Question 1

Which tire is taller, 275/35 R20 or 265/40 R21?

Accepted Answer

265/40 R21 is taller by 44.9 mm (6.41%) compared with 275/35 R20.

Question 2

What is the diameter difference between 275/35 R20 and 265/40 R21?

Accepted Answer

275/35 R20 measures 701 mm overall diameter, 265/40 R21 measures 745 mm — a difference of 44.9 mm (6.41%).

Question 3

How much speedometer error does this change create?

Accepted Answer

Switching from 275/35 R20 to 265/40 R21 changes the speedometer reading by +6.41%. At an indicated 100 km/h, your true speed becomes about 106.4 km/h.

Question 4

Is 265/40 R21 a safe replacement for 275/35 R20?

Accepted Answer

Over 5% diameter difference. This is outside the common safe range and can affect speedometer accuracy, ABS calibration and gearing. Not recommended without professional review.

Question 5

What else should I check before changing tire size?

Accepted Answer

Beyond diameter and speedometer error, verify wheel offset (ET), rim width, hub bore, load index, brake and suspension clearance, and your vehicle's manufacturer specification. Local regulations may also limit how far you can deviate from OEM.

Metric	275/35 R20	265/40 R21	Difference
Overall diameter	700.5 mm	745.4 mm	+44.9 mm (+6.41%)
Sidewall height	96.3 mm	106.0 mm	+9.8 mm
Circumference	2.201 m	2.342 m	+141.1 mm
Revs / km	454.4	427.0	-27.4
Ground clearance	reference	+22.4 mm	+22.4 mm
Speedometer @ 100 km/h	100.0 km/h	106.4 km/h	+6.41 km/h

275/35 R20 vs 265/40 R21

Detailed comparison

Verdict: danger

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