Is 275/40R20 bigger than 265/35R19?

275/40R20 is 2.36 inches taller and 10 mm wider. In overall diameter that is +8.97%, which exceeds the ±3% rule of thumb for a substitution.

How much will 275/40R20 throw off my speedometer?

Every reading scales by 1.08966. An indicated 60 mph becomes 65.4 mph, and every 100 miles on the odometer is really 109.0 miles.

How much does 275/40R20 change ground clearance over 265/35R19?

The axle centerline moves by 1.18 inches — half the diameter change, because half the extra height sits below the hub and half above it.

Will 275/40R20 fit where 265/35R19 fits?

Nothing derived from the size code can answer that. Clearance depends on wheel offset, suspension travel and body dimensions that no tire size contains. This page tells you exactly what changes dimensionally, which is the part that can be calculated.

265/35R19 vs 275/40R20

275/40R20 is +2.36″ in overall diameter and +10 mm in section width against 265/35R19 — a diameter change of +8.97%, which breaks the ±3% substitution rule. An indicated 60 mph would really be 65.4 mph.

Outside 3%

Every dimension

Difference between 265/35R19 and 275/40R20
Dimension	265/35R19 → 275/40R20	Change
Overall diameter	26.30″ → 28.66″	+2.36″ (+8.97%)
Section width	265 mm → 275 mm	+10 mm (+3.77%)
Sidewall height	92.7 mm → 110.0 mm	+17.3 mm
Rolling circumference	82.63″ → 90.04″	+7.41″
Revolutions per mile	766.8 → 703.7	−63.1
Axle height / clearance	13.15″ → 14.33″	+1.18″

265/35R19265 mm

275/40R20275 mm

265/35R19 26.30″275/40R20 28.66″

Which is taller, 265/35R19 or 275/40R20?

275/40R20 is the taller of the two, at 28.66″ against 26.30″. The gap is 2.36 inches, or 59.9 mm.

Both are metric sizes, so neither states its height directly. Both figures below are derived from the section width, aspect ratio and wheel diameter in the code. 265/35R19 is 265 mm wide with a 92.7 mm sidewall on a 19″ wheel; 275/40R20 is 275 mm wide with a 110.0 mm sidewall on a 20″ wheel.

What the speedometer will read

Indicated versus actual speed after the size change
Speedometer reads	Actual speed	Error
25 mph	27.2 mph	+2.2 mph
40 mph	43.6 mph	+3.6 mph
55 mph	59.9 mph	+4.9 mph
60 mph	65.4 mph	+5.4 mph
70 mph	76.3 mph	+6.3 mph
80 mph	87.2 mph	+7.2 mph

Fitting 275/40R20 in place of 265/35R19 multiplies every speed and distance reading by 1.08966. Over 10,000 indicated miles the odometer is out by +897 miles.

Effective gearing moves by the same proportion. A vehicle with 3.73 axles running 265/35R19 would need 4.06 to keep the same engine speed on 275/40R20. Work it out for your own axle ratio.

Full specification of each size

265/35R19

Derived dimensions for 265/35R19
Dimension	Metric	Imperial
Section width	265.0 mm	10.43″
Sidewall height	92.7 mm	3.65″
Wheel diameter	482.6 mm	19.0″
Overall diameter	668.1 mm	26.30″
Rolling circumference	2,098.9 mm	82.63″
Revolutions per mile	476.4 / km	766.8 / mile
Measuring rim (estimate)	229 mm	9″

275/40R20

Derived dimensions for 275/40R20
Dimension	Metric	Imperial
Section width	275.0 mm	10.83″
Sidewall height	110.0 mm	4.33″
Wheel diameter	508.0 mm	20.0″
Overall diameter	728.0 mm	28.66″
Rolling circumference	2,287.1 mm	90.04″
Revolutions per mile	437.2 / km	703.7 / mile
Measuring rim (estimate)	241 mm	9.5″

Rim widths differ too: 265/35R19 is designed for 8.5″–10″ and 275/40R20 for 9″–10.5″. Their measuring rims differ, so the same wheel will not be ideal for both.

Can you swap one for the other?

Outside the ±3% rule

The diameter difference of +8.97% exceeds the ±3% rule of thumb. Expect a speedometer error of about 5.4 mph at an indicated 60, and an odometer that is off by the same proportion. It is a common swap even so — it just needs the instruments recalibrated to stay honest.

Neither figure says anything about physical fitment. Whether 275/40R20 clears the strut, the fender liner and the steering stops depends on wheel offset and suspension geometry that a size code does not encode. For maintenance rather than sizing, Car Basics covers tire care.