So here's the text of Mark and I's chat on the subject. Thought I'd post on here and see people's opinions, though I'm pretty unlikely to change mine on this subject.

3:20 PM me: One thing that I was thinking of that makes me laugh...
WRC cars use magnesium and aluminum in most suspension components.
The HDPE plastic protection is probably to keep them from breaking from sharp
hits.
3:21 PM Lots of US rally cars copy the HDPE on it to protect steel arms.
3:23 PM Mark: why does that make you laugh?
3:59 PM me: Because in the WRC they are protecting from the shock of hitting rocks which can weaken and cause magnesium and aluminum to break.
Steel deforms and bends, doesn't shatter.
4:00 PM Mark: depends upon the steel
me: So spending time covering steel arms with HDPE is a waste of time and money.
Talking about stock style arms...
Look at Subaru front control arms for example.
4:01 PM Take an aluminum one and a steel one and give a concentrated direct hit of the same force. The aluminum will break whereas the steel one will deform. HDPE helps disperse the impact and absorb some of it.
Mark: it's also about changing the momentum or angle of impact
which is still good for steel arms
me: Just an example of people copying WRC and top cars pointlessly.
4:02 PM But totally unneeded...
Mark: not necessarily
me: I've seen the argument that it reduces wear and keeps the parts from rusting.
Mark: if instead of slapping the steel at x angle it hits at y angle and some of the z momentum is gone, it can prevent a bent arm
me: But the stock parts are so inexpensive and expected life span so short.
4:03 PM Mark: yes, but if it saves an entry fee, it's well worth it
me: But a rock impact to the middle of a trailing arm is not likely to bend it. Maybe dent it, but not bend it, at a quick short impact.
Mark: $4000+ to go to an event > $40 for LDPE
me: If it were mag or aluminum on the other hand...
That shock impact could easily break the arm.
4:04 PM Mark: a bent are will fuck up your alignment
it's not that much money in the scheme of things, it is damage prevention/limitation, and it's weight lower on the car
4:05 PM me: You will not bend a steel arm from a short term rock impact. Any impact that has the force to bend a steel arm would be so much that the HDPE wouldn't affect much.
It's unsprung weight which is the worst kind...
Mark: you don't need big fancy mud flaps either since the rules don't specify what size they have to be, but everyone gets sparco ones
me: No, that's easier than making your own and it bigger helps protect paint.
4:06 PM Mark: it will dissipate the impact, which is what you are going for
me: How have you survived without the HDPE>
Mark: oh, so now paint is important vs control arms
me: Sorry, it's pointless and a waste of time on steel arms.
If it's a hard enough impact to bend a steel arm, a little bit of HDPE is going to make little to no difference.

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Grant Hughes

I say it depends on the rock.

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Jon Burke - KI6LSW
Blog: http://psgrallywrx.blogspot.com/

Jon Burke Wrote:
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> I say it depends on the rock.
>
> Jon Burke - KI6LSW
> Blog:
> 'Holy Shit!' @ 4:10

Depends ware you play ...Arizona rock eats every thing ..Steel alum mag ...HDPE protected or not ... LOL...

HDPE ...Keeps the rock from flying around ...Right ....?

David

Hazardous Toys inc

Eats, but won't eat beyond the life span of the component anyhow. It's the sharp, shocking impacts that would fracture alu or mag that I think is really what's being protected against.
Interested to hear what someone like Tim Taylor who have a intimate knowledge of the metalurgy think...

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Grant Hughes



Edited 1 time(s). Last edit at 05/27/2009 08:12PM by NoCoast.

I've seen the subaru trailing arms get worn through from rocks hitting it. They wear through right at the bushing on the rear upright. $10 worth of hdpe will last multiple seasons and be cheaper than replacing the arms every 5-10 events.

I've also seen subaru aluminum front arms with gouges and chunks taken out of them, but no cracking or bending because of it.



Edited 1 time(s). Last edit at 05/27/2009 08:53PM by Carl S.

Grant, come rally on Washington roads with your bare, unprotected suspension and underbody. I dare ya. Think of a fire hose aimed at the bottom of your car, only instead of shooting water at full blast it's shooting sharp rocks, 1-2 inches in diameter. It will literally wear away the steel. I have seen multiple times the rear trailing links on Mazda GTX's wear away so thin that they snap and the rear bushings pull right out. Even the thick cast iron lower trailing arm bushing housing on a Subaru rear knuckle will eventually wear down to nothing without any protection. And it doesn't even require a big rock (though that will certainly do it) hitting a rear lateral arm on a Subie or Mitsu or whatever to bend it. Just the constant barrage of smaller rocks will bend them.

oh yeah. You hafta put hdpe under the car 'round these parts, if for no other reason than that you might want to be able to remove suspension bolts at some point, and find that job easier to do if said bolts are still bolt shaped, and not, say, rivet shaped.

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Jay Woodward
Snohomish, WA
'90 Mazdog Frankenprotege
Chronologically, 46...

We have floors disappear from under cage feet. Xmembers, control arms, bolt heads, mud flap attaching hardware, rocker panels all are subject to ruin without some sort of HDPE in the PNW. I've pulled logbooks from cars with too much rock damage.

I was really surprised to see Moro's Sube without any floor protection. ACP's Evo has carbon fibre panels that look like Shep the dog with all the fur on them.

Our cars have huge hardened 3/4" rod ends on the rear end of the trailing arms that hang down lower than the lateral links (Protege geometry, just remade with thicker arms and rod ends).

Without protection, the rod ends and the jamb nuts will erode from flack LONG before the joint "wears out."

The custom arms erode, too. They're all steel.

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Lurch
Eric Burmeister
The west coast...of Michigan

Here is another reason to look into plastic shielding on suspension parts or the bottoms of floors. Citroen has a body shop for their rally program that can only keep up with 6 cars since there is so much stone damage to the body of the cars after every rally. And that is 4 guys working full time.

http://www.racecar-engineering.com/articles/rallycar/173019/citroen-c4-wrc.html

I think the main thing that is being protected against as others have said is the wearing sanding / deterioration that occurs when all the little rocks keep pelting the parts not from large rocks bending things.

We just put HDPE up so that stuff doesn't get rock blasted into oblivion. Doesn't take long.

Any of you cronies have a good source for this stuff?

mcmastercarr.com has it.

so does www.indplastic.com (free shipping w/online orders over $150)

I have UHMW-PE, shit is tough as nails.

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Jon Burke - KI6LSW
Blog: http://psgrallywrx.blogspot.com/

alkun Wrote:
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> Any of you cronies have a good source for this
> stuff?

http://www.interstateplastics.com/

Al, just tell me how much you want I have an account with them.

-Tim

This thread has gone this long without some example pics?

Post them up if you've got them.... please

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-Jason