9 replies to this topic

[mcerqueira]

The general rule of thumb is that shorter gear ratios give better acceleration but lower top speed while the inverse is also true. Why is it then that all mega-fast road vehicles such as supercars, superbikes and also race cars, like F1, have long 1st gears, reaching and often surpassing 100 kph (62 mph)?

Wouldn't a shorter gear ratio allow for evem more stunning acceleration? Or is it a case of to much power having to be offset by a longer gear ratio on the first gears?

PS: what's (in average) the max speed for each gear in a F1 nowdays?

[Lukin]

The shorter the gear ratio's the lower the top speed. The idea of the gearing in F1 is to have the engine just hit the limit (or his just below) redline in top gear on the fastest part of the circuit and tailor the lower gears to suit.

While more gears would be better, more gears means heavier and bigger gearbox.

Williams trialled a CVT in the early 90's, that would allow the flexibility your talking about but was banned by the FIA.

[Greg Locock]

There's at leats two other factors

1) The rotational inertia of the engine is very significant in first gear, and its contribution is proportional to the overall gear ratio (engine to wheel) ^2

2) The available grip in first gear is limited by the weight transfer, since aero is no real help at low speeds.

Both of these reduce the improvement in acceleration you'd hope for from super high first gears .

[mcerqueira]

I also guess that due to wasted time while changing gears (in manual gearboxes) there may also be a drawback in having shorter gear ratios for better 0-62 times... Very powerfull engines (and/or very healthy power to wheight ratios) have a lot more to play with so I guess in more "mundane" engines (like a hot-hatch) having shorter ratios might help more than on a supercar... (?)

[McGuire]

Originally posted by mcerqueira
The general rule of thumb is that shorter gear ratios give better acceleration but lower top speed while the inverse is also true. Why is it then that all mega-fast road vehicles such as supercars, superbikes and also race cars, like F1, have long 1st gears, reaching and often surpassing 100 kph (62 mph)?

Wouldn't a shorter gear ratio allow for evem more stunning acceleration? Or is it a case of to much power having to be offset by a longer gear ratio on the first gears?

For vehicles like these, acceleration in first gear is essentially traction-limited. A bigger (numerically higher) gear would only achieve more wheelspin in most cases. Also: in production road vehicles, first gear range is selected not so much for top speed attainable (for that one would shift gears eh) but for parking lot and low-speed driving ease etc. An excessively short gear might be too rabbity, while drivers seldom wind out first gear in normal driving.

[Deepak]

Going by what has been said i would then infer that a softer suspension would lead to better grip hence better acceleration and thus a the need for a shorter 1st gear is reduced.

Is that so?

[david_martin]

Originally posted by Deepak
Going by what has been said i would then infer that a softer suspension would lead to better grip hence better acceleration and thus a the need for a shorter 1st gear is reduced.

Is that so?

Depends a lot on which wheels you are driving. Suspension which permits more front to rear weight transfer will be advantageous to pure straight line traction in a front engined rear wheel drive car, but the opposite in a engined front wheel drive car. Ever wondered why Dr. Porsche liked putting the engine in the rear of his designs?;)

[275 GTB-4]

Well I'm no freakin expert but.....

A close ratio box to me is......

a long first gear to get up to speed ....

followed by short stabs to maintain speed under every situation...!!!

[hydra]

For what its worth, my sentiments exactly

[JwS]

In my experience (primarily motorcycle) you've only got a discrete number of gears to work with, so you try to optimize the availible gears so that you are turning a proper number of revs at the most important corner exits. The next thought is for your top speed, if you run out of revs before the end of the longest straight then you're loosing time. The last thought is for the launch, first gear that is, because motorcycles usually do a standing start. First gear (on a street bike) is typically too low for a good race launch, you end up shifting and wasting time before you've really got going. Instead you usually want preferred a relatively high first gear (or sometimes start in second) and slip the clutch as required.
I guess with a semi-auto gearbox there may be other priorities, my biggest problem was my lousy downshifting and I guess general disinclination to shift at all if possible.... which colored my choice of final drive ratios.
JwS