285/70R17 vs 295/70R17: Height, Width and Speed

Calculated dimensions and changes from the original tire

The first row, 285/70R17, is the original reference. All dimensions come from the tire geometry engine. Candidate percentages and speed results use that same original; figures are rounded only for display.

A width step that also deepens the sidewall

The middle number is a percentage rather than a fixed sidewall measurement. Applying the same percentage to a larger width produces a larger sidewall. That is why this pair changes both lateral envelope and outside height even though only the first number changes. Read the sidewall row before deciding how much extra upper arch space the candidate might require.

A truck owner may be comparing adjacent catalog sizes within the same tire model. That is a useful controlled starting point, but each size can still have its own approved wheel range, weight and measured diameter. Obtain the specification for the exact candidate, not a general model description. If construction or service description differs between the two sizes, keep that difference in the record instead of calling them identical apart from width.

The calculated change from 285/70R17 to 295/70R17

Using 285/70R17 as original, 295/70R17 changes nominal diameter from 32.71 to 33.26 inches. The difference is +14.00 mm, or +1.69% of the original diameter. Nominal section width changes by +10.00 mm and one sidewall changes by +7.00 mm. Those figures are calculated from the complete markings. They describe different dimensions, so a diameter result cannot stand in for a lateral clearance result.

The ideal radius difference is +7.00 mm (+0.28 inches). This is the geometric contribution to wheel center height, not a verified loaded ground clearance change. At an indicated 60 mph, the candidate gives a theoretical 61.01 mph actual speed, or +1.01 mph actual minus indicated. The assumption is calibration to the original circumference with no other instrument error; actual vehicle readings require their own evidence.

What this pair means for the actual assembly

The calculated radius change is only the ideal dimensional contribution to axle clearance. It does not measure the position of every suspension component relative to the ground, and it does not describe clearance gained from a suspension modification. If a vehicle has been lifted, assess that modification separately. Otherwise a small tire related change can be incorrectly presented as the full difference observed between two vehicles.

Width is especially relevant when checking a truck through steering and suspension travel. The extra casing space may matter near a control arm, liner or body mount even when straight ahead clearance looks generous. The size code cannot locate those obstacles or account for an offset change. Use the table to identify which dimensions grew, then inspect the actual wheel and tire combination under the relevant movement.

Keep circumference, calibration and mounting separate

Circumference is calculated from diameter, and the candidate to original circumference ratio gives the theoretical actual speed multiplier. A taller circle travels farther per revolution, while a shorter one travels less. Reversing original and candidate changes the percentage denominator. Do not reverse this comparison by simply changing the sign of a rounded result; enter the actual original in the calculator and compute the other direction directly.

These calculations describe an ideal circle rather than a loaded rolling test. Exact product dimensions, wear, inflation and load can affect the real assembly. Wheel diameter matching does not establish an approved rim width, offset or vehicle clearance. Keep the actual tire model and complete service markings in the comparison record, and check the vehicle instructions if the dimensional change is outside its specified equipment.

Frequently asked questions

Why does an unchanged aspect ratio still produce extra height?

The ratio is applied to each tire's own width. A wider section at the same ratio has a deeper nominal sidewall, and the two deeper sidewalls increase the complete outside diameter.

Do the speed and radius figures establish real vehicle fitment?

No. They describe nominal geometry under a stated reference assumption. The exact tire and wheel, vehicle specifications and clearance through movement must be assessed separately; loaded dimensions and instrument behavior are not measured here.

What changes if 285/70R17 is the replacement rather than the original?

Reverse the inputs in the calculator. Percentage change uses the original diameter as denominator, and theoretical speed uses candidate circumference divided by original circumference. A reversed comparison therefore needs a fresh calculation rather than only a changed sign on the displayed percentage.

Continue your comparison

• Calculate a comparison using your documented original tire
• Read the metric size conversion method