The myth of "stiff frames" and "stiff wheels"

[Spats]

Doing actual measurements reveals that there is no quantitative difference between modern bike frames or wheels that can perceptibly affect ride quality. Read the following article:

http://draco.acs.uci.edu/rbfaq/FAQ/8e.2.html

Basically, the effects of tire inflation, seat rail flex, fork flex, and possibly handlebar flex render insignificant any flex in the wheels or the frame.

Summary: geometry is important, weight is a little bit important, material isn't.

[Il Eagle]

So did the guys who did the study acually RIDE?

[homerjay]

Then explain why my Ti frame is so much smoother than my aluminum frame.

[UTdave]

Material matters for more than stiffness. it is a factor in vibration transmission and damping. That said I know that aluminum frames can be stiff and comfortable to ride. I do agree that many people overplay the differences but when you get on bikes of different materials you can feel a difference (I'm talking same parts spec and geometry just different metals).

[lph]

Originally posted by UTdave
Material matters for more than stiffness. it is a factor in vibration transmission and damping. That said I know that aluminum frames can be stiff and comfortable to ride. I do agree that many people overplay the differences but when you get on bikes of different materials you can feel a difference (I'm talking same parts spec and geometry just different metals).

absolutely. i am by no means an experienced road biker. but the difference in my trek aluminum frame road bike and all carbon fiber road bike with the exact same components is easily noticeable. particularly the vibration transmission and damping.

[comish]

Ya, I gotta agree here. Went from an old Trek alum/carbon combo to a Ti Litespeed Vortex, to a Calfee and all three had distinctly different feels. I will agree that its probably more a matter of how much vibration the material transmits (where Carbon rules) verses stiffness, but you can't tell me some of those mid '90's Huge aluminum tubed Cannondales weren't stiffer than just about anything else out and it wasn't the seat, handlebars etc that was making the bike ride like a board.

[Viva]

Originally posted by Spats

Basically, the effects of tire inflation, seat rail flex, fork flex, and possibly handlebar flex render insignificant any flex in the wheels or the frame.

Except for when you're getting major BB flex (sprints, climbs- any kind of hard riding) or rear wheel flex- drive-side especially.

[schuss]

yeah, geometry doesn't play that huge a role, but material does. Aluminum hardtails are hard beasts, whereas chromo and Ti ride much smoother.

[Viva]

Don't be mistaken; geometry is very important.

[Spats]

I don't mean to be rude here, but did anyone actually read the article?

They put an 80 pound weight on a part of the bike, and measured how much this bent different parts of the bike.

The largest difference measured between any two frames (Specialized steel versus Cannondale AL) was .001 inch. I don't buy that any of us can tell a .001 inch difference.

There was no measurable difference in flex between any two wheelsets.

However, the deflection of the fork from 80# applied at the head tube *was* significant: it ranged from 54% to 83% of the deflection of the tires. Additionally, the smallest measured deflection was 65% of the largest, suggesting that fork dimension, construction, and material has a measurable effect on ride perception.

Also, though I have not done precise measurements, eyeballing the seat when I put weight on it indicates that significant flex comes from the seat padding and rails.

Therefore, I think we can conclude a few things:
1) Tire construction and tire pressure makes the most difference.
2) Seat construction and padding makes a great deal of difference.
3) Fork material and construction probably makes a big difference. Handlebar construction may also, but I have no data to support this.
4) Frame flex is roughly 1/100th as significant as flex in the tires and fork, and even less significant once seat and handlebar elasticity is factored in.

I am reminded of a test done by Sony when working on HDTV. They showed people two identical videos on two identical televisions -- yet one of the pictures was rated, on average, 27% sharper and clearer. The only difference between the two setups was that one had surround sound hooked up, and one had only stereo sound.

If someone can show me two bicycles with IDENTICAL builds (including tires, seat, fork, handlebars, and frame geometry), yet one rides very differently than another, I'll start looking for an X factor. But until then, in a conflict between tradition and data, I'll choose data every time.

[mntlion]

I have not read the link but from your info

80 pounds is not too much wieght. I would think that a biker, standing up in the pedals, hammering on an uphill, could make more than 80 pounds of pressure?
more like 400? 600? not usre of that number either.

Will be an intereting read when I get around to it

[Viva]

Originally posted by Spats
I don't mean to be rude here, but did anyone actually read the article?

They put an 80 pound weight on a part of the bike, and measured how much this bent different parts of the bike.

The largest difference measured between any two frames (Specialized steel versus Cannondale AL) was .001 inch. I don't buy that any of us can tell a .001 inch difference.

About all this proves (maybe) is that an 80 lb weight won't be able to tell the difference on a stationary bike.

Look at it this way, pursuant to my example above, consider a bike under a heavy load, e.g., sprinting in the big ring. There will be considerably more force than 80 lbs exerted on the bottom bracket. Different constructions, different metals, etc., will all play a role in how much BB flex there is. BTW, all bikes have BB flex and this is very noticible.

Suppose these "engineers" did an analogous study comparing skies by placing weights along the length and then concluding that bindings don't make a difference or that it's impossible to tell the difference between wood and foam-core skies?

[Artie Fufkin]

My most recent transition was from an early 90's Cannondale with a mixture of Suntour/Campy that was had a variety of mechanical issues to a brandnew 2002 Litespeed Classic. The Litespeed felt extremely smooth on the first few rides, I would imagine alot of that could be contributed to brand new components , wheels, etc.

I have not ridden enough bikes to be an expert on the stiffness of frames and wheelsets. But I would agree that geometry(angles and tube design)is probably pretty important. I would imagine a Litespeed Vortex(with larger tubes) is a stiffer ride than the traditional geometry of my Classic.

That article seemed to stressed the psychological factor of bikes, the perception of what you are riding and how it should feel and perform. Equipment matters, but the most technologically advanced equipment is not going to drag you up the hill or throw you across the line in the sprint, the legs, lungs and 5lbs shaved off from less booze and food are pretty important.

[Telephil]

Originally posted by Viva
About all this proves (maybe) is that an 80 lb weight won't be able to tell the difference on a stationary bike.

Look at it this way, pursuant to my example above, consider a bike under a heavy load, e.g., sprinting in the big ring. There will be considerably more force than 80 lbs exerted on the bottom bracket. Different constructions, different metals, etc., will all play a role in how much BB flex there is. BTW, all bikes have BB flex and this is very noticible.

Suppose these "engineers" did an analogous study comparing skies by placing weights along the length and then concluding that bindings don't make a difference or that it's impossible to tell the difference between wood and foam-core skies?

.

Doesn't a person "feel" what they're riding anyway, I don't know that a weight is able to.

[jayfrizzo]

Like you said Spats, sounds like the study just put a weight on a bike, and didn't deal with road "vibrations" at all. He even says himself that perhaps damping plays an effect.

Also, two materials may bend the same, but the speed they bend will play a huge role in forces applied to the rider. Maybe this is dampening, I dunno.

Good thing he didn't compare a recumbent, as I'm sure the study would prove them to be no more comfy than traditional bike .

J-

[phUnk]

I've got to agree with Spats on everything except for the use of an 80 pound weight. Hell, even I almost weigh more than that!

Seriously. They should have doubled the weight and put it in motion (or just tripled it) to see its true affect.

[Spats]

Let's suppose the amount of weight on the seat or handlebars is doubled, i.e. 160 pounds. (The article stated explicitly that all measurements were linear with increased or decreased weight.)

The difference in frame flex becomes a whopping .002 inches. But the fork flex and tire flex (not to mention seat and handlebar flex) also double, so the frame flex is no more significant than before (~1%), no matter how much weight you put on it.

The ski analogy is bad. An 160 pound weight on a ski will bend even the stiffest ski about two inches (I've measured this personally with my Volkl G41s), at which point vibration and damping are very significant. A motion of .002 inches (1000 times smaller), isolated from the rider by much greater motions from seat rails and padding on one end, and from tires, fork, stem, and handlebars on the other, is not significant.

Please note that the article does *not* contend that BB flex does not vary under torsional load, and that this difference isn't noticeable.

What it does contend is that an assertion of the nature "Frame X rides much smoother than frame Y" has no basis in measurable fact.

Originally posted by Viva
About all this proves (maybe) is that an 80 lb weight won't be able to tell the difference on a stationary bike.

Look at it this way, pursuant to my example above, consider a bike under a heavy load, e.g., sprinting in the big ring. There will be considerably more force than 80 lbs exerted on the bottom bracket. Different constructions, different metals, etc., will all play a role in how much BB flex there is. BTW, all bikes have BB flex and this is very noticible.

Suppose these "engineers" did an analogous study comparing skies by placing weights along the length and then concluding that bindings don't make a difference or that it's impossible to tell the difference between wood and foam-core skies?

[mtnrider]

hmm....interesting HYPOTHESIS. I guess I'll try making my next frame from copper then...

[phUnk]

[Telephil]

As do I, but I don't.

[freshies]

i am not a scientist (but i play one on tv..), but i have to disagree with the statement that it doesn't matter what the frame is made of. i am a bike rider, both road and mtb, and i have owned and ridden bikes made of just about every material out there: ti, steel, alum, carbon, scandium, etc.

and, i can +feel+ a difference between my Dean ti raod frame and my old aluminum Cannondale frame - no doubt.

Same goes for my MTB's: had a aluminum Cannondale, then an aluminum Kona, then a steel Yeti and now an aluminum Santa Cruz.....and beyong that my new bike is FS vs all the others were HT's, I noticed the differnce between the aluminum feel and ride on a HT vs that of steel.....quite noticable difference in trail 'feel" and "ride"....

[jayfrizzo]

I remember reading a study back in '95 that said clipless pedals made little difference because you can't get any energy on the upstroke. They just help you spin, but you can spin in clips and straps, or platforms.

I bet no one here believes that, either.

I also read a study from the 50s that said smoking's not harmful.

[phUnk]

Hey JayFrizzo, ever read this report?

JayFrizzo is gay.

[jayfrizzo]

Originally posted by phUnk
Hey JayFrizzo, ever read this report?

[SLCFreshies]

I've thought a bit about when people write about how a bike "feels." It's rampant on mtbr. VPP stiffens under braking. Horst-links have anti-squat. Chain growth, and no chain growth. Bob and no bob. Blah, blah, blah. There seems to be no shortage of garage physicists on that board.

I've always wondered how much of this stuff people can REALLY feel. I mean the majority of people, when blinded, cannot tell the difference between Coke and Pepsi even though most think they can. In drug studies, you expect about a 25% improvement in both objective and subjective measures with just a placebo. The fact is that there is a strong psychological component to everything that we experience.

If you get on a bike, it's certainly not blinded. So do you get on a carbon bike, expect the ride to be smoother, and then experience a smoother ride? Do you get on a VPP bike after reading about it on the web and then experience some "stiffening" under braking? The same with "harsh" aluminium frames and "forgiving" steel frames.

I think that people in general, including myself, exaggerate how good their sense is. It would be interesting to set up a study by getting a bunch of bikes with the same geometry and components but made of different materials, covering the frames somehow, and seeing if people could identify and differentiate the different frames by riding them. I think that if people were TRULY blinded, they would be surprised how little they would be able to tell apart.

All this stuff about how bikes "feel" does make for interesting conversations though.