195/55R15 vs 185/55R16: Tyre Size Comparison, Diameter Difference & Speedometer Effect

Comparing 195/55R15 with 185/55R16 comes down to four numbers for each size: diameter, sidewall, circumference and revs per mile. 185/55R16 is the taller tyre: its diameter is 609.9 mm against 595.5 mm, +14.4 mm (+2.4%) larger. The width changes by -10 mm (195 mm to 185 mm) and the sidewall by -5.4 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, 185/55R16 is +2.4% larger than 195/55R15, 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.

195/55R15 vs 185/55R16 side by side

Measurement 195/55R15 185/55R16 Difference
Overall diameter 595.5 mm (23.4 in) 609.9 mm (24.0 in) +14.4 mm (+2.4%)
Sidewall height 107.2 mm 101.8 mm -5.4 mm
Circumference 1870.8 mm 1916.1 mm +45.3 mm
Revolutions per mile 860.2 839.9 -20.3
Section width 195 mm 185 mm -10 mm
Rim diameter 15 in 16 in +1 in

Diameter difference between 195/55R15 and 185/55R16: +14.4 mm (+2.4%)

A +2.4% diameter change is small enough to sit inside the commonly used plus-or-minus 3% guideline, so the speedometer error it introduces stays modest. The circumference changes by +45.3 mm per revolution, and the revs per mile change by -20.3, which is the same story told from the car's point of view: the instruments count revolutions, so fewer revs per mile means the car travels further per revolution than the instruments assume. That drift also affects the odometer, so recorded mileage moves by the same percentage over time.

Speedometer error: 195/55R15 to 185/55R16 and back

Here is what the speedometer does in practice. Fit 185/55R16 where 195/55R15 was, and the dial understates or overstates speed by 2.4%: indicated 30 mph is really 30.7 mph, indicated 50 mph is really 51.2 mph, and indicated 70 mph is really 71.7 mph. Swap back from 185/55R16 to 195/55R15 and the error flips sign — 70 mph indicated becomes 68.3 mph. The odometer drifts by the same percentage in each direction, so recorded mileage and any service intervals based on it shift too.

Indicated speed Actual speed fitting 185/55R16 (from 195/55R15) Actual speed fitting 195/55R15 (from 185/55R16)
30 mph 30.7 mph 29.3 mph
50 mph 51.2 mph 48.8 mph
70 mph 71.7 mph 68.3 mph

Sidewall height and ride comfort: 195/55R15 vs 185/55R16

Look at the sidewalls next. 107.2 mm on 195/55R15, 101.8 mm on 185/55R16: a difference of -5.4 mm. That is the flexible part of the tyre, and it is the first thing that absorbs a bump. A shorter sidewall transmits more of the road to the driver, which feels more direct but less forgiving on rough surfaces. Aspect ratio (55% vs 55%) is simply the sidewall expressed as a share of the width.

Width, grip and fuel use: 195/55R15 vs 185/55R16

On width, the two sizes are 10 mm apart. The narrower tyre (185/55R16) 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: 195/55R15 vs 185/55R16

Think of the gearing change as the diameter change in disguise. The revs-per-mile gap is -20.3, which is 2.4% 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 2.4% and no more. Small percentages mean small effects, which is another reason the plus-or-minus 3% guideline is a useful yardstick.

Will 185/55R16 clear after 195/55R15? What to check before fitting

Do not skip the physical check. The diameter difference is +2.4% and the width difference is -10 mm, and both of those affect whether 185/55R16 fits where 195/55R15 did. Check the gap between the tyre and the arch, the gap to the suspension arms and struts, and the clearance at full steering lock in both directions. Repeat the check with weight in the car, because suspension travel changes the geometry. If the tyre touches anything at any point in that check, it does not fit, whatever the diameter percentage says. The load index and speed rating need confirming against the placard too, and the rim width must suit a 185 mm tyre.

Which size suits which priority: 195/55R15 or 185/55R16

Choose on the basis of what matters to you, not on the headline alone. If ride comfort matters most, the sidewall change of -5.4 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 +2.4% 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.

Related 195/55R15 vs 185/55R16 comparisons and tools

Frequently asked questions

What is the diameter difference between 195/55R15 and 185/55R16?

185/55R16 is +14.4 mm (+2.4%) larger in diameter than 195/55R15: 609.9 mm against 595.5 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 185/55R16 instead of 195/55R15?

For 195/55r15 vs 185/55r16, the point is this: The error follows the diameter ratio, +2.4%. At an indicated 30 mph the true speed would be 30.7 mph, at 50 mph indicated it would be 51.2 mph, and at 70 mph indicated it would be 71.7 mph. The full table in both directions is in the speedometer section above.

Is 185/55R16 wider than 195/55R15, and does that matter?

No — 185/55R16 is 185 mm wide against 195 mm for 195/55R15, 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 185/55R16 fit my car if 195/55R15 fits?

Not necessarily. 185/55R16 is taller by 14.4 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, 195/55R15 or 185/55R16?

Neither is better in general — it depends on what you want. 185/55R16 has a -5.4 mm sidewall difference, a -10 mm width difference and a +2.4% 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.