Choosing a Final Drive Ratio for Drifting: Computed Speed Per Gear, Not Forum Numbers

Almost every "best drift ratio" answer you will find is somebody quoting the ratio in their own car. That is not advice, it is a biography. What actually decides whether a ratio suits you is where second gear lands on your track, and that is pure arithmetic once you know three numbers: your gearbox ratios, your final drive, and your rolling diameter. So the tables below are computed, not copied. Every speed figure was calculated from published factory gear ratios and one stated tyre size, and the gear ratios themselves carry provenance tags so you can see which ones are factory specifications and which are forum consensus. The short answer, if you only want one: on a 235/40R17, a 4.083 puts second gear at 45 to 105km/h, which covers most Australian circuit layouts, and that is why the S-chassis world settled there.

How to read the tags

• [OEM-DOCUMENTED] traceable to a factory specification, workshop manual or manufacturer parts listing.
• [COMMUNITY RULE-OF-THUMB] consistent across builders and marque forums, no factory document behind it.
• [CONTESTED] credible sources disagree.
• [NOT VERIFIED] we could not source it, and it is named here rather than quietly dropped.

The speed tables themselves carry no tag, because they are not claims. They are arithmetic applied to the tagged ratios above them.

The arithmetic, so you can redo it with your own numbers

Road speed in km/h equals engine rpm, divided by gearbox ratio times final drive, multiplied by rolling circumference in metres, times 60, divided by 1000.

Rolling circumference comes from the tyre. A 235/40R17 has an overall diameter of 17 times 25.4, plus twice 40 percent of 235, which is 619.8mm, and a circumference of 1.947 metres. Every table below assumes 235/40R17 unless it says otherwise, and assumes no tyre growth and no slip, neither of which is true at speed but both of which move every row the same direction.

That last point matters more than people admit. A tyre change moves your gearing without touching the diff:

That is an 11km/h spread from tyre choice alone, which is roughly the difference between two adjacent factory final drives. Anyone quoting a ratio without a tyre size is quoting half a number. If you are also changing wheel size, run it through the wheel offset calculator first so you know what diameter you are actually landing on.

S13 and S14, FS5W71C five speed

Factory ratios 3.321, 1.902, 1.308, 1.000 and 0.759, with the S14 running a taller 0.838 fifth. [OEM-DOCUMENTED, factory service manual figures corroborated across multiple independent transcriptions] Note the widely quoted 3.214 and 1.925 pair is a 300ZX gearbox, not this one.

Speeds in km/h at 7000rpm:

The row that decides your purchase is second. Taking a usable band of 3000 to 7000rpm, second gear covers 42 to 99km/h on a 4.363, 45 to 105km/h on a 4.083, and 50 to 117km/h on a 3.692. Walk your local track in your head and put the entry speeds against those windows. A tight, low-speed layout wants the 4.363. A fast sweeper where you are already deep into third on a 4.363 wants the 3.692.

Factory final drives worth knowing, all [OEM-DOCUMENTED] except where flagged: S13 CA18DET 4.363, S13 SR20DET 4.083, S14 SR20DET Japanese market 4.083, S14 manual European and Australian delivered 3.692, S15 Spec-R 3.692, S15 Spec-S 4.083.

You will also see 4.111 quoted for the S13 SR20DET, and a widely copied manufacturer ratio guide lists it as a range of "4.111 to 4.363". [CONTESTED] It disagrees with every workshop manual transcription and with the tooth counts: 49 on 12 is 4.083 and 48 on 11 is 4.364, and there is no 4.111 tooth pair in that family. The same guide lists the R34 GT-T RB25DET at 4.111, which is a separate claim we could not settle either way. [NOT VERIFIED] If you are buying on ratio, read the tooth count stamp on the crownwheel rather than a chart.

S15 Spec-R, FS6R92A six speed

Factory ratios 3.626, 2.200, 1.541, 1.213, 1.000 and 0.767, with a 3.692 final drive. [OEM-DOCUMENTED]

Speeds in km/h at 7000rpm on 235/40R17:

This is the argument for the six speed in one table. On the factory 3.692 the six speed's second tops out at 101km/h, which is close to what the five speed gives you on a 4.083, and third arrives at 144 rather than 169. The gaps are smaller, so you land closer to the power band after every shift. It is also why fitting a 4.083 behind a six speed makes second quite short for anything but a very tight track.

JZX100 and the R154

Factory ratios 3.251, 1.955, 1.310, 1.000 and 0.753. [OEM-DOCUMENTED, Toyota parts listings against genuine gearbox 33030-2A600] JZX100 Tourer V manuals are commonly cited as 4.083 with autos on 3.909. [COMMUNITY RULE-OF-THUMB]

Speeds in km/h at 7000rpm on 235/40R17:

Notice how close the R154 on a 4.083 sits to the SR five speed on the same final drive: second within 3km/h across the whole band. The gearbox is doing less to differentiate these cars than the engine underneath it, which is worth remembering before you spend on gearing to fix something that is really a power delivery problem. Which engine actually suits your chassis is a separate argument, made in SR20 vs RB25 vs 1JZ.

VE and VF Commodore, TR6060 six speed

The LS3 cars use the MER variant: 3.006, 2.066, 1.426, 1.000, 0.709 and 0.567. [OEM-DOCUMENTED] Supercharged cars use a different, closer-ratio box and are not covered by these numbers.

Speeds in km/h at 6500rpm, and this table assumes 245/40R18, a 653mm diameter, because nobody runs 17s on one of these:

This is the clearest case in the article for leaving the diff alone and driving the car. The factory manual ratios of 3.45 and 3.70 put second at 112 and 105km/h, both entirely sensible drift gears. The 2.92 auto ratio puts second at 133km/h, which is a highway gear and genuinely lazy, and is the one case where re-gearing a Commodore for drift is worth the money. Ratio provenance and how to read it off the housing sticker is in the VE and VF Commodore diff guide.

The live-axle Australian chassis

If your car runs a BorgWarner banjo, the ratios available to you are a fixed menu rather than a catalogue: roughly 2.77 and 2.92 from Falcons, 3.08 from VN to VS, 3.23 from the injected VK, 3.45 from the VL, 3.7 and 3.9 from the R31 Skyline, and 4.11 from the Pintara. [COMMUNITY RULE-OF-THUMB] Dropped into a five speed with a 1.902 second on 235/40R17 at 7000rpm, the useful end of that menu gives second gear tops of 140km/h on a 3.08, 125 on a 3.45, 116 on a 3.7, 110 on a 3.9 and 105 on the Pintara 4.11, which lands on the same window the Nissan world reaches from the other direction. The interchange rules, and the pinion mesh question that decides whether a given gearset will even go in your housing, are in the BorgWarner 78 interchange guide.

One thing we could not source: a definitive Australian gear ratio set for the BA Falcon XR6 T5. American charts show at least four distinct sets sharing a 3.35 first, and no Australian source pinned the BA to one of them. [NOT VERIFIED] Read the tag number off the box rather than trusting a US chart.

What actually decides it

1. Pick for second gear, on your home track. Everything else follows.
2. Change one variable at a time. A tyre change and a diff change together will teach you nothing about either.
3. Ratio is the last thing to fix, not the first. A predictable diff and a car you can place matter more, which is the argument in 1.5-way vs 2-way LSD.
4. Buy the whole diff, not just the gears. Matched centre, gears and axles from one donor saves the interchange headache entirely, as the R180 vs R200 vs R230 guide sets out.
5. Check what the number assumes. Every quoted ratio hides a gearbox and a tyre. The chassis and diff family behind yours is in the chassis reference table.

When you know which ratio you want, the drivetrain listings are where complete diffs, centres and gearsets turn up. If you re-geared and the old crownwheel and pinion is in a box in the shed, list it free with the ratio in the title.