Are crush tubes as effective as impact absorbers?

[frankc]

I am thinking about changing my rear bumper supports from the US impact absorbers to the euro crush tubes, in addition to some other things, in order to save a little weight. My question is do the crush tubes perform as well when absorbing an impact?

Replacing the tubes if hit from behind is the least of my worries, I'm just wondering if the car will suffer increased damage under similar impact with the crush tubes vs. impact absorbers.

thanks,
Frank

[waynesco1]

Had same thought regarding weight ,The us absorbs hit of ? mph euro has kink at mount to help crush ? mph. Eather way damage will accure. Does pelican have a source for these ? would like some also

[island911]

IIRC the weight difference is very minimal.

knock the dirt of the OE spring back absorbers and call it a wash.

[CharlieB]

Will a Euro SC rear bumper fit the US rear impact absorbers without any modifications???

[euro911sc]

Well... the tubes should work just fine... once. the shock type could be useful multiple times.

Not sure if the ROW bumper will fit as it has a lot of holes in different places compared to the US version. Mostly due to different bumperettes. If you are in the Stuart area one day come on over and see if they look the same

Best regards,

Michael

[IROC]

The crush tubes will work adequately well...once.

I took my crush tubes off entirely. I simply have aluminum angle supporting my rear bumper. Very lightweight, but zero impact protection.

[ael911]

The rear crush tubes are a direct replacement of the bumper shocks. The front tubes have a larger center bolt and needs a little grinding of the mounting hole to make them work. I have them all the way around and it' quite a bit of weight loss when you compare 4 bumper shocks to 4 impact tubes. The downside is there is really no impact protection. But my car is so low that even a typical sedan's bumper will hit higher than my bumper in a collision so what difference would bumper shocks make anyway. I got mine used from DC Automotive but it took a while.

[RWebb]

I agree that the wt. savings is pretty decent - you can do a search and find the post where it is quantified.

Obviously a FG bumper is the first thing to do to lose wt. back there. It will be destroyed in a collision - HOWEVER, it will be the other guy's fault (not counting you spinning, etc.) and so he will get to pay.

[burgermeister]

We have "no fault" insurance, meaning it's always my fault (just like when I was a kid at home!)...

Where would you even find said crush tubes? I've never come across any...

[island911]

Are crush tubes as effective as impact absorbers?

I believe that the front bumper is pulled back a few mm's with the "crush tubes" --meaning, they have less travel during a hit, which likely means less energy absorption.

Randy, let's see some numbers. I remember pursuing the crush tubes until some one on the board here posted how beefy (and similar in weight) the crush tube where (wrt the US impact absorbers.)

[island911]

Ah, here it is: http://forums.pelicanparts.com/showthread.php?t=119074

Originally Posted by 1980SC

Bumper shocks-

I replaced my euro crush tubes with the USA style shocks.



The top shock is the USA style from a 3.2 Carrera. The bottom is the euro style, and in "used" condition.

The difference in weight between them was so small, I didn't even bother to put them on a scale. Don't waste your time.

-Rob
1980sc euro

[Won]

http://forums.pelicanparts.com/showthread.php?t=187549&highlight=euro+tube+weight

Around 12lb total savings for 4 tubes. It may not be much but how else can you lose 12lb at such extremities of the car, other than taking off bumper pads?

Instead of sourcing actual Euro tubes, one could cut off the mounting flanges off the US shocks and replace the shock body with some straight tubing with holes drilled across. They'll crush just fine.

[frankc]

Originally Posted by burgermeister

Where would you even find said crush tubes? I've never come across any...

Part #23 here:
http://www.pelicanparts.com/cgi-bin/PartsLookup/search.cgi?command=show_page&Catalog_Name=911_USA_74_77_KATALOG&Illustration=802-05&Line_Item=23

[don911]

I'm getting ready to do this right now. 12lbs is worth it to me for the tubes since I'm about out of places to save weight.
My plan is to put front crush tubes on the rear along with a 964 reinforcement bar. I may drill some lightening holes in the bar as well. A FG bumper cover will go over the top.
I'll post weight savings (hopefully) when I'm finished.

I may have Island come by and give me "opinions" on the design and verify my results.

As far as repeatability of the bumper shocks, don't count on it. Both of mine were bent after a low speed impact.

[island911]

Originally Posted by frankc

Part #23 here:
http://www.pelicanparts.com/cgi-bin/PartsLookup/search.cgi?command=show_page&Catalog_Name=911_USA_74_77_KATALOG&Illustration=802-05&Line_Item=23

And the fronts here: http://www.pelicanparts.com/cgi-bin/PartsLookup/search.cgi?command=show_page&Catalog_Name=911_USA_74_77_KATALOG&Illustration=802-00&Line_Item=9


Don, let me know when. ....but I rarely have opinions about anything.

Oh, and yeah, the an off-axis hit is likely going to bend even the bumper 'shocks'.

[RWebb]

Very interesting Don - can you post pics (and the wt.) of the 964 reinforcement bar?

[don911]

Originally Posted by island911

Don, let me know when. ....but I rarely have opinions about anything.

I know it's rare, only in your waking hours and non REM state. Also, as long as we're clear it's the .02 opinion....can't afford the professional one.

RWebb, Will do. Should have it in a couple weeks.

[island911]

Hey, for you Don, I'll step up to 4¢ worth of opinion, and give you the fellow engineer 50% professional discount.

Seriously, the crush tubes are looking like a good weight savings. A bit pricey, but still...

[frankc]

There are many threads debating the weight savings of crush tubes, so I didn't want to get into too much of that here. What I didn't see in my searches (and perhaps I missed it) was if anyone had any hard facts on how well the crush tubes actually do their job when compared to the impact absorbers. I realize the tubes are a one time use part, and I'm ok with that, but it may not be worth it to me if the car is more susceptible to damage from a minor impact out on the road.

A euro BMW I had with "crushable" bumper mounts was rear-ended once, and I was amazed at how well the mounts absorbed the impact and kept the car relatively unharmed. The truck that hit me had its entire front bumper smashed in. Of course the bumper mounts needed to be replaced, but they were cheap and did what they were designed to do.

Frank

[island911]

Steel has great (weight specific) toughness. Tho' the crush tubes likely absorb less total energy than the (heavier) impact absorbers.