Q We’re planning a driving holiday in France. I hear there are more speed cameras there now and that the gendarmes are cracking down on speeding. I have been told radar speed trap detectors are illegal. Is this true and, if so, is there another way to gain advance notice of cameras? - GW from Nottingham

A The smug answer is not to exceed the speed limit, but it’s easy to wander slightly above the maximum, especially when you’re mentally swapping mph and kph. Radar (or laser) detectors (détecteurs de radar) are illegal in France and if you carry one, even in the boot, you could be fined up to €1,500 (£1,192) and the device (and in some cases even your car) could be confiscated.

However, a speed trap locator (avertisseur de radar), is legal. Unlike radar detectors, these cannot pick up the beams from speed cameras or the handheld speed detectors used by police officers. Instead they contain databases of fixed and mobile speed trap locations and give advance warnings using a GPS receiver.

All the main speed trap locator manufacturers claim to have full European databases and you can view them at Pogo (www.pogogps.com ), Road Angel (www.blackspot.com ), Road Pilot (www.roadpilot.co.uk ) and Snooper (www.snooperuk.com ).

Some sat navs also contain speed trap locations, as do some road atlases, such as the AA Easy Read France at £12.99 (from bookshops or www.amazon.co.uk ), although it does not include mobile speed trap areas.

Go to www.controleradar.org for a full list of camera sites and types in France. Click on the British flag in the top right-hand corner to get the text in English.

Although it is legal to use radar detectors in the UK, there is a provision to ban them in the Road Safety Act recently approved by parliament. However, this particular part has yet to come into force. It is unclear when they will be outlawed but it is likely to be before the end of the year.

QI often take my grandchildren out in my Ford Focus C-Max. Is it safe to carry a six-year-old on a booster seat in the front and do I need to have the front passenger airbag disabled? A Ford dealer said I could have a switch fitted to disable the airbag but it would cost £300. - From LS of London

A Children are best carried in the rear, but if you are the only adult in the car, sometimes it is less distracting for you and more reassuring for the child to be in the front.

In this case you should always use a booster and move the passenger seat well back on its runners away from the airbag. However, there is no need to switch off the airbag - as this rule applies only when using a rear-facing infant carrier on the front seat.

Unlike some other family cars, the C-Max does not have an airbag cut-off switch fitted as standard. It is a dealer-fit item, listed in the accessory brochure, and cannot be installed on models with front and rear park assist.

Q My son will be 17 in six months and I need to change my car in the next month or two. I can’t decide whether to buy the car I want, something like a Volvo V50 estate or VW Golf, and get my son a low-powered car to learn to drive in (insured third party), or whether it would be better to buy one car for both of us and put him on my insurance. Can you suggest cars with good performance, reasonable space and reasonable fuel consumption? - TM from Yorkshire

AThis is a dilemma faced by many parents and there’s no hard and fast rule. We’d recommend you get some insurance quotes on the cars you are considering first, as this could be the deciding factor. You could try price comparison websites such as www.moneysupermarket.com or www.confused.com .

The best solution could be to buy a modestly powered car that you can share while your son is learning to drive. You could then pass this on to him when he has passed his test and turned 18 (which should reduce his insurance premiums, even if only slightly), allowing you to buy a higher-powered car in 18 months’ time and enabling your son to start building up his own no-claims bonus on his insurance.

You’ll need to keep to the lowest insurance group you can. The following medium-sized cars are all group 4 to insure: Mazda3 1.6 S, Peugeot 308 1.4 VTi, Volkswagen Golf Plus 1.4 Luna, Honda Jazz 1.4 i-DSI, Renault Scénic 1.4 dCi and Vauxhall Astra 1.3CDTi. The diesel models will give you the best fuel economy while the Golf Plus has the largest boot at 505 litres.

QI plan to visit British Columbia and Alberta, Canada, next year and will need to hire a car. I have heard hirers are loath to rent to older drivers. Do I need to get the holiday in before I turn 70 next June? - GB from London

ARental firms are indeed less likely to offer vehicles to people aged 70 or over. According to the British Vehicle Rental and Leasing Association, the problem lies with insurance companies, not its members.

Drivers over 70 and under 25 are generally considered a higher risk by insurers and therefore incur higher premiums. Some car rental firms therefore restrict their loans to the over25s and under70s rather than pay higher insurance costs.

The good news is that Budget (www.budget.co.uk ) and Europcar (www.europcar.com ) will cover you up to the age of 75 and both companies operate in the areas of Canada you plan to visit.

QI am about to buy a new car and would like a black model. However, I live in a hard water area and find the water leaves marks on dark paintwork. Should I just give up and buy silver? - KH from Reading

ARegardless of whether you live in a hard or soft water area, tap water contains chemicals (such as chlorine or fluoride) that mean it can dry with a white tinge.

One easy way to avoid this is to wipe the water off quickly with an absorbent cloth. The Halfords Easy Glide Chamois XL at £6.99 (0845 762 6625, www.halfords.com ) is an award-winning synthetic chamois and soaks up huge amounts of water because it’s so large.

If you want to go further, you can buy a water filter, such as the one marketed by Ionic systems (08452266 001, www.ionicsystems.com/cars ). This fits easily onto your garden hose. As the water passes through the filter, the chemicals are purged, leaving pure water and a streak-free finish (though you should still remove excess water). It costs £47.29 including UK carriage and typically lasts for 20 washes, depending on the size of the car.

Avoid continuing general paint damage by using microfibre cloths for washing and polishing (rather than scratchy old rags). In testing, Farécla Smart Edgeless Cloths (01920 465 041, www.farecla.co.uk ) did particularly well. They cost about £8 for a pack of two.

QI am planning to buy a BMW but can’t decide between a 3-series automatic with about 30,000 miles on the clock for £13,000 and a 5-series manual with about 48,000 miles for £14,000. Both are 2005 models. Which will be worth more in three years’ time? - EM from London

AFuture values are difficult to predict. The rise in the cost of diesel has recently started to affect the residual values of diesel-engined cars, for example. However, barring any unforeseen changes in the market, CAP, which provides valuations to the motor trade, predicts that both BMWs you mention will have similar residual values.

In three years’ time and with another 36,000 miles on the clock, the 3-series would be worth £6,500 while the 5-series would be worth £7,000. Your choice should rest on which car best suits your needs in terms of space and driving characteristics. Also, assuming the two have similar-sized petrol engines, your fuel consumption would be slightly lower in the 3-series, as would your insurance premiums.

Please e-mail your questions for our experts to carclinic@sunday-times.co.uk or write to Car Clinic, InGear, The Sunday Times, 1 Pennington Street, London E98 1ST. Please supply us with a daytime telephone number and as much detail about your car as you can. We cannot send personal replies or deal with every letter, so please do not send original documents or SAEs. Advice is offered without legal responsibility.