Data Sheet

#24 Choosing a tow car - which transmission for towing?

#24 #24 Choosing a tow car - which transmission for towing?

WEB Subaru Forester XT with Lineartronic

Transmission options - manual or automatic which is better for towing?

There are pros and cons to manual, automatic and semi-automatic gearboxes when towing. Let this guide help you choose. Benefit from free tow-matching when you join the Club.

One of the most important decisions to make when choosing a tow car is the type of gearbox. Provided you have well-matched car and caravan (see the Matching Car and Caravan Data Sheet at https://www.campingandcaravanningclub.co.uk/datasheets), and decided whether a petrol, diesel or hybrid engine best suits your needs (see the Which Fuel? Data Sheet), choosing between a manual and automatic transmission is probably next on your to-do list.

The choice you make may alter the car's kerbweight, legal towing limit and noseweight limit. Fuel economy will be affected, too, as will the ease with which you can start a car on a hill. In some cases, your choice of gearbox could mean it is wise to check with the dealer whether any additional cooling is required while towing to avoid overheating.

With some vehicles, the decision making does not end with the gearbox. It may be that your chosen tow car is available in two-wheel-drive and four-wheel-drive versions, in which case you will need to decide which suits your needs. Four-wheel drive may seem the obvious choice for towing a caravan or trailer, but the reality is not necessarily so straightforward.

Why choose a manual gearbox for towing?

The majority of new cars come with manual gearboxes. An automatic - if one is available - will usually be an extra, costing around £1,500.


So, a manual gearbox has the advantage of being cheaper to buy. As a rule it's also cheaper to fuel. For example, a 2020 Ford Galaxy 2.0 150PS EcoBlue six-speed manual returns 39.2-52.3mpg on the combined cycle, The same car with an eight-speed auto achieves 33.6-49.6mpg. That's enough to keep an extra £252.05 in your pocket for every 10,000 miles of driving (based on a diesel price of 130.4p per litre). As well as being more fuel-efficient, cars with a manual gearbox usually emit less carbon dioxide (CO2) than autos. In the Ford's case, the manual emits 134g/km, the auto 140g/km (both figures are for cars with 17-inch alloy wheels).


There are sound reasons to prefer the way a manual drives, too. It gives the driver direct control over the gearbox, so he or she can always select the appropriate ratio at the bottom of a hill or before overtaking. This control over gear selection also means drivers can use engine braking to control the outfit's speed when towing downhill.


Some automatics hunt around between ratios when towing, which can be annoying. With a manual gearbox, the driver is always in charge so this cannot happen.Manuals and automatics often have different towing limits. It's more common for the manual's limit to be higher, but that's not always the case. Take the Galaxy 2.0 150PS EcoBlue, which has a 1,800kg limit as a manual and a 2,000kg maximum as an auto.However, a 2020 Hyundai Santa Fe 2.2 CRDi 4WD has a 2,500kg maximum as a manual, that drops to 2,000kg for the auto.

 


So the only surefire way to know if the manual or auto version has the higher limit is to check. While the difference between a legal maximum of 2,500kg or 2,000kg may be of little practical difference to most caravanners, as the majority of tourers weigh less than two tonnes, it becomes more significant if the change in legal maximum makes towing impractical. For example, a Honda Civic 126hp VTEC manual has a towing limit of 1200kg, but that drops to 800kg for the auto, making it unsuitable for all but ultralight tourers.


It is also worth noting that some manufacturers reduce the maximum download on the towball for automatic models in line with the reduced legal towing limit.


Why choose an automatic gearbox for towing?

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A typical automatic selector with manual override on the left

If manuals are cheaper to buy, more fuel-efficient and may have higher legal towing limits than the same car with an automatic gearbox, why would you choose an auto?

Despite the advantages of a manual gearbox, there are many reasons why an automatic may suit you better. For one thing, automatics are generally slightly heavier than manuals, which benefits a car's matching ratio. In the case of the Ford Galaxy, the difference is 11kg. That pushes  the 85 per cent match figure up by 9kg, although really that's unlikely to be enough to sway a tow car buyer one way or the other.

A more compelling reason is that autos make driving easier and more comfortable, in daily use as well as when towing. In stop-start traffic an auto box spares the driver the chore of working the clutch pedal. Even when traffic is moving freely, leaving the gearbox to change gear for you makes towing a more relaxed experience.

Hill starts are more straightforward when driving a car with an automatic gearbox. There is no need to juggle the clutch and throttle pedals, you just release the parking brake and accelerate away.


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Jaguar 10 speed gearbox

It is a similar story when manoeuvring on a campsite. A gentle right foot on either the accelerator or brake is all that is needed, with no need to slip the clutch as you do when driving a manual car.

Although easy to drive, some drivers feel an auto does not give such precise control over the car, swapping gear ratios at inopportune moments or holding on to a high gear when towing down a steep hill, where engine braking would be a useful aid to stability.


This makes it important to select the ride mode for towing. There won't be a specific towing setting, but many autos have winter or sport modes. Often the 'sport' setting rather than 'drive' makes best use of the engine's performance. If the 'box tends to dither or allow the engine to labour, swapping to the sport mode will keep the car in a lower gear for longer and it will change down more readily when accelerating. This can be useful when towing uphill or overtaking, making it easier to hold speed on a gradient or accelerate promptly when required Almost all autos have a manual override function. Usually accessed by moving the lever sideways then pushing it forwards to change up or pulling it back to change down, this gives the driver control over gear selection. Some cars also have paddles behind the steering wheel, so the driver can change gear without having to take a hand from the wheel.

To a large degree this gives the driver the best of both worlds, with the convenience of an auto but the control of a manual.

As well as involving the driver more in recent times, automatic gearboxes have also improved in terms of efficiency. While it is still true that in most cases automatics are less economical than manuals, there are a handful of modern automatics that beat the fuel economy figures of their manual equivalents. Some automatic - boxes now have eight, nine or even ten forward gears, which means the engine spends more time operating in the most efficient part of the rev range. Having so many ratios also allows for a very high top gear for motorway cruising without any loss of performance. Modern torque converters lock-up at speed to prevent any power-sapping slip, while designs have become lighter and electronic control over the behaviour of the gearbox (and the engine, while the box changes gear) has become ever more sophisticated.

Take a 2020 BMW 318d Saloon as an example. The six-speed manual version emits just 109g/km of CO2, whereas the manual emits 113g/km. In practice there will be very little difference in the fuel economy a driver would achieve in everyday driving or while towing.


 

 

Why think twice about towing with an auto?

Not all reservations about automatic gearboxes have been fully addressed. Research by mechanical breakdown insurance provider, Warranty Direct, suggests autos are not as reliable as manuals. After analysing its 50,000 policies in 2013, Warranty Direct found that a claim to repair an auto cost an average of £1,070.49, while manuals cost £824.28. Not only did the research show that automatics were more expensive to repair, it also found they need attention more often. One in 80 automatics had suffered a problem in the previous 12 months, compared with one in 180 manuals.


Warranty Direct's study made no distinction between cars used for towing and those which were not, so it is possible the difference in reliability could be more marked among tow cars. Overheating automatic gearboxes has long been a worry for tow car drivers. Today, most automatic cars can tow without any great risk of overheating so long as the legal towing limit is respected.


Bill McDonough of independent gearbox specialist, Hardy Engineering, sees no reason to fit extra cooling to a modern automatic when towing. "We're not seeing modern vehicles with burnt out parts and a tow ball on the back," he says. "Although with vehicles from 15 years ago or more, additional cooling can't hurt."


If you do choose to fit additional cooling to an older car, the Federation of Automatic Transmission Engineers (www.fedauto.co.uk) will be able to point tow car drivers in the direction of a local specialist.


It is common to hear members comments that auto gearboxes are sealed for life so no oil or filter changes are needed. This can be misleading as the oil will degrade over time and debris due to the normal operation will collect in the filter. It is our understanding that this comment relates to normal use while within the life of the warranty, not the life of the vehicle and maybe the reason why autos reliability is questioned on used vehicles. 

It's worth checking your car's handbook and servicing schedule or speaking to the gearbox maker about any specific recommendations around towing and gearbox maintenance, For example, the German gearbox maker, ZF, recommends transmission oil changes every 80,000 miles or eight years, but warns that "many trips while towing a trailer" may lead to higher operating temperatures, ageing the oil sooner. So it's worth asking for the condition of the transmission oil to be checked when the car is serviced.

 


Something else to keep in mind: before choosing an older used car with the intention of towing, it's worth checking if the car comes with enhanced engine and gearbox cooling for cars that are ordered with a factory-fit tow bar. Otherwise identical cars that are subsequently fitted with aftermarket tow bars will not have the same cooling and could be more prone to overheating.

Fitting a tow bar to such a car without additional cooling could invalidate the original manufacturer's warranty if the car then develops a fault with the engine or gearbox. It is usually possible to retrofit the additional cooling but this can be a significant extra cost, sometimes thousands of pounds.

As a precaution, it is always worth checking with a car manufacturer if it recommends additional cooling if you are buying a used automatic car and plan to fit a tow bar. This is the only real exception to the rule of thumb that modern autos can tow quite happily without modification.


Towing with a semi-automatic transmission

Conventional automatic gearboxes use a torque converter (a type of hydraulic coupling) rather than a clutch to transmit the engine's power through the gears. However, semi-automatic transmissions are effectively mechanised manuals - they still have a clutch, but no clutch pedal since gear changes are electronically controlled.

WEB VW Golf DSG gearbox

VW DSG gearbox

In most respects this type of gearbox feels much like a normal automatic from behind the wheel. Leave the car in drive and it will change gear with no intervention from the driver. As with a modern auto, there is usually a manual override using the gear lever or paddles behind the wheel.

Some gearboxes of this kind use a single clutch like a conventional manual gearbox. Others, like the Volkswagen Group's Direct Shift Gearbox (DSG), use a dual-clutch and are effectively two gearboxes in one. The odd gear ratios are in one half of the gearbox, the even ratios are in the other. The next ratio is pre-selected, which makes for very quick gear changes. The best DSG-style systems change gear smoothly as well as quickly.

Different car makers use other names for their semi-automatic transmissions, but examples include Audi's S tronic, BMW's M DCT, and Ford's PowerShift.

WEB Lexus IS paddle_shift

Semi-autos are generally more efficient than a conventional torque- converter automatic, with less power loss leading to improved fuel economy. However, in recent years conventional autos have improved hugely so the fuel economy benefits of a DSG-style gearbox over a regular auto are not as pronounced as they used to be.

Whether a semi-automatic is more or less fuel-efficient than the manual equivalent depends on the particular car, the number of forward gears and the gear ratios chosen. But more often than not, it's slightly less economical than the manual. For example, a 2020 Volkswagen Passat Estate 2.0 TDI 150PS manual can achieve 54.3-57.6mpg on the combined cycle, compared with 51.4-55.4mpg for the DSG.


The legal towing limits for the same car with a manual or a semi-automatic gearbox are often the same, but it is always worth checking.

 

 

 

 


Towing with a CVT

As well as torque-converter automatics and semi-automatic transmissions, some cars are fitted with Continuously Variable Transmissions (CVTs). These use variable diameter pulleys to alter the gear ratio.

Subaru favours this kind of automatic transmission, and calls it Lineartronic. Audi has offered CVT transmissions, called Multitronic, in the past, although it now favours the DSG-style S tronic transmission instead. Honda fits CVT transmissions to some models, without a fancy name.

WEB Subaru Forester XT with Lineartronic

In theory, CVTs offer exceptional efficiency. Instead of jumping between stepped ratios, the gearing of a CVT varies continuously, as the name implies. This should mean the engine is always working at the optimum revs for either economy or acceleration.

In practice, CVTs take some getting used to. Press down on the throttle and the revs suddenly rise, then stay constant as the gear ratio adjusts to build acceleration. It can seem disconcerting for the engine to hold the same revs as the car gains speed, and means the volume of engine noise rises abruptly then dies away again just as quickly when the driver eases off on the throttle.

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A modern CVT drivebelt

Partly to address this, many CVTs have manual overrides with set ratios to mimic the behaviour of a normal gearbox. Some also use set ratios if the driver is accelerating hard, and behave as a conventional CVT on a light throttle.

They're certainly not for everyone, but, once used to their foibles some drivers become firm fans of CVTs' efficiency and smooth power delivery.

This type of transmission used to have a poor reputation for reliability, but recent designs are more robust and can have high towing limits. For example, the 2020 Subaru Forester e-Boxer has a 1,870kg limit.

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Nissan Xtronic CVT gearbox

CVTs are commonly used in hybrid cars, which combine an internal combustion engine with electric power. Lexus uses an E-CVT as the transmission in its NX hybrid SUV, for example. The 4x4 version of this car has a respectable 1,500kg towing limit. Power from the petrol engine only ever goes to the front wheels, but an electric motor can add drive to the rear wheels when needed. This cleverly makes the NX a 4x4 with no need for a driveshaft running from the petrol engine to the back of the car.




 

Should I tow with a 4x4?

Whatever style of gearbox is chosen, four-wheel drive has many advantages for towing.

The most obvious is the extra traction of a four-wheel-drive system. Because the engine's power is split between four wheels rather than two, the wheels are less likely to spin. It means a four-wheel-drive car will be better able to tow away from a muddy pitch. Low ratio transfer - boxes are a great help with this kind of low-speed manoeuvre, but electronic driver aids are increasingly taking the place of this form of mechanical help.

Do not forget, it is not just on rough ground or off-road that there is a benefit to four-wheel drive. The added traction is noticeable on tarmac, too, especially in wet weather.

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Mazda four wheel drive system

Another advantage is the extra weight of a 4x4. The 2020 Hyundai Santa Fe 2.2 CRDi 2WD has a minimum kerbweight of 1,825kg in two-wheel-drive form. The 4x4 weighs at least 1,890kg. So, an all-wheel-drive (AWD) car generally has better traction, onand off road, and will weigh more than a two-wheel-drive equivalent. However, an AWD model will also cost more to buy: the Santa Fe 4x4 is £1,810 more expensive than the front-wheel-drive model.

An AWD model will be less fuel efficient. In the Hyundai's's case, economy worsens from 43.5mpg to 41.5mpg. That makes for an extra £65.867 in fuel costs over 10,000 miles, based on a diesel price of 130.4p per litre.


The penalty at the pumps is not as big as it used to be, partly because many 4x4 systems operate as two-wheel drives until sensors detect the driven wheels are slipping. This can be a mixed blessing, though, as there is sometimes a slight delay while the front wheels struggle for grip before power is sent to the rear wheels as well.

Others 4x4s have selectable four-wheel drive and can be driven in two-wheel-drive mode until AWD traction is needed. However, even if a car is nominally two-wheel drive most of the time the extra weight of the four-wheel-drive hardware will take its toll on fuel economy and carbon dioxide emissions.

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GKN AWD running gear as fitted to 2016 Volvo XC90

Go for a big SUV-style 4x4, as opposed to a hatchback or estate with AWD, and you can usually expect a high kerbweight and towing limit. Always check before you buy, though. For example, it is easy to be caught out by a surprisingly low noseweight limit. Although many 4x4s have limits of 100kg or more, a 2011 Kia Sorento automatic has a noseweight limit of just 80kg.

On balance, should drivers choose a 4x4 for towing? If you tow regularly in all weathers and frequently stay on grass pitches, four-wheel drive is probably worth the extra purchase price and higher running costs. But even for a four-season caravanner, AWD is not essential. If you mostly restrict your touring to spring, summer and early autumn - specially if you favour hardstanding pitches - you should be fine with a two-wheel-drive car.