R

Tire Size & Wheel Calculator

Enter your tire size, for example 205/55 R16, and compare it with a new size. You get the diameter, rolling circumference, speedometer error, the effect of rim width and offset, and the age of your tires.

100% freeNo data storedSketch to scale

Current tire size

Your size205/55 R16
mm
%
"

New tire size

Your size225/45 R17
mm
%
"

Wheel: rim width & offset (ET)

You usually find these on the wheel itself, for example "7Jx17 ET45".

J
mm
J
mm

Markings: load, speed & DOT

The four digits in the oval at the end of the DOT number: week + year.

New tires, new consumption? Recalculate your fuel costs.

Go to the fuel cost calculator

Difference in diameter & rolling circumference

+0.38 %

205/55 R16 → 225/45 R17 · Ground clearance changes by +1.2 mm

Within the usual range (rule of thumb −2% to +1.5%)The difference is within the range the tire trade uses as a rule of thumb. That is not an approval: what counts are your vehicle papers (EC certificate of conformity), a type approval for the part or an expert report.

Old and new compared

ValueOldNewDifference
Overall diameter631.9 mm634.3 mm+2.4 mm
Rolling circumference (nominal)1,985 mm1,993 mm+8 mm
Sidewall height112.8 mm101.3 mm−11.5 mm
Tire width205 mm225 mm+20 mm
Rim diameter406.4 mm431.8 mm+25.4 mm
Revolutions per km504 502 −2

Sketch to scale

old: 205/55 R16new: 225/45 R17Ø 631.9 mmØ 634.3 mm

Both wheels at the same scale, standing on the same ground line. The dashed line marks the height of the old tire.

Speedometer error

If your speedometer was exact with the old size, with the new size you are actually doing:

Speedo shows 50

50.2

km/h actual (+0.2)

Speedo shows 100

100.4

km/h actual (+0.4)

Speedo shows 130

130.5

km/h actual (+0.5)

Caution: the new size is larger, so your speedometer shows less than before. Under UN ECE R39 a speedometer must never show less than the true speed. Whether your speedometer's built-in margin is enough can only be settled by an approval or an inspection.

Difference between actual and displayed speed

Factory speedometers usually overread a little (allowed under UN ECE R39: at most 10% + 4 km/h). The calculation only shows the part added by the new tire size.

Wheel: track width & clearance

Outer rim edge

+13.7 mm

+ = further out towards the wheel arch

Inner rim edge

+11.7 mm

+ = closer to the strut and brake

Track width per axle

+2.0 mm

Change in track width (2 × offset difference)

← insideoutside →ET 45Rim centreHub mounting faceold 6.5J ET46new 7.5J ET45

In Germany the wheels must stay adequately covered (§ 36a StVZO). Different wheels need a type approval (ABE) or a parts report; with a parts report an inspection is usually required (§ 19(3) StVZO).

Load capacity & maximum speed

LI 91 · Load capacity per tire

615 kg

1,230 kg per axle (2 tires)

V · maximum permitted speed

240 km/h

Show full tables

Load index

60: 25061: 25762: 26563: 27264: 28065: 29066: 30067: 30768: 31569: 32570: 33571: 34572: 35573: 36574: 37575: 38776: 40077: 41278: 42579: 43780: 45081: 46282: 47583: 48784: 50085: 51586: 53087: 54588: 56089: 58090: 60091: 61592: 63093: 65094: 67095: 69096: 71097: 73098: 75099: 775100: 800101: 825102: 850103: 875104: 900105: 925106: 950107: 975108: 1,000109: 1,030110: 1,060111: 1,090112: 1,120113: 1,150114: 1,180115: 1,215116: 1,250117: 1,285118: 1,320119: 1,360120: 1,400121: 1,450122: 1,500123: 1,550124: 1,600125: 1,650

kg per tire

Speed rating

L120 km/h
M130 km/h
N140 km/h
P150 km/h
Q160 km/h
R170 km/h
S180 km/h
T190 km/h
U200 km/h
H210 km/h
V240 km/h
W270 km/h
Y300 km/h

"ZR" in the size (e.g. 225/40 ZR18) marks tires for more than 240 km/h. In Germany, winter tires may have a lower rating than the car's top speed if a notice is placed in the driver's field of view (§ 36(5) StVZO).

Tire age (DOT)

Enter the last four digits of the DOT number to see the age.

There is no legal maximum age for car tires in Germany. Rubber hardens over time, though. Experts advise having tires checked every year from about 6 years and replacing them after 10 years at the latest.

Legal note

Which tire and wheel sizes are allowed on your car is stated in the EC certificate of conformity (CoC), a type approval (ABE) or a parts report. Sizes outside these papers need an expert inspection in Germany, otherwise the vehicle's operating permit can lapse (§ 19(2) StVZO). The ± values in this calculator are a rule of thumb, not a legal limit.

Email results

Was the tire size calculator helpful?

Kaffee ausgeben ☕

Speedometer reading low? See what speeding costs

Traffic Fine Calculator →

Guide: Tire Size, Speedometer & Tire Age

Explained clearly, with worked examples and the key rules

Tire Size Explained: Diameter, Circumference and Alternative SizesFeatured

Tire Size Explained: Diameter, Circumference and Alternative Sizes

What 205/55 R16 means, how to calculate diameter and circumference, which deviation is usual when switching sizes, and what the CoC, type approvals and inspections have to do with it.

2026-09-249 min read
How to Read Your Tire Size: What the Numbers and Letters Mean

How to Read Your Tire Size: What the Numbers and Letters Mean

Width, aspect ratio, construction, rim size, load index and speed rating: how to read the sidewall correctly, with tables and examples.

2026-09-245 min read
Speedometer Error from Different Tires: Working Out Your Real Speed

Speedometer Error from Different Tires: Working Out Your Real Speed

Bigger wheels, wrong speedometer? How the rolling circumference changes the reading, what UN ECE R39 requires and why your speedometer overreads from the factory.

2026-09-245 min read
Tire Age from the DOT Code: How Old Can Tires Be?

Tire Age from the DOT Code: How Old Can Tires Be?

How to read the production week and year from the DOT code, why rubber ages, when experts recommend replacing tires and what to check when buying.

2026-09-245 min read
Winter Tire Rules in Germany: Alpine Symbol, Fines and Tread Depth

Winter Tire Rules in Germany: Alpine Symbol, Fines and Tread Depth

Germany's situational winter tire rule under § 2(3a) StVO explained: which tires count, why M+S alone is no longer enough, what the fines are and how much tread you need.

2026-09-245 min read

You might also find useful

Traffic Fine Calculator

Calculate fine, points & driving ban — speeding, distance, red light & phone under Germany's 2026 fine catalogue

Calculate now →

Fuel Cost Calculator

Calculate fuel costs per trip and annually

Calculate now →

Vehicle Tax Calculator

Calculate vehicle tax and compare cars

Calculate now →

Frequently Asked Questions

Multiply the width by the aspect ratio as a percentage to get the sidewall height. For 205/55 R16 that is 205 × 0.55 = 112.75 mm. The diameter is the rim in millimetres plus twice the sidewall: 16 × 25.4 + 2 × 112.75 = 631.9 mm. The circumference is diameter × π, here about 1,985 mm.

There is no fixed legal percentage. The tire trade's rule of thumb is: at most about 1.5% larger and 2% smaller than the original size. What is binding, however, is only what the EC certificate of conformity (CoC), a type approval or an expert report states for your car. Other sizes must be checked by an expert.

The speedometer counts wheel revolutions. A larger tire covers more distance per revolution, so at the same reading you are going faster. With +2% circumference the speedometer shows 100 km/h while you are really doing 102 km/h. Under UN ECE R39 a speedometer must never show less than the true speed.

Not if the size is listed in your vehicle papers. Many sizes are not in the registration certificate but in the CoC document. If the size is missing there, you need a type approval (ABE) or a parts report. With a parts report an inspection by an expert is usually required. Without it the operating permit can lapse (§ 19 StVZO).

The offset is the distance between the wheel's centre line and the mounting face at the hub, in millimetres. A lower offset pushes the wheel outwards: the track gets wider, by twice the difference per axle. Going from ET 45 to ET 35 widens the track by 20 mm. A wider rim also reaches half the extra width further in and further out.

Look for "DOT" on the sidewall. The last four digits in an oval show the production week and year. 2219 means calendar week 22 of 2019. Tires with only three digits were made before 2000. Enter the digits in the calculator above to see the exact age.

There is no legal maximum age for car tires in Germany. Rubber hardens over the years, even if the tread is still deep enough. Experts recommend having tires checked every year from about six years and replacing them after ten years at the latest.

After the size you will see something like "91V". 91 is the load index: 615 kg per tire. V is the speed rating: up to 240 km/h. New tires must meet at least the values in your vehicle papers. Only winter tires may have a lower speed rating, provided a notice is displayed in the driver's field of view.

Yes, but depending on conditions: in black ice, packed snow, slush, ice or frost you may only drive on winter or all-season tires (§ 2(3a) StVO). Since 1 October 2024 only tires with the Alpine symbol (mountain with snowflake) count. Driving without them costs €60 and one penalty point.