175/70R14 vs 185/60R15: Tyre Size Comparison, Diameter Difference & Speedometer Effect

If you are choosing between 175/70R14 and 185/60R15, the first question is how far apart they really are. 185/60R15 is the taller tyre: its diameter is 603.0 mm against 600.6 mm, +2.4 mm (+0.4%) larger. The sidewall goes from 122.5 mm to 111.0 mm (-11.5 mm), the circumference from 1886.8 mm to 1894.4 mm, and the revs per mile from 852.9 to 849.5. 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.

The short version: a +0.4% diameter difference is inside the commonly used plus-or-minus 3% guideline, which is the usual yardstick for keeping speedometer error small. But diameter is only the first check. The two sizes also differ in width by 10 mm and in rim size (14 inches against 15 inches), so a swap means different wheels as well unless the rims already match. Read the whole comparison before deciding — the clearance and load-index sections matter as much as the headline percentage.

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.

175/70R14 vs 185/60R15 side by side

Measurement 175/70R14 185/60R15 Difference
Overall diameter 600.6 mm (23.6 in) 603.0 mm (23.7 in) +2.4 mm (+0.4%)
Sidewall height 122.5 mm 111.0 mm -11.5 mm
Circumference 1886.8 mm 1894.4 mm +7.6 mm
Revolutions per mile 852.9 849.5 -3.4
Section width 175 mm 185 mm +10 mm
Rim diameter 14 in 15 in +1 in

Diameter difference between 175/70R14 and 185/60R15: +2.4 mm (+0.4%)

Put the percentage in context. The plus-or-minus 3% guideline exists because small diameter changes produce small speedometer errors, and this change is +0.4%, which is inside that band. In revs per mile the shift is -3.4 (852.9 to 849.5), and in circumference it is +7.6 mm per turn. Those are not abstract figures: every mile you drive, the car covers +7.6 mm more or less per wheel revolution than the instruments expect, and the gap accumulates exactly like interest.

Speedometer error: 175/70R14 to 185/60R15 and back

Here is what the speedometer does in practice. Fit 185/60R15 where 175/70R14 was, and the dial understates or overstates speed by 0.4%: indicated 30 mph is really 30.1 mph, indicated 50 mph is really 50.2 mph, and indicated 70 mph is really 70.3 mph. Swap back from 185/60R15 to 175/70R14 and the error flips sign — 70 mph indicated becomes 69.7 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 185/60R15 (from 175/70R14) Actual speed fitting 175/70R14 (from 185/60R15)
30 mph 30.1 mph 29.9 mph
50 mph 50.2 mph 49.8 mph
70 mph 70.3 mph 69.7 mph

Sidewall height and ride comfort: 175/70R14 vs 185/60R15

Sidewall height moves by -11.5 mm between these two sizes (122.5 mm to 111.0 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 70% to 60%.

Width, grip and fuel use: 175/70R14 vs 185/60R15

On width, the two sizes are 10 mm apart. The wider tyre (185/60R15) offers more rubber on the road, which tends to mean more grip in the dry and slightly more resistance to roll. 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: 175/70R14 vs 185/60R15

Think of the gearing change as the diameter change in disguise. The revs-per-mile gap is -3.4, which is 0.4% 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 0.4% and no more. Small percentages mean small effects, which is another reason the plus-or-minus 3% guideline is a useful yardstick.

Will 185/60R15 clear after 175/70R14? What to check before fitting

Do not skip the physical check. The diameter difference is +0.4% and the width difference is +10 mm, and both of those affect whether 185/60R15 fits where 175/70R14 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: 175/70R14 or 185/60R15

For 175/70r14 vs 185/60r15, the point is this: Weigh the four effects separately. Sidewall (-11.5 mm) for comfort. Width (+10 mm) for grip and rolling resistance. Diameter (+0.4%) 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 175/70R14 vs 185/60R15 comparisons and tools

Frequently asked questions

What is the diameter difference between 175/70R14 and 185/60R15?

185/60R15 is +2.4 mm (+0.4%) larger in diameter than 175/70R14: 603.0 mm against 600.6 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 185/60R15 instead of 175/70R14?

On this page, 175/70r14 vs 185/60r15 is the case in point: The error follows the diameter ratio, +0.4%. At an indicated 30 mph the true speed would be 30.1 mph, at 50 mph indicated it would be 50.2 mph, and at 70 mph indicated it would be 70.3 mph. The full table in both directions is in the speedometer section above.

Is 185/60R15 wider than 175/70R14, and does that matter?

Yes — 185/60R15 is 185 mm wide against 175 mm for 175/70R14, a difference of +10 mm. A wider tyre generally gives more dry grip and can increase rolling resistance and road noise slightly. Width also affects clearance, so check the arches and suspension at full lock.

Will 185/60R15 fit my car if 175/70R14 fits?

Not necessarily. 185/60R15 is taller by 2.4 mm and 10 mm wider, and it needs a 15-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, 175/70R14 or 185/60R15?

Neither is better in general — it depends on what you want. 185/60R15 has a -11.5 mm sidewall difference, a +10 mm width difference and a +0.4% 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.