Steel vs. Fiberglass Fender Flairs...Is Stiffness and Ride Superior...., Just had a guy tell me that the stiffness is better with steel... Options

[MikeInMunich]

Hi guys,

just had a call on my white car from a guy who's not interested (any more) because I have fiberglass instead of steel fenders. This idea is new to me and want to read your (better informed) opinions on the statment, "the difference in stiffness is like night and day".

I personally seriously doubt that I or anyone else would be able to notice the difference in stiffness in the car with fiberglass fenders vs. one with steel fenders. All I could tell the guy was that this idea is very new to me, since the entire suspension has nothing to do with the fenders themselves.

So, just to be sure...please, lemme know your thoughts.

Thanks!

Mike in Munich (IMG:style_emoticons/default/smilie_flagge6.gif)

[Superhawk996]

In the most theoretical sense . . . yes.

Practically speaking. It wouln't be something you can feel as an increse in chassis stiffness while driving.

The structure of the 914 is in the underbody unibody that consists primarily of the longitudinals and the fore and aft bulkheads. That is what carries the loads transmitted from the supension.

The Class A exterior panels like fenders don't carry much load at all. Do they carry some loads as the rest of the chassis flexes? I'm sure they do . . . ever so slightly. A fender panel with a big semi circle missing out of it (wheel opening) isn't a very effective load carrying memeber. I don't think any driver would be able detect the difference in chassis stiffness due to presence of steel flares vs. fiberglass.

Now the other question is whether fiberglas flares flex and cause paint cracking (over time) . . . . that is most certainly a YES. I have fiberglass flares on my chassis and I can see the evidence of the flexing on one side. I will eventually migrate to steel flares when I completely strip the body to go back to OEM color. I hate red cars but that will be a while before I get to a repaint.

[MikeInMunich]

OK. Lovely. Thanks for that feedback!

[mb911]

In the most theoretical sense . . . yes.

Practically speaking. It wouln't be something you can feel as an increse in chassis stiffness while driving.

The structure of the 914 is in the underbody unibody that consists primarily of the longitudinals and the fore and aft bulkheads. That is what carries the loads transmitted from the supension.

The Class A exterior panels like fenders don't carry much load at all. Do they carry some loads as the rest of the chassis flexes? I'm sure they do . . . ever so slightly. A fender panel with a big semi circle missing out of it (wheel opening) isn't a very effective load carrying memeber. I don't think any driver would be able detect the difference in chassis stiffness due to presence of steel flares vs. fiberglass.

Now the other question is whether fiberglas flares flex and cause paint cracking (over time) . . . . that is most certainly a YES. I have fiberglass flares on my chassis and I can see the evidence of the flexing on one side. I will eventually migrate to steel flares when I completely strip the body to go back to OEM color. I hate red cars but that will be a while before I get to a repaint.

(IMG:style_emoticons/default/agree.gif) and one more thing is different expansion and contraction rates really show up with fiberglass attached to steel

[EdwardBlume]

No. The longs and various cross points yes, but steel fenders no.

I had an issue with one fender sticking out funny once, but that was when the entire battery area and long was massively repaired on Dads car. It went on a C bench and was corrected, but the fender was considered superficial.

GLWTS

[barefoot]

Now the other question is whether fiberglas flares flex and cause paint cracking (over time) . . . . that is most certainly a YES. I have fiberglass flares on my chassis and I can see the evidence of the flexing on one side. I will eventually migrate to steel flares when I completely strip the body to go back to OEM color. I hate red cars but that will be a while before I get to a repaint.

I expect seeing evidence of cracked paint at the glass to steel joint is mainly due to differential thermal expansion & not to structural flexure.
The coefficient of thermal expansion of glass filled polyester is several times higher than carbon steel. Cars parked in southern sun get pretty warm !

[Superhawk996]

Now the other question is whether fiberglas flares flex and cause paint cracking (over time) . . . . that is most certainly a YES. I have fiberglass flares on my chassis and I can see the evidence of the flexing on one side. I will eventually migrate to steel flares when I completely strip the body to go back to OEM color. I hate red cars but that will be a while before I get to a repaint.

I expect seeing evidence of cracked paint at the glass to steel joint is mainly due to differential thermal expansion & not to structural flexure.
The coefficient of thermal expansion of glass filled polyester is several times higher than carbon steel. Cars parked in southern sun get pretty warm !

(IMG:style_emoticons/default/agree.gif)

I agree that the thermal expansion delta between steel and fiberglass is a long term issue.

However, I also see light cracking / checking on one side that is entirely over the fiberglass portion.

Maybe from people leaning on it during maintenace while hanging into engine compartment? It's definately not paint adhesion issue. Also see a light hairline paint crack up at the transitoion to the sail panel (at the rear) that I belive might be from the mass of the flare being shaken back and forth cross car from road impacts. Nothing major, but I don't belive any of this would occur with steel flares.

I can try to get some pictures, but suspect they won't photo well, they are very small and depend on the lighting as to whether they are visible or not.

[Root_Werks]

914's being of unibody construction, the fenders are part of the structure and I would imagine, play a role in keeping the twisting and flexing reduced.