 mm
Circumference 1894.4 mm 1936.5 mm +42.1 mm
Revolutions per mile 849.5 831.1 -18.4
Section width 185 mm 175 mm -10 mm
Rim diameter 15 in 16 in +1 in

Diameter difference between 185/60R15 and 175/60R16: +13.4 mm (+2.2%)

Put the percentage in context. The plus-or-minus 3% guideline exists because small diameter changes produce small speedometer errors, and this change is +2.2%, which is inside that band. In revs per mile the shift is -18.4 (849.5 to 831.1), and in circumference it is +42.1 mm per turn. Those are not abstract figures: every mile you drive, the car covers +42.1 mm more or less per wheel revolution than the instruments expect, and the gap accumulates exactly like interest.

Speedometer error: 185/60R15 to 175/60R16 and back

Going from 185/60R15 to 175/60R16, the diameter grows by +2.2%, so the true speed is the indicated speed multiplied by 1.022. At 30 mph on the dial the car is really doing 30.7 mph; at 50 mph indicated it is 51.1 mph; at 70 mph indicated it is 71.6 mph. The speedometer therefore reads low after the change, which matters most at motorway speed, where even a small percentage is a real difference in miles per hour. Going the other way, from 175/60R16 back to 185/60R15, the error reverses exactly: the ratio becomes 0.978, so 70 mph indicated is really 68.5 mph.

Indicated speed Actual speed fitting 175/60R16 (from 185/60R15) Actual speed fitting 185/60R15 (from 175/60R16)
30 mph 30.7 mph 29.3 mph
50 mph 51.1 mph 48.9 mph
70 mph 71.6 mph 68.5 mph

Sidewall height and ride comfort: 185/60R15 vs 175/60R16

Sidewall height moves by -6.0 mm between these two sizes (111.0 mm to 105.0 mm), and that is enough to feel. A taller sidewall flexes more, which softens sharp impacts and gives the tyre more give over potholes; a shorter sidewall flexes less, which sharpens the steering response and leaves the rim closer to the road surface on a hard hit. Which of those you get depends on the direction of the change — here the sidewall shrinks — and on the aspect ratio shift from 60% to 60%.

Width, grip and fuel use: 185/60R15 vs 175/60R16

On width, the two sizes are 10 mm apart. The narrower tyre (175/60R16) offers less rubber on the road, which tends to mean lower rolling resistance and a small fuel saving, traded against a little dry grip. Do not expect a dramatic change in fuel use from a width change of this size; the bigger influences on fuel use are the tyre compound, the pressure and the way the car is driven.

Revolutions per mile and gearing: 185/60R15 vs 175/60R16

Think of the gearing change as the diameter change in disguise. The revs-per-mile gap is -18.4, which is 2.2% of the original figure — the same percentage as the diameter gap. That is because revs per mile is just a mile divided by the circumference, and the circumference is pi times the diameter. So everything the gearing does — engine speed at a given road speed, acceleration in each gear, cruising refinement — shifts by 2.2% and no more. Small percentages mean small effects, which is another reason the plus-or-minus 3% guideline is a useful yardstick.

Will 175/60R16 clear after 185/60R15? What to check before fitting

Clearance is the check the numbers cannot do for you. 175/60R16 is taller and 10 mm narrower than 185/60R15, so check the wheel arches, the suspension components and the steering lock: turn the wheel fully in both directions and check for contact, and check again with the suspension compressed and the car loaded as it will actually be used. A size that clears when the car is stationary and unloaded can still rub over a bump or at full lock. This page does not claim that 175/60R16 clears your car, and no diameter table can — only a physical check on your vehicle can confirm it. Also confirm the load index and speed rating of 175/60R16 meet what your placard asks for, and that the 16-inch rim suits the car.

Which size suits which priority: 185/60R15 or 175/60R16

Choose on the basis of what matters to you, not on the headline alone. If ride comfort matters most, the sidewall change of -6.0 mm is the figure to weigh. If grip matters most, the width change of -10 mm is the one to weigh. If keeping the instruments accurate matters most, the diameter change of +2.2% is the one to weigh — and if it is outside the plus-or-minus 3% guideline, ask about recalibration. And if the answer to the clearance check is uncertain, that outranks all three: a tyre that rubs is not a viable option at any percentage. That is the point this page works through for 185/60r15 vs 175/60r16.

Related 185/60R15 vs 175/60R16 comparisons and tools

Frequently asked questions

What is the diameter difference between 185/60R15 and 175/60R16?

175/60R16 is +13.4 mm (+2.2%) larger in diameter than 185/60R15: 616.4 mm against 603.0 mm. That is inside the commonly used plus-or-minus 3% guideline for keeping speedometer error small.

How much will my speedometer be out if I fit 175/60R16 instead of 185/60R15?

Taking 185/60r15 vs 175/60r16 as the case in point: The error follows the diameter ratio, +2.2%. At an indicated 30 mph the true speed would be 30.7 mph, at 50 mph indicated it would be 51.1 mph, and at 70 mph indicated it would be 71.6 mph. The full table in both directions is in the speedometer section above.

Is 175/60R16 wider than 185/60R15, and does that matter?

No — 175/60R16 is 175 mm wide against 185 mm for 185/60R15, a difference of -10 mm. A narrower tyre generally gives less rolling resistance and can behave better in standing water, with slightly less dry grip. Width also affects clearance, so check the arches and suspension at full lock.

Will 175/60R16 fit my car if 185/60R15 fits?

Not necessarily. 175/60R16 is taller by 13.4 mm and 10 mm narrower, and it needs a 16-inch rim. Check the wheel arches, suspension and steering lock at full lock in both directions, with the car loaded, and confirm the load index and speed rating against your door-jamb placard. A tyre professional can confirm fitment on your vehicle.

Which size is better, 185/60R15 or 175/60R16?

Neither is better in general — it depends on what you want. 175/60R16 has a -6.0 mm sidewall difference, a -10 mm width difference and a +2.2% diameter difference, so the trade-offs are comfort, grip and instrument accuracy respectively. If the diameter is within the plus-or-minus 3% guideline and the clearance check passes, the choice is a matter of preference; if not, resolve those two points first.