165/75R14 vs 175/70R14: Tyre Size Comparison, Diameter Difference & Speedometer Effect

Comparing 165/75R14 with 175/70R14 comes down to four numbers for each size: diameter, sidewall, circumference and revs per mile. 175/70R14 is the shorter tyre: its diameter is 600.6 mm against 603.1 mm, -2.5 mm (-0.4%) smaller. The width changes by +10 mm (165 mm to 175 mm) and the sidewall by -1.3 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.

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 14 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.

165/75R14 vs 175/70R14 side by side

Measurement 165/75R14 175/70R14 Difference
Overall diameter 603.1 mm (23.7 in) 600.6 mm (23.6 in) -2.5 mm (-0.4%)
Sidewall height 123.8 mm 122.5 mm -1.3 mm
Circumference 1894.7 mm 1886.8 mm -7.9 mm
Revolutions per mile 849.4 852.9 +3.5
Section width 165 mm 175 mm +10 mm
Rim diameter 14 in 14 in +0 in

Diameter difference between 165/75R14 and 175/70R14: -2.5 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 +3.5 (849.4 to 852.9), and in circumference it is -7.9 mm per turn. Those are not abstract figures: every mile you drive, the car covers -7.9 mm more or less per wheel revolution than the instruments expect, and the gap accumulates exactly like interest.

Speedometer error: 165/75R14 to 175/70R14 and back

The maths is a single ratio. 175/70R14 over 165/75R14 is 0.996, so every indicated speed after the swap is multiplied by that number to get the true speed: 30 becomes 29.9, 50 becomes 49.8 and 70 becomes 69.7 mph. In the reverse direction the ratio is 1.004, so 70 mph indicated is 70.3 mph in reality. The table below shows both directions at all three speeds, so you can check whichever direction applies to your car without doing the arithmetic yourself.

Indicated speed Actual speed fitting 175/70R14 (from 165/75R14) Actual speed fitting 165/75R14 (from 175/70R14)
30 mph 29.9 mph 30.1 mph
50 mph 49.8 mph 50.2 mph
70 mph 69.7 mph 70.3 mph

Sidewall height and ride comfort: 165/75R14 vs 175/70R14

The sidewall is where the ride difference lives. 165/75R14 has 123.8 mm of sidewall and 175/70R14 has 122.5 mm, a change of -1.3 mm. Less sidewall generally means sharper steering response and less cushioning, so more of the road surface reaches the cabin. The aspect ratios tell the same story in percentage terms: 75% for 165/75R14 against 70% for 175/70R14. Sidewall height also affects vulnerability to kerb damage — a shorter sidewall leaves less rubber between the rim and the road.

Width, grip and fuel use: 165/75R14 vs 175/70R14

On width, the two sizes are 10 mm apart. The wider tyre (175/70R14) 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: 165/75R14 vs 175/70R14

Gearing follows the circumference. 175/70R14 covers 1886.8 mm per revolution against 1894.7 mm for 165/75R14, so it needs +3.5 fewer revolutions per mile. At a fixed road speed the engine speed drops or rises by the same 0.4% as the diameter change. With the shorter size the engine sits slightly higher in the rev range at cruising speed, which sharpens response a little at the cost of a small amount of fuel. Either way the effect is proportional to the diameter difference, not larger than it.

Will 175/70R14 clear after 165/75R14? What to check before fitting

Whether 175/70R14 physically fits is a question for your car, not for this table. The numbers say it is shorter by 2.5 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: 165/75R14 or 175/70R14

The decision comes down to priorities. Comfort follows the sidewall (-1.3 mm here). Grip follows the width (+10 mm here). Instrument accuracy follows the diameter (-0.4% here). Gearing and cruising engine speed follow the revs-per-mile change (+3.5). None of those is large in this comparison, which is why the practical checks — clearance, load index, speed rating, rim width — deserve as much attention as the numbers. Get those right and the size choice becomes a matter of preference rather than a risk.

Related 165/75R14 vs 175/70R14 comparisons and tools

Frequently asked questions

What is the diameter difference between 165/75R14 and 175/70R14?

175/70R14 is -2.5 mm (-0.4%) smaller in diameter than 165/75R14: 600.6 mm against 603.1 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 175/70R14 instead of 165/75R14?

The error follows the diameter ratio, -0.4%. At an indicated 30 mph the true speed would be 29.9 mph, at 50 mph indicated it would be 49.8 mph, and at 70 mph indicated it would be 69.7 mph. The full table in both directions is in the speedometer section above. That is the point this page works through for 165/75r14 vs 175/70r14 tyre size comparison.

Is 175/70R14 wider than 165/75R14, and does that matter?

Yes — 175/70R14 is 175 mm wide against 165 mm for 165/75R14, 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 175/70R14 fit my car if 165/75R14 fits?

Not necessarily. 175/70R14 is shorter by 2.5 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, 165/75R14 or 175/70R14?

Neither is better in general — it depends on what you want. 175/70R14 has a -1.3 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.