155/70R14 vs 165/65R14: Tire Size Comparison, Diameter Difference & Speedometer Effect

155/70R14 and 165/65R14 look like near neighbours on paper, but the numbers tell a more precise story. 165/65R14 is the shorter tire: its diameter is 570.1 mm against 572.6 mm, -2.5 mm (-0.4%) smaller. Width moves +10 mm, sidewall height moves -1.3 mm, and the circumference changes by -7.9 mm, which is what the speedometer feels. This comparison works through the side-by-side measurements, the speedometer error at 30, 50 and 70 mph in both directions, and the practical effects on ride comfort, grip and wheel-arch clearance.

Before the tables, keep the context straight. These are nominal new-tire dimensions, computed from the size codes: real tyres vary slightly by brand, model, wear and inflation pressure. A -0.4% 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.

155/70R14 vs 165/65R14 side by side

Measurement 155/70R14 165/65R14 Difference
Overall diameter 572.6 mm (22.5 in) 570.1 mm (22.4 in) -2.5 mm (-0.4%)
Sidewall height 108.5 mm 107.2 mm -1.3 mm
Circumference 1798.9 mm 1791.0 mm -7.9 mm
Revolutions per mile 894.6 898.6 +4.0
Section width 155 mm 165 mm +10 mm
Rim diameter 14 in 14 in +0 in

Diameter difference between 155/70R14 and 165/65R14: -2.5 mm (-0.4%)

The diameter gap of -2.5 mm (-0.4%) 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 -7.9 mm and the revs-per-mile difference of +4.0 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: 155/70R14 to 165/65R14 and back

Here is what the speedometer does in practice. Fit 165/65R14 where 155/70R14 was, and the dial understates or overstates speed by 0.4%: indicated 30 mph is really 29.9 mph, indicated 50 mph is really 49.8 mph, and indicated 70 mph is really 69.7 mph. Swap back from 165/65R14 to 155/70R14 and the error flips sign — 70 mph indicated becomes 70.3 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 165/65R14 (from 155/70R14) Actual speed fitting 155/70R14 (from 165/65R14)
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: 155/70R14 vs 165/65R14

Sidewall height moves by -1.3 mm between these two sizes (108.5 mm to 107.2 mm), and that is enough to feel. A taller sidewall flexes more, which softens sharp impacts and gives the tire 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: 155/70R14 vs 165/65R14

Taking 155/70r14 vs 165/65r14 tire size comparison as the case in point: Width changes by +10 mm, from 155 mm to 165 mm. A wider tire puts a broader contact patch on the road, which generally helps dry grip and braking, but it can also increase road noise and rolling resistance, and it needs more clearance around the suspension and arches. Fuel use moves with rolling resistance, so a wider tire can cost a small amount of fuel over time — the effect is real but modest for a change of this size, and it is not something this page can put a precise number on without knowing the exact tire models involved.

Revolutions per mile and gearing: 155/70R14 vs 165/65R14

Think of the gearing change as the diameter change in disguise. The revs-per-mile gap is +4.0, 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 165/65R14 clear after 155/70R14? What to check before fitting

Whether 165/65R14 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 165 mm tire. A tire 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: 155/70R14 or 165/65R14

Weigh the four effects separately. Sidewall (-1.3 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 155/70R14 vs 165/65R14 comparisons and tools

Frequently asked questions

What is the diameter difference between 155/70R14 and 165/65R14?

165/65R14 is -2.5 mm (-0.4%) smaller in diameter than 155/70R14: 570.1 mm against 572.6 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 165/65R14 instead of 155/70R14?

Taking 155/70r14 vs 165/65r14 tire size comparison as the case in point: 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.

Is 165/65R14 wider than 155/70R14, and does that matter?

Yes — 165/65R14 is 165 mm wide against 155 mm for 155/70R14, a difference of +10 mm. A wider tire 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 165/65R14 fit my car if 155/70R14 fits?

Not necessarily. 165/65R14 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 tire professional can confirm fitment on your vehicle.

Which size is better, 155/70R14 or 165/65R14?

Neither is better in general — it depends on what you want. 165/65R14 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.