GEAR RATIOS
Gearing is a game of ‘give-andtake’; the more top speed you have in any given gear, the slower it will accelerate. This is why specialist race cars are carefully geared with the aim of just touching the rev limiter in top gear on the specific track on question. That way they aren’t handicapping any top speed potential but are also maximising the possible acceleration too.
The difference changing the gearing can make often has to be felt to be believed. It can accelerate like a totally different machine, like a car with much more power. While custom gear ratios are expensive, there are far cheaper options that can give a similar result.
It’s easiest on RWD cars, as you can leave the gearbox alone and fit a differential with an alternative final drive ratio instead. And the best bit, and we have Ford’s parts-bin sharing to thank for this, many similar models or different trim levels of the same model, can easily be fitted in place to change the final drive ratio. For example the Sierra/ Scorpio diffs range from as tall as 3.36:1 to as short as 4.27:1 – to put that in perspective, using a 2WD Cosworth as an example that would mean a speed of 118.8mph at 5,000rpm in 5th with the 3.36 diff, but considerably slower – but faster accelerating – speed of 93.5mph for the 4.27 diff.
4WD cars can potentially swap final drive ratios in the diffs too, but as both the front and rear diffs need swapping it tends to be far more complex and expensive. Therefore, for most FWD and 4WD cars, a gearbox swap from a different model is the only viable option without going to a full aftermarket gearbox – but do that and you can choose from a huge selection of ratios to suit your needs.