[smartyiak]

General Question:

While looking for a new bike I was repeatedly told to go with Steel or Al due to my size (6'4", 250). However, I notice when tested (I can't find the link, but it's on WW and here (somewhere) the stiffest frames in BB and in lateral compliance are CF frames. Leading the pack is the Canyon and the R3. The only AL frame even in the mix is the CAAD9.

I understand that they probably don't include steel frames in the mix b/c there aren't too many race quality frames that are mass produced, but aluminum frames seem less stiff (at least in the two tests I have seen).

Given this, doesn't it seem as though a big guy would actually want a CF frame like the Canyon, R3, or Scott?

Engineers....UP!

 

[TylerDurden]

i'm a junior in engineering, but here's a guess, maybe in this case stiffer does not mean stronger. even though CF is stiffer it may have durability issues with heavier riders?

 

[bikeboy389]

Not an engineer...

...but I'll just note that pure lateral stiffness isn't the whole thing. A bike that's built to be laterally stiff but properly vertically compliant for a lighter rider the same height may not be strong enough vertically for the extra loading a heavier rider will put on it.

If you're heavy for your height (like me--I'm 4 inches shorter and weigh only 15 pounds less), that kind of thing is a consideration.

The stiffest bike I own is a lugged steel custom, with tubing chosen specifically for my size/weight. My aluminum bike is a noodle in comparison, as are my other two steel bikes. I always attributed that difference to the fact that the non-custom frame designers expect me to weigh something more like 170-180, tops. I assume similar problems would happen with a stock carbon frame.

Based on this, it seems silly for a bike shop to assert that an aluminum or steel frame will work better for you than carbon--assuming you're heavier than the mass market designs imagined, you're likely to find them ALL less stiff-feeling than they would be for someone who weighs less.

If you're not going custom, and thereby insuring that you'll get a bike designed to your weight (and I wouldn't if you can get a geometry that works), I don't see much reason not to get a carbon frame if it sounds good to you. There are some fragility issues (as there are with aluminum), but those are more about crashing than riding stresses.

 

[smartyiak]

Which makes sense...except that bikes like the R3, Specialized, and Trek have lifetime warranties. I undestand that each company treats "lifetime" in different ways, but if the frame falls apart after a year, or two, or three...and you get a new frame....the durability issue isn't as big of a deal.

 

[Sledgehammer03]

It all comes down to what you want form the bike, and the reliability/longevity you require. CF can provide a very stiff yet supple frame but a guy your size might run into a reliability issue. AL and steel are basically equal. Al is 1/3 the density of steel, but the modulus of elastisity is also 1/3, so you need 3 times as much. Bike manufacturers, both mass produced and custom play alot with tube sizes, butting, etc to minimize weight. My suggestion is find a bike you like to ride, in your price range and have at. When I was looking there were Italian hand made steel frames available for about $1350 US. Frames of like price all weigh about the same the big difference is in the components.

 

[smartyiak]

I undestand the basics priciples behind frame design. I undestand that frames of all materials can be designed stiff, compliant, too stiff to ride, so compliant they are noodly...all by means of material manipulation and the like.

I'm looking for the science behind stock frames. Is there any science behind individuals stating that "AL is what you should use" or "you have to have custom steel", or "You'll love this CF frame." Not for me (or someone my size) specifically, but the science behind it all.

The tests I refer to show that, among stock frames, the stiffest available are CF frames.

 

[Dr. Paul Proteus]

I'm looking for the science behind stock frames. Is there any science behind individuals stating that "AL is what you should use" or "you have to have custom steel", or "You'll love this CF frame." Not for me (or someone my size) specifically, but the science behind it all.

No there isn't. However, if you are looking for specific characteristics, some materials work better than others. For instance, compared to most other bike frame materials, aluminum has relatively poor fatigue life, so you will not find an ultra-compliant all aluminum frame - at least not one that will remain in one piece for a long, long time. Carbon is a great material, but in it's usual application to bike frames has low impact resistance, etc.

In reality, the engineering of the bike is what makes the difference. Unfortunately, a lot of bikes in shops these days are styled, not engineered.

 

[cmg]

visit PRINT EDITION: 2006 VELONEWS | ISSUE 5, DEPARTMENTS
TECH REPORT
Lightweight frames put to stiffness tests

I would take the Mondonico frame that is tested in this article hands down. Stiffness shouldn't be your guiding deciding factor.

 

[bigrider]

I am 6'2" and 240 lbs. I have been riding a 97 CF Trek for years. You could get a frame made with any material. Just don't get any frame that's touted as ultra lightweight unless you have really done your homework on it.

 

[Dave_Stohler]

Well, I am an engineer, and let me tell you, it ain't that simple. I have an AL frame on one bike, a Cannondale (BTW, I'm a big guy as well), and this frame is very stiff. Tried a 60cm Bianchi AL frame once, and it felt like a wet noodle. I've tried noodly CF bikes as well, but have enough knowlege about CF to know that, properly built, there is nothing stronger on the market. It all depends on design and manufacture.

 

[rogger]

I am 6'2" and 240 lbs. I have been riding a 97 Trek for years. You could get a frame made with any material. Just don't get any frame that's touted as ultra lightweight unless you have really done your homework on it.

I have to second that, forget about frame material, forget about vertical compliance. As long as you get a frame that's stiff enough, you really don't *need* the über stiff ones, you only need to worry about the fit. Excluding ultralight means you can eyeball the aluminum frames that are going for much less than CF.

 

[varoadie]

Take a look at the bottom brackets on some of these "stiff" carbon bikes compared to the metal ones. The carbon frames have a huge mass of material there, put that same mass of material on an AL or other and it'll also be stiffer, may be heavier, but it'll be stiff.
I was noticing this on my older C-40 bike (circa 1997) versus a new Cervelo and the difference at the BB was astounding.

 

[asgelle]

... put that same mass of material on an AL or other and it'll also be stiffer, may be heavier, but it'll be stiff.

Same mass, heavier weight - neat trick.

 

[Dave_Stohler]

Same mass, heavier weight - neat trick.

Gravity must be greater there.......

 

[rufus]

visit PRINT EDITION: 2006 VELONEWS | ISSUE 5, DEPARTMENTS
TECH REPORT
Lightweight frames put to stiffness tests

I would take the Mondonico frame that is tested in this article hands down. Stiffness shouldn't be your guiding deciding factor.

is that available online anywhere? and what's the date of the print issue? i'd really like to see that, and sadly, no bookstores in my area carry VeloNews, so i only pick it up sporadically.

could you possibly scan the pages and post it here to be read? being a Mondonico owner, I'd like to see what they had to say about it. and my frame feels plenty stiff, no BB wag at all.

 

[Stogaguy]

Metallurgy for Cyclists

I am not an engineer but I play one in internet discussion forums (just kidding). Here is link to an interesting article covering the "science" behind this issue.

http://www2.sjsu.edu/orgs/asmtms/artcle/articl.htm

I agree with posters that say that you can probibly get a bike that will suit your needs made out of AL, CF or Steel. It all depends on how it is engineered.

 

[elvisVerde]

What you were originally told was, if I may translate, is...

don't get CF. From a performance perspective, with a time frame of a couple of years, that was not good info, as you have suspected.

However, if the folks who advised you were thinking about a time frame that includes passing the bike onto your "large boned" children, it may make sense. In support of the current crop of CF designers and builders, however, it must be noted that our present view of CF bikes is based on what we have seen from the first decade or so of mass-produced CF bikes and forks. Nobody can predict with certainty what current materials and building methods will do in time.

Afterthought: the test of frames in Velonews was somewhat lame. The methods were only sketchily described, and the bike choice was not fully representative of the "lightweight frames" of today. The steel was not cutting edge, the Trek was ancient (and by their own admission, possibly damaged), and they left off the list many frames that enthusiasts would have liked to have known about. I am not sure what they hoped to show, but it did make me think about riding a Cannondale if I get a chance. Not the Cervelo as I think they are ugly.

 

[merckxman]

Read this

http://www.damonrinard.com/EFBe/frame_fatigue_test.htm

 

[Stogaguy]

Great Article

Thank you for this. Very interesting stuff

 

[smartyiak]

That's what I'm talkin bout....muchos gracias