Do we really need all that safety stuff?

[Fingie]

My Celica has a driver side airbag, ABS, side-impact bars, and safety glass. Looks fine to me :-)

[oldtamiyaphile]

Originally Posted by RunningStrong

A 500 kg car, with weaker, low-assistance brakes and a smaller contact patch would probably struggle to match a modern 1000 kg car.

Handling and braking

While slightly heavier than other Caterhams the CSR still upholds Colin Chapman's philosophy of "add lightness."[2] Weighing only 575 kg (1,268 lb), the CSR has excellent handling, making it extremely agile. On the skidpad, the Caterham outperforms many supercars. Its 1.05 lateral g-force beats the 2007 Porsche 997 Turbo's 0.94 G, the Ferrari F50's 1.03 G, and the Ferrari Enzo's 1.01 G.

In braking tests, the CSR performs well. From 70 mph (110 km/h) to a complete stop, the CSR took 140 feet (43 m). The 997 Turbo, stopping from 60 mph took 99 feet (30 m).[3] The Ferrari F50 performed well, stopping from 60 mph (97 km/h) in 119 feet (36 m).[4] For comparison, an average 2011 road car (2011 Chevrolet Cruze LS) takes 167 feet (51 m) to completely stop from 70 mph (110 km/h)

Caterham 7 CSR - Wikipedia, the free encyclopedia

Keeping in mind the Caterham is something an average DIY mechanic can build from scratch and doesn't have ABS, EBD, brake assist etc, that the others do. Porsches have always stopped quickly because the rear weight bias controls weight transfer under heavy braking.

Think about it this way, you're out on a drive and for whatever reason you need to stop suddenly (you happen to have 43m to do it), the dangerous light weight car stops without a scratch, while the safety ladden Cruze sends you to the hospital and probably the morgue.

There are of course some unavoidable accidents, but in general good handling/ braking cars could reduce accident severity at least as much as passive systems.

I wonder what would happen to the road toll if governments gave manufacturers the option to build actively safe cars in return for lower crash requirements. It seems like safer cars don't translate with any significant meaning to reduced death and injury statistics.

[IamIan]

Sorry ... but ... no ... all else being equal the larger heavier vehicle is inferior to the otherwise equal lighter vehicle... for breaking / stopping ... and for cornering.

#1> tire/road friction doesn't necessarily increase with mass ... ie the component of your mass that acts perpendicular to the road surface ... the 'normal' force .. is what increases the tire/road friction ... ie you have less tire traction/friction (but same mass) going up or down hill.

#2> However .. no matter what the angle is .. up hill or down hill .. momentum always increases with mass.

All else being equal... A heavier vehicle has to take a longer distance to break going down hill ... due to angle , it has less 'normal force' thus less road/tire traction/friction ... but it's momentum from the higher mass is still just as much higher .. and the additional mass means it has a greater gravitational pull downward as well.

Down hill ... all else being equal ... Heavier vehicle always at a breaking disadvantage/penalty.

- - - - - -

the ... 'all else being equal' ... part is the only way that engineer's can try to compensate for the higher mass automatic penalties .. by investing in bigger/wider tires, bigger brakes, etc.

But .. a lighter car can also be engineered with those wider tires .. bigger brakes , etc ... thus it can get those benefits and have less mass to brake.

If anything the finite limits of materials put the larger / heavier vehicle at a scientific and engineering disadvantage ... as far as trying to scale up and keep pace with the increased vehicle mass ... The same thing happens to larger buildings .. and why an ant wouldn't be as proportionally as strong if it were the size of a house... ie there are automatic and unavoidable penalties to scaling up.

- - - - -

And just for fun ... even if we want to ignore all that ... statistically overall if you lump it all together ... for whatever reasons you might think are the cause ... generally one is more likely to die driving a heavier vehicle than a lighter one.

It's something many people get completely backwards .. mostly because some of the figures taken by themselves can be misleading.

So here goes

First ... what are all those safety requirements worth ? ... big or small vehicle ... they save lives... total death rate per billion miles vastly decreased over time as we implement these features.

Now the one graph seems to look like the heavier vehicle's have lower rate of deaths ... it looks like a decreasing rate of death as vehicle weight increases ... but look closer.

The Numbers:
In 1988 vehicles 3,500 lbs and over had on average 100 deaths.

Same year 1988 vehicles 2,500 lbs and less had on average 150 deaths.

Sure 150 looks bigger than 100 ... and that makes it 'look' like the heavier vehicles were statistically safer ... but ... it becomes a question of that other part of the description ... per million registered vehicles ... that's important.

Because when we look at the other graph ... to see what the distribution of that 1 million registered vehicles was for that same year ... out of every 1 million registered vehicles 150,000 were 3,500 lbs or more ... but ... 500,000 of them were 2,500 lbs or less.

So out of every 1 million registered vehicles in 1988.

150,000 vehicles (3,500+ Lbs) had 100 deaths = Death rate of 1,500 vehicles per death.

500,000 vehicles (2,500- Lbs) had 150 deaths = Death rate of 3,333 Vehicles per death.

For whatever reason you like ... those driving 3,500+ Lbs vehicles were twice as likely to die as those driving 2,500 lbs or less vehicles.

No .. I didn't just make up numbers ... reputable reference source used for and sited on each graph.

[ksa8907]

I see crazy drivers every day. I drive through 3 very accident prone intersections twice a day. I also do a fair amount of city driving when I go to college 2 days a week.

I'm married with a 2 year old some and another on the way, safety is important to me. Yes I drive carefully, I have even had smith driving classes but that doesn't protect against crazy scenarios and idiot/drunk drivers.

Personally, give me all the safety equipment possible. On that same token, I do wish cars weighed less. I think with CAFE standards vehicles will get lighter, but the days of 1500lb(700kg) cars is long gone.

[P-hack]

lol, married with kids as excuse for driving 3800 lb car, emotional, completely misses the point.

For whatever reason you like ... those driving 3,500+ Lbs vehicles were twice as likely to die as those driving 2,500 lbs or less vehicles.

[Frank Lee]

Don't forget to put a "Baby on Board" sign in the window- you know, so I smash into anything but that vehicle.

[Grant-53]

Design geometry and material strength are key to crash safety. Good braking and handling are key to accident prevention. Safer drivers in safer cars means fewer fatalities. When air bags first came out people were afraid of them. Now we know how well they work. The only downside is that nobody smokes a pipe in their car anymore.

[spacemanspif]

Anyone ever take note of how much baby seats resemble racing seat setups? How about bolstered seats and 5point harnesses in every car? Maybe a comfortable bike helmet that works with a HANS device to not limit visibility or effect comfort of the drivers? Shouldn't we all be driving tube chassis race cars anyway?

[jcp123]

Originally Posted by P-hack

lol, married with kids as excuse for driving 3800 lb car, emotional, completely misses the point.

I disagree. Ever taken a vacation with kids in a subcompact? We do it but it's not fun. I'm going to keep the Echo, but the Kia's gotta go. My fun car is yet to be determined, once I sell the Mustang I'll decide, but it could very well be a classic 9-passenger wagon.

[some_other_dave]

Originally Posted by RedDevil

Friction increases with mass...

You're assuming that tires follow the classical friction model. They don't--if they did, no cars would be able to accelerate at more than 1G. Tires actually physically interlock with the road; the bits of the tread key into irregularities in the surface of the road. Those interactions are not improved by the amount of force pushing down on the tire, so weight doesn't help.

The "road-hugging weight" ads from the 70s were pure BS. Lighter cars corner harder, brake shorter, and accelerate harder than heavier ones--given the same tires, brakes, engines, etc.

-soD