185/60R15 vs 185/55R16: Tyre Size Comparison, Diameter Difference & Speedometer Effect

185/60R15 and 185/55R16 look like near neighbours on paper, but the numbers tell a more precise story. 185/55R16 is the taller tyre: its diameter is 609.9 mm against 603.0 mm, +6.9 mm (+1.1%) larger. Width moves +0 mm, sidewall height moves -9.2 mm, and the circumference changes by +21.7 mm, which is what the speedometer feels. This comparison works through the side-by-side measurements, the speedometer error at 30, 50 and 70 mph in both directions, and the practical effects on ride comfort, grip and wheel-arch clearance.

Two things decide whether this swap makes sense: the diameter difference and the physical fit. On diameter, 185/55R16 is +1.1% larger than 185/60R15, which is inside the plus-or-minus 3% guideline. On physical fit, the width change of +0 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 185/55R16 side by side

Measurement 185/60R15 185/55R16 Difference
Overall diameter 603.0 mm (23.7 in) 609.9 mm (24.0 in) +6.9 mm (+1.1%)
Sidewall height 111.0 mm 101.8 mm -9.2 mm
Circumference 1894.4 mm 1916.1 mm +21.7 mm
Revolutions per mile 849.5 839.9 -9.6
Section width 185 mm 185 mm +0 mm
Rim diameter 15 in 16 in +1 in

Diameter difference between 185/60R15 and 185/55R16: +6.9 mm (+1.1%)

The diameter gap of +6.9 mm (+1.1%) is the number to carry away from this section. It is inside the plus-or-minus 3% guideline, and it shows up directly in the speedometer tables below. The circumference difference of +21.7 mm and the revs-per-mile difference of -9.6 are the same change expressed differently — the first is what the road sees, the second is what the car's sensors count. Neither is a safety judgement on its own; both are inputs to the fitment checks further down the page.

Speedometer error: 185/60R15 to 185/55R16 and back

Here is what the speedometer does in practice. Fit 185/55R16 where 185/60R15 was, and the dial understates or overstates speed by 1.1%: indicated 30 mph is really 30.3 mph, indicated 50 mph is really 50.6 mph, and indicated 70 mph is really 70.8 mph. Swap back from 185/55R16 to 185/60R15 and the error flips sign — 70 mph indicated becomes 69.2 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 185/60R15) Actual speed fitting 185/60R15 (from 185/55R16)
30 mph 30.3 mph 29.7 mph
50 mph 50.6 mph 49.4 mph
70 mph 70.8 mph 69.2 mph

Sidewall height and ride comfort: 185/60R15 vs 185/55R16

The sidewall is where the ride difference lives. 185/60R15 has 111.0 mm of sidewall and 185/55R16 has 101.8 mm, a change of -9.2 mm. Less sidewall generally means sharper steering response and less cushioning, so more of the road surface reaches the cabin. The aspect ratios tell the same story in percentage terms: 60% for 185/60R15 against 55% for 185/55R16. Sidewall height also affects vulnerability to kerb damage — a shorter sidewall leaves less rubber between the rim and the road.

Width, grip and fuel use: 185/60R15 vs 185/55R16

The width gap is 0 mm (185 mm against 185 mm). Because the width is identical, grip differences here depend on the specific tyre rather than the size code. Remember that width also decides whether the tyre fits the rim: a 185 mm tyre needs a rim width within the range its maker approves, and a rim that suited 185/60R15 may not suit 185/55R16. That is a separate check from the diameter comparison, and it belongs on the list before anything is fitted.

Revolutions per mile and gearing: 185/60R15 vs 185/55R16

The revs-per-mile figures (849.5 for 185/60R15, 839.9 for 185/55R16) describe the gearing effect. 185/55R16 turns -9.6 fewer times per mile, so at any given road speed the engine turns slightly slower with 185/55R16 fitted — the gearing is effectively longer. That can make cruising a touch more relaxed and can trim fuel use slightly, but it also means slightly less acceleration from the same throttle opening, because each gear is effectively taller. The change is 1.1% either way, so the effect on everyday driving is subtle rather than transformative.

Will 185/55R16 clear after 185/60R15? What to check before fitting

Whether 185/55R16 physically fits is a question for your car, not for this table. The numbers say it is taller by 6.9 mm and 0 mm the same width, and those are the dimensions that decide clearance — but the actual gaps depend on your arches, suspension and steering geometry. Check at full lock both ways, check with the suspension compressed, and check with the car loaded. Check the placard for the load index and speed rating, and check the rim width for a 185 mm tyre. A tyre professional can confirm all of it in one visit, and that confirmation is the step that turns a comparison into a fitment.

Which size suits which priority: 185/60R15 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 -9.2 mm is the figure to weigh. If grip matters most, the width change of +0 mm is the one to weigh. If keeping the instruments accurate matters most, the diameter change of +1.1% 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 185/60R15 vs 185/55R16 comparisons and tools

Frequently asked questions

What is the diameter difference between 185/60R15 and 185/55R16?

185/55R16 is +6.9 mm (+1.1%) larger in diameter than 185/60R15: 609.9 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 185/55R16 instead of 185/60R15?

On this page, 185/60r15 vs 185/55r16 tyre size comparison is the case in point: The error follows the diameter ratio, +1.1%. At an indicated 30 mph the true speed would be 30.3 mph, at 50 mph indicated it would be 50.6 mph, and at 70 mph indicated it would be 70.8 mph. The full table in both directions is in the speedometer section above.

Is 185/55R16 wider than 185/60R15, and does that matter?

Neither — 185/55R16 is 185 mm wide against 185 mm for 185/60R15, a difference of +0 mm. With the same width, grip differences come from the specific tyre rather than the size. Width also affects clearance, so check the arches and suspension at full lock.

Will 185/55R16 fit my car if 185/60R15 fits?

Not necessarily. 185/55R16 is taller by 6.9 mm and 0 mm the same width, 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 185/55R16?

Neither is better in general — it depends on what you want. 185/55R16 has a -9.2 mm sidewall difference, a +0 mm width difference and a +1.1% 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.