Tire size comparison
185/55R15 vs 185/65R15
185/65R15 is +6.3% taller than 185/55R15: 24.5 in vs 23.0 in (+1.46 in), and the same width. With 185/65R15 on a vehicle set up for 185/55R15, the speedometer shows 60 mph at an actual 63.8 mph. That is more than the ±3% difference many shops use as a rule of thumb, so check carefully before switching.
Set up for: going bigger (185/65R15 instead of 185/55R15) · Different situation?
Your current size
e.g. 265/70R17, 2657017 or 33x12.50R20
Where do I find my size?
It's on the tire sidewall, e.g. P265/70R17 115T, and on the tire placard sticker on the driver's door jamb (also in the owner's manual). The placard shows the size the vehicle came with; the sidewall shows what is fitted now. If they differ, use the placard as your starting point. Digits are enough here: 2657017 or 33125020.
Size you're considering
185/55R15 vs 185/65R15: full comparison
| 185/55R15 | 185/65R15 | Difference | |
|---|---|---|---|
| Overall diameter | 23.01 in | 24.47 in | +1.46 in (+6.3%) |
| Width | 7.28 in | 7.28 in | ±0.00 in (±0.0%) |
| Sidewall height | 4.01 in | 4.73 in | +0.73 in |
| Circumference | 72.3 in | 76.9 in | +4.6 in |
| Revs per mile (nominal) | 876 | 824 | −52 |
| Wheel diameter | 15 in | 15 in | ±0 in |
| Diameter in mm | 584 | 622 | +37 mm |
Speedometer difference
Your speedometer is calibrated for 185/55R15. Fitted with 185/65R15, the actual speed is the reading × 24.47 ÷ 23.01.
| Speedometer shows | Actual speed | Difference |
|---|---|---|
| 20 mph | 21.3 mph | +1.3 mph |
| 30 mph | 31.9 mph | +1.9 mph |
| 45 mph | 47.8 mph | +2.8 mph |
| 55 mph | 58.5 mph | +3.5 mph |
| 60 mph | 63.8 mph | +3.8 mph |
| 70 mph | 74.4 mph | +4.4 mph |
| 80 mph | 85.1 mph | +5.1 mph |
Real tires: published diameters
185/55R15: 22.9–23.1 in published by 4 makers; 185/65R15: 24.3–24.5 in published by 4 makers. Calculated figures assume a nominal tire; the exact difference between two specific tires depends on their models.
More about each size: 185/55R15 · 185/65R15
Related comparisons
FAQ
Which is bigger, 185/55R15 or 185/65R15?
185/65R15 is +6.3% taller than 185/55R15: 24.5 in vs 23.0 in (+1.46 in).
How much will my speedometer be off with 185/65R15 instead of 185/55R15?
The speedometer is calibrated for 185/55R15. With 185/65R15 it shows 60 mph when you are doing 63.8 mph, and 70 mph at 74.4 mph (+6.3%). Your speedometer also has its own factory tolerance.
Can I replace 185/55R15 with 185/65R15?
The diameter difference is +6.3%. Whether it fits depends on things this calculation can't see: wheel width and offset, clearance at full lock and over bumps, load index and speed rating, and your vehicle maker's approval. Check your door-jamb placard and owner's manual and ask a tire professional.