155/70R13 vs 165/65R13: Tire Size Comparison, Diameter Difference & Speedometer Effect

Comparing 155/70R13 with 165/65R13 comes down to four numbers for each size: diameter, sidewall, circumference and revs per mile. 165/65R13 is the shorter tire: its diameter is 544.7 mm against 547.2 mm, -2.5 mm (-0.5%) smaller. The width changes by +10 mm (155 mm to 165 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.

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 -0.5% 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.

155/70R13 vs 165/65R13 side by side

Measurement 155/70R13 165/65R13 Difference
Overall diameter 547.2 mm (21.5 in) 544.7 mm (21.4 in) -2.5 mm (-0.5%)
Sidewall height 108.5 mm 107.2 mm -1.3 mm
Circumference 1719.1 mm 1711.2 mm -7.9 mm
Revolutions per mile 936.2 940.5 +4.3
Section width 155 mm 165 mm +10 mm
Rim diameter 13 in 13 in +0 in

Diameter difference between 155/70R13 and 165/65R13: -2.5 mm (-0.5%)

A -0.5% 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 -7.9 mm per revolution, and the revs per mile change by +4.3, 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: 155/70R13 to 165/65R13 and back

Going from 155/70R13 to 165/65R13, the diameter grows by -0.5%, so the true speed is the indicated speed multiplied by 0.995. At 30 mph on the dial the car is really doing 29.9 mph; at 50 mph indicated it is 49.8 mph; at 70 mph indicated it is 69.7 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 165/65R13 back to 155/70R13, the error reverses exactly: the ratio becomes 1.005, so 70 mph indicated is really 70.3 mph.

Indicated speed Actual speed fitting 165/65R13 (from 155/70R13) Actual speed fitting 155/70R13 (from 165/65R13)
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: 155/70R13 vs 165/65R13

The sidewall is where the ride difference lives. 155/70R13 has 108.5 mm of sidewall and 165/65R13 has 107.2 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: 70% for 155/70R13 against 65% for 165/65R13. 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: 155/70R13 vs 165/65R13

For 155/70r13 vs 165/65r13 tire size comparison, the point is this: 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: 155/70R13 vs 165/65R13

On this page, 155/70r13 vs 165/65r13 tire size comparison is the case in point: Think of the gearing change as the diameter change in disguise. The revs-per-mile gap is +4.3, which is 0.5% 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 0.5% and no more. Small percentages mean small effects, which is another reason the plus-or-minus 3% guideline is a useful yardstick.

Will 165/65R13 clear after 155/70R13? What to check before fitting

Whether 165/65R13 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: 155/70R13 or 165/65R13

Choose on the basis of what matters to you, not on the headline alone. If ride comfort matters most, the sidewall change of -1.3 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 -0.5% 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 tire that rubs is not a viable option at any percentage.

Related 155/70R13 vs 165/65R13 comparisons and tools

Frequently asked questions

What is the diameter difference between 155/70R13 and 165/65R13?

165/65R13 is -2.5 mm (-0.5%) smaller in diameter than 155/70R13: 544.7 mm against 547.2 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 165/65R13 instead of 155/70R13?

The error follows the diameter ratio, -0.5%. 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 155/70r13 vs 165/65r13 tire size comparison.

Is 165/65R13 wider than 155/70R13, and does that matter?

Yes — 165/65R13 is 165 mm wide against 155 mm for 155/70R13, 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 165/65R13 fit my car if 155/70R13 fits?

Not necessarily. 165/65R13 is shorter by 2.5 mm and 10 mm wider, and it needs a 13-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, 155/70R13 or 165/65R13?

Neither is better in general — it depends on what you want. 165/65R13 has a -1.3 mm sidewall difference, a +10 mm width difference and a -0.5% 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.