Tire Size Change Calculator

What this number means

A tire swap is a gearing change whether you touch the axles or not. Going from 33s to 37s makes 4.10 gears drive like 3.66s: lazier acceleration, a transmission that hunts, a speedometer that lies low, and a crawl ratio that quietly gives back what the lift giveth. This calculator prices all of it in ratio points.

What to change next

The restore-stock ratio is the floor, not the target — it returns factory manners on the new tire. Off-road builds usually go one step deeper than restore-stock (you added weight and rolling resistance too). Highway-heavy builds stop at restore-stock. The Decision System's worksheet weighs your actual use mix; this page gives you the raw exchange rate.

Worked example

JL Sahara, 3.45 gears, factory 32.1-inch tires. On 35s the effective ratio is 3.16 — the Jeep feels like it lost a gear it never had. Restore-stock is 3.76, so 3.73s return factory feel and 4.10s put you one honest step deeper. Every number above updates as you type.