255/55R19 Tyre Size: Dimensions, Alternatives & Speedometer Effect
If you are looking up the 255/55R19 tyre size, the figures that matter are the diameter (763.1 mm, or 30.0 inches), the sidewall (140.2 mm), the circumference (2397.3 mm) and the revolutions per mile (671.3). The size code itself tells you the ingredients — 255 mm of width, an aspect ratio of 55%, a 19-inch rim — and this page shows how those ingredients combine into the measurements above, which sizes sit closest to it, and what happens to your speedometer if you fit one of them instead. Every figure here is computed from the size code, not estimated, so you can use it to check a tyre you already own or one you are thinking of buying.
Before the numbers, one practical point. A tyre size is only correct for your car if it matches what the manufacturer specified, and the place to find that is the placard on the driver's door jamb, not the size currently fitted — a previous owner may have changed it. The dimensions on this page tell you exactly what a 255/55R19 measures, so you can compare it against the placard figure and against any alternative you are considering. If the two do not match, the tables further down show how far apart they are and whether the difference stays inside the commonly used plus-or-minus 3% guideline.
This is a calculation, not a safety approval. Always check your vehicle's door-jamb placard, load index and speed rating, and confirm fitment with a tyre professional before fitting a different tyre size.
What does 255/55R19 mean?
Read the code left to right. 255 means the tyre is 255 mm wide across the tread. 55 is the aspect ratio, so the sidewall is 55% of the width — 255 x 0.55 = 140.2 mm of rubber between rim and tread. R19 means it mounts on a 19-inch rim (482.6 mm). The overall diameter is the rim plus two sidewalls: 482.6 mm + 140.2 mm + 140.2 mm = 763.1 mm. Once you can do that sum, you can decode any size code you meet, and you can see why two sizes with the same rim can still be very different heights.
255/55R19 dimensions
| Measurement | Value |
|---|---|
| Overall diameter | 763.1 mm (30.0 in) |
| Sidewall height | 140.2 mm |
| Circumference | 2397.3 mm |
| Revolutions per mile | 671.3 |
| Rim diameter | 19 in |
The revs-per-mile figure, 671.3, deserves attention because it is the number your car actually senses. Speedometers and odometers count wheel revolutions and multiply by an assumed circumference; change the circumference and the maths drifts. With a 2397.3 mm circumference, this tyre turns 671.3 times per mile, and any replacement with a different circumference will turn a different number of times over the same mile. The diameter (763.1 mm, 30.0 in) and the sidewall (140.2 mm) complete the picture. Remember these are nominal new-tyre figures — real tyres vary slightly by brand, model, wear and inflation pressure, so two tyres with the same size code can differ by a millimetre or two in practice.
Closest alternative sizes to 255/55R19
If you are looking for a substitute, start here. These are the three nearest sizes by overall diameter, limited to rims within one inch of 19 inches so the wheel itself stays realistic. 255/60R18 is the nearest at +0.0% (+0.1 mm difference). Anything within plus or minus 3% is generally treated as acceptable from a speedometer point of view, but diameter is only one of the checks: the replacement also needs the right load index and speed rating, and enough clearance around the suspension and arches at full steering lock.
| Alternative size | Diameter | Sidewall | Diameter difference | Within ±3% guideline? |
|---|---|---|---|---|
| 255/60R18 | 763.2 mm (30.0 in) | 153.0 mm | +0.0% | Within the guideline |
| 255/50R20 | 763.0 mm (30.0 in) | 127.5 mm | -0.0% | Within the guideline |
| 235/65R18 | 762.7 mm (30.0 in) | 152.8 mm | -0.1% | Within the guideline |
Speedometer effect of changing from 255/55R19
The speedometer effect is a straight ratio. Fitting 255/60R18 (763.2 mm) in place of 255/55R19 (763.1 mm) changes the diameter by +0.0%, so every indicated speed is multiplied by 1.000 to get the real speed. At 30 mph on the dial the true speed is 30.0 mph, at 50 mph it is 50.0 mph, and at 70 mph it is 70.0 mph. The table below shows the same working for all three alternatives, so you can see at a glance which swap keeps the error negligible and which one starts to matter.
| Replacement size | Diameter change | Actual speed at 30 mph indicated | Actual speed at 50 mph indicated | Actual speed at 70 mph indicated |
|---|---|---|---|---|
| 255/60R18 | +0.0% | 30.0 mph | 50.0 mph | 70.0 mph |
| 255/50R20 | -0.0% | 30.0 mph | 50.0 mph | 70.0 mph |
| 235/65R18 | -0.1% | 30.0 mph | 50.0 mph | 70.0 mph |
Wider, narrower or taller than 255/55R19: what actually changes
What actually changes if you move away from 255/55R19? Width first: a wider tyre puts more rubber on the road, which usually helps dry grip and can hurt fuel use a little through extra rolling resistance. Height second: because the sidewall is 55% of the width, widening without lowering the aspect ratio raises the diameter, lengthens the gearing and lifts the car slightly. A shorter sidewall sharpens steering response but transmits more of the road surface into the cabin. The practical rule is to hold the diameter as steady as you can — that is what the alternative table above is for — and to check that a wider tyre still clears the suspension and arches at full lock before committing.
How to check 255/55R19 fits your vehicle
Start with the placard on the driver's door jamb: it lists the size, load index and speed rating the manufacturer specified for your vehicle, and it outranks whatever is currently fitted. Check that the load index of any replacement is at least the placard figure — a lower load index is not acceptable even if the size matches. Check the speed rating the same way, and check the rim width: a 255 mm tyre needs a rim within the width range the tyre maker approves for it. Then check clearance with the steering at full lock in both directions and the suspension compressed, and check the tyre-pressure monitoring system still reads correctly after the change. If any of those checks is unclear, a tyre professional can confirm fitment in minutes. The diameter being checked in this case is 763.1 mm for the 255/55R19.
Mistakes to avoid with 255/55R19
The most common mistake is reading the size off the tyre already fitted and assuming it is the correct size — a previous owner may have changed it. The second is going wider without adjusting the aspect ratio, which quietly makes the tyre taller and throws the speedometer off. The third is ignoring the load index and speed rating, which matter as much as the dimensions. The fourth is fitting different sizes on the same axle, which the car was not designed for. And the fifth is forgetting that the spare, the pressure-monitoring system and the speedometer all assume the standard size — change the size and all three need a thought. For a 255/55R19, that means checking the 255 mm width, the 55% aspect ratio and the 19-inch rim against the placard before you buy.
Related 255/55R19 sizes and tools
- 255/35R19 tyre size
- 255/40R19 tyre size
- Use the Tyre Size Calculator to compare 255/55R19 against any other size.
- Use the Plus Sizing Calculator to find a wider size that keeps the diameter close to 255/55R19.
Frequently asked questions
What is the overall diameter of a 255/55R19 tyre?
The overall diameter of a new 255/55R19 tyre is 763.1 mm, which is 30.0 inches. That is the rim diameter (482.6 mm) plus twice the sidewall height (140.2 mm). It is a nominal figure, so an individual tyre can vary slightly by brand, model, wear and inflation pressure.
How tall is the sidewall on a 255/55R19 tyre?
The sidewall is 140.2 mm tall, because the aspect ratio is 55% of the 255 mm width (255 x 55/100 = 140.2 mm). A medium-profile sidewall like this one means a balanced sidewall that splits the difference between handling response and ride comfort. The sidewall height is the main thing that decides how much cushioning the tyre gives over bumps.
How many revolutions per mile does a 255/55R19 tyre do?
A 255/55R19 tyre completes 671.3 revolutions per mile, based on its 2397.3 mm circumference. That figure matters because the speedometer and odometer count revolutions: fit a tyre with a different circumference and the readings drift by the same percentage as the diameter change.
What is the closest alternative size to 255/55R19?
The closest size in the chart is 255/60R18, which differs in diameter by +0.0% (+0.1 mm). The commonly used guideline is to stay within plus or minus 3% of the original diameter, and the alternative table on this page shows which sizes meet that. Diameter is only one check, though — load index, speed rating and physical clearance still need confirming.
Will changing from 255/55R19 affect my speedometer?
Yes. The speedometer assumes the original circumference, so a diameter change shifts every reading by the same percentage. Fitting 255/60R18 instead of 255/55R19 changes the diameter by +0.0%, so an indicated 70 mph would really be 70.0 mph. Keep the diameter within plus or minus 3% to keep that error small, and check the placard before fitting anything different.