245/35R19 Tyre Size: Dimensions, Alternatives & Speedometer Effect

If you are looking up the 245/35R19 tyre size, the figures that matter are the diameter (654.1 mm, or 25.8 inches), the sidewall (85.8 mm), the circumference (2054.9 mm) and the revolutions per mile (783.2). The size code itself tells you the ingredients — 245 mm of width, an aspect ratio of 35%, 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.

People usually land on this page for one of three reasons: checking a tyre already on the car, shopping for a replacement, or wondering whether a slightly different size will work. In all three cases the approach is the same — start with the exact measurements, then compare. A 245/35R19 is a mid-width size, a short, stiff sidewall that sharpens steering response but leaves less cushioning over potholes and kerbs, and the tables below let you hold it up against the nearest alternatives on diameter, sidewall and revs per mile. The disclaimer box just below is part of that comparison: these are calculations, and the final fitment check belongs to your placard and a tyre professional.

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 245/35R19 mean?

Read the code left to right. 245 means the tyre is 245 mm wide across the tread. 35 is the aspect ratio, so the sidewall is 35% of the width — 245 x 0.35 = 85.8 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 + 85.8 mm + 85.8 mm = 654.1 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.

245/35R19 dimensions

Measurement Value
Overall diameter 654.1 mm (25.8 in)
Sidewall height 85.8 mm
Circumference 2054.9 mm
Revolutions per mile 783.2
Rim diameter 19 in

The diameter of 654.1 mm (25.8 in) is the headline number because everything else follows from it. The circumference, 2054.9 mm, is pi times the diameter, and it is the distance the car travels each time the wheel turns once. Divide a mile (63,360 inches) by the circumference in inches and you get 783.2 revolutions per mile — the figure the speedometer and odometer effectively count. A tyre with fewer revs per mile covers more ground per turn, so the car travels faster than the speedometer thinks if you fit a taller tyre without recalibrating. All of these are nominal new-tyre figures: real tyres vary slightly by brand, model, wear and inflation pressure, so treat the decimals as precise maths on a nominal size, not a measurement of your individual tyre.

Closest alternative sizes to 245/35R19

The three sizes below are the closest matches to 245/35R19 in the chart, drawn from the same rim or one inch either side and ranked by diameter difference. The closest, 245/40R18, differs by -0.1% (-0.9 mm). The commonly used guideline is to stay within plus or minus 3% of the original diameter, which keeps the speedometer error small and the gearing close to standard. That guideline is about the speedometer and the car's calibration, not about whether the tyre physically clears the arches — a size can be within 3% on diameter and still rub if it is much wider, so width and clearance need their own check.

Alternative size Diameter Sidewall Diameter difference Within ±3% guideline?
245/40R18 653.2 mm (25.7 in) 98.0 mm -0.1% Within the guideline
215/45R18 650.7 mm (25.6 in) 96.8 mm -0.5% Within the guideline
275/35R18 649.7 mm (25.6 in) 96.2 mm -0.7% Within the guideline

Speedometer effect of changing from 245/35R19

The speedometer effect is a straight ratio. Fitting 245/40R18 (653.2 mm) in place of 245/35R19 (654.1 mm) changes the diameter by -0.1%, so every indicated speed is multiplied by 0.999 to get the real speed. At 30 mph on the dial the true speed is 30.0 mph, at 50 mph it is 49.9 mph, and at 70 mph it is 69.9 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
245/40R18 -0.1% 30.0 mph 49.9 mph 69.9 mph
215/45R18 -0.5% 29.8 mph 49.7 mph 69.6 mph
275/35R18 -0.7% 29.8 mph 49.7 mph 69.5 mph

Wider, narrower or taller than 245/35R19: what actually changes

What actually changes if you move away from 245/35R19? 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 35% 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 245/35R19 fits your vehicle

The checks are the same whatever size you are considering. First, the door-jamb placard: size, load index and speed rating. Second, the rim: a 19-inch rim of the right width for a 245 mm tyre. Third, clearance — arches, suspension components and steering lock, with the car loaded as it will actually be used. Fourth, the pressure-monitoring system, which may need a reset or new sensors after a change. Fifth, the spare: if the spare is a different size, know its speed and distance limits before you need it. None of these is a formality, and together they are what turns a calculation into a safe fitment. For the 245/35R19, the 245 mm width and 85.8 mm sidewall are part of that same check.

Mistakes to avoid with 245/35R19

Watch for these traps. Assuming the current tyre is the correct one, instead of checking the placard. Changing width without compensating the aspect ratio, so the diameter drifts. Buying on size alone and overlooking load index and speed rating. Mixing different sizes on the same axle. And skipping the clearance check at full lock, which is exactly where a wider tyre usually makes contact. If you avoid those five, and keep the diameter within plus or minus 3% of the placard size, you have dealt with the common errors before they happen. A 245/35R19 is 245 mm wide on a 19-inch rim with a 654.1 mm overall diameter, so those are the numbers the placard check has to match.

Related 245/35R19 sizes and tools

Frequently asked questions

What is the overall diameter of a 245/35R19 tyre?

The overall diameter of a new 245/35R19 tyre is 654.1 mm, which is 25.8 inches. That is the rim diameter (482.6 mm) plus twice the sidewall height (85.8 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 245/35R19 tyre?

The sidewall is 85.8 mm tall, because the aspect ratio is 35% of the 245 mm width (245 x 35/100 = 85.8 mm). A low-profile sidewall like this one means a short, stiff sidewall that sharpens steering response but leaves less cushioning over potholes and kerbs. The sidewall height is the main thing that decides how much cushioning the tyre gives over bumps. That is the point this page works through for 245/35r19 tyre size.

How many revolutions per mile does a 245/35R19 tyre do?

A 245/35R19 tyre completes 783.2 revolutions per mile, based on its 2054.9 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 245/35R19?

The closest size in the chart is 245/40R18, which differs in diameter by -0.1% (-0.9 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 245/35R19 affect my speedometer?

Yes. The speedometer assumes the original circumference, so a diameter change shifts every reading by the same percentage. Fitting 245/40R18 instead of 245/35R19 changes the diameter by -0.1%, so an indicated 70 mph would really be 69.9 mph. Keep the diameter within plus or minus 3% to keep that error small, and check the placard before fitting anything different.