Lower speed cuts petrol consumption

WITH reference to Peter Horton’s letter (Yorkshire Post, May 31), he bases his argument on a falsehood; that at constant revs the engine gives the same power and fuel consumption. Pedal position determines the fuel flow, not revs. Presumably, he chose 1,500 as it is the engine’s sweet spot, but this gives the best efficiency of use of any fuel flow rate, ie, it maximises the power from the fuel sent by the pedal.

Start with a stationary car, not in gear. A gentle touch on the pedal gives 1,500 revs but with very little fuel used or power developed, merely sufficient to turn over the engine against internal friction.

In first gear, again little fuel is used at 1,500 revs (on the level, no potholes, no acceleration) since at very low car speed the air resistance is negligible. The low power is used to overcome internal engine friction, plus that of other moving parts such as the gearbox and wheels; call these frictions added together machinery-friction.

Machinery-friction mainly depends on revs, and when averaged changes little with car speed, because use of the gears prevents over-revving as you speed up.

Air resistance in contrast rises quickly as speed rises (stick your hand out from 0-70mph!) At roughly 20mph air resistance equals machinery-friction. Hence when well above 20 the fuel is being used almost entirely to overcome the now vastly greater and dominant air resistance.

Cutting speed from 70mph to 45mph should very roughly halve your fuel consumption. At 15mph, you have entered the zone where machinery-friction is dominant, and at constant revs more fuel would indeed be needed for a slower journey.

While on the subject of saving fuel, a car with gears is a fuel-wasting dinosaur because of the varying revs. It could be designed as for diesel-electric trains, where the diesel engine runs continuously at sweet spot revs for fuel economy, the engine generating electricity to drive an electric motor, so avoiding the need for a gearbox.

Public needs protection

From: William Snowden, Butterbowl Gardens, Farnley Ring Road, Leeds.

YOUR Editorial comment “Scales of Justice” (Yorkshire Post, June 8) is guilty of sophistry and condescension.

The central premise that “prison is not working” is fallacious: prison does work, for the simple but irrefutable fact that the criminal is no longer at liberty to commit further crimes.

Far from reforming criminals or, indeed, deterring potential criminals, so-called “community sentences” will serve only to encourage them, because they would have even less reason to fear the consequences of being caught than they do at present. This flawed concept is a non-sequitur.

There is nothing “liberal” about pursuing policies that undermine justice and the public’s confidence in the rule of law. It is not the role of politicians, but that of judges to determine the appropriate sentence, based on the nature and severity of the crime, and the criminals.

Kenneth Clarke should remember that the primary duty of government is to protect the public.

Football’s game plan

From: Trev Bromby, Sculcoates Lane, Hull.

REGARDING Sepp Blatter and the Fifa fiasco, there is a golden opportunity to drive the proverbial stake into the heart of this multi-million pound worldwide madness (Bernard Ingham, Yorkshire Post, June 8).

Urge the sponsors to ditch their dosh from the corrupt, overrated game that is loved by thousands and thrust on to millions who can’t stand it.

Bring the overpaid prima donnas back into the real world. Wages reach £250,000 a week, yet numerous clubs are millions of pounds in debt to pay the wage bill.

The inequality in pay from one end of the field to the other is nothing short of criminal. The tax man is always last on the list for payment.

When, or if, this game ever returns to the halls of reality, make them ditch the outdated offside rule. The boots, balls and players are lighter than yesteryear, and pitches are no longer quagmired. Give it its own secluded TV channel please!

Hooray for Hannah

From: Janet Davies, Mcrae Court, Padbury, Perth, Western Australia

I LOVED your recent story about Hannah Hauxwell. I have her books and video and lived in Leeds when she was on the TV.

There are some things you that never forget and seeing your story about this lovely lady took me back.

Thank you from a Yorkshire lass down under.