Vehicles

Each platform page records three things: the tire sizes fitted from the factory across trims, the wheel diameters those sizes came on, and — where the figure could be confirmed — the factory axle ratio options. From those, the page computes the arithmetic of every size its owners commonly step up to: how much taller, how much wider, how far out the speedometer goes, and which ratio would restore the original engine speed.

What "commonly stepped up to" means, and what it does not

It means a size that a large number of owners of that platform are observed to fit. It is a record of what people do.

It is not a statement that the size fits, clears, or is legal on any particular vehicle. Two examples of the same truck can differ because one has had its suspension changed, or its bumper, or its wheels. That is why these pages give you the arithmetic and stop.

Why these pages have holes in them

Some platforms below show a factory axle ratio and others show nothing in that column. None yet carries a full transmission ratio set. Those gaps are deliberate: unsourced fields are left empty rather than filled, because an invented ratio produces confidently wrong engine-speed arithmetic on a page that looks every bit as authoritative as a correct one. The sourcing rule in full, including what each record records about its own provenance, is at how every figure on this site is computed.

The authoritative record for your own vehicle is not on this site at all — it is the placard inside the driver's door jamb, which names the size the vehicle left the factory with and the pressures its systems were calibrated against. Where that disagrees with anything here, it wins.

The most useful thing a platform page tells you

Usually it is not the upgrade table. It is the spread between the factory sizes.

Most modern platforms are sold across several wheel diameters and hold rolling diameter almost constant while doing it — the sidewall shrinks as the wheel grows, and the overall height barely moves. Owners frequently assume the trim with the bigger wheels has the bigger tires, and on many platforms it has slightly smaller ones.

That matters because it means the trim you own barely changes the arithmetic of an upgrade. If every factory size on your platform is within a fifth of an inch of the others, then everybody asking the same upgrade question on that platform is starting from the same place, whatever badge is on the tailgate.

How to use one of these pages

Start with the factory sizes and compare them to your own placard. They should agree; if they do not, the placard is right and the page is describing a trim you do not have.

Then work down the upgrade table, which gives the arithmetic of each common step — how much taller, how far the speedometer moves, and where the axle ratio would need to sit to restore the original engine speed.

What the table cannot settle is clearance, and that is usually the real question. For why that question is a different kind of problem and what actually answers it, see will 33s fit? what the question really means.