245/40R18 vs 255/40R19Tire Size Comparison

Not Recommended

The 5.1% diameter difference exceeds 5% and could affect ABS and traction control.

245/40R18653mm dia255/40R19687mm dia+16.7mm

Comparison Details

Overall Diameter653.2 vs 686.6 mm (+33.4 mm)
Diameter Difference+5.11%
Section Width245 vs 255 mm (+10 mm)
Sidewall Height98.0 vs 102.0 mm (+4.0 mm)
Circumference2052.1 vs 2157.0 mm
Clearance Change+16.7 mm
Speedometer Error+5.11%
Revs/Mile784 vs 746

Speedometer Correction

When switching from 245/40R18 to 255/40R19, your speedometer will differ from actual speed.

SpeedometerActual SpeedDifference
30 km/h31.5 km/h+1.5 km/h
40 km/h42.0 km/h+2.0 km/h
50 km/h52.6 km/h+2.6 km/h
60 km/h63.1 km/h+3.1 km/h
70 km/h73.6 km/h+3.6 km/h
80 km/h84.1 km/h+4.1 km/h
90 km/h94.6 km/h+4.6 km/h
100 km/h105.1 km/h+5.1 km/h
110 km/h115.6 km/h+5.6 km/h
120 km/h126.1 km/h+6.1 km/h
130 km/h136.6 km/h+6.6 km/h

Vehicles Using These Sizes

Vehicles with 245/40R18

2025 Audi A4Premium 40 TFSI2025 Audi A4Premium Plus 45 TFSI quattro2024 Audi A4Premium Plus 45 TFSI quattro2023 Audi A4Premium Plus 45 TFSI quattro2022 Audi A4Premium Plus 45 TFSI quattro2021 Audi A4Premium Plus 45 TFSI quattro2020 Audi A4Premium Plus 45 TFSI quattro2025 Mercedes-Benz C-ClassC 3002025 Mercedes-Benz C-ClassC 300 4MATIC2024 Mercedes-Benz C-ClassC 3002024 Mercedes-Benz C-ClassC 300 4MATIC2023 Mercedes-Benz C-ClassC 3002023 Mercedes-Benz C-ClassC 300 4MATIC

Vehicles with 255/40R19

2025 Acura TLXA-Spec2024 Acura TLXA-Spec2021 Acura TLXA-Spec2025 Ford MustangGT2024 Ford MustangGT2023 Ford MustangGT2022 Ford MustangGT2021 Ford MustangGT2020 Ford MustangGT

Individual Tire Size Details

245/40R18
Full specifications, compatible vehicles, and alternatives
255/40R19
Full specifications, compatible vehicles, and alternatives

Practical Guidance

A 5.1% diameter difference is significantly outside the safe replacement range. Switching from 245/40R18 to 255/40R19 can cause dangerous speedometer inaccuracy, ABS/traction control malfunctions, and potential clearance issues. This change is not recommended without professional verification and possible ECU recalibration.

The 3% diameter tolerance is a widely accepted industry guideline referenced by the ETRTO and most vehicle manufacturers. When in doubt, consult your vehicle's owner's manual or a qualified tire professional. For U.S. tire safety standards and recalls, see the NHTSA Tire Safety page.

Frequently Asked Questions

Not Recommended. The overall diameter differs by 5.11%, width changes by 10mm.

Speedometer error will be 5.11%. At an indicated 100 km/h, actual speed is about 105.1 km/h.

Ground clearance changes by +16.7mm per side.