225/45R17 vs 305/70R17
New overall diameter
33.81″
was 24.97″
True speed at an indicated 60
81.2 mph
your speedo reads low
Revolutions per mile
596
was 808, −211
| Measurement | 225/45R17 | 305/70R17 | Change |
|---|---|---|---|
| Overall diameter | 24.97″ | 33.81″ | +8.84″ (+35.4%) |
| Sidewall height | 3.99″ (101.3 mm) | 8.41″ (213.5 mm) | +112.3 mm |
| Tread width | 225 mm | 305 mm | +80 mm |
| Circumference | 78.45″ | 106.22″ | +27.77″ |
| Revs per mile | 808 | 596 | −211 |
| Speedometer error | baseline | +35.4% | reads low |
Diameter overlay
225/45R17 305/70R17
Speedometer check
With 305/70R17 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
33.8 mph actual
35 mph shown
47.4 mph actual
45 mph shown
60.9 mph actual
55 mph shown
74.5 mph actual
65 mph shown
88.0 mph actual
75 mph shown
101.5 mph actual
Common questions
- Will 305/70R17 fit instead of 225/45R17?
- 35.4% is past the 5% mark, which is where this stops being a tire choice and starts being a project. Expect rubbing, meaningful speedometer error, and extra load on ABS, stability control and the drivetrain. Recalibration is the usual fix. Your speedometer will read low, so you are going faster than it says. Overall diameter goes from 24.97″ to 33.81″, a change of +35.4%. The rule of thumb most shops use: under 3% is fine, 3 to 5% needs a clearance check, over 5% needs recalibration.
- How far off will my speedometer read on 305/70R17?
- At an indicated 60 mph you are really doing about 81.2 mph, a +35.4% error. The speedometer reads low, so you are going faster than it shows.
- What is the difference in revolutions per mile between 225/45R17 and 305/70R17?
- 225/45R17 turns about 808 times per mile and 305/70R17 turns about 596, a difference of −211. Your speedometer and odometer both count rotations, so this number is what throws them off.