Is 255/35R19 bigger than 265/35R18?

255/35R19 is 0.72 inches taller and 10 mm narrower. In overall diameter that is +2.86%, which stays inside the ±3% rule of thumb for a substitution.

How much will 255/35R19 throw off my speedometer?

Every reading scales by 1.02863. An indicated 60 mph becomes 61.7 mph, and every 100 miles on the odometer is really 102.9 miles.

How much does 255/35R19 change ground clearance over 265/35R18?

The axle centerline moves by 0.36 inches — half the diameter change, because half the extra height sits below the hub and half above it.

Will 255/35R19 fit where 265/35R18 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.

265/35R18 vs 255/35R19

255/35R19 is +0.72″ in overall diameter and −10 mm in section width against 265/35R18 — a diameter change of +2.86%, which stays inside the ±3% substitution rule. An indicated 60 mph would really be 61.7 mph.

Within 3%

Every dimension

Difference between 265/35R18 and 255/35R19
Dimension	265/35R18 → 255/35R19	Change
Overall diameter	25.30″ → 26.03″	+0.72″ (+2.86%)
Section width	265 mm → 255 mm	−10 mm (−3.77%)
Sidewall height	92.8 mm → 89.2 mm	−3.5 mm
Rolling circumference	79.49″ → 81.77″	+2.28″
Revolutions per mile	797.1 → 774.9	−22.2
Axle height / clearance	12.65″ → 13.01″	+0.36″

265/35R18265 mm

255/35R19255 mm

265/35R18 25.30″255/35R19 26.03″

Which is taller, 265/35R18 or 255/35R19?

255/35R19 is the taller of the two, at 26.03″ against 25.30″. The gap is 0.72 inches, or 18.4 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. 265/35R18 is 265 mm wide with a 92.8 mm sidewall on a 18″ wheel; 255/35R19 is 255 mm wide with a 89.2 mm sidewall on a 19″ wheel.

What the speedometer will read

Indicated versus actual speed after the size change
Speedometer reads	Actual speed	Error
25 mph	25.7 mph	+0.7 mph
40 mph	41.1 mph	+1.1 mph
55 mph	56.6 mph	+1.6 mph
60 mph	61.7 mph	+1.7 mph
70 mph	72.0 mph	+2.0 mph
80 mph	82.3 mph	+2.3 mph

Fitting 255/35R19 in place of 265/35R18 multiplies every speed and distance reading by 1.02863. Over 10,000 indicated miles the odometer is out by +286 miles.

Effective gearing moves by the same proportion. A vehicle with 3.73 axles running 265/35R18 would need 3.84 to keep the same engine speed on 255/35R19. Work it out for your own axle ratio.

Full specification of each size

265/35R18

Derived dimensions for 265/35R18
Dimension	Metric	Imperial
Section width	265.0 mm	10.43″
Sidewall height	92.8 mm	3.65″
Wheel diameter	457.2 mm	18.0″
Overall diameter	642.7 mm	25.30″
Rolling circumference	2,019.1 mm	79.49″
Revolutions per mile	495.3 / km	797.1 / mile
Measuring rim (estimate)	229 mm	9″

255/35R19

Derived dimensions for 255/35R19
Dimension	Metric	Imperial
Section width	255.0 mm	10.04″
Sidewall height	89.2 mm	3.51″
Wheel diameter	482.6 mm	19.0″
Overall diameter	661.1 mm	26.03″
Rolling circumference	2,076.9 mm	81.77″
Revolutions per mile	481.5 / km	774.9 / mile
Measuring rim (estimate)	229 mm	9″

Rim widths differ too: 265/35R18 is designed for 8.5″–10″ and 255/35R19 for 8.5″–10″. They share a measuring rim, so one wheel can usually carry either.

Can you swap one for the other?

Inside the ±3% rule

The diameter difference of +2.86% is within the ±3% that fitters use as the boundary for a substitution, so the speedometer, odometer and wheel-speed-derived systems stay close enough to calibration. The section width difference of −10 mm is a separate question and is the one that decides whether it rubs.

Neither figure says anything about physical fitment. Whether 255/35R19 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.