RE: Light cars are not the answer: Tell Me I'm Wrong
Discussion
adma23 said:
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.
I don't buy it that the electronics are responsible for the biggest part of the lap times, it has to be basically right to do it in the first place, the GTR's pace is down to 550 bhp, massive grip, good aerodynamics (for a road car), four wheel drive traction and some very talented engineers.The electronics work to improve things but switch it all off its still massively fast, in the hands of a pro driver I suspect it wont make much difference to lap its times, it isn't like a Eurofighter, i.e. cant be flown without the computers keeping it all together.
For me as a Automotive and motorsport designer lightweight is the only way.
There are no advantages to heavy cars other than the added comforts inside for a world of lazy drivers. To think that once we had to manually wind down a window seems a very distance memory. Most of us would rather carry around all the extra weight or motors and electrics because it's too much effort to move our arms a little.
Ride comfort has nothing to do with weight. If you have correctly valved dampers and correctly setup suspension with low unsprung weight you will have a fantastically comfortable and rewarding car to drive. Oh and wheels and tyres that are suitable for a light weight car does not mean 19inch wheels with low profile tyres. The lighter the car the smaller the wheel diameter and the bigger the tyre profile required.
It's also down to development, you need to look at how many good 1500kg+ cars are designed and built each year, thousands of them. Compared to the number of mass produced good quality low weight cars under 900kg designed each year which you could count on one hand if any at all.
There has been very little development into lightweight cars and suspension, damping and steering for light weight road cars.
I have seen a post about heavier cars having better steering feel. This is crazy and completely wrong. Weight has nothing to do with this. A lightweight car will always be more responsive and with a good steering systems give far better feedback due to very little if any assistance needed.
I am a massive Alfa fan but they have never been known for building cars with correctly setup dampers for English roads. Also another down fall of the 4c is its massive heavy wheels and low profile tyres neither of which suit a lightweight car.
There are no advantages to heavy cars other than the added comforts inside for a world of lazy drivers. To think that once we had to manually wind down a window seems a very distance memory. Most of us would rather carry around all the extra weight or motors and electrics because it's too much effort to move our arms a little.
Ride comfort has nothing to do with weight. If you have correctly valved dampers and correctly setup suspension with low unsprung weight you will have a fantastically comfortable and rewarding car to drive. Oh and wheels and tyres that are suitable for a light weight car does not mean 19inch wheels with low profile tyres. The lighter the car the smaller the wheel diameter and the bigger the tyre profile required.
It's also down to development, you need to look at how many good 1500kg+ cars are designed and built each year, thousands of them. Compared to the number of mass produced good quality low weight cars under 900kg designed each year which you could count on one hand if any at all.
There has been very little development into lightweight cars and suspension, damping and steering for light weight road cars.
I have seen a post about heavier cars having better steering feel. This is crazy and completely wrong. Weight has nothing to do with this. A lightweight car will always be more responsive and with a good steering systems give far better feedback due to very little if any assistance needed.
I am a massive Alfa fan but they have never been known for building cars with correctly setup dampers for English roads. Also another down fall of the 4c is its massive heavy wheels and low profile tyres neither of which suit a lightweight car.
Edited by bnracing on Thursday 8th January 12:40
gifdy said:
After reading the title I had 'You're wrong' bouncing about in my head, but you have a persuasive argument. Made me rethink my initial reaction which is what a good article should do. Nicely done !
Me too!Interesting point about the use of double wishbones in the XE - weight well 'spent' maybe?
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.
This.Added weight will help grip and ride in steady state maneuvers but makes changing speed or direction more difficult.
Weight has not been called a vicious circle in engineering terms for nothing.
- Increased unsprung weight as you need bigger brakes to ensure equivalent stopping power;
- Increased unsprung weight as you need bigger wheels (well, smaller sidewalls) to give you back some of the turn-in response*;
- More expensive dampers to give you equivalent ride quality and body control. Doubly so if you've got the smaller sidewalls above;
- More power needed to give the same bhp/tonne, which means more weight in the powertrain;
- Worse fuel economy as the car is heavier and the engine bigger (and thus less efficient due to greater thermal losses).
- Sharper on-limit break-away due to the dynamic compromises required.
...so you end up with a more expensive, more thirsty car that still doesn't do as much as the lighter car, dynamically. It's just got more kit / toys / etc. than the lighter car (or not, in the case of the F-Type...).
You cherry picked or mis-applied your examples too:
- chassis stiffness is going OTT right now - I can't recall my old DC2 Integra lacking in the precision department (quite the opposite), yet it was based on a mildly-reinforced 1993 hatchback platform. In an accident it would definitely have suffered more than a modern car**, but the selective reinforcement was quite enough to provide the responsiveness and precision required.
- An '80s Fiesta is a rather extreme contrarian example too.
- Double-wishbone vs MacP struts is a few kg and a little bit more of a packaging headache, not a game-changer weight wise. Most mfrs have moved away for packaging benefits, not weight.
Oh, and to finish, the F-Type is a bad example to use, quite frankly - exactly how is it a better dynamic platform than the 200kg lighter Cayman-S/Boxster-S - oh, that's right, it's not! Also JLR on-the-cheap used a modified XK chassis (overweight) and on-the-cheap used the existing V8 block as the basis for the V6 (excess weight). If it didn't look as good as it does and have the (possibly OTT) exhaust theatrics, would we be as enthusiastic about it? Nope...it's too expensive for what it does and the markets appear to agree - JLR are notably off their sales targets - for their halo model which has had more press plaudits than anything from them since the E-Type.
* Yes, you can achieve this with geometry...but then you're compromising elsewhere.
** But that's a different discussion to your point.
The article is confusing ride comfort with weight and other variables here.
There is no reason a car can't be lightweight and smooth and comfy to drive... just no one is making it yet.
But it's possibly quite a bit to do with sprung/unsprung weight ratio, that is harder to get good on lighter cars as wheels and brakes etc always weigh something... and unlike the body and interior etc, you can't take fundamental parts out of wheels/suspension/hubs/tyres etc.
Dave
There is no reason a car can't be lightweight and smooth and comfy to drive... just no one is making it yet.
But it's possibly quite a bit to do with sprung/unsprung weight ratio, that is harder to get good on lighter cars as wheels and brakes etc always weigh something... and unlike the body and interior etc, you can't take fundamental parts out of wheels/suspension/hubs/tyres etc.
Dave
bnracing said:
Ride comfort has nothing to do with weight. If you have correctly valved dampers and correctly setup suspension with low unsprung weight you will have a fantastically comfortable and rewarding car to drive. Oh and wheels and tyres that are suitable for a light weight car does not mean 19inch wheels with low profile tyres. The lighter the car the smaller the wheel diameter and the bigger the tyre profile required.
For something like a Jag XE, which is first and foremost a passenger car - can you explain how you correctly valve the dampers so that the car offers a good ride quality when empty bar the driver and a few litres of fuel as well as still driving properly when at maximum gross weight?Edited by bnracing on Thursday 8th January 12:40
Clearly, mass damping is a function of the mass to be damped. Cars are indeed a compromise but it's less of a compromise if the sprung mass doesn't really change - e.g. a single seater racing car. The driver remains constant and the fuel load varies - that's it. A 5 seat passenger car with a large boot and a 60 litre fuel tank can probably vary in mass by half a tonne from empty to fully laden. You can't "just get correctly valved dampers" for something which weighs 1500kg one day and 2000kg the next.
In that respect, something like a 2.7 tonne Discovery varying its payload by half a tonne has much less effect on the damping that it has on an 1100kg Sierra varying its payload by half a tonne.
otolith said:
The comment about weight providing more grip seems to be contrary to both basic physics and real world lateral g figures.
I think you are correct.The writer has got confused about downforce and weight being the same thing.
Downforce only pushes the car in one direction - down, that 1000kg of downforce he talks about does not cause any lateral g or create added weight to braking and acceleration.
Adding 1000kg of weight to a car will not only push it down and add more grip, it will increase the lateral g's therefore reducing that grip and increasing the power required to accelerate or stop the car.
BGarside said:
Would love to run something light and responsive, like a Westfield or Caterham, for fun and a heavier, comfier car for longer trips. It would be nice to have the best of both worlds.
This is what I do. Caterham Supersport and Merc E-class Estate. It really is the best of both Worlds and I highly recommend it 
O/p is wrong. Not only are lighter cars more fun to drive (in general) you also get the benefit of improved mpg. JLR arnt investing millions of pounds on aluminium built cars just because they like the look of it. Although the XE weight might lead you to beleive this. Dont tell me we are all making excuses to continue building overly heavy road cars, just when I though manufacturers where starting to improve the weight saving from new models...
I remember years ago I purchased a Porsche 2.7 RS and drove it through France on the Autoroute. I was doing about a hundred when the car seemed to jump slightly.Later when I spoke to Autofarm about this they said "don't worry they all do that". Another time again on the Autoroute there was a huge downpour I slowed to about forty and turned the steering to change lanes nothing happened I just kept travelling in a straight line. I slowed further and eventually pulled onto the hard shoulder and waited for the rain to stop. In my current car Mercedes SL it is completely stable at speed on a motorway and to date no hairy moments in the rain.Apart from the obvious huge differences between the two cars large weight difference
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