Question 1

Which tire is taller, 235/35 R19 or 285/30 R20?

Accepted Answer

285/30 R20 is taller by 31.9 mm (4.93%) compared with 235/35 R19.

Question 2

What is the diameter difference between 235/35 R19 and 285/30 R20?

Accepted Answer

235/35 R19 measures 647 mm overall diameter, 285/30 R20 measures 679 mm — a difference of 31.9 mm (4.93%).

Question 3

How much speedometer error does this change create?

Accepted Answer

Switching from 235/35 R19 to 285/30 R20 changes the speedometer reading by +4.93%. At an indicated 100 km/h, your true speed becomes about 104.9 km/h.

Question 4

Is 285/30 R20 a safe replacement for 235/35 R19?

Accepted Answer

Between 3% and 5% diameter difference — speedometer drift is noticeable. Consider recalibration and confirm clearance with your vehicle's manufacturer specification.

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	235/35 R19	285/30 R20	Difference
Overall diameter	647.1 mm	679.0 mm	+31.9 mm (+4.93%)
Sidewall height	82.3 mm	85.5 mm	+3.3 mm
Circumference	2.033 m	2.133 m	+100.2 mm
Revs / km	491.9	468.8	-23.1
Ground clearance	reference	+16.0 mm	+16.0 mm
Speedometer @ 100 km/h	100.0 km/h	104.9 km/h	+4.93 km/h

235/35 R19 vs 285/30 R20

Detailed comparison

Verdict: warning

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