Front engine safer than rear?

[peterbredde]

Driving home from work last night and I am met with 911 approaching on the wrong side of the road while overtaking. No real danger and no drama - but it got me thinking? In general, who comes off better in an accident, the guy in the front engine car, or the guy in the rear/mid engine car (assuming similar size etc). Surely you'd be better off in a front engine car with all that mass to absorb the impact? Or is the existence of the engine in front of the driver a hazard? Or is the whole thing much more complex than that?

[kambites]

I'd have thought the rear engined car.

The important thing in surviving an impact is that the car slows the rate of deceleration as much as possible. A rear engined car has more freedom to design front crumple zones to perform properly. If you assume the same distance from the drivers' feet to the front bumper, the front engined car can use that distance minus the thickness of the (non-deformable) engine block to slow the passenger cell in a controller manner, the rear engined car can use the whole distance.

ETA: That is, of course, assuming that both cars have a strong enough passenger safety cell that it doesn't deform until the crumple zone is fully compressed.

Edited by kambites on Thursday 21st August 11:27

[John D.]

In a 911 you are more likely to enter a hedge backwards. Fact.

[peterbredde]

John D. said:

In a 911 you are more likely to enter a hedge backwards. Fact.

Agreed, but is that the same thing as me driving my front engine car forwards into a hedge? Perhaps its safer, as the seats would absorb my body weight rather than some reinforced canvas strap across my chest. And I'd go down smiling.

[Baryonyx]

It will be interesting to see the crash cell structures of the new rear engined Renault Twingo and the VW mid-engined cars which are coming out. I suspect that they'll also have thickish tyres and understeery geometry from the factory, to stop a generation of cack handed drivers binning them on their first trip out.

[J4CKO]

John D. said:

In a 911 you are more likely to enter a hedge backwards. Fact.

Or be immolated by the wonky engine.

[Bill]

kambites said:

I'd have thought the rear engined car.

The important thing in surviving an impact is that the car slows the rate of deceleration as much as possible. A rear engined car has more freedom to design front crumple zones to perform properly. If you assume the same distance from the drivers' feet to the front bumper, the front engined car can use that distance minus the thickness of the (non-deformable) engine block to slow the passenger cell in a controller manner, the rear engined car can use the whole distance.

OTOH there's more mass in/behind the passenger cell for the crumple zone to deal with, and AIUI the engine is designed into the crumple zone and moves back and down in a big enough crash.

[hoegaardenruls]

With proper crumple zones, and without a lump of metal in the front you'd assume rear-engined would be safer in a like-for like collision. You just reverse the situation when you disappear off the road backwards in a 911..

Wasn't the original Merc A-class designed so that the engine went under the passenger compartment in a frontal collision? Still, that assumes it didn't see an elk and topple over..

[Rude-boy]

OP is Ralph Nader AICMFP

[ZesPak]

Of course, this all depends on design.

But, in theory the car with no engine in front can be better designed to absorb an impact.
It's one of the reasons the Tesla S supposedly is one of the safest cars ever build.

That said, they also need "space" to absorb impact. While a Smart might be rear engined, there's no room to have any impact absorption in the front. A long-bonnet car without an engine in front (like a lot of sports cars) would be ideal to develop the best crumple zone.

In reality, your Ferrari will go underneath the "Bint that didn't see you"'s Q7 and you'll die with an Audi rim in your face.

[alangla]

hoegaardenruls said:

Wasn't the original Merc A-class designed so that the engine went under the passenger compartment in a frontal collision? Still, that assumes it didn't see an elk and topple over..

I was under the impression that most modern cars were designed to eject the engine downwards in a severe collision, meaning it didn't penetrate the passenger space & gave the crumple zone more space.

[hoegaardenruls]

alangla said:

hoegaardenruls said:

Wasn't the original Merc A-class designed so that the engine went under the passenger compartment in a frontal collision? Still, that assumes it didn't see an elk and topple over..

I was under the impression that most modern cars were designed to eject the engine downwards in a severe collision, meaning it didn't penetrate the passenger space & gave the crumple zone more space.

As with a lot of things, I think Mercedes just did it first and the rest followed - the original A-class was a mid-90's design, when you average French hatchback would have been lucky to scrape two stars in an NCAP test. The height of the A-class just made it a bit easier to achieve.

[ZesPak]

hoegaardenruls said:

As with a lot of things, I think Mercedes just did it first and the rest followed - the original A-class was a mid-90's design, when you average French hatchback would have been lucky to scrape two stars in an NCAP test. The height of the A-class just made it a bit easier to achieve.

While I agree to an extend, don't sell the frenchies short on safety. Renault have been topping the charts for over a decade.

[hoegaardenruls]

ZesPak said:

While I agree to an extend, don't sell the frenchies short on safety. Renault have been topping the charts for over a decade.

Totally agree on the change in that respect, as the comparison was with French stuff of the same era - I wouldn't have fancied a head on collision in the Mk 1 Clio I owned..don't think I would have come off to well.

Nowadays, I just need to hope I'm OK when I leave the road backwards..

[paulrussell]

I'd say a front engine car would be safer, as with a rear engine car you've got a fuel tank in front of you.

[Baryonyx]

hoegaardenruls said:

As with a lot of things, I think Mercedes just did it first and the rest followed - the original A-class was a mid-90's design, when you average French hatchback would have been lucky to scrape two stars in an NCAP test. The height of the A-class just made it a bit easier to achieve.

The original A Class was notoriously unstable though, wasn't it?

[kambites]

paulrussell said:

I'd say a front engine car would be safer, as with a rear engine car you've got a fuel tank in front of you.

I'd have thought most rear engined (as in with the engine behind the passengers) cars have the fuel tank in the back? Mine certainly does.

[anonymous-user]

The limiting factor in most frontal impacts these days is the wheel/tyre assy. (massive stiff wheel, that gets forced backwards into the footwells........)

[kambites]

Max_Torque said:

The limiting factor in most frontal impacts these days is the wheel/tyre assy. (massive stiff wheel, that gets forced backwards into the footwells........)

Surely it can't be hard to design a system which deflects the wheels out beyond the sills in an impact?

[balls-out]

one of the reasons that the inline 6 is becoming rare is the added challenge of crumple zone with such a long rigid lump at the front.

whilst off topic. The beetle used to be one of the best cars to be hit BY as a pedestrian. nice low front bumper to 'sweep' you off your feet, then a bonnet that could deform without an engine to stop it suddenly