Tire size comparison
305/45R17 vs 315/35R17
315/35R17 is −7.6% shorter than 305/45R17: 25.7 in vs 27.8 in (−2.13 in), and 0.4 in wider. With 315/35R17 on a vehicle set up for 305/45R17, the speedometer shows 60 mph at an actual 55.4 mph. That is more than the ±3% difference many shops use as a rule of thumb, so check carefully before switching.
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). If your current tires aren't the original size, the placard shows what the vehicle came with. Digits are enough here: 2657017 or 33125020.
Size you're considering
305/45R17 vs 315/35R17: full comparison
| 305/45R17 | 315/35R17 | Difference | |
|---|---|---|---|
| Overall diameter | 27.81 in | 25.68 in | −2.13 in (−7.6%) |
| Width | 12.01 in | 12.40 in | +0.39 in (+3.3%) |
| Sidewall height | 5.40 in | 4.34 in | −1.06 in |
| Circumference | 87.4 in | 80.7 in | −6.7 in |
| Revs per mile (nominal) | 725 | 785 | +60 |
| Wheel diameter | 17 in | 17 in | ±0 in |
| Diameter in mm | 706 | 652 | −54 mm |
Speedometer difference
Your speedometer is calibrated for 305/45R17. Fitted with 315/35R17, the actual speed is the reading × 25.68 ÷ 27.81.
| Speedometer shows | Actual speed | Difference |
|---|---|---|
| 20 mph | 18.5 mph | −1.5 mph |
| 30 mph | 27.7 mph | −2.3 mph |
| 45 mph | 41.6 mph | −3.4 mph |
| 55 mph | 50.8 mph | −4.2 mph |
| 60 mph | 55.4 mph | −4.6 mph |
| 70 mph | 64.6 mph | −5.4 mph |
| 80 mph | 73.9 mph | −6.1 mph |
Real tires: published diameters
305/45R17: 27.8 in published by 1 maker; 315/35R17: 25.55–25.7 in published by 2 makers. Calculated figures assume a nominal tire; the exact difference between two specific tires depends on their models.
More about each size: 305/45R17 · 315/35R17
FAQ
Which is bigger, 305/45R17 or 315/35R17?
315/35R17 is −7.6% shorter than 305/45R17: 25.7 in vs 27.8 in (−2.13 in).
How much will my speedometer be off with 315/35R17 instead of 305/45R17?
The speedometer is calibrated for 305/45R17. With 315/35R17 it shows 60 mph when you are doing 55.4 mph, and 70 mph at 64.6 mph (−7.6%). Your speedometer also has its own factory tolerance.
Can I replace 305/45R17 with 315/35R17?
The diameter difference is −7.6%. 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.