More gears feel like progress. Five-speed sounds old. Six-speed sounds serious. Seven-speed sounds like a modern car trying to keep emissions engineers happy.
The number of gears matters less than what the ratios actually do.
Where the extra gear goes
A good six-speed can be excellent. It can keep the lower gears close together for acceleration, then give you a relaxed overdrive for cruising. For a peaky engine, that can mean every shift lands in the useful rev range. For a road car, sixth can make motorway driving quieter and less thirsty.
The extra ratio has to be spent somewhere, and there are only two places to spend it. It can close up the gaps between the existing gears, or it can add a taller top gear. Some boxes do a bit of both. Which one your candidate does is the whole question, and a spec sheet that just says “six” will not tell you.
A worked comparison
Take three example gearboxes. These are illustrative ratios, not any specific named box. All three sit on a 3.90 final drive and a 205/55R16 tyre, and shift at 6,500 rpm.
- Example A, five-speed: 3.14, 1.89, 1.33, 1.00, 0.81.
- Example B, six-speed with closer gaps: 3.14, 2.19, 1.62, 1.25, 1.00, 0.81.
- Example C, six-speed with an overdrive: 3.14, 1.89, 1.33, 1.00, 0.81, 0.68.
The RPM after an upshift is shift RPM x (next ratio / current ratio). From 6,500 in first on box A, that is 6,500 x (1.89 / 3.14), which lands at about 3,910 rpm. Notice that the diff and tyres do not appear in that sum. The drop between gears belongs to the gearbox alone.
| Gearbox | 1st to 2nd lands at | 2nd gear at 6,500 | RPM at 70 mph in top |
|---|---|---|---|
| A, five-speed | about 3,910 | 105 km/h | about 2,990 |
| B, close six | about 4,530 | 91 km/h | about 2,990 |
| C, overdrive six | about 3,910 | 105 km/h | about 2,510 |
Box B is the performance box. Every shift lands higher, and the nastiest drop, first to second, is about 620 rpm kinder than on A. The price is that second runs out at 91 km/h instead of 105, so you shift more often. On the motorway it is identical to the five-speed. Same top ratio, same 2,990 rpm at 70 mph.
Box C is the road box. First to fifth are exactly the same as A, so it accelerates exactly like A. Sixth simply knocks about 480 rpm off the cruise. That is a real improvement for a long-distance car and no improvement at all on a circuit.
Same gear count, two completely different cars. That is why you read the ratio chart, not the badge.
When sixth barely does anything
A six-speed is not automatically better. Some six-speeds do not have a meaningfully taller top gear than a five-speed. Some have awkward spacing. Some are heavier, larger, more expensive and harder to fit.
Run the same car with a sixth gear of 0.78 instead of the five-speed’s 0.81. At 70 mph that is about 2,880 rpm instead of 2,990. A saving of roughly 110 rpm is under 4 percent. You would struggle to hear it over the tyres. If sixth gear only drops the cruise RPM by a tiny amount, you may have bought an extra shift fork and a smug gear knob.
A good five-speed is not a consolation prize
A good five-speed can be perfect. It may be lighter, cheaper, simpler and strong enough for the job. If first is usable, the middle gears suit the engine and fifth gives acceptable cruise RPM, there is no moral failure in having five gears. Plenty of properly good cars do.
Put it on your diff and tyres
The first question is not “five or six?” It is “what road speed do I get in each gear?” Use redline speed, cruising RPM and RPM drop between shifts. Compare the gearbox with your actual diff and tyres. A six-speed with the wrong final drive can be worse than a five-speed with the right one.
The flip side is where an overdrive six earns its keep. Put example C on a shorter 4.30 diff and gears one to five all become about 10 percent shorter than box A on its 3.90, so the car feels sharper everywhere. Sixth still cruises at about 2,770 rpm at 70 mph, below the five-speed’s 2,990. The tall top gear buys room for a shorter diff without a noisier motorway. That is a good reason to want six. “Six is a bigger number” is not.
The job decides what the extra gear is worth
Use case decides the value of the extra gear. Track cars may benefit from closer spacing. Road cars may benefit from a taller overdrive. Drift cars care about the gear they use for wheel speed. Drag cars care about shift count and crossing the line in the right gear. Off-road builds may care far more about low range than sixth.
Packaging and the hidden bill
Also consider packaging. A six-speed swap can bring tunnel clearance issues, shifter position problems, clutch changes, propshaft work, wiring changes and more cost. None of that is a problem if the result is worth it. It is a problem if the five-speed was already doing the job.
Before you commit, check a few things on paper:
- Where each upshift lands against the rev range your engine actually pulls in.
- Cruise RPM at 70 mph in top, on the tyre size you will really run.
- Speed at the shift point in second and third, the gears you use most on the road.
- Whether the new box is longer, heavier or needs a different crossmember, propshaft or speed signal.
- Whether the gain survives being priced against a diff change on the gearbox you already own.
BoxSelector will put two boxes side by side on the same diff and tyres, which settles most of these arguments in about a minute. It also helps to know how the speed in each gear is worked out, so you can sanity check any figure you are handed.
More gears are useful when they solve a real problem. They are not useful when they just make the spec sheet look newer.