Fiberglass vs. Carbon Fiber - 986 Forum - The Community for Porsche Boxster & Cayman Owners

blinkwatt · 05-01-2007, 06:23 PM

I'm lost on the difference in all the aftermarket stuff I see,especially spoilers and front bumpers. Can someone explain to me the difference between all of fiberglass,fibreglass,carbon fiber & carbon fibre? What are the pro and cons to each?

yellowboxster01 · 05-02-2007, 11:57 AM

Quote:

Originally Posted by blinkwatt

I'm lost on the difference in all the aftermarket stuff I see,especially spoilers and front bumpers. Can someone explain to me the difference between all of fiberglass,fibreglass,carbon fiber & carbon fibre? What are the pro and cons to each?

fiberglass/fibreglass
carbon fiber/carbon fibre

same thing different spelling. I believe in euro english they spell it "re" instead of "er", same material though. Kind of like tyres and tires.

Personally, if it were me, I'd get it in carbon fiber because, cf has the tensile strength of steel. Fiberglass tends to be too flimsy and brittle.

EPIQTodd · 05-02-2007, 12:04 PM

Don't forget OEM parts as well - poly resin. Fiberglass is light and cheap - racers use it because of those reasons, and often racers have extra body parts with them at the track when they get hit, because fiberglass will shatter. It's not desirable for a bumper if you drive on the street. Whereas an OEM (poly) bumper may crack or dent, a fiberglass bumper will crack and shatter - far more damage and much larger crack than the poly bumper. Carbon fiber is the lightest, but also most expensive, and near impossible to repair properly.

blinkwatt · 05-02-2007, 12:14 PM

Thanks for the input! So does anyone see a problem with putting on an aftermarket rear spoiler made out of fiberglass on a Boxster?

Topless · 05-02-2007, 01:16 PM

Fiberglass
A fairly generic term in which you take fiberglass mat or cloth and lay it up with resin to form nearly any shape. Found everywhere, boats, surfboards, airplanes, car bodies, rocket motors, space shuttle etc.
Pros- good strength to weight, easy to work with, can be made very flexible,low cost.
Cons- repeated flex can cause failure, gets brittle when uncoated/painted and exposed to sunlight. Glass fibers get in your skin when sanding and make you crazy.

Carbon Fiber
The same basic process as fiberglass only using carbon fiber cloth and high quality resins to get the highest tensile strength, highest strength to weight, and achieve a very rigid shape or structure.
Pros- Ultra high strength, ultra rigid, resists damage from sunlight when unpainted.
Cons- does not flex, if flexed it shatters like glass. very expensive.

Traditionally this was only found on ultra high tech applications (fighter jets, space shuttle, F-1 race cars, world class racing yachts) due to its high cost. It is now much more mainstream (even NASCAR bodies use carbon fiber now I think) and has become a fashion accessory of the Rice racers and others who have body and dash panels laid up with carbon fiber just for the look. Most of these panels are not pure carbon fiber but common plastic/metal panels with carbon fiber skin. No lighter in weight or stronger than fiberglass. Just pure bling. All foam...no beer.

So do you want carbon? Is ultra high strength/ultra rigid important for your application? If so then carbon fiber is the way to go if you can bear the extra cost.

Topless · 05-02-2007, 02:01 PM

Quote:

Originally Posted by blinkwatt

Thanks for the input! So does anyone see a problem with putting on an aftermarket rear spoiler made out of fiberglass on a Boxster?

Just get the Ruf. They actually test their stuff. You will be glad you did.

Perfectlap · 05-02-2007, 02:15 PM

fiberglass is hit or miss.

Its only as good as the shop making it. I had a fiberglass aero kit on a previous kit made by Racing Beat who specializ in RX7 and Miatas and it was well made stuff. I spoke to someone who once worked there and they told me they threw out a great deal of product that didn't meet quality control standards. He said he bought allot of rejects for his own cars because it was a matter of minor blemishes imperfections that could have been fixed with a little time.
98% of Fiberglass makers will not be so attentive and will use as low grade materials as possible.
This means horrible fits where body panels don't line up properly and since most of these aftermarket parts are on sport suspensions they end up taking lots of punishment...paint starts to crack and looks like a wrinkled shirt in no time.

Now Composites like carbonfiber are another matters. It's a fairly low tech manufacturing procedure and risky for craftsmen to work with. Thus you don't see allot of genuinely well made carbon fiber. I was one of the first among my friends to buy an all carbon bicycle back in the very early 90's and it was actually made in Taiwan by Giant! I turned away from expensive aluminum because of its short shelf life. But as far automotive, it still seems to be standard for everything from ultra expensive racing helmets to mirrors.

Polyurethane, polyresins etc. used in factory aero parts from Porsche are well made, resilient and lazer cut so there's never an issue with fit. But its very expensive.

yellowboxster01 · 05-02-2007, 02:17 PM

I'm pretty sure this bumper is fiberglass.

insite · 05-02-2007, 02:37 PM

Quote:

Originally Posted by Topless

Carbon Fiber
The same basic process as fiberglass only using carbon fiber cloth and high quality resins to get the highest tensile strength, highest strength to weight, and achieve a very rigid shape or structure.
Pros- Ultra high strength, ultra rigid, resists damage from sunlight when unpainted.
Cons- does not flex, if flexed it shatters like glass. very expensive.

i take exception to the last statement. carbon fiber can be designed to flex very well (think golf club shaft or corvette leaf springs). CF properties can be greatly varied depending on the manufacturing methods (resins, mold types, cure method, etc.).

Perfectlap · 05-02-2007, 02:43 PM

^ very true you should see my carbon fiber bicycle's rear triangle flex when out of the saddle hill climbing. These guys can do amazing things nowadays.
But ohh so expensive. I lusted after a Fondriest frame made from F1 grade CF (they had a former F1 Ferrari engineer) but they couldn't make the darn things for less than $6K and eventually went out of business. Too bad, best bike I ever owned (partially CF).

Topless · 05-02-2007, 02:44 PM

Insite,

You are right. I forgot golf shafts. My experience with CF was on racing yachts where it was chosen and designed to eliminate flex.

EPIQTodd · 05-02-2007, 02:57 PM

For a spoiler, fiberglass is just fine. No advantage for polyresin on that one.

Regarding carbon fiber and composites, I wholly disagree that it is a 'low tech' process - if done poorly, it is, but done correctly, it is VERY high tech, and difficult to do. Those who do the half-ass method of just using resin and drying in the open air are just making fiberglass with carbon fiber sheets. True carbon fiber and composites must be cured in a heated vacuum, and that is what makes good carbon fiber what it is.

yellowboxster01 · 05-02-2007, 03:35 PM

i've heard the mount holes on some of the aftermarket spoilers crack out after time. i believe there was a thread on here a couple weeks ago about it.

SC986 · 05-02-2007, 04:06 PM

If you/can you paint the carbon fiber what will the finish look like? Will you see the fiber or can it be matched in a smooth finish like the bumper?

markab986 · 05-02-2007, 04:37 PM

Quote:

Originally Posted by SC986

If you/can you paint the carbon fiber what will the finish look like? Will you see the fiber or can it be matched in a smooth finish like the bumper?

Yes, you can make a super smooth finish.
It depends on the tooling/cure process, fill & sand, and the desired finish.
Most composite components will need some sort of buildup, insert, or stiffener in the hole areas to prevent cracking.

BTW...fiberglass is a composite material too!

SC986 · 05-02-2007, 05:09 PM

Interesting. I was wondering because I love the rear diffuser bumper but have not heard good things about the fiberglass diffuser add ons.

[986] · 05-02-2007, 09:09 PM

Very informative thread! I was looking at some bumpers on Mashaw's site but only fibreglass or carbon fibre are available.. from everyone's experiences what would be more suited to a street driven car?

insite · 05-03-2007, 04:17 AM

Quote:

Originally Posted by [986]

Very informative thread! I was looking at some bumpers on Mashaw's site but only fibreglass or carbon fibre are available.. from everyone's experiences what would be more suited to a street driven car?

urethane or FRP. they're flexible. carbon fiber is good, but usually the layups are not done in a manner condusive to high flexibility. cost is also prohibitive, and unless the vacuum bag / autoclave process is sound, they'll have to use too much material, negating the weight savings over fiberglass, FRP or urethane. plus, much of the carbon fiber stuff on the market is actually fiberglass with one outer layer of carbon fiber fabric for looks.

MNBoxster · 05-03-2007, 07:57 AM

Hi,

The term Carbon Fiber encompasses many different materials and processes - too many to discuss in length here.

Most CF on the Aftermarket is not pure CF, but (CRP) Carbon Reinforced Plastic. The plastic is most often epoxy, but other plastics, such as polyester, vinyl ester or nylon, are also used. Some composites contain both carbon fiber and fiberglass reinforcement. Less commonly, the term graphite-reinforced plastic is also used.

One way of producing graphite epoxy parts is by layering sheets of carbon fiber cloth into a mold in the shape of the final product. The alignment and weave of the cloth fibers is carefully selected to optimize the strength, stiffness, or flexibility of the final product, depending upon it's application.

In demanding applications, all air is evacuated from the mold, but in applications where cost is more important than structural rigidity, this step is skipped. The mold is then filled with epoxy and is heated or air cured.

The resulting part will not corrode in water and is very strong, especially for its weight. If the mold contains air, small air bubbles will be present in the material, reducing strength. Most composite parts are manufactured by draping cloth over a mold, with epoxy either preimpregnated into the fibers (also known as prepreg), or "painted" over it. Hobby or cosmetic parts are often made this way, as are high performance aerospace parts. High performance parts using single molds are often vacuum bagged and/or autoclave cured.

There are very few Aftermarket parts which are made of CF or CRP which are produced for anything more than the 'Trick' look and so are pretty cheaply made - no vacuum or heat. These pretty much perform on par with fibreglass and don't offer any real strength advantages, though they are slightly more robust - but only slightly due to the amount of air bubbles (mostly internal and not visible) they contain.

Happy Motoring!... Jim'99

markab986 · 05-03-2007, 07:58 AM

I agree, urethane for the bumper.

cf is stiff, light weight, and well suited for many applications. But it’s probably not what you want on the street, due to initial cost, and high cost of a specialty shop doing repairs, if an unfortunate event were to occur. It also must be kept from UV, with some sort of protectant, which normally negates the "cool factor" of the exposed weave of the fiber.

One other thing...cf is not corrosive by nature, but when in contact with AL and moisture...you will have an electrolysis effect with the metal. The contact area must be protected using fiberglass.

The choice is really up to you.