How much bigger is a 35 than a 33?

Exactly two inches, because the names say so

This is the rare tire question with an exact answer, and the reason is notation rather than engineering. Flotation codes state overall diameter in the first number, so 35x12.50R17 minus 33x12.50R17 is 33.00 in subtracted from 35.00 in. No aspect ratio to work through, no millimetre conversion, no rounding to argue about: +2.00 in.

None of the increase is width

Both sizes are 12.50 in of section width. The step from a 33 to a 35 in this notation buys height and nothing else — the extra 2.00 in is 1.00 in of additional sidewall at the top of the tire and 1.00 in at the bottom, and the casing is no wider at its shoulder than it was. Width in flotation sizing moves in a separate number, which is why a 35x11.50R17 and a 35x12.50R17 are both 35s.

What the two inches cost in reading error

6.06% is what a speedometer calibrated for the 33 will be out by once the 35 is on. In practice that is an indicated 70 mph covering ground at 74.2 mph, and an odometer that logs 100 miles while the truck has travelled 106.1. The full speed table for the pair shows where the gap opens fastest — it grows with speed, so the error is largest exactly where it is easiest to collect a ticket for it.

Half of it lands at the axle, the other half at the arch

Ride height rises by 1.00 in, because the axle sits at the centre of the wheel and only the bottom half of the diameter change is under it. The other 1.00 in goes upward, into whatever clearance exists above the tire. Those two inches are usually discussed as one number and they land in two entirely different places on the vehicle. The radius grows by 1.00 in, so at any given suspension position the crown of the tire is an inch closer to whatever is above it than it was before — a measurement to take at full compression rather than sitting in a driveway.