Tooth counts, where published: 1st 9:34, 2nd 17:35, 3rd 50:63, 4th 58:54 (0.93) or 23:26 (0.89). Ring & pinion 8:35 = 4.375, 8:33 = 4.125, 8:31 = 3.875. Source: CSP transmission tech.

3.78 or 3.80 for 1st? Both appear in print. The tooth count is 34:9, which is 3.7778, so 3.78 is the real figure and 3.80 is a rounding convention that spread through the reference tables. They are the same gear. Sources: CSP, Volksconversions gearbox codes, Kennedy Engineered Products chart.

Type 181 is genuinely disputed. Volksconversions lists code AK as 1.26 third and 0.93 fourth. The VW 181 Facts & Figures register lists 1970 through Feb 1973 cars as 1.22 third and 0.82 fourth on the same 3.875 ring & pinion. The calculator offers both; pick the one that matches the gears in your box, not the one that matches the year on the title. Source: VW 181 Facts & Figures.

A split-window Bus has a spur-gear reduction hub at the outboard end of each axle tube, downstream of the ring & pinion. It is a plain series reduction, so the three stages simply multiply: gear ratio × ring & pinion × hub reduction. Leave the hub reduction out and every number you calculate is roughly 26 to 40 percent optimistic.

There are two hub reductions, not one. The commonly quoted 1.39 is correct for the 1956–63 style hub. The taller 1.26 hub arrives with the 1964 ¾-ton and runs through 1967 — which is exactly why a late split bus pulls highway speed on a stock box and an early one won’t. Note the 1964 1-ton stays on 1.39, so the year alone does not settle it; the 36 hp chart row is quoted at 1.40, a third value. Assume 1.39 across the board and every 1964–67 ¾-ton calculation comes out about 10 percent wrong. Check the table above for your chassis, and count teeth if you are spending money on it. Sources: Kennedy Engineered Products chart, type2.com reduction boxes.

Single source The split-bus ratio rows above trace to one chart. We could not find a second independent publication of them. Treat them as a good starting point and confirm against your own box before you spend money on gears. One small arithmetic note: the source chart prints the 1964 ¾-ton effective final drive as 5.50, but 4.375 × 1.26 is 5.5125, and that is the figure the calculator uses. Buses from 1950 to 1959 used a non-synchro crash box whose ratios we could not source at all — those are not in the tool.

Reduction hubs were deleted for 1968, so a bay window has one final drive like a Beetle. The 091 case came in on US models for 1976; everything before that is a 002, with 1975 a one-year case in between.

Verified ring & pinion tooth counts: 32:7 = 4.571, 34:7 = 4.857, 43:8 = 5.375, 38:7 = 5.4286. Sources: type2.com 091 transmission data, Limebug gearbox code table.

Where the sources fight. Limebug and the Kennedy chart both put 5.428 on 1972–75 buses. David Schwarze's 091 data page argues that 5.375 ran through the end of 1973 and calls the 38:7 a "bastard trans." He also rejects the widely quoted mid-1973 chassis number as the 0.82-to-0.89 fourth gear cutoff, having found a late 1973 bus still on 0.82. Both readings are offered in the presets. His warning is worth repeating: published transmission specs for these boxes are unreliable, and you cannot be sure what you have until you open it and look.

The air-cooled Vanagon runs an 091 case, but it is not the same box as a bay window and should not be treated as one. The clearest single tell is fourth gear: 0.85 is a Vanagon ratio and appears nowhere in the 1968–79 bus tables.

Read this before you rely on it This is the thinnest-sourced family in the tool. Two sources agree on first and second and on the 4.57 / 4.86 / 5.43 final-drive family, but they split on whether third is 1.23 or 1.26, and one of them mislabels the engine column. Weddle independently confirms 0.85 as the stock air-cooled Vanagon fourth in the fitment notes for its 0.82 overdrive gear. Codes DT and DU are deliberately left out — the specification sheets date them to the 1.9 water-boxer era, outside this family. Sources: Vantopia gearbox codes, Vanagon transmission specifications, Weddle Vanagon overdrive gears.

Sources: Weddle Industries ring & pinion sets, Rancho Performance Transaxles catalog, SoCal Auto Parts on freeway flyers.

There is no 3.78 ring & pinion for a Type 1. 3.78 is a first gear ratio, 34 teeth on 9. It gets quoted as a final drive often enough that it is worth saying plainly: no vendor sells one, and if a build sheet lists 3.78 as a ring & pinion, somebody copied the wrong column.

First and second are cut on one mainshaft and are bought as a pair. Third and fourth are individual gears, which is why almost every street build changes those two and the ring & pinion and leaves the bottom of the box alone.

Sources: Weddle Sportsman gear ratios, Rancho catalog, SCAT close ratio gear set. These are current availability lists, not a fixed permanent range — a ratio in the tool means it has been offered, not that it is in stock today. Nobody publishes tooth counts for aftermarket gears; call the manufacturer if you need them.

The named builds. Freeway flyer is not one thing. The common versions are a 0.89 fourth behind a 3.88 ring & pinion, a 0.82 fourth behind a 4.12, and both together for what people call a double flyer. Be careful with the percentages people quote: the 11 and 18 percent figures in circulation are each fourth gear’s own overdrive (1 − 0.89 and 1 − 0.82), not what you gain over a stock box. Measured against a stock 4.12 with a 0.89 fourth — 3.671 overall — the real gains are about 6 percent for 0.89 on a 3.88 (3.449), 9 percent for 0.82 on a 4.12 (3.383), 16 percent for the double flyer (3.178) and 30 percent for a 0.82 on a 3.44 (2.821). Run them through the calculator above and read the overall ratio column rather than trusting a headline number. There is no canonical Baja or sand gear stack — vendors sell a menu, not a package — so the tool offers documented example builds and lets you change every number.

Tire height moves your speed calculation as hard as the ring & pinion does. The sizes in the dropdown carry published diameters from tire manufacturers wherever we could find one, rather than a formula's guess.

Two things worth knowing. A size written without an aspect number, like 165R15, is an 80 percent aspect, not the 82 percent that circulates in VW tables — checked against eight published-measured tires, the 82 percent assumption came out high on all eight. And a loaded tire rolls roughly 3 percent smaller than its free diameter, which is the "loaded rolling" option in the tool. Sources: Coker tire size reference, Tire Rack dimensions, Longstone Tyres specifications.