Set your parameters above and hit Calculate
Enter your engine above and select transmissions on the Input tab. Links below will update automatically and open Google search in a new tab.
Select transmissions and transfer cases on the Input tab (4WD mode). Links below search for adaptor plates between your chosen gearbox and transfer case and will open Google in a new tab.
What it does
A gear ratio calculator for gearbox swaps, rebuilds and regearing
Pick a gearbox from the list, or type in your own transmission ratios. Set the diff. Enter the tyre you will actually run. BoxSelector works out the mechanical top speed in every gear, the cruise RPM at road speed and, for 4WD builds with a transfer case, the crawl ratio in low range. Compare up to four gearboxes side by side. A 3.90 final drive on one box and a 3.42 on another is not a fair fight until both are on the same chart.
The ratio maths is the easy part of a transmission swap. The hard part is bolting the box to the engine. The Adaptor Search tab builds an adapter plate and bellhousing search for your engine family and each gearbox you have picked, and the TC Adaptor tab does the same for gearbox-to-transfer-case plates. The FAQ covers the questions that turn up every week. The articles cover the planning that should happen before the parts do.
Browse every gearbox in the list: ratios, steps and road speeds, one page per box, with the document the figures came from.
Articles
Read before you buy
Short reads on gearboxes, diffs and tyre sizes, so the calculator inputs come from a plan rather than a forum thread.
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