I have no experience of six-speed gearboxes, but if the ratios given by Doctor Diesel on page 85 of the last issue are typical, it is disturbing that sixth is only a super top to a standard five gears, rather than facilitating a more evenly spread five gears, including a fourth gear that is usable in towns, a fifth gear that will pull from about 40mph – and preferably also a second gear that will give an easy start on the level. Sixth should be high enough to be used solely for motorway travel at 60 to 70 mph, in the absence of a strong headwind. Too much is surely made of the supposed nuisance of having to drop down into fifth gear on steep hills or in heavy traffic?
J R Turner
I’m somewhat surprised, John, that you have managed to escape owning/driving a six-speed transmission car, as they’ve been around for a good while now. The example given in Back to Basics compared a 1.6-litre diesel with a 2.0-litre diesel and was intended to highlight the fact that a bigger engine can pull a higher top gear, and thus often be as economical, or better than, the same car with a smaller engine, in certain types of motoring. I’m generalising here, without too many facts to hand, but I think that most “family” cars tend to go the economy route, with gearing set to optimise fuel consumption. But with “performance” cars, or sporty model variants, acceleration and road performance are usually optimised, which means offering a closer set of (almost inevitably) six gears, with no obvious gaps, allowing seamless acceleration. Of course such performance motoring is a little unseemly these days, and one rarely has the opportunity to so indulge without causing inconvenience or offence to other road users, or the threat of a speeding ticket!
With the wide spread of torque of a diesel engine though, surely it should not be too difficult to have the best of both worlds, with six speeds? There’s surely little to be gained in UK motoring, with a 70mph speed limit, by offering an extremely high top gear, where you may need to change down for headwinds and hills on motorways. Do German market get cars with longer gears, to take account of the high motorway cruising speeds allowable, I’m wondering? I think it’s probably most unlikely. I’m possibly sitting on the fence here John, but I’m happy enough to change down to fifth on a motorway in difficult traffic circumstances, to have suitable power available to accelerate away from potential trouble, but I don’t think sixth gear should be so high (in a UK context) as to require dropping down from sixth to fifth for a steeper hill or strong headwind. But then those circumstances are far less likely with the extra power and torque of a bigger engine – say one of 2.0-litres rather than 1.6-litres.
I’m not sure I’ve really added much to the debate, and I haven’t mentioned eight-speed and future nine-speed automatic transmissions, which are justifiable on the grounds of better fuel economy, and have extremely high gearing in the upper ratios. If we could drive as well as these computer controlled automatics, six speed manual transmissions would be universally specified, save for city cars, where five are quite adequate. Of course neither of us has mentioned CVT transmissions, which allow a very wide ratio spread, but don’t always seem to produce the hoped for remarkable fuel consumption in cars fitted with them. Nissan has a new CVT transmission available on the new Qashqai with the rather excellent 1.6-litre dCi engine, but I’ve seen no reports on it yet.