RE: Light cars are not the answer: Tell Me I'm Wrong
Discussion
A thought-provoking article. As ever, there are poor lightweight cars, and good heavy cars, and vice versa. In my own view, a heavy car is always going to offer better refinement - forget for a moment the additional mass from adding acres of sound-deadening and seals - reduce the car to a simple spring-mass system and you can see that heavy cars offer more potential to have a higher ratio of sprung (body) to unsprung (wheel/hub/brakes etc) mass. The larger the ratio, the less the body is disturbed by the movement of the wheels. To quote from something I wrote some time ago:
"Simplifying somewhat, the bigger the ratio between the sprung bit and the unsprung, the better the wheel control, therefore the better the ride and handling. As the car is made lighter, more and more effort needs to go into reducing the weight of the unsprung parts to ensure the ratio doesn’t diminish. This issue was encountered by Gordon Murray with the revered McLaren F1. An article by Autocar on the F1 published back in 1994 stated the ratios for the F1 are 5.5:1 front, 5.8:1 rear; for comparison it quotes a typical hatchback of the time (Peugeot 306 1.8 XT) as being much greater, 9.8:1 and 7.3:1 respectively. Both weigh 1100kg. The bigger stopping power required for the F1 means bigger brakes, bigger wheels to clear them, bigger tyres, bigger suspension loads and therefore heavier unsprung parts, and lower ratios."
When you have large performance, and/or low weight, it becomes very difficult (expensive) to get a large enough ratio to offer good refinement. A heavy car won't encounter this issue to the same degree. But as ever, there are many more variables involved, and getting it right takes time, effort and experience.
(Source: http://ramblecar.wordpress.com/2014/06/27/ramble-r...
"Simplifying somewhat, the bigger the ratio between the sprung bit and the unsprung, the better the wheel control, therefore the better the ride and handling. As the car is made lighter, more and more effort needs to go into reducing the weight of the unsprung parts to ensure the ratio doesn’t diminish. This issue was encountered by Gordon Murray with the revered McLaren F1. An article by Autocar on the F1 published back in 1994 stated the ratios for the F1 are 5.5:1 front, 5.8:1 rear; for comparison it quotes a typical hatchback of the time (Peugeot 306 1.8 XT) as being much greater, 9.8:1 and 7.3:1 respectively. Both weigh 1100kg. The bigger stopping power required for the F1 means bigger brakes, bigger wheels to clear them, bigger tyres, bigger suspension loads and therefore heavier unsprung parts, and lower ratios."
When you have large performance, and/or low weight, it becomes very difficult (expensive) to get a large enough ratio to offer good refinement. A heavy car won't encounter this issue to the same degree. But as ever, there are many more variables involved, and getting it right takes time, effort and experience.
(Source: http://ramblecar.wordpress.com/2014/06/27/ramble-r...
iwantcheese5 said:
The weight adding grip point is a bit more complicated than just more weight=more grip. Sure adding mass increases traction (friction force=mu x mass) but it also increases momentum (momentum=speed x mass) and kinetic energy (1/2 x mass x speed^2) so these make changing direction more difficult. The added momentum dulls the car's response to inputs giving you the smoother ride as it can't react to the high frequency inputs and it reduces the effect of jolts etc. Technically you get the same traction force regardless of tyre width as well...just you can't put down as much energy.
Added weight will help grip and ride in steady state maneuvers but makes changing speed or direction more difficult.
It does come across as swallowing Nissan's PR bull. It might be fair to say that a light car generally has a low moment of inertia - and thus spins quickly once rear traction is exceeded - allowing heavier cars to have a more progressive feel.Added weight will help grip and ride in steady state maneuvers but makes changing speed or direction more difficult.
I do wander, in the mythical days when daily drivers aren't driven, leaving the only cars that are to be lightweight specials, if anyone will miss shuffling along a heavy motor or not.
My previous S2000's were relatively lightweight and I couldn't feel anything through the steering wheel (more down to the steering though), and in the winter and wet and cold it actually made some sense to weigh the rear end down with stuff in the boot for more traction! My C63 was a 'lardy' 1700kg's, but I could feel so much through the excellent steering and it certainly did not feel it's weight.
Like people have said there is a time for both, but it is good to have a balance between unnecessary weight and needed weight.
Like people have said there is a time for both, but it is good to have a balance between unnecessary weight and needed weight.
iwantcheese5 said:
TurboHatchback said:
no effect on fuel economy at a constant speed.
It does have an effect, the rolling resistance is higher with increased mass, admittedly at motorway speed the main problem is air resistance.Monty Python said:
From my overly simplistic view, I'd have thought that a lighter car is better as the magnitude of the forces involved are lower and hence easier to control.
A light car car doesn't need beefy suspension, it doesn't need massive brakes and it doesn't need massive power to get the performance out of it (better economy).
Indeed, and stuctural stiffness in only a valid parameter in relation to, erm, weight. Making a car lighter whilst retaining structural stiffness has the same result as making the structure stiffer at the same weight (which won't likely happen unless going for more expensive materials etc.) - only in the first cars, the loads the drivetrain components, brakes, tyres and everything else on the car have to deal with for a given performance level will be lower, also. A light car car doesn't need beefy suspension, it doesn't need massive brakes and it doesn't need massive power to get the performance out of it (better economy).
Weight = stability? At steady state conditions, maybe - but at the higher weight you will need bigger tyre footprints to achieve the same lateral and longitudinal g, which brings the pressure per square inch of contact patch back to where it was before...
It' not necessarily whether it's light or not for me.
You can have a heavier car but it requires appropriate levels of grip, chassis dynamics and braking to make sure that one area is not compromised.
I find the original Lotus Elise under powered once you get upto decent speeds because it has no torque, sure the handling is epic but a good car needs to have the the right amount of fun in all areas to tick all the boxes.
You can have a heavier car but it requires appropriate levels of grip, chassis dynamics and braking to make sure that one area is not compromised.
I find the original Lotus Elise under powered once you get upto decent speeds because it has no torque, sure the handling is epic but a good car needs to have the the right amount of fun in all areas to tick all the boxes.
paranoid airbag said:
It might be fair to say that a light car generally has a low moment of inertia - and thus spins quickly once rear traction is exceeded - allowing heavier cars to have a more progressive feel.
On that note, I recall being told by an engineer of a rally car company (fairly sure it was Prodrive and their WRC Subarus) that once they focused absolutely on reducing the moments of inertia, placing all the weight in the centre of the car. The drivers complained the car was too nervous and responsiv;, they couldn't keep up with the changes in direction. Ballast was added under the front and rear bumpers to increase the inertia, and the drivers were a lot happier as the car was now responding at a rate they could deal with. They were more confident, and went faster. Some other engineers I've dealt with in motorsport suggest that the car should be as nervous and responsive as possible, and it's down to the driver to be good enough to make it work, rather than the other way around. That may be part of what separates world champions from the merely great, but now I'm digressing.paranoid airbag said:
It does come across as swallowing Nissan's PR bull. It might be fair to say that a light car generally has a low moment of inertia - and thus spins quickly once rear traction is exceeded - allowing heavier cars to have a more progressive feel.
I do wander, in the mythical days when daily drivers aren't driven, leaving the only cars that are to be lightweight specials, if anyone will miss shuffling along a heavy motor or not.
In the case of the GT-R they did some very clever stuff with the chassis and electronics and it has very wide tires to help contain the bulk. The moment of inertia can be adjusted by the placement of the mass in the car and the wheelbase etc. You could have a car with a high moment of inertia that is still relatively light and thus not as scary when it loses traction.I do wander, in the mythical days when daily drivers aren't driven, leaving the only cars that are to be lightweight specials, if anyone will miss shuffling along a heavy motor or not.
Charlie Michael said:
Aero is then the bigger problem I'd guess at that point for fuel economy.
Yes, but for a given shape car the lighter one will use less fuel. At the end of the day all areas of the car need to be optimised.An easy way to reduce the weight of cars would be to make them smaller...
There's engineers who understand all this stuff better than I do, but just from a logic point of you;
It's not really fair to lump all 'lightening' processes in together but hand pick various positive heavy examples.
All lightening is good and all extra weight isn't bad. But this article is trying to say lighter isn't better when compared to selected examples of heavy cars.
It's 'general rule' versus selected examples.
It's not really fair to lump all 'lightening' processes in together but hand pick various positive heavy examples.
All lightening is good and all extra weight isn't bad. But this article is trying to say lighter isn't better when compared to selected examples of heavy cars.
It's 'general rule' versus selected examples.
iwantcheese5 said:
In the case of the GT-R they did some very clever stuff with the chassis and electronics and it has very wide tires to help contain the bulk. The moment of inertia can be adjusted by the placement of the mass in the car and the wheelbase etc. You could have a car with a high moment of inertia that is still relatively light and thus not as scary when it loses traction.
I point in the direction of the Caterham Seven (or if a more refined vehicle is desired the Ginetta G40,or GT86). Or indeed the MX5.There are plenty of very lightweight front engined RWD cars that are intuitively controllable when the tyres are spinning. The relative masses of engine up front and cabin/diff./etc. automatically create a high polar inertia, with far less shenanigans like relocating the washer bottle!
Mid engined is a different matter.
the argument for lightweight cars is that the power unit can be more frugal given the reduced effort required to make the car 'sporty'. The connection of light weight = fun is a misnomer in my view.
If the car has the right dynamics (i.e. an engine that provides enough oomph mated to a well engineered chassis etc.. ) then driver enjoyment should follow - whether the car is light or not is is just a consequence of the engineering choices made to define the dynamics and purpose of the vehicle.
Cant say i've ever seen a F1 driver or recent years get out of the car and say that was a 'fun' drive - the dynamics and purpose of the car is to ensure you can cover the given distance as quick as possible, not to get enjoyment by power sliding through eu rouge, for example.
If the car has the right dynamics (i.e. an engine that provides enough oomph mated to a well engineered chassis etc.. ) then driver enjoyment should follow - whether the car is light or not is is just a consequence of the engineering choices made to define the dynamics and purpose of the vehicle.
Cant say i've ever seen a F1 driver or recent years get out of the car and say that was a 'fun' drive - the dynamics and purpose of the car is to ensure you can cover the given distance as quick as possible, not to get enjoyment by power sliding through eu rouge, for example.
I drive one of the lightest cars - a Caterham weighing 590kg (even though it is advertised as 500). If you haven't driven a car as light it really is an extraordinary experience - you can make very swift progress without using the brakes at all and when you do use them , even though they are tiny little discs , the car just stops , often many metres before you expected it to . There is no sense of inertia(?) whatever. It's a mobile physics lesson but I wouldn't want to get hit by a truck in one
Reference to the GTR is mis-leading as electronics play the biggest part in the lap times achieved by this car. Weight dis-advantages can be cleverly ironed out when resorting to electronics. When electronics do not play a part however, aero dynamics (downforce) can most times compensate for the relative instability caused by a lack of weight but the opposite is not achievable. The only way to compensate for weight (electronics apart) is to shed it.
Someone said it at last, fun and enjoying the drive is the whole point of buying the car, not obsessing over every kg.
Don't get me wrong lighter is better as it benefits fuel economy and performance etc, but it's not the be all and end all, a bigger engine with more cylinders is nice too and that adds weight....
Don't get me wrong lighter is better as it benefits fuel economy and performance etc, but it's not the be all and end all, a bigger engine with more cylinders is nice too and that adds weight....
Cars are compromises. No car is better for being heavier. Some are heavier for being better.
There are performance related compromises - more sophisticated suspension, more powerful engines, stiffer construction all tend to add weight, and the car may turn out a better drive if you live with that, but most of the weight-adding compromises come down to comfort, space and safety. Most people, even many people on PH, prioritise those over how well a car drives.
Whether light cars are the answer depends on what the question is, and the tastes of the person asking.
There are performance related compromises - more sophisticated suspension, more powerful engines, stiffer construction all tend to add weight, and the car may turn out a better drive if you live with that, but most of the weight-adding compromises come down to comfort, space and safety. Most people, even many people on PH, prioritise those over how well a car drives.
Whether light cars are the answer depends on what the question is, and the tastes of the person asking.
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