185/80R15 vs 185/75R16: Tyre Size Comparison, Diameter Difference & Speedometer Effect

185/80R15 and 185/75R16 look like near neighbours on paper, but the numbers tell a more precise story. 185/75R16 is the taller tyre: its diameter is 683.9 mm against 677.0 mm, +6.9 mm (+1.0%) larger. Width moves +0 mm, sidewall height moves -9.2 mm, and the circumference changes by +21.6 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.

For 185/80r15 vs 185/75r16 tyre size comparison, the point is this: Before the tables, keep the context straight. These are nominal new-tyre dimensions, computed from the size codes: real tyres vary slightly by brand, model, wear and inflation pressure. A +1.0% difference is within the plus-or-minus 3% guideline that is commonly used for speedometer accuracy, and the speedometer tables below show exactly what that percentage means at real road speeds. The rest of the page covers sidewall, grip, gearing and the clearance checks that decide whether the larger size can physically fit.

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.

185/80R15 vs 185/75R16 side by side

Measurement 185/80R15 185/75R16 Difference
Overall diameter 677.0 mm (26.7 in) 683.9 mm (26.9 in) +6.9 mm (+1.0%)
Sidewall height 148.0 mm 138.8 mm -9.2 mm
Circumference 2126.9 mm 2148.5 mm +21.6 mm
Revolutions per mile 756.7 749.0 -7.7
Section width 185 mm 185 mm +0 mm
Rim diameter 15 in 16 in +1 in

Diameter difference between 185/80R15 and 185/75R16: +6.9 mm (+1.0%)

A +1.0% 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 +21.6 mm per revolution, and the revs per mile change by -7.7, 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: 185/80R15 to 185/75R16 and back

Going from 185/80R15 to 185/75R16, the diameter grows by +1.0%, so the true speed is the indicated speed multiplied by 1.010. At 30 mph on the dial the car is really doing 30.3 mph; at 50 mph indicated it is 50.5 mph; at 70 mph indicated it is 70.7 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 185/75R16 back to 185/80R15, the error reverses exactly: the ratio becomes 0.990, so 70 mph indicated is really 69.3 mph.

Indicated speed Actual speed fitting 185/75R16 (from 185/80R15) Actual speed fitting 185/80R15 (from 185/75R16)
30 mph 30.3 mph 29.7 mph
50 mph 50.5 mph 49.5 mph
70 mph 70.7 mph 69.3 mph

Sidewall height and ride comfort: 185/80R15 vs 185/75R16

Look at the sidewalls next. 148.0 mm on 185/80R15, 138.8 mm on 185/75R16: a difference of -9.2 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 (80% vs 75%) is simply the sidewall expressed as a share of the width.

Width, grip and fuel use: 185/80R15 vs 185/75R16

On width, the two sizes are 0 mm apart. The width is the same, so neither size has a contact-patch advantage over the other. Both are 185 mm wide, so the difference here is the aspect ratio (80% vs 75%) and the rim (15 in vs 16 in). 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: 185/80R15 vs 185/75R16

The revs-per-mile figures (756.7 for 185/80R15, 749.0 for 185/75R16) describe the gearing effect. 185/75R16 turns -7.7 fewer times per mile, so at any given road speed the engine turns slightly slower with 185/75R16 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 1.0% either way, so the effect on everyday driving is subtle rather than transformative.

Will 185/75R16 clear after 185/80R15? What to check before fitting

Whether 185/75R16 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: 185/80R15 or 185/75R16

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 +1.0% 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 185/80R15 vs 185/75R16 comparisons and tools

Frequently asked questions

What is the diameter difference between 185/80R15 and 185/75R16?

185/75R16 is +6.9 mm (+1.0%) larger in diameter than 185/80R15: 683.9 mm against 677.0 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 185/75R16 instead of 185/80R15?

For 185/80r15 vs 185/75r16 tyre size comparison, the point is this: The error follows the diameter ratio, +1.0%. At an indicated 30 mph the true speed would be 30.3 mph, at 50 mph indicated it would be 50.5 mph, and at 70 mph indicated it would be 70.7 mph. The full table in both directions is in the speedometer section above.

Is 185/75R16 wider than 185/80R15, and does that matter?

Neither — 185/75R16 is 185 mm wide against 185 mm for 185/80R15, 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 185/75R16 fit my car if 185/80R15 fits?

Not necessarily. 185/75R16 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, 185/80R15 or 185/75R16?

Neither is better in general — it depends on what you want. 185/75R16 has a -9.2 mm sidewall difference, a +0 mm width difference and a +1.0% 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.