Are lightweight road cars worse?

[Frimley111R]

Of course, weight is the energy of speed and all that but IME I can't help feeling that whilst weight may hinder a car on the road, high powered engines, strong brakes, excellent modern suspension and TC/SC systems means that weight in a road car is of little matter in today's performance cars.

For example, in driving my Megane RS265 and having also driven a 911 Turbo and Impreza I can see that this weight adds security to cornering in terms of making the car feel planted whereas my old Elise 111R S/C, although much, much lighter, didn't have this and the excellent feedback could be actually unsettling. I'm not sure that I could drive a light road car on the road as fast as a modern normal/heavy one (obviously up to a point).

(Oh, and this is of course assuming I would drive in such a way which of course I wouldn't! )

[TEKNOPUG]

Frimley111R said:

Of course, weight is the energy of speed and all that but IME I can't help feeling that whilst weight may hinder a car on the road, high powered engines, strong brakes, excellent modern suspension and TC/SC systems means that weight in a road car is of little matter in today's performance cars.

For example, in driving my Megane RS265 and having also driven a 911 Turbo and Impreza I can see that this weight adds security to cornering in terms of making the car feel planted whereas my old Elise 111R S/C, although much, much lighter, didn't have this and the excellent feedback could be actually unsettling. I'm not sure that I could drive a light road car on the road as fast as a modern normal/heavy one (obviously up to a point).

(Oh, and this is of course assuming I would drive in such a way which of course I wouldn't! )

A lighter car will always be faster than a heavier car, all things being equal. Take that 911 Turbo and start stripping it out and swapping to lightweight components, whilst at the same time reducing the engine power to keep the power-to-weight the same as a stock car. Which will be quicker? Which will change direction quicker? Which will stop quicker? Which has less mass to contend with at every corner? Alternatively, add weight to stock 911 Turbo and increase power to maintain parity. Will it be faster now that it's heavier?

The fact that it so easy to get big, reliable power out of small engines; that brakes & suspension are greatly improved is a result of cars gaining so much weight (not least to do safety & emmissions). They are borne out of necessity. 2.0 Sierra weights 1200k, a 2.0 Mondeo 1600k. That's a 1/3 heavier. So instead of sufficing with 150bhp, they now need 200bhp to maintain performance. And better brakes. And better suspension. It's progress, of a sort.

The reason that you think that you can drive faster in a heavier car is not the security of physical cornering, rather the security a heavier car gives you in terms of crashing (or rather survivability). Therefore you feel more confident in driving faster.

[thegreenhell]

TEKNOPUG said:

The reason that you think that you can drive faster in a heavier car is not the security of physical cornering, rather the security a heavier car gives you in terms of crashing (or rather survivability). Therefore you feel more confident in driving faster.

I agree with most of your post, but the effect has to be more than just psychological. The extra weight of the car, all other things being equally optimised to the task, should push the tyre into the road surface more, increasing stability over bumps and reducing aquaplaning potential. The tyres will just be less likely to lose contact with the road surface.

The survivability in a crash is interesting, because a more heavily-built car may protect its own occupants better, but will make it worse for anybody else external to your vehicle that has to absorb the extra energy, hence people wanting a bigger car than everyone else from this perspective.

[Clem2k3]

thegreenhell said:

I agree with most of your post, but the effect has to be more than just psychological. The extra weight of the car, all other things being equally optimised to the task, should push the tyre into the road surface more, increasing stability over bumps and reducing aquaplaning potential. The tyres will just be less likely to lose contact with the road surface.

The survivability in a crash is interesting, because a more heavily-built car may protect its own occupants better, but will make it worse for anybody else external to your vehicle that has to absorb the extra energy, hence people wanting a bigger car than everyone else from this perspective.

On the weight giving extra grip thing I cant provide you with any equations that prove this train of thought wrong, but, if weight helped traction enough to overcome the issues then racecars would be heavier ...You never hear of an F1 car being penalised for being overweight

[likesachange]

As a road car for b road blasts, a very light car can contradict its self almost. I had an Ariel atom running on A048's... stiff suspension and 550kg meant it just badly skipped across the bumpy British b roads and to get any sort of temps in the tyres with it being so light meant constant hard driving which in turn was a challenge! On a smooth track then its a different kettle ...

I imagine the Nomad so much better at around 750kg? and loads of movement in suspension.

Id have thought sub 700kg in a car for the road is starting to loose benefits of being so light and over 1200kg starting to get penalised for its weight.

[SirSquidalot]

Nope, lower weight makes a car better. A heavy car may feel more sure footed, but i can assure you the same car but lighter would feel just as sure footed and more nimble.

[ChocolateFrog]

Frimley111R said:

Of course, weight is the energy of speed

Nope, you'll have to explain that one to me.

[otolith]

You could set the suspension geometry of an Elise up so it felt as "planted" (i.e. stable and inert) as a heavier car. Doing the reverse, not so easy.

[alock]

The lighter the car, the narrower the window you have for the optimal suspension and dampening. A 100kg difference in a 2.5 ton Bentley makes far less difference than it does in a 600kg Caterham.

[LordGrover]

ChocolateFrog said:

Frimley111R said:

Of course, weight is the energy of speed

Nope, you'll have to explain that one to me.

Predictive text/auto-correct? energy enemy

[thegreenhell]

Round a track, the same car on same tyres but with different weights, yes the lighter car will always be faster, and F1 cars use downforce to load the tyres without the weight penalty, but we're not talking about F1 cars on smooth circuits. I don't think we're even talking about absolute performance here, rather what an average individual driver is comfortable with on an average country road.

A well sorted heavy car like a 911 Turbo will be less likely to be unsettled by a mid-corner bump than a lightweight Lotus or Caterham. It's a question of inertia, of being able to resist outside disturbances, much like it's easier to push over a skinny guy than a big rugby prop forward, even though the skinny guy should run rings around the rugby guy on something like a tight obstacle course.

[AdamIndy]

I have both an ST170(170bhp/1300ish kgs) and an MK Indy with a 140bhp Xflow weighing about 600kgs.

The MK would wipe the floor with the focus on probably 70% of roads, BUT I am a lot more confident pushing on in the focus. It is forgiving whereas the MK would happily spit me off the road at a moments notice.

The focus controls its weight very well and I wouldn't be surprised if it had more outright grip than the MK.

As said above with the atom, the MK will skip and hop along bumpy roads, not exactly confidence inspiring, whereas the focus will stay perfectly manageable and predictable. With the best will in the world, I don't think the MK suspension could be set up in a way that it would stay settled on a bumpy road, there is not enough weight to keep it planted.


Straight line, no competition the light car will win every time. A bumpy, twisty road, I'm not so sure. I'm not the best driver in the world so maybe a properly good driver would prove me wrong.

Interesting subject though.

[blindswelledrat]

Frimley111R said:

Of course, weight is the energy of speed and all that but IME I can't help feeling that whilst weight may hinder a car on the road, high powered engines, strong brakes, excellent modern suspension and TC/SC systems means that weight in a road car is of little matter in today's performance cars.

For example, in driving my Megane RS265 and having also driven a 911 Turbo and Impreza I can see that this weight adds security to cornering in terms of making the car feel planted whereas my old Elise 111R S/C, although much, much lighter, didn't have this and the excellent feedback could be actually unsettling. I'm not sure that I could drive a light road car on the road as fast as a modern normal/heavy one (obviously up to a point).

(Oh, and this is of course assuming I would drive in such a way which of course I wouldn't! )

Agree completely, but that's probably just because we aren't very good drivers.
I could definitely drive a heavier car faster on the roads purely because, as you say, it feels safer to do so.
On a track with big run-offs I suspect we'd both find a lightweight car much better

[Boosted LS1]

Tyre pressures could be lessened perhaps on the lightweight car?

[james_gt3rs]

Surely the "skippyness" is down to setup. E.g. comparing a Caterham to an S class on a bumpy road is like comparing a 205 to <insert heavy car with bad ride>, meaning that weight isn't the common factor in how it drives on bumpy roads.

[Equus]

For very lightweight cars (and I'm talking about stuff like Caterhams, not modern-day Elises, which are getting a bit lardy to say the least) the limitation is sprung:unsprung weight ratio and damping.

You need very high-quality dampers to do it well, and even then the bottom line is that you have to transmit the inertia of your unsprung mass hitting a bump to the chassis within little more than a single of cycle of the suspension frequency, so if the unsprung weight is a high proportion of the overall weight, that's relatively speaking a lot of force trying to disrupt your chassis and reducing grip.

On less-than-perfect tarmac (like the typical British country lane), a heavier car with more favourable ratio of unsprung weight will quite easily outpace a real lightweight like a Seven, as the latter will be skipping about all over the place, no matter how good its damping.

[PositronicRay]

TEKNOPUG said:

The fact that it so easy to get big, reliable power out of small engines; that brakes & suspension are greatly improved is a result of cars gaining so much weight (not least to do safety & emmissions). They are borne out of necessity. 2.0 Sierra weights 1200k, a 2.0 Mondeo 1600k. That's a 1/3 heavier. So instead of sufficing with 150bhp, they now need 200bhp to maintain performance. And better brakes. And better suspension. It's progress, of a sort.
.

You're having a laugh, 2.0 Sierra 150 bhp.

[TheRocket]

Boosted LS1 said:

Tyre pressures could be lessened perhaps on the lightweight car?

My old LCC Rocket (sub 400 kg) on 45 profile tires, 14 psi front and 18 psi rear...

[Krikkit]

likesachange said:

As a road car for b road blasts, a very light car can contradict its self almost. I had an Ariel atom running on A048's... stiff suspension and 550kg meant it just badly skipped across the bumpy British b roads and to get any sort of temps in the tyres with it being so light meant constant hard driving which in turn was a challenge! On a smooth track then its a different kettle ...

But that's a fundamental design issue from the start - the Ariel's suspension was too stiff for the roads you were on, and the tyres needed a compound with a much lower working range.

As you said the Nomad would probably be better suited to rough B-roads (although too far off-road biased no doubt), but on track it's no contest...

[dlockhart]

One thing which I haven't seen mentioned is the profile of the tyre. Over the past 20 years cars have had lower profile tyres and this has lead to the suspension ironing out the bumps. Which hasn't been an issue if you are running a 2 ton Range Rover.

Lightweight cars epitomize this low profile approach, but if you were to increase the profile of the tyres and make the car less sport (increasing body roll) then the car would handle better on the road and should glide over bumps and pot holes. It is a different philosophy to the two setups described by the OP. I don't think having a car setup like this makes it worse.