Speedometer Error 165/70R13 to 175/65R13: Indicated vs Actual Speed at 30, 50 & 70 mph

Changing from 165/70R13 to 175/65R13 changes the speedometer by -0.62%, because the overall diameter moves from 561.2 mm to 557.7 mm. That is the whole calculation: the speedometer was calibrated for the rolling circumference of the original size, and the new size covers a different distance per revolution, so the dial reads wrong by exactly the diameter percentage. This page works the error out step by step, shows the indicated-versus-actual speed at 30, 50 and 70 mph, and explains what the change does to the odometer, the gearing and the legal position — with the disclaimer below applying throughout.

The direction matters as much as the size. Because 175/65R13 is smaller than 165/70R13, the car travels slower than the speedometer shows, so at an indicated 70 mph the actual speed is 69.6 mph. If the new size were smaller the opposite would be true. The diameter difference is 3.5 mm, which is 0.62% — inside the ±3% guideline commonly used for keeping speedometer error small, and the sections below show the full table, the formula, the odometer effect and when a recalibration is worth doing.

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.

How the speedometer error is calculated for speedometer error 165/70r13 to 175/65r13

Taking speedometer error 165/70r13 to 175/65r13 as the case in point: The arithmetic is short. First find the percentage change: error % = (new diameter − old diameter) ÷ old diameter × 100. Then find the actual speed: actual speed = indicated speed × (new diameter ÷ old diameter). Both formulas use the nominal new-tyre diameters from the size codes, and the tables in this article use those figures throughout. A positive result means the replacement tyre is larger, so the true speed is higher than the indicated speed and the odometer under-records; a negative result means the replacement is smaller, so the true speed is lower than the indicated speed and the odometer over-records. The same percentage applies at every speed, so one calculation covers the whole speed range.

What the speedometer actually measures for speedometer error 165/70r13 to 175/65r13

On this page, speedometer error 165/70r13 to 175/65r13 is the case in point: The speedometer does not measure speed directly. It counts wheel revolutions — from a sensor on the gearbox output, a wheel-speed sensor or the ABS system, depending on the vehicle — and multiplies by the rolling circumference the manufacturer programmed in. That circumference belongs to the original tyre size, so fitting a different diameter changes the distance covered per revolution while the speedometer keeps using the old figure. The result is a fixed percentage error: if the new tyre is 2% larger in diameter, the actual speed is 2% higher than the indicated speed at every speed, and the odometer under-records by the same 2%. The error does not grow or shrink with speed; it is the same percentage at 30 mph and at 70 mph, which is what the tables below show.

Worked example: 165/70R13 to 175/65R13

165/70R13 measures 561.2 mm in overall diameter (22.09 in), with a 115.5 mm sidewall, a 1763.1 mm circumference and 912.8 revolutions per mile. 175/65R13 measures 557.7 mm (21.96 in), with a 113.8 mm sidewall, a 1752.1 mm circumference and 918.5 revolutions per mile. The diameter difference is -3.5 mm, and the error % is (557.7 − 561.2) ÷ 561.2 × 100 = -0.62%. The circumference difference is -11.0 mm and the revolutions-per-mile difference is +5.7, which is the same change seen from the other side: more revolutions per mile means less distance per revolution. All of these are nominal new-tyre figures; real tyres vary slightly by brand, model, wear and inflation pressure.

Indicated vs actual speed: 165/70R13 to 175/65R13

Error: -0.62%. Actual speed = indicated speed × (557.7 ÷ 561.2).

Indicated speed Actual speed Difference
30 mph 29.8 mph -0.2 mph
50 mph 49.7 mph -0.3 mph
70 mph 69.6 mph -0.4 mph

At an indicated 70 mph the actual speed is 69.6 mph, a difference of -0.4 mph, and the odometer is out by the same -0.62% — it records +0.62% more miles than the car actually covers. The diameter change of 0.62% is inside the ±3% guideline commonly used for keeping speedometer error small. If the change is outside that band, or if the dial now under-reads, a recalibration is worth considering, and the placard should be checked and fitment confirmed with a tyre professional before fitting a different tyre size.

speedometer error 165/70r13 to 175/65r13: Size comparison table

Measurement 165/70R13 175/65R13
Overall diameter 561.2 mm (22.09 in) 557.7 mm (21.96 in)
Sidewall height 115.5 mm 113.8 mm
Circumference 1763.1 mm 1752.1 mm
Revolutions per mile 912.8 918.5
Rim diameter 13 in 13 in

Common causes of a wrong speedometer for speedometer error 165/70r13 to 175/65r13

On this page, speedometer error 165/70r13 to 175/65r13 is the case in point: The causes divide into calibration and faults, and the distinction decides the fix. Calibration causes are tyre diameter changes, wear and inflation pressure: all of them change the distance covered per wheel revolution, and all of them produce a steady percentage error that the formulas on this page can predict. Fault causes are a failing wheel-speed sensor, a damaged reluctor ring, a worn speedometer cable on older vehicles, or a fault in the instrument cluster itself — these usually make the reading jump, stick or drop to zero rather than sit a steady percentage out. If the error is the same percentage at every speed, it is calibration; if it changes with speed or the needle behaves erratically, it is a fault and the vehicle needs diagnosis rather than a recalibration.

How to fix a speedometer error for speedometer error 165/70r13 to 175/65r13

The fix is chosen by vehicle, not by preference. Modern vehicles with electronic speedometers are usually corrected by reprogramming the tyre-size setting with a diagnostic tool or a handheld programmer, which adjusts the speedometer and the odometer together. Older vehicles with a cable-driven speedometer need a different speedometer drive gear, and the new gear is selected using the diameter ratio — new teeth = old teeth × (old diameter ÷ new diameter) — so the gear compensates exactly for the size change. Where neither is available, an inline signal calibrator fitted to the speed sensor wiring can scale the reading. A dealer may be needed where the setting is locked behind manufacturer software. In every case, measure the error against GPS before and after the fix, at a steady speed on a straight road, to confirm the dial is right. That is the point this page works through for speedometer error 165/70r13 to 175/65r13.

Common mistakes with speedometer error for speedometer error 165/70r13 to 175/65r13

On this page, speedometer error 165/70r13 to 175/65r13 is the case in point: Mistakes usually start with the wrong reference. The first is comparing the dial with another vehicle's dial — both can be out by the same amount. GPS speed, measured at a steady speed on a straight road, is the practical reference, though it has its own limits at low speed and on hills. The second mistake is treating the error as a fixed mph figure: a 3% error is 0.9 mph at 30 mph and 2.1 mph at 70 mph, so a single-speed check does not describe the whole picture. The third is forgetting that most speedometers already read slightly high from the factory, so the error after a tyre change is measured from that baseline, not from zero. And the fourth is the dangerous one: fitting larger tyres makes the dial read low, so the car is going faster than the driver believes, and driving to the indicated limit in that condition means exceeding it.

Related pages for speedometer error 165/70r13 to 175/65r13

Frequently asked questions

What is the speedometer error from 165/70R13 to 175/65R13?

The error is -0.62%, because the diameter moves from 561.2 mm to 557.7 mm. At an indicated 70 mph the actual speed is 69.6 mph, and the odometer is out by the same -0.62%. The change is inside the ±3% guideline commonly used for keeping speedometer error small.

Do I need to recalibrate after changing to 175/65R13?

It depends on the size of the error and its direction. A 0.62% change is inside the ±3% guideline, so many owners would not recalibrate, though the dial now reads high and the difference is worth knowing about. The correct method depends on the vehicle, so check the owner's manual or ask a specialist.

Will changing to 175/65R13 affect my odometer?

Yes, by the same -0.62%. The odometer counts wheel revolutions just as the speedometer does, so it records +0.62% more miles than the car actually covers. Over 10,000 actual miles that is a difference of about 62 miles.

How do I check my speedometer against GPS?

For speedometer error 165/70r13 to 175/65r13, the point is this: Drive at a steady speed on a straight, level road and compare the dial with a GPS speed reading. GPS is least reliable at low speed, while accelerating or braking, and on hills or in tunnels, so take the reading at a steady cruise. A difference that is the same percentage at several speeds is a calibration error; a needle that jumps or sticks is a fault.

Does tyre wear affect the speedometer?

On this page, speedometer error 165/70r13 to 175/65r13 is the case in point: Yes, slightly. A worn tyre has a smaller diameter than a new one, so the speedometer reads slightly high as the tread wears — typically well under 1% over the life of the tyre. Under-inflation has the same direction of effect by reducing the effective rolling radius. Both are small compared with a size change, but they are real.