Tire Size Box

205/70R18 vs 325/40R19

325/40R19 compared with 205/70R18

−0.2% diameter, +4.7" width

325/40R19 is 29.24" tall vs 29.30". Within the 3% rule, so usually interchangeable.

29.3"18" rim5.6"8.1" wide
205/70R18 (solid) compared with 325/40R19 (dashed outline), drawn to scale

With 325/40R19 tires, when your speedometer says 60 mph you are really going

59.9 mph

325/40R19 is −0.06 inches (−0.2%) in overall diameter. That is within the 3% most shops and makers allow.

205/70R18325/40R19Difference%
Overall diameter29.30"29.24"−0.06"−0.2%
Section width8.07"12.80"+4.72"+58.5%
Sidewall height5.65"5.12"−0.53"−9.4%
Circumference92.05"91.85"−0.20"−0.2%
Revolutions per mile688.4689.8+1.5+0.2%

Speedometer difference

If your vehicle came with 205/70R18 and you fit 325/40R19, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.0 mph0.0 mph
30 mph29.9 mph−0.1 mph
40 mph39.9 mph−0.1 mph
50 mph49.9 mph−0.1 mph
60 mph59.9 mph−0.1 mph
65 mph64.9 mph−0.1 mph
70 mph69.8 mph−0.2 mph
75 mph74.8 mph−0.2 mph
80 mph79.8 mph−0.2 mph

Each size on its own

Questions

Which is bigger, 205/70R18 or 325/40R19?
205/70R18 is taller by 0.06 inches (29.30" vs 29.24"). 325/40R19 is wider by 4.72 inches.
Can I replace 205/70R18 with 325/40R19?
Usually, yes. The diameter difference is −0.2%, inside the 3% rule of thumb most tire shops use. Check that the wider or taller tire clears your suspension and fenders, and that its load index meets your placard.
How much will 325/40R19 change my speedometer?
When your speedometer reads 60 mph with 325/40R19 fitted (calibrated for 205/70R18), your real speed is 59.9 mph. Your odometer will over-count miles by about 0.2%.
Will 325/40R19 lift my vehicle?
Ride height changes by half the diameter difference: −0.03 inches of ground clearance at the axle.

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