145/80R13 vs 155/70R14: Tyre Size Comparison, Diameter Difference & Speedometer Effect

145/80R13 and 155/70R14 look like near neighbours on paper, but the numbers tell a more precise story. 155/70R14 is the taller tyre: its diameter is 572.6 mm against 562.2 mm, +10.4 mm (+1.8%) larger. Width moves +10 mm, sidewall height moves -7.5 mm, and the circumference changes by +32.7 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.

For 145/80r13 vs 155/70r14 tyre size comparison, the point is this: 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 +1.8% 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.

145/80R13 vs 155/70R14 side by side

Measurement 145/80R13 155/70R14 Difference
Overall diameter 562.2 mm (22.1 in) 572.6 mm (22.5 in) +10.4 mm (+1.8%)
Sidewall height 116.0 mm 108.5 mm -7.5 mm
Circumference 1766.2 mm 1798.9 mm +32.7 mm
Revolutions per mile 911.2 894.6 -16.6
Section width 145 mm 155 mm +10 mm
Rim diameter 13 in 14 in +1 in

Diameter difference between 145/80R13 and 155/70R14: +10.4 mm (+1.8%)

A +1.8% 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 +32.7 mm per revolution, and the revs per mile change by -16.6, 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: 145/80R13 to 155/70R14 and back

The maths is a single ratio. 155/70R14 over 145/80R13 is 1.018, so every indicated speed after the swap is multiplied by that number to get the true speed: 30 becomes 30.6, 50 becomes 50.9 and 70 becomes 71.3 mph. In the reverse direction the ratio is 0.982, so 70 mph indicated is 68.7 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 155/70R14 (from 145/80R13) Actual speed fitting 145/80R13 (from 155/70R14)
30 mph 30.6 mph 29.5 mph
50 mph 50.9 mph 49.1 mph
70 mph 71.3 mph 68.7 mph

Sidewall height and ride comfort: 145/80R13 vs 155/70R14

The sidewall is where the ride difference lives. 145/80R13 has 116.0 mm of sidewall and 155/70R14 has 108.5 mm, a change of -7.5 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: 80% for 145/80R13 against 70% for 155/70R14. 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: 145/80R13 vs 155/70R14

On width, the two sizes are 10 mm apart. The wider tyre (155/70R14) 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: 145/80R13 vs 155/70R14

The revs-per-mile figures (911.2 for 145/80R13, 894.6 for 155/70R14) describe the gearing effect. 155/70R14 turns -16.6 fewer times per mile, so at any given road speed the engine turns slightly slower with 155/70R14 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 1.8% either way, so the effect on everyday driving is subtle rather than transformative.

Will 155/70R14 clear after 145/80R13? What to check before fitting

Do not skip the physical check. The diameter difference is +1.8% and the width difference is +10 mm, and both of those affect whether 155/70R14 fits where 145/80R13 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 155 mm tyre.

Which size suits which priority: 145/80R13 or 155/70R14

Weigh the four effects separately. Sidewall (-7.5 mm) for comfort. Width (+10 mm) for grip and rolling resistance. Diameter (+1.8%) 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 145/80R13 vs 155/70R14 comparisons and tools

Frequently asked questions

What is the diameter difference between 145/80R13 and 155/70R14?

155/70R14 is +10.4 mm (+1.8%) larger in diameter than 145/80R13: 572.6 mm against 562.2 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 155/70R14 instead of 145/80R13?

The error follows the diameter ratio, +1.8%. At an indicated 30 mph the true speed would be 30.6 mph, at 50 mph indicated it would be 50.9 mph, and at 70 mph indicated it would be 71.3 mph. The full table in both directions is in the speedometer section above.

Is 155/70R14 wider than 145/80R13, and does that matter?

Yes — 155/70R14 is 155 mm wide against 145 mm for 145/80R13, 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 155/70R14 fit my car if 145/80R13 fits?

Not necessarily. 155/70R14 is taller by 10.4 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, 145/80R13 or 155/70R14?

Neither is better in general — it depends on what you want. 155/70R14 has a -7.5 mm sidewall difference, a +10 mm width difference and a +1.8% 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.