145/80R13 vs 165/70R13: Tyre Size Comparison, Diameter Difference & Speedometer Effect

Comparing 145/80R13 with 165/70R13 comes down to four numbers for each size: diameter, sidewall, circumference and revs per mile. 165/70R13 is the shorter tyre: its diameter is 561.2 mm against 562.2 mm, -1.0 mm (-0.2%) smaller. The width changes by +20 mm (145 mm to 165 mm) and the sidewall by -0.5 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.

On this page, 145/80r13 vs 165/70r13 is the case in point: 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 -0.2% 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 165/70R13 side by side

Measurement 145/80R13 165/70R13 Difference
Overall diameter 562.2 mm (22.1 in) 561.2 mm (22.1 in) -1.0 mm (-0.2%)
Sidewall height 116.0 mm 115.5 mm -0.5 mm
Circumference 1766.2 mm 1763.1 mm -3.1 mm
Revolutions per mile 911.2 912.8 +1.6
Section width 145 mm 165 mm +20 mm
Rim diameter 13 in 13 in +0 in

Diameter difference between 145/80R13 and 165/70R13: -1.0 mm (-0.2%)

The diameter gap of -1.0 mm (-0.2%) 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 -3.1 mm and the revs-per-mile difference of +1.6 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: 145/80R13 to 165/70R13 and back

Here is what the speedometer does in practice. Fit 165/70R13 where 145/80R13 was, and the dial understates or overstates speed by 0.2%: indicated 30 mph is really 29.9 mph, indicated 50 mph is really 49.9 mph, and indicated 70 mph is really 69.9 mph. Swap back from 165/70R13 to 145/80R13 and the error flips sign — 70 mph indicated becomes 70.1 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 165/70R13 (from 145/80R13) Actual speed fitting 145/80R13 (from 165/70R13)
30 mph 29.9 mph 30.1 mph
50 mph 49.9 mph 50.1 mph
70 mph 69.9 mph 70.1 mph

Sidewall height and ride comfort: 145/80R13 vs 165/70R13

Look at the sidewalls next. 116.0 mm on 145/80R13, 115.5 mm on 165/70R13: a difference of -0.5 mm. That is the flexible part of the tyre, and it is the first thing that absorbs a bump. A shorter sidewall transmits more of the road to the driver, which feels more direct but less forgiving on rough surfaces. Aspect ratio (80% vs 70%) is simply the sidewall expressed as a share of the width.

Width, grip and fuel use: 145/80R13 vs 165/70R13

On width, the two sizes are 20 mm apart. The wider tyre (165/70R13) 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 165/70R13

Gearing follows the circumference. 165/70R13 covers 1763.1 mm per revolution against 1766.2 mm for 145/80R13, so it needs +1.6 fewer revolutions per mile. At a fixed road speed the engine speed drops or rises by the same 0.2% 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 165/70R13 clear after 145/80R13? What to check before fitting

Do not skip the physical check. The diameter difference is -0.2% and the width difference is +20 mm, and both of those affect whether 165/70R13 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 165 mm tyre.

Which size suits which priority: 145/80R13 or 165/70R13

Weigh the four effects separately. Sidewall (-0.5 mm) for comfort. Width (+20 mm) for grip and rolling resistance. Diameter (-0.2%) 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 165/70R13 comparisons and tools

Frequently asked questions

What is the diameter difference between 145/80R13 and 165/70R13?

165/70R13 is -1.0 mm (-0.2%) smaller in diameter than 145/80R13: 561.2 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 165/70R13 instead of 145/80R13?

The error follows the diameter ratio, -0.2%. At an indicated 30 mph the true speed would be 29.9 mph, at 50 mph indicated it would be 49.9 mph, and at 70 mph indicated it would be 69.9 mph. The full table in both directions is in the speedometer section above.

Is 165/70R13 wider than 145/80R13, and does that matter?

Yes — 165/70R13 is 165 mm wide against 145 mm for 145/80R13, a difference of +20 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 165/70R13 fit my car if 145/80R13 fits?

Not necessarily. 165/70R13 is shorter by 1.0 mm and 20 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 tyre professional can confirm fitment on your vehicle.

Which size is better, 145/80R13 or 165/70R13?

Neither is better in general — it depends on what you want. 165/70R13 has a -0.5 mm sidewall difference, a +20 mm width difference and a -0.2% 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.