265/70R17 vs 285/70R17: Tyre Size Comparison, Diameter Difference & Speedometer Effect

265/70R17 and 285/70R17 look like near neighbours on paper, but the numbers tell a more precise story. 285/70R17 is the taller tyre: its diameter is 830.8 mm against 802.8 mm, +28.0 mm (+3.5%) larger. Width moves +20 mm, sidewall height moves +14.0 mm, and the circumference changes by +87.9 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.

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 +3.5% difference is outside 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.

265/70R17 vs 285/70R17 side by side

Measurement 265/70R17 285/70R17 Difference
Overall diameter 802.8 mm (31.6 in) 830.8 mm (32.7 in) +28.0 mm (+3.5%)
Sidewall height 185.5 mm 199.5 mm +14.0 mm
Circumference 2522.1 mm 2610.0 mm +87.9 mm
Revolutions per mile 638.1 616.6 -21.5
Section width 265 mm 285 mm +20 mm
Rim diameter 17 in 17 in +0 in

Diameter difference between 265/70R17 and 285/70R17: +28.0 mm (+3.5%)

The diameter gap of +28.0 mm (+3.5%) is the number to carry away from this section. It is outside the plus-or-minus 3% guideline, and it shows up directly in the speedometer tables below. The circumference difference of +87.9 mm and the revs-per-mile difference of -21.5 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: 265/70R17 to 285/70R17 and back

The maths is a single ratio. 285/70R17 over 265/70R17 is 1.035, so every indicated speed after the swap is multiplied by that number to get the true speed: 30 becomes 31.0, 50 becomes 51.7 and 70 becomes 72.4 mph. In the reverse direction the ratio is 0.966, so 70 mph indicated is 67.6 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 285/70R17 (from 265/70R17) Actual speed fitting 265/70R17 (from 285/70R17)
30 mph 31.0 mph 29.0 mph
50 mph 51.7 mph 48.3 mph
70 mph 72.4 mph 67.6 mph

Sidewall height and ride comfort: 265/70R17 vs 285/70R17

Look at the sidewalls next. 185.5 mm on 265/70R17, 199.5 mm on 285/70R17: a difference of +14.0 mm. That is the flexible part of the tyre, and it is the first thing that absorbs a bump. A taller sidewall soaks up more of the impact before it reaches the suspension, at the cost of a slightly less direct feel through the steering wheel. Aspect ratio (70% vs 70%) is simply the sidewall expressed as a share of the width.

Width, grip and fuel use: 265/70R17 vs 285/70R17

The width gap is 20 mm (265 mm against 285 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 285 mm tyre needs a rim width within the range its maker approves, and a rim that suited 265/70R17 may not suit 285/70R17. That is a separate check from the diameter comparison, and it belongs on the list before anything is fitted.

Revolutions per mile and gearing: 265/70R17 vs 285/70R17

Gearing follows the circumference. 285/70R17 covers 2610.0 mm per revolution against 2522.1 mm for 265/70R17, so it needs -21.5 fewer revolutions per mile. At a fixed road speed the engine speed drops or rises by the same 3.5% as the diameter change. With the taller size the engine sits slightly lower in the rev range at cruising speed, which some drivers like and which can help fuel use a little. Either way the effect is proportional to the diameter difference, not larger than it.

Will 285/70R17 clear after 265/70R17? What to check before fitting

Do not skip the physical check. The diameter difference is +3.5% and the width difference is +20 mm, and both of those affect whether 285/70R17 fits where 265/70R17 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 285 mm tyre.

Which size suits which priority: 265/70R17 or 285/70R17

Choose on the basis of what matters to you, not on the headline alone. If ride comfort matters most, the sidewall change of +14.0 mm is the figure to weigh. If grip matters most, the width change of +20 mm is the one to weigh. If keeping the instruments accurate matters most, the diameter change of +3.5% is the one to weigh — and if it is outside the plus-or-minus 3% guideline, ask about recalibration. And if the answer to the clearance check is uncertain, that outranks all three: a tyre that rubs is not a viable option at any percentage.

Related 265/70R17 vs 285/70R17 comparisons and tools

Frequently asked questions

What is the diameter difference between 265/70R17 and 285/70R17?

285/70R17 is +28.0 mm (+3.5%) larger in diameter than 265/70R17: 830.8 mm against 802.8 mm. That is outside the commonly used plus-or-minus 3% guideline for keeping speedometer error small.

How much will my speedometer be out if I fit 285/70R17 instead of 265/70R17?

The error follows the diameter ratio, +3.5%. At an indicated 30 mph the true speed would be 31.0 mph, at 50 mph indicated it would be 51.7 mph, and at 70 mph indicated it would be 72.4 mph. The full table in both directions is in the speedometer section above.

Is 285/70R17 wider than 265/70R17, and does that matter?

Yes — 285/70R17 is 285 mm wide against 265 mm for 265/70R17, 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 285/70R17 fit my car if 265/70R17 fits?

Not necessarily. 285/70R17 is taller by 28.0 mm and 20 mm wider, and it needs a 17-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, 265/70R17 or 285/70R17?

Neither is better in general — it depends on what you want. 285/70R17 has a +14.0 mm sidewall difference, a +20 mm width difference and a +3.5% 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.