Can carbon frames be too light?

Discuss light weight issues concerning road bikes & parts.
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mellowJohnny
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by mellowJohnny

I'm with you - can't see how 150g of extra weight would make the bike track better, or as he puts it in the article "stick" better.

Crap - I just realized I'm mixing up two bike tests - the one I'm referring to is for a 10.9 lb SuperSix Evo Black Inc. "Project Lightweight" that RBA built up. Same conclusion though, Shirley felt it was to light to descend well.

The full article is in the Feb. issue of Road Bike Action. Sorry if I've confused anyone!

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theremery
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by theremery

What Charles said:
:thumbup:
Spot on, Charles.
e.
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CharlesM
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by CharlesM

I'll tip my cap to Neil all day long (though he'll very likely be too far ahead of me to see it). I Hope you're right Mellow, I didnt see an author for the artile we're talking about here.

Either way I just dont see weight alone being the deciding factor in handling.

If I take the 12 pound bike out with full bottles and ride to the top of south mountain, the handling doesnt suddenly turn to shit on my way down when they're empty... The extra pound or two of bike weight just isn't it.

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mellowJohnny
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by mellowJohnny

Hey Charles - unfortunately I was referring to a different article, although the comments were similar. Maybe Shirley did the BH review too...that article is reprinted from the Oct. 2011 issue - the print version has no by-line either.

I'm referring to an article in the Feb. issue of RBA where they built up a SuperSix Evo Black Inc. to 10.9 pounds for Shirley to race at the Mt. Charleston Hill Climb in NV. At the end of the article he also says the project bike was a bit too light to decend well, feeling that a few extra pounds would have made it a bit more stable.

Totally agree with you - can't see how weight alone would make such a difference.

Apologies for mixing the reviews up!

Neil Shirley's "Verdict":

Image

The Build list:

Image

styrrell
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by styrrell

I don't think a couple of pounds will effect handling all that much, but I have went from heavy training wheels to a light circa 1200 gram set of wheels.

On the initial ride the feel is way more noticeable than you'd guess. I thin the gyroscopic effects of the wheels is imortant. That said, after a few rides the bike with the light whees feels normal. That experience always made me wonder what it must feel like to go from normal weight wheels to something like a 700 gram pair of AX?dash exotics.

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elviento
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by elviento

The truth might be somewhere in the middle:

An 11lb bike may very well handle quite differently than a 16lb bike. It doesn't necessarily mean it's inferior. You could get used to it after 20 hours in the saddle.
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wolfesquire
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by wolfesquire

As someone who is 200 lb. I don't feel "safe" on a bike under 15 lb.

mdeth1313
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by mdeth1313

It also looks as if they're using mfg claimed weights from their list of parts- anyone ever have sram red levers come in at 284g ?
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eric
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by eric

wolfesquire wrote:As someone who is 200 lb. I don't feel "safe" on a bike under 15 lb.


You're descending at 50 mph wearing four ounces of spandex and a small chunk of styrofoam strapped to your head but you're worried about overall bike weight?

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CharlesM
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by CharlesM

:lol:

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Mattias Hellöre
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by Mattias Hellöre

Good morning.

I want to chime in here with some basic knowledge about carbon and its counterparts like titanium and aluminum.

First of all, the sentence: Can carbon frames be too light.
Invalid statement, too light?, too flexy so it breaks during a one year use?

If a frame is manufactured properly, it will be at same stiffness as nearest competitor, in this case a titanium frame like Litespeed Ghisallo.

Bear in mind pure carbon for example Torayca T1000 have about 10x tensile strength compared to aluminum 7075. About 10x as strong as 3al 2.5v titanium.
So a 800 gram Ghisallo could be 80 gram carbon frame.
Of course I am crazy? really not.

Material specifications is one thing. Real world is a another thing.
Resin systems that are a must in carbon fiber composites does drag down the overall stiffness to around 4x to 7075 al and 3al 2.5v titanium.
Then we have manufacturing problems and limitations.
That can be roughly optimally translated to 2x better than metal counterparts.

A 800 gram Ghisallo frame will be around 400 grams in carbon fiber. In theory.

So a 700-800 gram frame made of carbon fiber composites too light. NO.
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sugarkane
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by sugarkane

I have an 11lb bike and it descends like a weapon..
It makes no difference whether I use my 1450g wheelset or my 990g wheel set either.
Good tires at the right pressures and some good skills make the biggest difference.
Plus a healthy set of nerves.
Tapered headsets help a lot but geo and wheelbase really dictate how a bike handles.
Unless the thing is a noodle I don't see a light bike as much of an issue.
If your not a good descender then you might find a real light bike a bit un-nerving but me...
I love it. I love a quick responding nimble bike with little mass and wet or dry I don't have to much trouble riding around the outside of most people..

latman
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by latman

I agree they can , as the overall weight gets less and the tubes larger diameter (even non round) the wall thickness gets scary thin and impact durability is compromised , eventually overall stiffness must follow the same way as the walls are too thin and they can fold under load .

fdegrove
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by fdegrove

Hi,

eventually overall stiffness must follow the same way as the walls are too thin and they can fold under load .


When something lacks stiffness it then follows that it will bend/fold. When something is very stiff it will not bend but break/shatter.

Ciao, ;)
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thisisatest
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by thisisatest

A material can be very stiff but not brittle. In this particular case, we are talking about something that is stiff geometrically. A large diameter aluminum tube is very stiff, but it will definitely bend when overloaded.
As a very general rule of thumb, a tube's wall thickness should not be smaller than 1/50th its diameter. Beyond that, you can get buckling, etc. Like that party trick where someone stands on an empty coke can, then someone else gives the side of the can a tiny tap and it collapses. The rule is for homogenous materials like metals...

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