Moved tubular bumpers closer to car

[Redline]

Yes, chassis as in unibody.

You're right that the bumpers were designed to elastically deform (i.e. no damage) at up to 5 mph with the old regulations. So for the Spider, they could absorb about 2500J of energy. In a crash, they will have probably a vanishingly small role in energy dissipation. Rough calculations: less than 4% of the total crash energy can be absorbed by the bumper for a 25 mph collision, less than 2% of the total energy for a 40 mph impact. Whether or not the bumper sticks out 4 inches or 4 feet, assuming the same performance of the bumper supports, the only thing that will matter is that the car is crumpling to absorb that energy; it makes no difference to the occupants.

One small benefit of the bumpers, and a much more important role these days with well-designed crash structures, is that the bumper ties the two sides of the car together, so an offset impact on one side can be (partially) deflected to the opposite collapsible unibody structure.

So for cosmetic impacts, the bumpers are valuable. For bigger hits, it won't really matter whether or not you have the bumpers.

[SoFlaFiat]

Keep smiling Richard!!

[DieselSpider]

Yes, chassis as in unibody.

You're right that the bumpers were designed to elastically deform (i.e. no damage) at up to 5 mph with the old regulations. So for the Spider, they could absorb about 2500J of energy. In a crash, they will have probably a vanishingly small role in energy dissipation. Rough calculations: less than 4% of the total crash energy can be absorbed by the bumper for a 25 mph collision, less than 2% of the total energy for a 40 mph impact. Whether or not the bumper sticks out 4 inches or 4 feet, assuming the same performance of the bumper supports, the only thing that will matter is that the car is crumpling to absorb that energy; it makes no difference to the occupants.

One small benefit of the bumpers, and a much more important role these days with well-designed crash structures, is that the bumper ties the two sides of the car together, so an offset impact on one side can be (partially) deflected to the opposite collapsible unibody structure.

So for cosmetic impacts, the bumpers are valuable. For bigger hits, it won't really matter whether or not you have the bumpers.

Enough could be, probably, etc there to make it a toss as to whether they will or will not matter however as installed the bumpers did in the actual 30 MPH crash testing done on the 1978 work to protect the fuel tank along with the cars occupants and without any fuel leaking. The car performed better than many had thought it would with the twin tube bumpers and shocks.

[toplessexpat]

I'm no expert on crash regulations. It does feel though that given the relatively low ride height of our spiders and the ever increasing height of modern cars, the tubular bumpers likely provide an excellent "step" up and over the vehicle

This is in no way meant to condone or condem the bumper - just a musing that the world we live in now is not the same one that the bumpers were designed for....

[rjkoop]

Keep smiling Richard!!

Still smiling. I hope this thread doesn't get to be 7 pages long like the one that inspired me!

http://www.fiatspider.com/f15/viewtopic ... il#p113153

[spiderdan]

Still smiling.

Of course you are Richard and so am I.
It's December and you live in Ottawa.
No snow on the ground, no salt on the roads.
Spider still being driven.
Good reason to smile.

[toplessexpat]

Dragging this completely off thread.... I was going to drive the 2000 last weekend. It was a bit chilly so put the heater on ...... and no heat!

Fiddled with the valve for 5 mins. It appeared to be moving freely - but no luck. I've not really fiddled with them before (living in Texas and all). Can they lock up but appear to be moving fine?

[DieselSpider]

I'm no expert on crash regulations. It does feel though that given the relatively low ride height of our spiders and the ever increasing height of modern cars, the tubular bumpers likely provide an excellent "step" up and over the vehicle

This is in no way meant to condone or condem the bumper - just a musing that the world we live in now is not the same one that the bumpers were designed for....

I was surprised at the results of the tests they did back then. I did not think they would fair as well as they did.

[Redline]

https://youtu.be/owcXQqFBu-w

[DieselSpider]

https://youtu.be/owcXQqFBu-w

Stellar performance compared to even modern Chinese vehicles.

This one is just unbelievable:
https://www.youtube.com/watch?v=D827IxEJVS4

The entire passenger compartment is the crumple zone in a 40 mph crash. Thankfully export of that vehicle to Europe or the USA was not allowed.

[Redline]

Before we get too smug, note that the passenger seats completely collapsed in the 124. While a modern system like WHIPS in a Volvo allows a certain degree of controlled mobilisation to spread out the crash pulse, falling into the back seat isn't the best outcome.

This is interesting to watch, for anyone who wants to draw their own conclusions of the contribution of tube-and-shock bumpers to overall energy absorption. Look when the bumper hits, when the crumpling of the body itself starts and when the occupants start to move relative to the seat (which indicates when any meaningful deceleration and energy absorption is taking place).

https://youtu.be/Xnu935Hq7YQ

Like I said, draw your own conclusions.

[RRoller123]

They didn't seem to do a damned thing is my conclusion.

[DieselSpider]

They appeared to keep the fuel tank from rupturing and kept the rails from spreading. Be interesting to see other tests done with the old style bumpers for comparison. Still would have to be better than that Chinese Crew Cab Truck. In the early 80's Fiat was doing some pretty wild crash testing using a machine to toss the cars sideways through the air and roll them. Have not found more than the one rear crash test video on the 1978 124 though.

[RRoller123]

Moving them in closer would likely still help keep the rails from spreading, but it would be a shame to have damage occur from the pretty common occurrence of the bumper bump in parking lots, etc. (i.e. around ~5mph)

[DieselSpider]

The newer style shopping carts that have the baskets so high that they are above the bumpers on even a pickup truck are what probably do the most damage around here.

There are some add-on foam bumper guards that can lend a bit more shock absorption to the OEM bumpers too some with 4 inches of energy foam inside them.

As a biker I can as earlier mentioned attest to how well even a few fractions of an inch of energy absorbing foam can work to minimize the severity of things even when your hitting the pavement in a 40/50 mph crash so the potential is there.