175/80R15 vs 195/70R15: Tyre Size Comparison, Diameter Difference & Speedometer Effect

If you are choosing between 175/80R15 and 195/70R15, the first question is how far apart they really are. 195/70R15 is the shorter tyre: its diameter is 654.0 mm against 661.0 mm, -7.0 mm (-1.1%) smaller. The sidewall goes from 140.0 mm to 136.5 mm (-3.5 mm), the circumference from 2076.6 mm to 2054.6 mm, and the revs per mile from 775.0 to 783.3. The tables below lay all of that out, then work through the speedometer effect in each direction and the clearance checks that matter before either size goes on the car.

The short version: a -1.1% 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 20 mm and in rim size (15 inches against 15 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.

175/80R15 vs 195/70R15 side by side

Measurement 175/80R15 195/70R15 Difference
Overall diameter 661.0 mm (26.0 in) 654.0 mm (25.7 in) -7.0 mm (-1.1%)
Sidewall height 140.0 mm 136.5 mm -3.5 mm
Circumference 2076.6 mm 2054.6 mm -22.0 mm
Revolutions per mile 775.0 783.3 +8.3
Section width 175 mm 195 mm +20 mm
Rim diameter 15 in 15 in +0 in

Diameter difference between 175/80R15 and 195/70R15: -7.0 mm (-1.1%)

A -1.1% 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 -22.0 mm per revolution, and the revs per mile change by +8.3, 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: 175/80R15 to 195/70R15 and back

Going from 175/80R15 to 195/70R15, the diameter grows by -1.1%, so the true speed is the indicated speed multiplied by 0.989. At 30 mph on the dial the car is really doing 29.7 mph; at 50 mph indicated it is 49.5 mph; at 70 mph indicated it is 69.3 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 195/70R15 back to 175/80R15, the error reverses exactly: the ratio becomes 1.011, so 70 mph indicated is really 70.7 mph.

Indicated speed Actual speed fitting 195/70R15 (from 175/80R15) Actual speed fitting 175/80R15 (from 195/70R15)
30 mph 29.7 mph 30.3 mph
50 mph 49.5 mph 50.5 mph
70 mph 69.3 mph 70.7 mph

Sidewall height and ride comfort: 175/80R15 vs 195/70R15

Look at the sidewalls next. 140.0 mm on 175/80R15, 136.5 mm on 195/70R15: a difference of -3.5 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: 175/80R15 vs 195/70R15

The width gap is 20 mm (175 mm against 195 mm). Going wider usually buys dry grip and a more planted feel, and it costs a little in rolling resistance and road noise. Remember that width also decides whether the tyre fits the rim: a 195 mm tyre needs a rim width within the range its maker approves, and a rim that suited 175/80R15 may not suit 195/70R15. That is a separate check from the diameter comparison, and it belongs on the list before anything is fitted.

Revolutions per mile and gearing: 175/80R15 vs 195/70R15

Gearing follows the circumference. 195/70R15 covers 2054.6 mm per revolution against 2076.6 mm for 175/80R15, so it needs +8.3 fewer revolutions per mile. At a fixed road speed the engine speed drops or rises by the same 1.1% 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 195/70R15 clear after 175/80R15? What to check before fitting

Clearance is the check the numbers cannot do for you. 195/70R15 is shorter and 20 mm wider than 175/80R15, so check the wheel arches, the suspension components and the steering lock: turn the wheel fully in both directions and check for contact, and check again with the suspension compressed and the car loaded as it will actually be used. A size that clears when the car is stationary and unloaded can still rub over a bump or at full lock. This page does not claim that 195/70R15 clears your car, and no diameter table can — only a physical check on your vehicle can confirm it. Also confirm the load index and speed rating of 195/70R15 meet what your placard asks for, and that the 15-inch rim suits the car.

Which size suits which priority: 175/80R15 or 195/70R15

Weigh the four effects separately. Sidewall (-3.5 mm) for comfort. Width (+20 mm) for grip and rolling resistance. Diameter (-1.1%) 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 175/80R15 vs 195/70R15 comparisons and tools

Frequently asked questions

What is the diameter difference between 175/80R15 and 195/70R15?

195/70R15 is -7.0 mm (-1.1%) smaller in diameter than 175/80R15: 654.0 mm against 661.0 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 195/70R15 instead of 175/80R15?

The error follows the diameter ratio, -1.1%. At an indicated 30 mph the true speed would be 29.7 mph, at 50 mph indicated it would be 49.5 mph, and at 70 mph indicated it would be 69.3 mph. The full table in both directions is in the speedometer section above.

Is 195/70R15 wider than 175/80R15, and does that matter?

Yes — 195/70R15 is 195 mm wide against 175 mm for 175/80R15, 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 195/70R15 fit my car if 175/80R15 fits?

Not necessarily. 195/70R15 is shorter by 7.0 mm and 20 mm wider, and it needs a 15-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, 175/80R15 or 195/70R15?

Neither is better in general — it depends on what you want. 195/70R15 has a -3.5 mm sidewall difference, a +20 mm width difference and a -1.1% 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.