175/65R13 vs 185/55R14: Tyre Size Comparison, Diameter Difference & Speedometer Effect

Comparing 175/65R13 with 185/55R14 comes down to four numbers for each size: diameter, sidewall, circumference and revs per mile. 185/55R14 is the taller tyre: its diameter is 559.1 mm against 557.7 mm, +1.4 mm (+0.3%) larger. The width changes by +10 mm (175 mm to 185 mm) and the sidewall by -12.0 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.

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 +0.3% 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.

175/65R13 vs 185/55R14 side by side

Measurement 175/65R13 185/55R14 Difference
Overall diameter 557.7 mm (22.0 in) 559.1 mm (22.0 in) +1.4 mm (+0.3%)
Sidewall height 113.8 mm 101.8 mm -12.0 mm
Circumference 1752.1 mm 1756.5 mm +4.4 mm
Revolutions per mile 918.5 916.2 -2.3
Section width 175 mm 185 mm +10 mm
Rim diameter 13 in 14 in +1 in

Diameter difference between 175/65R13 and 185/55R14: +1.4 mm (+0.3%)

Put the percentage in context. The plus-or-minus 3% guideline exists because small diameter changes produce small speedometer errors, and this change is +0.3%, which is inside that band. In revs per mile the shift is -2.3 (918.5 to 916.2), and in circumference it is +4.4 mm per turn. Those are not abstract figures: every mile you drive, the car covers +4.4 mm more or less per wheel revolution than the instruments expect, and the gap accumulates exactly like interest.

Speedometer error: 175/65R13 to 185/55R14 and back

Going from 175/65R13 to 185/55R14, the diameter grows by +0.3%, so the true speed is the indicated speed multiplied by 1.003. At 30 mph on the dial the car is really doing 30.1 mph; at 50 mph indicated it is 50.1 mph; at 70 mph indicated it is 70.2 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 185/55R14 back to 175/65R13, the error reverses exactly: the ratio becomes 0.997, so 70 mph indicated is really 69.8 mph.

Indicated speed Actual speed fitting 185/55R14 (from 175/65R13) Actual speed fitting 175/65R13 (from 185/55R14)
30 mph 30.1 mph 29.9 mph
50 mph 50.1 mph 49.9 mph
70 mph 70.2 mph 69.8 mph

Sidewall height and ride comfort: 175/65R13 vs 185/55R14

Look at the sidewalls next. 113.8 mm on 175/65R13, 101.8 mm on 185/55R14: a difference of -12.0 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 (65% vs 55%) is simply the sidewall expressed as a share of the width.

Width, grip and fuel use: 175/65R13 vs 185/55R14

On width, the two sizes are 10 mm apart. The wider tyre (185/55R14) 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. That is the point this page works through for 175/65r13 vs 185/55r14 tyre size comparison.

Revolutions per mile and gearing: 175/65R13 vs 185/55R14

The revs-per-mile figures (918.5 for 175/65R13, 916.2 for 185/55R14) describe the gearing effect. 185/55R14 turns -2.3 fewer times per mile, so at any given road speed the engine turns slightly slower with 185/55R14 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 0.3% either way, so the effect on everyday driving is subtle rather than transformative.

Will 185/55R14 clear after 175/65R13? What to check before fitting

Do not skip the physical check. The diameter difference is +0.3% and the width difference is +10 mm, and both of those affect whether 185/55R14 fits where 175/65R13 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: 175/65R13 or 185/55R14

Choose on the basis of what matters to you, not on the headline alone. If ride comfort matters most, the sidewall change of -12.0 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 +0.3% 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 175/65R13 vs 185/55R14 comparisons and tools

Frequently asked questions

What is the diameter difference between 175/65R13 and 185/55R14?

185/55R14 is +1.4 mm (+0.3%) larger in diameter than 175/65R13: 559.1 mm against 557.7 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 185/55R14 instead of 175/65R13?

The error follows the diameter ratio, +0.3%. At an indicated 30 mph the true speed would be 30.1 mph, at 50 mph indicated it would be 50.1 mph, and at 70 mph indicated it would be 70.2 mph. The full table in both directions is in the speedometer section above.

Is 185/55R14 wider than 175/65R13, and does that matter?

Yes — 185/55R14 is 185 mm wide against 175 mm for 175/65R13, 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 185/55R14 fit my car if 175/65R13 fits?

Not necessarily. 185/55R14 is taller by 1.4 mm and 10 mm wider, and it needs a 14-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, 175/65R13 or 185/55R14?

Neither is better in general — it depends on what you want. 185/55R14 has a -12.0 mm sidewall difference, a +10 mm width difference and a +0.3% 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.