frame stiffness quantified?

[1] Is there an accepted way of quantifying the power transfer (as applicable to climbing,say) of bike frames.

[2] Could anyone provide estimates of this value for various ALU and Carbon frames; e.g. would a "giant TCR" climb noticeably worse than a "TCR Composite". I think +/- ??kg of bike weight vs 70kg rider means the power transfer is the real issue.

I've ridden alu giant, old scott cr1 (pre softening of geometry), and a low + mid range ALU mountainbikes. Naturally I can definitely tell the difference between the ALU and the carbon, and the improved ALU of the mid vs low end MTB.

My question is whether or not you can get ALU that has power-transfer to match the carbon but with weight tradeoff.... and can anyone recommend frames?

The issue is selection of a frame for an everyday bike that (i) I wont freak out if it gets rained on, (ii) but which will still make me want to ride it, having been spoiled by the high end stuff
I tend to ride little & often (eg ~20miles/day) as opposed to weekend long-rides but do want something I can take on longer excursions too (the 'not freaking out if it gets rained on' being important there)

 

Frame stiffness is a great marketing item and it may influence the non tangible road feel of a bike but there really aren't any well structured studies that have connected stiffer bikes to faster bikes even for things like climbing and sprinting. Sure some have tried but I've yet to see an actual set of test data that shows that stiffer bikes are faster. Sure the bike industry makes a lot of money by implying stiffer is 'better' and you might like the way a stiffer bike feels but you'll be hard pressed to prove that stiffer is faster.

If substantial power is being dissipated in the frame when it flexes then that power has to go somewhere. It can't simply disappear, the first law of thermodynamics or conservation of energy demands that energy losses yield some other form of energy. For instance your brakes dissipate energy by getting hot or IOW transfer kinetic energy of motion to thermal energy. So where does the 'lost' energy in a flexy frame go? Even if it's just the loss of a couple of a single watt due to frame flexing that works out to 3.6 kj per hour of thermal energy. Do flexy frames get warm to the touch?

Sure someone might figure out where that lost energy is going and actually quantify it but if that's been done I sure haven't seen actual measured results that demonstrate the widely held belief that power is 'lost' due to frame flex.

-Dave

 

So, just to clarify: you're claiming that a flexy alu bike is basically like a spring bobbing up and down a bit more as you pedal; the force still ends up making you go forward?
Maybe you're right and its just 'feel' - but I'm certain my carbon bike climbed perceptibly faster than my alu one; rigidity was the better explanation than weight. (eg 80kg rider+bike ->78 kg rider+bike or whatever it was). other changes.. bladed spokes. probably not so significant for me.

Perhaps the frames are not getting warm to the touch due to windchill

Well I hope you're right because Alu would save me money on my 'daily' bike
Bikes are competing with laptop/computer bits for budget... and having 2 carbon frames would be silly. perhaps i'm too obsessed with carbon and I have enjoyed riding alu bikes far.

hmm. Like I say my alu mountain bike (old specialized stumpjumper) did feel it must have been a higher grade of alu than my first ALU road bike (giant FCR, which was the old OCR frame I think) since it was also 'perceptible stiffer'.

Something also making me want going back to ALU & hence wanting someone to tell me to be 'ok' is the slight feeling of fragility (like walking on egshells) whenever one is around the Carbon bike.. an ALU secondary bike would be more relaxed in that respect.

Any more opinions are welcome...

 

The heating of the material through flexion will happen. Ideal springs spring back just as they were and transfer then same energy out that was stored in the flex. But there is no such thing as an ideal spring. Hysteresis results in energy lost from the spring motion into heating the material. A good example is the valve springs in a car engine, which, in race applications, can glow red hot purely as a result of being made to flex under high force many times per second.

It would also happen to a bike frame; it's just that we humans can't actually put that much flex into the material to make this heat loss noticeable.

The closest anyone, I know of, has ever gotten to testing frame stiffness is Ride Magazine, who built a jig to clamp a bike into. They hang weights off a test crank and measure frame deflections with dial gauges. Of course they never actually test a statistically reliable sample or quote their uncertainties so all you can get is a ball park number. And this also tells you nothing about how the bike is to ride (which is an entirely subjective idea anyway).

As Dave said actually testing bikes to see if one is faster than the other is a frought task. First you have to isolate the part you want to test (in the case frame or frame and fork) and keep EVERYTHING else on the bike exactly the same (this means grouppo, wheels, tyres, bars, saddle etc) all of these will have some bearing on how the bike feels (how much no-one knows becasue no-one has been bothered to test it). Then you have to test under some kind of controlled conditions using purely objective data (power, speed time etc). Guessing from "feel" is not objective in any way. My bike tends to feel subtly different to me depending on the day of the week.

 

Very simple concept to me.
When I can see frame X's bottom bracket 'swingin' in the breeze' when bolted into my trainer while doing intervals, I know it's time to get rid of frame X.
When frame Y is rock solid while doing those same intervals while bolted into my trainer, then I know I'm keeping frame Y.
Will I ever keep a frame that I know 'swings in the breeze' when doing intervals on the trainer? Never!
Is there a quantifiable difference, on average, between the two frames in terms of wattage seen on my PT display - you better believe it!
Does that difference in stiffness translate into a measurable and verifiable difference in peak wattages seen during sprints (and overall riding in general) on average, and over time? Indeed it does.
My admittedly unscientific, but nonetheless empirical data, is extremely valid for me. YMMV...

 

Hi ebola, this is a very interesting question?

If the road surface was perfectly smooth then I would definitely go for a very stiff frame with geometry that propels the bike forward with each pedal stroke. This difference can easily be witnessed between a hard tail MTB and a road bike. The MTB front suspension absorbs the forward motion of each pedal stroke and causes the MTB to bob up and down. A lot of forward momentum is lost by this action. Thus, the road bike rolls a lot faster and higher gearing can be used

Unfortunately, road surfaces are not perfectly smooth, and because of this a very stiff frame will be bounced up and down and as such some forward momentum is lost by this action. This can also cause the rider to tier, some more quickly than others. This is one of the reasons that CF frames have become quite popular, because they can be stiff and shield the rider from these not so smooth and even very rough roads. This is also one of the reasons that steel is still popular

Having said that, hill climbing is much slower, so the road surface is not as important but forward propulsion is important. Of course if the road surface is really rough then frame material and geometry to absorb the bumps, but still propel the bike forward, is important

So, what frame to get ... well a frame that can absorb rough road vibration (which will keep the rider fresh) and regardless of the road surface frame geometry that will propel the bike forward with each pedal stroke (not up and down). Does such a perfect frame exist ... it would appear not :-(

Good luck and let us know what you decide to get

 

Thanks for the interesting replies.
>>"Good luck and let us know what you decide to get :-"
Most likely, Both
I currently have 2 carbon bikes, of differing spec.
The 'alpha' bike will definitely remain Carbon - but its spec is too high for daily riding*

I'm erring toward replacing the 'beta' bike with Alu now; I'm thinking, since I have an example of one alu bike feeling 'quite ok' (but not as good as the alpha bike), it must be possible to get a decent enough alu replacement for the beta bike's frame.

The components are fine, not needing replacement.. (this was previously the alpha bike and alternated with the older alu bike & MTB for volume riding)
The frame replacement is happening due to a sizing error at purchase many years ago. (my longlimbed proportions confused the bikeshop advisor, impulse purchase urge , and subsequent crash & seatpost rusting in prevent sale of the inapropriate item.... ). Its been enjoyably rideable with a short stem but isn't as good as one size down.

Getting the frame size corrected to my current preferences will go much further toward me "wanting to ride it". Also one very silly consideration: I think having 2 colour schemes rather than 2 'stealth' bikes will also help a little

* Another question (for another thread perhaps) is whether or not I can fix this by using *Training Wheels* and accepting more frequent component replacement on the alpha bike. I suspect the answer here is "No" since I understand multiple bikes are the most common solution to the problem mentioned above.

 

Of course now the question is WHICH aluminium frame should I be considering.
some older threads rave about specialized E5 alu, which they DONT appear to do as a frameset any more.. GRRR.
are there comparable alloy framesets that anyone can recomend ?

 

Good discussion on an ageless topic. In addition to the energy lost in frame flex, seems to me there may be greater loss via in the tire due to the sideways loads imposed as the wheel is twisted alternately out of the line of travel during hard sprints or standing climbing. It may be possible to calculate or directly measure this loss via a test rig.

Believe Lon Haldeman, the guru of the RAAM (Race Across America), once said he preferred a "flexy" bike for his non-stop record-setting time trials across the US due to the comfort factor. If he wasn't concerned with the speed lost to frame flex, I know it's nothing I need to worry about on my mere century events.

Cannondale CAAD 10 frames ought to be near the top of the list for aluminum frame quality; that's the one I'd pick anyway.

 

eBay is your friend if you must have this frame...

 

There is a book about some of those topics, its called "bicycling science" I have an copy of it and it is pretty informative about some of these topics.

Apparently (as this book says) my nexus-7 hub has only a 91% efficiency in power transfer (or something) whilst some other deraileaurs have a higher efficiency.

I also read a few things about the stiffness of various materials, composites etc.

Ofcourse allthough its good to know some of those things in order not to make a very bad choice I dont think I would ever notice the efficiency difference if I havent read that from the book (not that I do notice it now). /img/vbsmilies/smilies/rolleyes.gif

But I do notice some differences when riding very different bikes. It all depends on where you are riding too.

Anyway I think that this book was a very interesting book but as far as choosing frames etc, since I am not racing I usually try choose the best balance between quality and performance.


btw I saw a few of "high end racing components" (like carbon seatposts etc) listed in the CSPC website as "potentially dangerous"... /img/vbsmilies/smilies/frown.gif

 

seriously dude? your afraid to ride carbon fiber in a little bit of rain? clean your bike afterwards or as you said yourself, stop being a snob and get an aluminum framed bike

 

>>"seriously dude? your afraid to ride carbon fiber in a little bit of rain? clean your bike afterwards or as you said yourself, stop being a snob and get an aluminum framed bike"

Nope, not afraid to ride carbon in the rain, I understand carbon doesn't rust.
its the higher end components on the 'alpha' bike that I dont want trashed.

>>" or as you said yourself, ...get an aluminum framed bike"

yeah, thats the plan.
Hence the purpose of this thread.

 

Hi ebola, actually you should probably have a look at Titanium frames, also. Some riders say the stiffness of CF but the forgiveness of steel, and will ride nothing else

I have never had a Ti frame but I wouldn't rule it out.

Au can be quite tiresome when riding long distances

 

>>Hi ebola, actually you should probably have a look at Titanium frames, also.
Good point, I've heard that elsewhere too.

>>Au can be quite tiresome when riding long distances.
the vast majority of my riding is "little & often" (extended commutes & lunchhour)

But when it comes to bike parts I like how you're thinking here. A nicer frame will make me want to ride it more.. could be a great investment.

On the ALU, the CAAD9 seems to get raved about .. but I strangely dislike the look of cannondales.

 

hmm, my aluminum framed bike is full ultegra, I guess it must be low end.

Seriously dude, your a perfect candidate for a bikesdirect bike you can get a nicely equipped bike for short money there, including one made of CF.

BTW, bike parts getting destroyed by rain is such a myth it's ridiculous. Guys ride MTB's through mud on the regular and don't ruin them. you won't ruin your road bike riding on paved streets when they are a little bit dirty, it's really more of an annoyance with having to clean the bike off.

The biggest issues to worry about with rain water are the lower half of the headset and the bottom bracket. If you occassionaly ride in the rain, its not going to be a big deal. even if you ride in the rain all the time, your still only looking at needing to check out the grease in teh bearings every 6months to a year and it's an easy DIY job or your lbs can do it for far less than buying a whole new bike.

 

I don't get it, the whole thing is he is associating rain with damaging of components. It doesn't matter what the hell the frame is made out of. If you want a cheap rain bike, get a Giant Defy3 and call it a day. Sora components, about $800, and a comfort based geometry ideal for comfort on longer rides.

Sorry to sound like a prick but in my opinion, the snobbery of being used to a high end bike is the real issue here. proper cleaning after riding in rain will keep your bike in good working order and quite frankly, riding in the rain in the warm months really isn't all that bad, it's winter riding where your bike is picking up the salt thats been put on the roads that would be considered more problematic.

 

I would suggest it's all in the mind of the rider.

 

ambai, I also think a lot of it is in our perceptions. A stiff frame, like hard tires, makes the bike feel racier. My Fuji Track bike had a stiff steel frame, heavy flex-free crankarms, stem and handlebars. It felt more responsive for sprints and standing climbing as a result, even though it weighed about 5 lbs more than my AL/CF road bike. The lack of flex when yanking on the handlebars on low-cadence climbs was particularly noticeable. In addition to the weight penalty of the heavy-duty frame and components, the ride was harsher than my road bike. Anyone who thinks steel always has a better ride quality than AL or CF should ride a real track bike for a day.

ebola, understand your lack of interest in C'dales; I'm the same way but not sure exactly why. Maybe it's their legacy of the OS downtube al frames, or their early emphasis on touring/recreational riders rather than "real racers". Brand-names are important to a lot of us, even though we don't admit it. But from a quality/strength/durability aspect, I think they are as good as anything available. A buddy put about 100K miles on his CAAD 3 frame, including the Boston-Montreal-Boston and Paris-Brest-Paris 1200K non-stop jaunts.

 

Orbea had an aluminium bike a few years ago, based on the aluminium bike that Iban Mayo used to smash the record on Mt Ventoux. By all accounts his bike had to have weights on it to bring it upto the UCI regulation 14.9lbs and was about the stiffest bike he'd even ridden. Apparently way stiffer than a Cannondale.

http://autobus.cyclingnews.com/photos/2004/jun04/dauphine/index.php?id=stage4/cycling-fra-dauphine-may-21

... and in that pic he looks like he could be in the big ring. EPO or not... that is Godlike.