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.
Set up for: going smaller (315/35R17 instead of 305/45R17) · 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
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.