30x9.50R15 vs 33x12.50R17

33x12.50R17 is the taller of the two, at 33.00″ against 30.00″. The gap is 3.00 inches, or 76.2 mm.

One of these is a flotation size, which states its overall diameter on the sidewall, while the metric size only implies one — so the comparison is between a stated height and a derived one. 30x9.50R15 is 241.29999999999998 mm wide with a 190.5 mm sidewall on a 15″ wheel; 33x12.50R17 is 317.5 mm wide with a 203.2 mm sidewall on a 17″ wheel.

Neither figure says anything about physical fitment. Whether 33x12.50R17 clears the strut, the fender liner and the steering stops depends on wheel offset and suspension geometry that a size code does not encode. For maintenance rather than sizing, Car Basics covers tire care.

Is 33x12.50R17 bigger than 30x9.50R15?

33x12.50R17 is 3.00 inches taller and 76 mm wider. In overall diameter that is +10.00%, which exceeds the ±3% rule of thumb for a substitution.

How much will 33x12.50R17 throw off my speedometer?

Every reading scales by 1.10000. An indicated 60 mph becomes 66.0 mph, and every 100 miles on the odometer is really 110.0 miles.

How much does 33x12.50R17 change ground clearance over 30x9.50R15?

The axle centerline moves by 1.50 inches — half the diameter change, because half the extra height sits below the hub and half above it.

Will 33x12.50R17 fit where 30x9.50R15 fits?

Nothing derived from the size code can answer that. Clearance depends on wheel offset, suspension travel and body dimensions that no tire size contains. This page tells you exactly what changes dimensionally, which is the part that can be calculated.