165/70R14 vs 175/65R14: Tyre Size Comparison, Diameter Difference & Speedometer Effect

Comparing 165/70R14 with 175/65R14 comes down to four numbers for each size: diameter, sidewall, circumference and revs per mile. 175/65R14 is the shorter tyre: its diameter is 583.1 mm against 586.6 mm, -3.5 mm (-0.6%) smaller. The width changes by +10 mm (165 mm to 175 mm) and the sidewall by -1.7 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.

Two things decide whether this swap makes sense: the diameter difference and the physical fit. On diameter, 175/65R14 is -0.6% smaller than 165/70R14, which is inside the plus-or-minus 3% guideline. On physical fit, the width change of +10 mm and the rim change from 14 to 14 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.

165/70R14 vs 175/65R14 side by side

Measurement 165/70R14 175/65R14 Difference
Overall diameter 586.6 mm (23.1 in) 583.1 mm (23.0 in) -3.5 mm (-0.6%)
Sidewall height 115.5 mm 113.8 mm -1.7 mm
Circumference 1842.9 mm 1831.9 mm -11.0 mm
Revolutions per mile 873.3 878.5 +5.2
Section width 165 mm 175 mm +10 mm
Rim diameter 14 in 14 in +0 in

Diameter difference between 165/70R14 and 175/65R14: -3.5 mm (-0.6%)

A -0.6% 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 -11.0 mm per revolution, and the revs per mile change by +5.2, 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: 165/70R14 to 175/65R14 and back

Going from 165/70R14 to 175/65R14, the diameter grows by -0.6%, so the true speed is the indicated speed multiplied by 0.994. At 30 mph on the dial the car is really doing 29.8 mph; at 50 mph indicated it is 49.7 mph; at 70 mph indicated it is 69.6 mph. The speedometer therefore reads high 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 175/65R14 back to 165/70R14, the error reverses exactly: the ratio becomes 1.006, so 70 mph indicated is really 70.4 mph.

Indicated speed Actual speed fitting 175/65R14 (from 165/70R14) Actual speed fitting 165/70R14 (from 175/65R14)
30 mph 29.8 mph 30.2 mph
50 mph 49.7 mph 50.3 mph
70 mph 69.6 mph 70.4 mph

Sidewall height and ride comfort: 165/70R14 vs 175/65R14

On this page, 165/70r14 vs 175/65r14 is the case in point: Sidewall height moves by -1.7 mm between these two sizes (115.5 mm to 113.8 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 65%.

Width, grip and fuel use: 165/70R14 vs 175/65R14

The width gap is 10 mm (165 mm against 175 mm). Going wider usually buys dry grip and a more planted feel, and it costs a little in rolling resistance and road noise. Remember that width also decides whether the tyre fits the rim: a 175 mm tyre needs a rim width within the range its maker approves, and a rim that suited 165/70R14 may not suit 175/65R14. That is a separate check from the diameter comparison, and it belongs on the list before anything is fitted.

Revolutions per mile and gearing: 165/70R14 vs 175/65R14

Think of the gearing change as the diameter change in disguise. The revs-per-mile gap is +5.2, which is 0.6% 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 0.6% and no more. Small percentages mean small effects, which is another reason the plus-or-minus 3% guideline is a useful yardstick.

Will 175/65R14 clear after 165/70R14? What to check before fitting

Whether 175/65R14 physically fits is a question for your car, not for this table. The numbers say it is shorter by 3.5 mm and 10 mm wider, 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 175 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: 165/70R14 or 175/65R14

Taking 165/70r14 vs 175/65r14 as the case in point: Choose on the basis of what matters to you, not on the headline alone. If ride comfort matters most, the sidewall change of -1.7 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 -0.6% 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 165/70R14 vs 175/65R14 comparisons and tools

Frequently asked questions

What is the diameter difference between 165/70R14 and 175/65R14?

175/65R14 is -3.5 mm (-0.6%) smaller in diameter than 165/70R14: 583.1 mm against 586.6 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 175/65R14 instead of 165/70R14?

Taking 165/70r14 vs 175/65r14 as the case in point: The error follows the diameter ratio, -0.6%. At an indicated 30 mph the true speed would be 29.8 mph, at 50 mph indicated it would be 49.7 mph, and at 70 mph indicated it would be 69.6 mph. The full table in both directions is in the speedometer section above.

Is 175/65R14 wider than 165/70R14, and does that matter?

Yes — 175/65R14 is 175 mm wide against 165 mm for 165/70R14, 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 175/65R14 fit my car if 165/70R14 fits?

Not necessarily. 175/65R14 is shorter by 3.5 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, 165/70R14 or 175/65R14?

Neither is better in general — it depends on what you want. 175/65R14 has a -1.7 mm sidewall difference, a +10 mm width difference and a -0.6% 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.