A When people talk about car sharing, they usually mean sharing a lift with somebody driving the same route on a regular basis. London Liftshare (www.londonliftshare.com) has 118,000 people using the scheme in the capital alone. North London’s car share scheme (www.northlondontransport.org) can link you to several thousand commuters either looking for or offering lifts, or try National CarShare (www.nationalcarshare.co.uk).

Alternatively, if you want access to cars you can drive yourself on a short-term hire basis, a car club is more suitable. London-based Streetcar (www.streetcar.co.uk) is free to join and allows you to book a vehicle instantly either by telephone or on the internet. The minimum hire period is 30 minutes and the hourly charge is £4.95. The first 30 miles of fuel costs each day are free; additional mileage is charged at 19p per mile.

The club has more than 150 cars and just over 5,000 members and claims there is a “95% chance” a car will be available at any given time. Cars are left in designated parking bays at 70 locations around London and unlocked using a smart card that is pressed against a sensor on the windscreen. Entering a pin number into the radio keypad starts the engine. Loans can be extended for weekends or longer. A 30-day hire costs £695. There are no restrictions on how far you take the car within the UK and breakdown cover is included. Streetcar also operates in Brighton and Southampton.

WhizzGo (www.whizzgo.co.uk) and CityCarClub (www.citycarclubs.co.uk) operate a similar system from £2.80 per hour in the capital.

Q I have an Audi A4 that had its first service when the service indicator demanded. The next month I got a card from the garage saying the brake fluid was due to be changed. How frequently should brake fluid be changed, and why isn’t it tied in with the servicing? — DP from Macclesfield

A Audi operates a servicing system called LongLife whereby the optimum time between services is calculated by the on-board computer based on the way the car is driven. A light on the dashboard then tells the driver when to take the car in for its service.

However, regardless of when the car is serviced, Audi, in common with most manufacturers, recommends a change of brake fluid every two years.

We imagine what has happened here is that your LongLife service reminder appeared just before the two years was up. At the two-year marker Audi dispatched the standard notification about the brake fluid. This highlights the

problems of relying totally on computers and automated systems. At one time the mechanic working on your car would have realised the brake fluid change was due shortly and suggested you might as well have it done at the same time as the service.

This would have saved money and inconvenience in terms of dropping the car off, collecting it, possibly taking time off work, etc. You’ll now have to take the car in for a second time. In future you might prefer to revert to conventional annual servicing periods (Audi will allow this), ensuring fluid changes fall at the same time.

Q I have a Renault Espace with a digital dashboard. Speed is indicated in mph in large digital figures in the centre of the display. I am planning to go to France later this year and would like to see my speed in kph. Can I get my dashboard display switched to kph? — PL from Shropshire

A All Espaces with digital readouts can be changed from mph to kph and back. The details are in the vehicle handbook.

With the ignition switched off, press and hold the button on the end of the right-hand steering column stalk and press the engine start button. The speedo will flash for a few seconds then the new measurement will be displayed. Release the button on the steering column stalk and the job’s done. Repeat the process when you want to switch back to mph..

Q I have been driving Saabs, mainly the 9-5 or equivalent, for many years and find there is a good deal of tyre noise. As speed cameras and penalty points, to say nothing of a geriatric sense of responsibility, have killed off the boy racer in me, what tyres would you suggest for someone who now puts a quiet life at the top of their wish list? — RB from Dublin

A You’re not alone in finding tyre noise a problem, and most manufacturers now include it as one of the key factors (along with grip and longevity) when developing new tyres.

We spoke to Black Circles (0845 200 0022, www.blackcircles.com), an internet tyre specialist. It advised that directional tyres (which have to be fitted to a specific side of the car as denoted by arrows on the sidewall), tend to be noisier, so should be avoided where possible.

The new Dunlop SP Sport 01 is considered to be one of the quietest tyres available while still offering good grip levels and long life. They’re about £104 each. A good budget buy would be the Hankook Ventus — about £65 each. Prices include Vat and fitting.

Q I own an X-reg VW Beetle 2 litre automatic. I love most things about it except its thirst (26-29mpg). Can you suggest an economical (maybe diesel) alternative automatic with some character? I also need enough room to carry my golf clubs — GP from Nottingham

A The combination of diesel power and an automatic gearbox is relatively rare, although with improvements to the power and refinement of diesel engines and automatic transmissions it is likely to become more common.

The new Mercedes-Benz A-class offers the option. An automatic A 160 CDI three-door Classic starts at £15,945 and returns 52.3mpg combined. Or take a look at the latest Seat Leon 2.0 TDI DSG. It costs £17,295, has 140bhp under the bonnet and returns 48.7mpg in the combined cycle with a sprightly 0-62mph time of just 9.3sec.

Q I want to buy a five-door hatchback automatic that is economical on petrol, has lots of space for luggage or shopping and costs no more than £15,000. What would you recommend? — MGH from London

A The new Nissan Note could fit the bill. A 1.6 litre SVE auto costs £13,395 and comes with a long list of standard equipment including air-conditioning, alloy wheels and part leather seats. The boot is a reasonable 280 litres with excellent depth and it does 40.4mpg in the combined cycle.

We’d also suggest you look at the Ford Focus. It comes with a range of engines and specifications but you should consider the 1.6 Zetec five-door auto at £15,195. It returns 42.2mpg (combined cycle) and has a huge 367-litre boot. A large dealer network with reasonable servicing costs and a three-year/ 60,000-mile warranty support both cars.

Q I have just bought a 2002 Audi A3 with 15,000 miles. The dealer is offering a comprehensive RAC one-year warranty for £500. Is it worth the money or are Audis reliable enough to take a risk? — TH from Birmingham

A As with all such warranties, it’s a gamble. If the car behaves, your premium has bought you nothing tangible although you will have had the benefit of peace of mind. Of course, if it doesn’t and blows a turbo or wrecks its gearbox, you’ll be breathing a huge sigh of relief.

You’re right to say that Audis are well built and generally reliable and the mileage is extremely low, but nevertheless it wouldn’t take much to go wrong for you to recoup your premium.

Aftermarket warranties are often much more restrictive than those provided by manufacturers on new cars, so make sure you know what the policy covers and, more importantly, what it doesn’t cover. Some require that you service with a specific dealer, which can work out as expensive.

Although the price seems fair, it’s worth checking at least one more company for a comparison; try a warranty specialist such as Warranty Direct (0800 731 7001, www.warrantydirect.co.uk). The Office of Fair Trading has some useful information on its website at www.oft.gov.uk.

E-mail your questions for our experts to carclinic@sunday-times.co.uk or write to Car Clinic, Driving, The Sunday Times, 1 Pennington Street, London E98 1ST. Please give a daytime telephone number. We cannot send personal replies or deal with every letter. Please do not send original documents or SAEs. Advice is offered without legal responsibility.