15-inch rim · tyre size comparison
175/65 R15 vs 185/55 R15
185/55 R15 is 24 mm (0.94 in) shorter than 175/65 R15, a -3.94% difference in overall diameter. That is just outside the ±3% limit commonly used to screen a tire size change, so expect a noticeable speedometer error; it is a nominal calculation, not a fitment approval.
- Diameter difference
- -24 mm
- -0.94 in · -3.94%
- Indicated 70 mph
- 67.2 mph
- Actual speed on 185/55 R15, if the speedometer was accurate on 175/65 R15.
- Sidewall height
- -12 mm
- 113.75 mm to 101.75 mm.
Dimensions side by side
| Measurement | 175/65 R15 | 185/55 R15 | Difference |
|---|---|---|---|
| Overall diameter | 608.5 mm23.96 in | 584.5 mm23.01 in | -24 mm (-3.94%)-0.94 in |
| Section width | 175 mm6.89 in | 185 mm7.28 in | +10 mm+0.39 in |
| Sidewall height | 113.75 mm4.48 in | 101.75 mm4.01 in | -12 mm-0.47 in |
| Circumference | 1,911.66 mm75.26 in | 1,836.26 mm72.29 in | -75.4 mm-2.97 in |
| Rim diameter | 381 mm15 in | 381 mm15 in | 0 mm0 in |
| Revolutions per mile | 841.86 | 876.42 | +34.57 |
| Revolutions per km | 523.11 | 544.58 | +21.48 |
Calculated from the nominal size codes, without load or tread wear. Real tyres vary by model, rim width and pressure, so the exact tyre's published dimensions take priority.
Speedometer with 185/55 R15
If the speedometer was accurate on 175/65 R15, fitting 185/55 R15 means the car is travelling 3.94% slower than it shows, and the odometer over-records distance by about the same amount.
| Speedometer shows | Actual on 185/55 R15 | Difference |
|---|---|---|
| 30 mph | 28.82 mph | -1.18 mph |
| 50 mph | 48.03 mph | -1.97 mph |
| 60 mph | 57.63 mph | -2.37 mph |
| 70 mph | 67.24 mph | -2.76 mph |
| 50 km/h | 48.03 km/h | -1.97 km/h |
| 100 km/h | 96.06 km/h | -3.94 km/h |
UN ECE Regulation 39, used in the UK and EU, does not allow a speedometer to show less than the true speed, so many read slightly high from the factory. A shorter tyre adds to it. Calibration varies by car; these figures are the tyre-size effect only.
What changes from 175/65 R15 to 185/55 R15
Wheels
Both fit 15-inch wheels. Our rim-width starting estimate is 4.5 to 5.5 inches for 175/65 R15 and 5.5 to 6.5 inches for 185/55 R15, so a 5.5-inch wheel sits in both ranges. The exact tyre's approved rim range takes priority.
Sidewall and ride comfort
185/55 R15 has 12 mm less sidewall (101.75 vs 113.75 mm). A shorter sidewall usually sharpens steering response, but rides a little firmer and leaves the rim more exposed to potholes and kerbs.
Contact width
185/55 R15 is 10 mm wider in nominal section width (5.7%). A wider tyre usually puts a wider, shorter contact patch on the road, which can help dry grip, but it may follow ruts more, clear standing water less readily and add some rolling resistance.
Wheel well clearance
Ride height changes by about -12 mm, and the top of the tyre moves the same distance away from the arch. On the same wheel width and offset, each sidewall moves about 5 mm further out towards the arch lip and further in towards the suspension. Check clearance at full steering lock and full suspension compression, especially on a lowered car.
Gearing
The effective final drive changes by +4.11%: 3,000 rpm at a given road speed becomes about 3,120 rpm. Gearing gets noticeably shorter, so acceleration in each gear sharpens and cruising revs rise.
ABS, stability control and AWD
These systems compare wheel speeds. Fit the same size on both ends of an axle; with a 3.9% diameter gap, never mix 175/65 R15 and 185/55 R15 on an AWD car, and follow the car maker's rolling-circumference limits, which can be much tighter than 3%.
General tendencies from the nominal numbers, not a test of any tyre. Load index, speed rating, tyre construction and the car's approved sizes matter more than these rules of thumb.
Explained in our guides
- Plus-sizing wheels: tyre diameter and speedometer changesWork through a 17 to 18 inch wheel change, compare tyre diameters and speedometer effects, and understand why a 3% rule cannot approve fitment.
- Staggered vs square wheels: tyres, rotation and AWDCompare square and staggered wheel setups, calculate front-to-rear tyre diameter, and understand rotation limits and all-wheel-drive requirements.
- How to read a tyre size, load index and sidewall markingsDecode tyre width, aspect ratio, rim diameter, load and speed markings, then calculate sidewall height and diameter using a 225/45 R17 example.
Cars in our guides using these sizes
Factory trims and popular community setups from our fitment guides. A popular setup is not a factory approval; each guide explains its trims, axles and clearance limits.
175/65 R15
- Honda Fit / Jazz GE (2007–2014)Factory trim
185/55 R15
- Toyota MR2 Roadster / MR-S ZZW30 (1999–2007)Factory trim
- Volkswagen Golf Mk2 (1983–1992)Popular setup
More comparisons
185/55 R15 compared
Questions
Can I use 185/55 R15 instead of 175/65 R15?
Both fit 15-inch wheels. The diameter difference is -3.94%, just outside the ±3% screening limit, so most fitters would treat it as a different size class rather than a direct replacement. That does not approve fitment: check the car maker's approved sizes, load index, speed rating, rim width and clearance first.
How much bigger is 185/55 R15 than 175/65 R15?
Overall diameter is 24 mm (0.94 in) smaller: 584.5 vs 608.5 mm. Section width is 10 mm wider, and the sidewall is 12 mm shorter. These are nominal figures; real tyres vary by model and rim width.
Will 185/55 R15 change my speedometer reading?
Yes, by 3.94%. If the speedometer was accurate on 175/65 R15, an indicated 60 mph would be about 57.6 mph on 185/55 R15, and an indicated 100 km/h about 96.1 km/h. You would be going slower than the speedometer shows.
Which is better, 175/65 R15 or 185/55 R15?
Neither in general. 175/65 R15 has the taller sidewall, which usually rides more comfortably; 185/55 R15 usually steers more sharply. 185/55 R15 is wider, which can help dry grip; the narrower size is usually better in standing water and snow. The size listed for your car's trim, on its placard or in the handbook, is the safe default.
Check the exact tyre
Size codes give nominal dimensions. Before buying, confirm the size is approved for your car and check the exact tyre's load and speed ratings and published dimensions.