Is 255/35R19 bigger than 255/40R17?

255/35R19 is 1.00 inches taller and 0 mm wider. In overall diameter that is +3.98%, which exceeds the ±3% rule of thumb for a substitution.

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

Every reading scales by 1.03979. An indicated 60 mph becomes 62.4 mph, and every 100 miles on the odometer is really 104.0 miles.

How much does 255/35R19 change ground clearance over 255/40R17?

The axle centerline moves by 0.50 inches — half the diameter change, because half the extra height sits below the hub and half above it.

Will 255/35R19 fit where 255/40R17 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.

255/40R17 vs 255/35R19

255/35R19 is +1.00″ in overall diameter and 0 mm in section width against 255/40R17 — a diameter change of +3.98%, which breaks the ±3% substitution rule. An indicated 60 mph would really be 62.4 mph.

Outside 3%

Every dimension

Difference between 255/40R17 and 255/35R19
Dimension	255/40R17 → 255/35R19	Change
Overall diameter	25.03″ → 26.03″	+1.00″ (+3.98%)
Section width	255 mm → 255 mm	0 mm (0.00%)
Sidewall height	102.0 mm → 89.2 mm	−12.8 mm
Rolling circumference	78.64″ → 81.77″	+3.13″
Revolutions per mile	805.7 → 774.9	−30.8
Axle height / clearance	12.52″ → 13.01″	+0.50″

255/40R17255 mm

255/35R19255 mm

255/40R17 25.03″255/35R19 26.03″

Which is taller, 255/40R17 or 255/35R19?

255/35R19 is the taller of the two, at 26.03″ against 25.03″. The gap is 1.00 inches, or 25.3 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. 255/40R17 is 255 mm wide with a 102.0 mm sidewall on a 17″ 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	26.0 mph	+1.0 mph
40 mph	41.6 mph	+1.6 mph
55 mph	57.2 mph	+2.2 mph
60 mph	62.4 mph	+2.4 mph
70 mph	72.8 mph	+2.8 mph
80 mph	83.2 mph	+3.2 mph

Fitting 255/35R19 in place of 255/40R17 multiplies every speed and distance reading by 1.03979. Over 10,000 indicated miles the odometer is out by +398 miles.

Effective gearing moves by the same proportion. A vehicle with 3.73 axles running 255/40R17 would need 3.88 to keep the same engine speed on 255/35R19. Work it out for your own axle ratio.

Full specification of each size

255/40R17

Derived dimensions for 255/40R17
Dimension	Metric	Imperial
Section width	255.0 mm	10.04″
Sidewall height	102.0 mm	4.02″
Wheel diameter	431.8 mm	17.0″
Overall diameter	635.8 mm	25.03″
Rolling circumference	1,997.4 mm	78.64″
Revolutions per mile	500.6 / km	805.7 / 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: 255/40R17 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?

Outside the ±3% rule

The diameter difference of +3.98% exceeds the ±3% rule of thumb. Expect a speedometer error of about 2.4 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 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.