Every driver around the world has had their wallets feeling lighter and lighter as we all witness the dramatic increase in gas prices. To the producers of the so called “Gas Saving” additives saw this as a golden opportunity to load up their bank accounts. By all means, I am not saying that the additive issue is a complete myth; however, you should educate yourself, and think twice before investing a dime into an additive.
It is in human nature to fall for fancy, scientifically sounding marketing campaigns, but beware, and do not allow advertisers blind you by science. Think rationally, not emotionally. Hence, research lead to a conclusion that FTC (Federal Trade Commission) in warning consumers of any gas-saving claims for oil and gas additives. It has been concluded that even those additives that do indeed save gas, the savings rarely pays for the price of the bottle.
If you were to search the internet for such products, you are about to encounter awakening statements, those that advertise for quote on quote breakthrough the chemical and physical properties of gasoline. You are about to read testimonials stating overall savings of anywhere between 12 to 25 percent. Something that a lot of consumer don’t think of is that, industry leaders, that dedicate billions of dollars annually for research and development do not claim to have such products” why is it, every amazing product made by names never heard of?”
On an ending note, I would like to mention that the USEPA (United States Environmental Protection Agency) has yet to find a product that improves gas mileage notably. The EPA has evaluated over a hundred products that claim to be gas savers, and the results proved otherwise. This is only the first of a series of articles dedicated to educating the consumers on gas additives. Hence, those that really protect your engine and others that hurt the engine.
Saturday, July 28, 2007
Thursday, July 26, 2007
Auto Maintenance - The Money Saver
Taking care of your auto and spending a little money on it now will save you money in the long run.
How true the expression “pay me now or pay me more later is”. For instance;
Spend a little extra money to do the wheel alignment if your tires wore out from uneven wear. If you don’t the new tires will wear out prematurely and you will spend more money on tires again.
Replace those spark plugs and wires as suggested by your auto manufacturer. It’s cheaper to do it as maintenance than develop a misfire or break down on a long trip causing more expensive damage plus inconvenience.
Change that oil every 3 to 4 thousand miles to keep the engine clean. Dirty oil creates sludge and lessens gas mileage not to mention major engine repairs for lack of maintenance.
Check those brakes. Brakes usually last 30 thousand miles in the front and somewhat longer in the rear. It is much cheaper to replace the brake pads and shoes when they are getting thin rather than wait until they are metal on metal and ruin the drums and rotor.
If the car drifts one way or another and/or the steering wheel shakes while driving it should be check very soon. This condition can cause other components to wear plus it is a safety issue.
A “check engine” light on, misfire, stalling condition, or hesitation should be checked immediately. These symptoms can rapidly cause other damage and can lead to very expensive repairs if ignored.
Many of today’s autos have timing belts. These are of the same basic materials that the other drive (fan) belts are made of. The timing belt is probably one of the more expensive and more important maintenance items you will have to do. Follow your manufacturer’s time and mileage recommendations for this service. Many of today’s engines are called “interference engines”. This means if your timing belt skips or breaks the valve and pistons are no longer in sync and will hit each other causing very extensive damage internally to the point of having to replace the complete engine itself. A timing belt is a VERY IMPORTANT SERVICE.
With all of the expenses we occur in today’s age it is very easy to put off auto maintenance because there is always tomorrow. Unfortunately tomorrow may be the time you are on a long trip for vacation and the car breaks down. This may very well be MUCH more expensive to repair than what it would have cost for routine maintenance not to mention a vacation cut short and ruined.
How true the expression “pay me now or pay me more later is”. For instance;
Spend a little extra money to do the wheel alignment if your tires wore out from uneven wear. If you don’t the new tires will wear out prematurely and you will spend more money on tires again.
Replace those spark plugs and wires as suggested by your auto manufacturer. It’s cheaper to do it as maintenance than develop a misfire or break down on a long trip causing more expensive damage plus inconvenience.
Change that oil every 3 to 4 thousand miles to keep the engine clean. Dirty oil creates sludge and lessens gas mileage not to mention major engine repairs for lack of maintenance.
Check those brakes. Brakes usually last 30 thousand miles in the front and somewhat longer in the rear. It is much cheaper to replace the brake pads and shoes when they are getting thin rather than wait until they are metal on metal and ruin the drums and rotor.
If the car drifts one way or another and/or the steering wheel shakes while driving it should be check very soon. This condition can cause other components to wear plus it is a safety issue.
A “check engine” light on, misfire, stalling condition, or hesitation should be checked immediately. These symptoms can rapidly cause other damage and can lead to very expensive repairs if ignored.
Many of today’s autos have timing belts. These are of the same basic materials that the other drive (fan) belts are made of. The timing belt is probably one of the more expensive and more important maintenance items you will have to do. Follow your manufacturer’s time and mileage recommendations for this service. Many of today’s engines are called “interference engines”. This means if your timing belt skips or breaks the valve and pistons are no longer in sync and will hit each other causing very extensive damage internally to the point of having to replace the complete engine itself. A timing belt is a VERY IMPORTANT SERVICE.
With all of the expenses we occur in today’s age it is very easy to put off auto maintenance because there is always tomorrow. Unfortunately tomorrow may be the time you are on a long trip for vacation and the car breaks down. This may very well be MUCH more expensive to repair than what it would have cost for routine maintenance not to mention a vacation cut short and ruined.
Tuesday, July 24, 2007
Diesel Cars
FORGET THE SMOKY, clattering diesel engines you encounter in taxis and lorries. The woeful clamour and sooty flatulence they emit are completely unnecessary in today's world, for the fact is that a modern, well-tuned diesel engine is neither noisy nor dirty. Diesel's day is here. Or at least, it should be, given how far modern diesel-powered cars have come.
So far it's mostly Western Europeans who have caught on to the fact. In their part of the world, diesel power now accounts for roughly half of all new cars sold, and in markets like Austria and Belgium, almost two out of three new cars is powered by diesel
The rise of diesel power has been nothing short of spectacular. The latest diesels have made huge strides in refinement, cleanliness and efficiency again, with current technology capitalising on the diesel motor's frugality to eke out amazing fuel economy.
What makes a diesel so frugal? First, the engines work completely differently from petrol engines. While a petrol motor ignites fuel with an electric spark, a diesel engine fires up on compression ignition.
Gases get hotter as you compress them, and a diesel engine can run compression ratios as high as 25 to 1 (roughly double that of petrol engines) to get the air in its cylinders as hot as 900 degrees Celsius. The diesel is injected into the hot air, which is what ignites it. Glow plugs (metal filaments which heat up when electricity is applied through them) are sometimes used to warm up the engine for cold starts, but these are rarely used beyond the first few seconds of a diesel engine's operation.
The high compression ratios contribute to the engine's efficiency and adding a turbocharger to compress the air before it enters the cylinders only makes things better.
Another factor that makes diesel-burners so frugal is that the fuel itself is denser than petrol. Although a kilogramme of petrol and diesel contain almost the same number of calories (a measurement of energy), fuel is sold by the litre. And since diesel is denser than petrol by about 15 percent, you actually get more energy per litre of the stuff. That, coupled with the higher efficiency of the diesel engine, is a large part of why you can get up to much further with a diesel engine than you can with a similarly powerful petrol motor.
An automatic BMW 325i that runs on petrol, for example, sprints to 100km/h in 7.7 seconds, while a diesel-powered 330d smokes it at 6.8 seconds. And yet the diesel-burner uses some 20 percent less fuel!
Naturally, because carbon dioxide emissions are directly proportionate to the amount of fuel burnt, the diesel churns out less of the greenhouse gas, too: 197 grammes per kilometer, versus 218 grammes for its petrol counterpart.
But what about black smoke? The latest, Euro 4 standards compliant diesels have particulate filters that comb the stuff from exhaust gases. Engine computing and fuel injector technology have also improved to the point that diesels control their fuelling so well that they can run as clean as many petrol or CNG variants.
Diesels have even begun to flex their muscles on the racetrack. Audi created history this year by becoming the first manufacturer to win with diesel power at the 24 hours of Le Mans race, the most prestigious and challenging endurance race in motorsports. Running on regular Shell diesel, the 650bhp Audi R10 followed up its Le Mans win with a victory at another endurance race in the US three months later. So much for diesels being slow then…
But perhaps the most telling sign of the diesel engine's rise to prominence came at the 2003 Paris motor show where Mercedes-Benz had brought along what were then concept versions of the B-Class and R-Class MPVs. But what caught the eye was the fact that, apart from the pair of prototypes, not a single petrol-powered car was to be found at the Mercedes stand.
Arguably the most forward-thinking car maker in the world had turned up at an A-list international motor show with an all-diesel line-up. Which should tell you something, really.
Commercial Break
Citroen's super-clean Berlingo van gives us an idea of just how far diesel technology has come - and precisely what many drivers are deprived of in Singapore
While you wouldn't currently drive a diesel saloon locally due to prohibitively high import taxes, you can enjoy the latest Euro 4 diesel emissions technology if you run a company and choose to buy a commercial vehicle.
Lets take the latest Citroen Berlingo 1.6 HDI Turbo diesel van for a spin to see how its oil-burner stacks up to similar sized four cylinder petrol engines.
Fire-up the Berlingo and after an initial couple of seconds of a muted and deep-throated rattle that all diesels are synonymous with, the idle speed settles down to an almost silent hum. If you didn't know better, you might think with was petrol-powered. Open up the throttle at road speeds and it's a similar story, although at higher rpm and once road speeds exceed 70kmh there's a distinct difference in the aural feedback. Now it certainly doesn't sound like a petrol engine anymore - but it certainly doesn't sound like a diesel of yesteryear either. It has a refined note, with a hushed background rumble that just starts to feed its way through the cabin.
From the word go though it still performs like a diesel through and through. And that's a very good thing. What diesels are blessed with are bagfuls on instant torque. The Berlingo's peak torque of 175Nm is reached at only 1,750rpm. With most petrol engines you are still struggling to get into the power band at that engine speed. It made strong, safe overtaking in the Berlingo a cinch without having to fight with the five speed manual gearbox. In fact, so flexible is the torque curve on this 75bhp unit that it can pull away in third gear from nearly standstill without the drive-train stuttering and feeling like everything is going to stall with a sickening crunch. If you are lazy, just leave it in third half the time and drive it like an auto.
Fuel Miser
One thing that diesel engines are even more accomplished at than great pulling power is the ability to return astonishing fuel returns. After filling the Berlingo's tank to the brim with Shell's Ultra Low Sulphur Diesel and running it around Singapore's expressways and CBD areas for a total of 163 kilometres, it took just 7.2 litres of fuel to top it up again. That equates to just 4.4 l/100km. Granted, the van wasn't loaded at the back, but it is also fair to say we were deliberately heavy on the accelerator pedal too. It would clearly have made even better returns without the stop-start driving of the inner city areas.
So far it's mostly Western Europeans who have caught on to the fact. In their part of the world, diesel power now accounts for roughly half of all new cars sold, and in markets like Austria and Belgium, almost two out of three new cars is powered by diesel
The rise of diesel power has been nothing short of spectacular. The latest diesels have made huge strides in refinement, cleanliness and efficiency again, with current technology capitalising on the diesel motor's frugality to eke out amazing fuel economy.
What makes a diesel so frugal? First, the engines work completely differently from petrol engines. While a petrol motor ignites fuel with an electric spark, a diesel engine fires up on compression ignition.
Gases get hotter as you compress them, and a diesel engine can run compression ratios as high as 25 to 1 (roughly double that of petrol engines) to get the air in its cylinders as hot as 900 degrees Celsius. The diesel is injected into the hot air, which is what ignites it. Glow plugs (metal filaments which heat up when electricity is applied through them) are sometimes used to warm up the engine for cold starts, but these are rarely used beyond the first few seconds of a diesel engine's operation.
The high compression ratios contribute to the engine's efficiency and adding a turbocharger to compress the air before it enters the cylinders only makes things better.
Another factor that makes diesel-burners so frugal is that the fuel itself is denser than petrol. Although a kilogramme of petrol and diesel contain almost the same number of calories (a measurement of energy), fuel is sold by the litre. And since diesel is denser than petrol by about 15 percent, you actually get more energy per litre of the stuff. That, coupled with the higher efficiency of the diesel engine, is a large part of why you can get up to much further with a diesel engine than you can with a similarly powerful petrol motor.
An automatic BMW 325i that runs on petrol, for example, sprints to 100km/h in 7.7 seconds, while a diesel-powered 330d smokes it at 6.8 seconds. And yet the diesel-burner uses some 20 percent less fuel!
Naturally, because carbon dioxide emissions are directly proportionate to the amount of fuel burnt, the diesel churns out less of the greenhouse gas, too: 197 grammes per kilometer, versus 218 grammes for its petrol counterpart.
But what about black smoke? The latest, Euro 4 standards compliant diesels have particulate filters that comb the stuff from exhaust gases. Engine computing and fuel injector technology have also improved to the point that diesels control their fuelling so well that they can run as clean as many petrol or CNG variants.
Diesels have even begun to flex their muscles on the racetrack. Audi created history this year by becoming the first manufacturer to win with diesel power at the 24 hours of Le Mans race, the most prestigious and challenging endurance race in motorsports. Running on regular Shell diesel, the 650bhp Audi R10 followed up its Le Mans win with a victory at another endurance race in the US three months later. So much for diesels being slow then…
But perhaps the most telling sign of the diesel engine's rise to prominence came at the 2003 Paris motor show where Mercedes-Benz had brought along what were then concept versions of the B-Class and R-Class MPVs. But what caught the eye was the fact that, apart from the pair of prototypes, not a single petrol-powered car was to be found at the Mercedes stand.
Arguably the most forward-thinking car maker in the world had turned up at an A-list international motor show with an all-diesel line-up. Which should tell you something, really.
Commercial Break
Citroen's super-clean Berlingo van gives us an idea of just how far diesel technology has come - and precisely what many drivers are deprived of in Singapore
While you wouldn't currently drive a diesel saloon locally due to prohibitively high import taxes, you can enjoy the latest Euro 4 diesel emissions technology if you run a company and choose to buy a commercial vehicle.
Lets take the latest Citroen Berlingo 1.6 HDI Turbo diesel van for a spin to see how its oil-burner stacks up to similar sized four cylinder petrol engines.
Fire-up the Berlingo and after an initial couple of seconds of a muted and deep-throated rattle that all diesels are synonymous with, the idle speed settles down to an almost silent hum. If you didn't know better, you might think with was petrol-powered. Open up the throttle at road speeds and it's a similar story, although at higher rpm and once road speeds exceed 70kmh there's a distinct difference in the aural feedback. Now it certainly doesn't sound like a petrol engine anymore - but it certainly doesn't sound like a diesel of yesteryear either. It has a refined note, with a hushed background rumble that just starts to feed its way through the cabin.
From the word go though it still performs like a diesel through and through. And that's a very good thing. What diesels are blessed with are bagfuls on instant torque. The Berlingo's peak torque of 175Nm is reached at only 1,750rpm. With most petrol engines you are still struggling to get into the power band at that engine speed. It made strong, safe overtaking in the Berlingo a cinch without having to fight with the five speed manual gearbox. In fact, so flexible is the torque curve on this 75bhp unit that it can pull away in third gear from nearly standstill without the drive-train stuttering and feeling like everything is going to stall with a sickening crunch. If you are lazy, just leave it in third half the time and drive it like an auto.
Fuel Miser
One thing that diesel engines are even more accomplished at than great pulling power is the ability to return astonishing fuel returns. After filling the Berlingo's tank to the brim with Shell's Ultra Low Sulphur Diesel and running it around Singapore's expressways and CBD areas for a total of 163 kilometres, it took just 7.2 litres of fuel to top it up again. That equates to just 4.4 l/100km. Granted, the van wasn't loaded at the back, but it is also fair to say we were deliberately heavy on the accelerator pedal too. It would clearly have made even better returns without the stop-start driving of the inner city areas.
Sunday, July 22, 2007
All Wheel Drive
Many people go through their entire motoring lives without bothering about what goes on under the hoods of their cars. And that includes not knowing which wheels provide the drive that propels the vehicle. That said, how your car gets its power down to the road surface should be a fairly important consideration for any buyer.
Traditionally, cars tend to fall into two broad categories, front wheel drive and rear wheel drive. Of late however, all-wheel drive has become an increasingly popular layout in road cars, thanks chiefly to the cachet generated by its successful application in the muddy world of rallying. But what are the actual advantages, if any?
Front-Wheel Drive
In the case of front-wheel-drive-cars, the front wheels handle both the steering and the task of getting all the engine's power effectively to the road surface. One advantage is improved packaging; there's no need for a bulky drive shaft to transfer power from the engine to the rear wheels so that saves on interior space.
One disadvantage of this layout however, is the fact that there is a limit to how much power you can apply through wheels that also have to do the job of steering. Anybody who's had to multi-task at work will understand how difficult it is to perform two jobs as well as if you had to do just one. Aside from steering, the front tyres' also lose traction (or 'grip') under hard acceleration as the inertial weight of the car transfers rearwards and momentarily keeps the front driving wheels from pressing onto the road surface.
When this happens, the driver can feel the car steering left or right under acceleration. Among the techno-minded in the car industry, this phenomenon is dubbed 'torque steer.' This is why the engines in front wheel drive cars are rarely very powerful.
Rear-Wheel-Drive
Manufacturers of more sports-biased cars usually adopt a rear-wheel-drive layout, BMW being one notable example. By keeping the front pair of wheels free to focus solely on steering, and leaving the pair at the rear to focus solely on delivering torque to the road surface, a real-wheel-drive car can deliver an arguably purer driving experience than a front wheel drive car. You can also afford to have much more powerful engines as the inertial weight transfer that causes traction problems in front-wheel drive cars works to the rear-wheel drive car's advantage. Some would also argue that it takes more skill to drive a powerful rear-wheel drive car at the limit; although today's electronic traction control devices do make them much more manageable.
All-Wheel-Drive
All-wheel drive, or four-wheel drive cars, as the names imply, distribute engine power to all four wheels. The distribution is often not equal, depending on the manufacturer and also on intended use. The first four-wheel drive systems were solely the preserve of high-level motor racing. Even Formula One teams dabbled with four-wheel drive setups at one point but development costs and regulations prevented their being more widely accepted.
Subaru built the world's first mass-produced AWD car in 1972 in the shape of the Leone Station Wagon. Until this time, four-wheel-drive vehicles had been strictly limited to 'off-road' utility vehicles from companies like Jeep and Land Rover. It wasn't until the 1980s when Audi introduced its famous quattro rally car that four-wheel drive really started to come into vogue. Since then the World Rally Championships (WRC) have been dominated by all wheel drive rally cars like the Subaru WRX. The success of cars like the WRX hasn't been exclusively due to their having more grip over cars with two wheel drive, which is a common misconception, but rather their heightened ability to appropriately channel the engine's torque to the road surface.
The application of all-wheel-drive becomes easier to understand in the context of a very powerful engine. Imagine a 500bhp car with 600Nm of torque channelled through only the front or rear wheels, without sophisticated traction control. It would be very difficult for the car to effectively use all that power. There is a limit to how much engine torque a wheel can transmit to the road surface before it overcomes the wheel's ability to grip the road surface. If you split torque amongst four wheels instead of two, there's less chance of torque overwhelming grip, and hence better traction.
Of course, the application of all-wheel drive isn't limited to cars with powerful engines, an average family saloon can also take advantage of the traction benefits too.
Types of All-Wheel-Drive Systems
For road cars, there are several different ways of apportioning power to all four wheels. Some systems utilise a device called a Haldex clutch coupled to the gearbox. Suitable for cars with transversely mounted engines that sit perpendicularly to the car's body length.
The Haldex clutch enables torque to be sent rearwards. The system however, is also not 'full-time'. This means it operates only under conditions when sensors detect a significant loss of traction at the front. Then as much as 50 percent of the engine's torque is sent to the rear wheels - at all other times torque is sent to the front wheels alone.
Other cars have longitudinally, or lengthwise mounted engines, necessitating a different setup to that in Haldex-based systems. The longitudinal mounting of the engine and likewise the gearbox means that torque only has to split at the front and rear axles, and this can be accomplished with a system called a Torsen, or TORque SENsing differential.
This system, unlike the Haldex clutch, is purely mechanical. Conventional differentials are not able to allow for a large degree of torque difference between the drive shafts. The Torsen differential takes extra torque from the shaft that is travelling more quickly and transfers it to the slower moving shaft. This helps mitigate the effects of different front and rear wheel speeds.
Subaru's Symmetrical All-Wheel Drive System
Subaru has cultivated a strong racing heritage through the World Rally Championship and, like Audi, it has brought its race-bred all-wheel-drive (AWD) technology to its road cars. One of the key features of Subaru's all-wheel drive system is the laterally symmetrical layout of the drivetrain.
Due to layout and packaging constraints, most other four-wheel-drive cars have all their mechanical components 'asymmetrically' laid out. For example, the engine and gearbox may not be perfectly oriented in line with the car's longitudinal axis and this would naturally present some problems with left-right weight distribution.
Subaru's symmetrical AWD system ensures that all major components are oriented to their cars' longitudinal axes. So if you were to 'chop' the cars in half lengthwise, each section would be a mirror image of the other.
Subaru uses a viscous coupling instead of a mechanical differential to split the drive shaft. This consists of two sets of plates, one connected to the front drive shaft and one connected to the rear. A viscous silicone fluid is used to bridge the gap between the plates. If one driveshaft starts to spin faster than the other, the fluid heats up and becomes even more sticky or 'viscous' and this helps transfer torque to the slower moving half of the driveshaft.
The main advantage of Subaru's Symmetrical AWD layout however, is equal weight distribution on the left and right sides of the car. This has obvious benefits for handling and traction. Traction, as we mentioned earlier, is the ability of a car to transfer torque to the road surface. If you start off with even loading on the left and right sides of the car you minimise any traction imbalance right from the start. Subaru is also the only manufacturer to offer an AWD system for all its vehicles, not just for its top spec models.
If its packaging and interior space, then a front wheel drive layout may suit you best. If you're an old-school purist then nothing less than rear wheel drive will suffice, but if you want the added peace of mind that comes from sure-footed traction then all-wheel-drive is for you.
Traditionally, cars tend to fall into two broad categories, front wheel drive and rear wheel drive. Of late however, all-wheel drive has become an increasingly popular layout in road cars, thanks chiefly to the cachet generated by its successful application in the muddy world of rallying. But what are the actual advantages, if any?
Front-Wheel Drive
In the case of front-wheel-drive-cars, the front wheels handle both the steering and the task of getting all the engine's power effectively to the road surface. One advantage is improved packaging; there's no need for a bulky drive shaft to transfer power from the engine to the rear wheels so that saves on interior space.
One disadvantage of this layout however, is the fact that there is a limit to how much power you can apply through wheels that also have to do the job of steering. Anybody who's had to multi-task at work will understand how difficult it is to perform two jobs as well as if you had to do just one. Aside from steering, the front tyres' also lose traction (or 'grip') under hard acceleration as the inertial weight of the car transfers rearwards and momentarily keeps the front driving wheels from pressing onto the road surface.
When this happens, the driver can feel the car steering left or right under acceleration. Among the techno-minded in the car industry, this phenomenon is dubbed 'torque steer.' This is why the engines in front wheel drive cars are rarely very powerful.
Rear-Wheel-Drive
Manufacturers of more sports-biased cars usually adopt a rear-wheel-drive layout, BMW being one notable example. By keeping the front pair of wheels free to focus solely on steering, and leaving the pair at the rear to focus solely on delivering torque to the road surface, a real-wheel-drive car can deliver an arguably purer driving experience than a front wheel drive car. You can also afford to have much more powerful engines as the inertial weight transfer that causes traction problems in front-wheel drive cars works to the rear-wheel drive car's advantage. Some would also argue that it takes more skill to drive a powerful rear-wheel drive car at the limit; although today's electronic traction control devices do make them much more manageable.
All-Wheel-Drive
All-wheel drive, or four-wheel drive cars, as the names imply, distribute engine power to all four wheels. The distribution is often not equal, depending on the manufacturer and also on intended use. The first four-wheel drive systems were solely the preserve of high-level motor racing. Even Formula One teams dabbled with four-wheel drive setups at one point but development costs and regulations prevented their being more widely accepted.
Subaru built the world's first mass-produced AWD car in 1972 in the shape of the Leone Station Wagon. Until this time, four-wheel-drive vehicles had been strictly limited to 'off-road' utility vehicles from companies like Jeep and Land Rover. It wasn't until the 1980s when Audi introduced its famous quattro rally car that four-wheel drive really started to come into vogue. Since then the World Rally Championships (WRC) have been dominated by all wheel drive rally cars like the Subaru WRX. The success of cars like the WRX hasn't been exclusively due to their having more grip over cars with two wheel drive, which is a common misconception, but rather their heightened ability to appropriately channel the engine's torque to the road surface.
The application of all-wheel-drive becomes easier to understand in the context of a very powerful engine. Imagine a 500bhp car with 600Nm of torque channelled through only the front or rear wheels, without sophisticated traction control. It would be very difficult for the car to effectively use all that power. There is a limit to how much engine torque a wheel can transmit to the road surface before it overcomes the wheel's ability to grip the road surface. If you split torque amongst four wheels instead of two, there's less chance of torque overwhelming grip, and hence better traction.
Of course, the application of all-wheel drive isn't limited to cars with powerful engines, an average family saloon can also take advantage of the traction benefits too.
Types of All-Wheel-Drive Systems
For road cars, there are several different ways of apportioning power to all four wheels. Some systems utilise a device called a Haldex clutch coupled to the gearbox. Suitable for cars with transversely mounted engines that sit perpendicularly to the car's body length.
The Haldex clutch enables torque to be sent rearwards. The system however, is also not 'full-time'. This means it operates only under conditions when sensors detect a significant loss of traction at the front. Then as much as 50 percent of the engine's torque is sent to the rear wheels - at all other times torque is sent to the front wheels alone.
Other cars have longitudinally, or lengthwise mounted engines, necessitating a different setup to that in Haldex-based systems. The longitudinal mounting of the engine and likewise the gearbox means that torque only has to split at the front and rear axles, and this can be accomplished with a system called a Torsen, or TORque SENsing differential.
This system, unlike the Haldex clutch, is purely mechanical. Conventional differentials are not able to allow for a large degree of torque difference between the drive shafts. The Torsen differential takes extra torque from the shaft that is travelling more quickly and transfers it to the slower moving shaft. This helps mitigate the effects of different front and rear wheel speeds.
Subaru's Symmetrical All-Wheel Drive System
Subaru has cultivated a strong racing heritage through the World Rally Championship and, like Audi, it has brought its race-bred all-wheel-drive (AWD) technology to its road cars. One of the key features of Subaru's all-wheel drive system is the laterally symmetrical layout of the drivetrain.
Due to layout and packaging constraints, most other four-wheel-drive cars have all their mechanical components 'asymmetrically' laid out. For example, the engine and gearbox may not be perfectly oriented in line with the car's longitudinal axis and this would naturally present some problems with left-right weight distribution.
Subaru's symmetrical AWD system ensures that all major components are oriented to their cars' longitudinal axes. So if you were to 'chop' the cars in half lengthwise, each section would be a mirror image of the other.
Subaru uses a viscous coupling instead of a mechanical differential to split the drive shaft. This consists of two sets of plates, one connected to the front drive shaft and one connected to the rear. A viscous silicone fluid is used to bridge the gap between the plates. If one driveshaft starts to spin faster than the other, the fluid heats up and becomes even more sticky or 'viscous' and this helps transfer torque to the slower moving half of the driveshaft.
The main advantage of Subaru's Symmetrical AWD layout however, is equal weight distribution on the left and right sides of the car. This has obvious benefits for handling and traction. Traction, as we mentioned earlier, is the ability of a car to transfer torque to the road surface. If you start off with even loading on the left and right sides of the car you minimise any traction imbalance right from the start. Subaru is also the only manufacturer to offer an AWD system for all its vehicles, not just for its top spec models.
If its packaging and interior space, then a front wheel drive layout may suit you best. If you're an old-school purist then nothing less than rear wheel drive will suffice, but if you want the added peace of mind that comes from sure-footed traction then all-wheel-drive is for you.
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