195/70R15 vs 185/70R16: Tyre Size Comparison, Diameter Difference & Speedometer Effect

If you are choosing between 195/70R15 and 185/70R16, the first question is how far apart they really are. 185/70R16 is the taller tyre: its diameter is 665.4 mm against 654.0 mm, +11.4 mm (+1.7%) larger. The sidewall goes from 136.5 mm to 129.5 mm (-7.0 mm), the circumference from 2054.6 mm to 2090.4 mm, and the revs per mile from 783.3 to 769.9. The tables below lay all of that out, then work through the speedometer effect in each direction and the clearance checks that matter before either size goes on the car.

Two things decide whether this swap makes sense: the diameter difference and the physical fit. On diameter, 185/70R16 is +1.7% larger than 195/70R15, 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.

195/70R15 vs 185/70R16 side by side

Measurement 195/70R15 185/70R16 Difference
Overall diameter 654.0 mm (25.7 in) 665.4 mm (26.2 in) +11.4 mm (+1.7%)
Sidewall height 136.5 mm 129.5 mm -7.0 mm
Circumference 2054.6 mm 2090.4 mm +35.8 mm
Revolutions per mile 783.3 769.9 -13.4
Section width 195 mm 185 mm -10 mm
Rim diameter 15 in 16 in +1 in

Diameter difference between 195/70R15 and 185/70R16: +11.4 mm (+1.7%)

The diameter gap of +11.4 mm (+1.7%) 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 +35.8 mm and the revs-per-mile difference of -13.4 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: 195/70R15 to 185/70R16 and back

Here is what the speedometer does in practice. Fit 185/70R16 where 195/70R15 was, and the dial understates or overstates speed by 1.7%: indicated 30 mph is really 30.5 mph, indicated 50 mph is really 50.9 mph, and indicated 70 mph is really 71.2 mph. Swap back from 185/70R16 to 195/70R15 and the error flips sign — 70 mph indicated becomes 68.8 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 185/70R16 (from 195/70R15) Actual speed fitting 195/70R15 (from 185/70R16)
30 mph 30.5 mph 29.5 mph
50 mph 50.9 mph 49.1 mph
70 mph 71.2 mph 68.8 mph

Sidewall height and ride comfort: 195/70R15 vs 185/70R16

For 195/70r15 vs 185/70r16, the point is this: Sidewall height moves by -7.0 mm between these two sizes (136.5 mm to 129.5 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 70% to 70%.

Width, grip and fuel use: 195/70R15 vs 185/70R16

The width gap is 10 mm (195 mm against 185 mm). Going narrower usually trims rolling resistance and can improve behaviour in standing water, and it costs a little in dry grip. 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 195/70R15 may not suit 185/70R16. That is a separate check from the diameter comparison, and it belongs on the list before anything is fitted.

Revolutions per mile and gearing: 195/70R15 vs 185/70R16

Think of the gearing change as the diameter change in disguise. The revs-per-mile gap is -13.4, which is 1.7% 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 1.7% and no more. Small percentages mean small effects, which is another reason the plus-or-minus 3% guideline is a useful yardstick.

Will 185/70R16 clear after 195/70R15? What to check before fitting

Whether 185/70R16 physically fits is a question for your car, not for this table. The numbers say it is taller by 11.4 mm and 10 mm narrower, 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: 195/70R15 or 185/70R16

Weigh the four effects separately. Sidewall (-7.0 mm) for comfort. Width (-10 mm) for grip and rolling resistance. Diameter (+1.7%) for the speedometer, odometer and gearing. And clearance for whether the swap is physically possible at all. If the diameter is inside the plus-or-minus 3% guideline and the clearance check passes, the remaining differences are small enough to be a matter of taste; if either of those fails, the comparison is academic until it is resolved.

Related 195/70R15 vs 185/70R16 comparisons and tools

Frequently asked questions

What is the diameter difference between 195/70R15 and 185/70R16?

185/70R16 is +11.4 mm (+1.7%) larger in diameter than 195/70R15: 665.4 mm against 654.0 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 185/70R16 instead of 195/70R15?

Taking 195/70r15 vs 185/70r16 as the case in point: The error follows the diameter ratio, +1.7%. At an indicated 30 mph the true speed would be 30.5 mph, at 50 mph indicated it would be 50.9 mph, and at 70 mph indicated it would be 71.2 mph. The full table in both directions is in the speedometer section above.

Is 185/70R16 wider than 195/70R15, and does that matter?

No — 185/70R16 is 185 mm wide against 195 mm for 195/70R15, 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 185/70R16 fit my car if 195/70R15 fits?

Not necessarily. 185/70R16 is taller by 11.4 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, 195/70R15 or 185/70R16?

Neither is better in general — it depends on what you want. 185/70R16 has a -7.0 mm sidewall difference, a -10 mm width difference and a +1.7% 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.