Frame Material Engineering
 

Being on BF i have realized one thing, many like to voice their opinions, yet there is typically a lack of proof or data to back up claims.

The long held debate between the vast selection of frame materials and ride comfort could easily be "tested" yet i have not seen hard facts surrounding this.

To end this debate, all it requires is a simple Design of experiments, a few strategically placed high frequency accelerometers and some analysis. This would quantify your 'ride quality' and go a long way in putting logic behind the debate.

The other debate about component groups is equally lacking true engineering information, but that would require a much larger set of metrics... i'll leave that for another day.

ok, and where would you like to put these accelerometers?

Check out Bicycling magazine from about 30 years ago.

At that time they comissioned Gary Klein (I think) who built the terantula, a fixture which measured frame flex when a measured load was applied to the crank arm. As I recall, the terantula data didn't compare very well with test rider's subjective assessments.

Bicycling doesn't conduct objective testing anymore - and they never encounter a product they don't like.

under the seat, handlebars near your hands, near wheel hubs, Bottom bracket. They are quite small, it shouldnt be a problem...

ok well that just means they are not testing properly or are not performing the right tests. Last time i checked, magazines are more interested in creating articles than truly creating data. I'm not talking about lab simulation of road data, im talking about actually measuring real road vibration levels with the operator on the bike...

the "softer ride" of carbon frames is purely speaking of damping out high frequency vibration... this should be fairly straight forward.

bet you tire inflation pressure and tire choice will be the #1 change in comfort.
I can honestly say while interested, am too lazy to wire up accelerometers to feed data into a data recording device.

but maybe one can just record data straight from an iphone, which has a built in accelerometer, and possibility of mounting it to the bars.

Doing a DOE would help you evaluate current frames, but it wouldn't tell you much. These days metal tube forming has progressed a lot. It seems that if you do the design correctly and spend the money for tooling, you can manipulate the ride characteristics of steel, aluminum and titanium in much the same way as you can with changing the shape and thickness of carbon fiber frame sections. If you could not manipulate the metal tube shapes and thicknesses, what you say would probably be true.

http://www.youtube.com/watch?v=YjutFgj0tLY

Pick a route with pool table roads, chip and seal sections, maybe some cobblestones. Ride several different bikes down the same route.

Didn't Giant do something like this when comparing their TCR Advanced to other frames?

That would be a test of bicycles, not materials. Think about it some more.

For extra accuracy, swap the same wheelset and tires from bike to bike to keep pressures, etc. consistent.

And what do you get? Objective data that can not be accurately correlated to a subjective quality.

I :love: "Arm Chair Engineers"

Pretty much.

You're better off riding many examples and buying what feels best. Screw science.

EDIT: Says the guy who is shopping used based primarily on what other people think about their bikes. :lol:

that and it's a bit hard to compare data from different people.

That's why I was thinking one person should do it on the same wheelset/tire combo swapped from bike to bike over the same course.

But really, what will that tell us?

I think it would be easy to setup some sort of laser reader to detect flex in the frame on hard sprints, climbing, etc.

But that's really a test of the bike and it's engineering and not the material. Both of those tests would be measuring the bike and not the material.

Too many parameters on a built up bike on the road for a doe. Maybe you can do it virtually.

You also take rider comments. Then take a PSD of the accelerometer data and correlate that data with the rider comments. Finding the road input transmissibility would allow you to quantitatively measure the attributes that riders like/dislike.

Deflection testing has it's place, but it's not a substitute for something like this.

To start life out, I'd stick an accelerometer on the seat post clamp and stem. You can't use an iphone. It's not sensitive enough and the filitering wouldn't be right. I'd use about a 50g accelerometer with a 100Hz low-pass filter and a sample rate of maybe 250-500 Hz.

Not that I've thought about it or anything.

Similar. From their website it sounds like they did their analysis with something called an impact hammer. It's a good way to characterize things like this, but not as conclusive as a road test IMO.

What i get is a sensitivity analysis that provides me with trends. Through the relatively simple study, i think you would see trends fall out of the data that gives a ranking of influence to certain features on a bike.

I would expect to see that the primary driver is tires, next is spoke/wheel design, then something else... and possibly somewhere in the middle of the list we would see frame material. If all factors have equal weight, then fine, but its highly doubtful.

You are forgetting the fact that the claim is objective... 'carbon reduces road vibration' this can be quantified. I'll tell you one thing, if automotive engineers thought the way you guys do, we would never have the vehicle dynamics and ride quality that you currently enjoy... You'd be surprised how objective numbers are designed to give a certain subjective "feel". Bikes are quite simple machines which means analysis is easier... (i.e. less variables)

and who are you calling "Arm chair"...

umm... not really. Trust me, a bike DOE is orders of magnitude less complex than other forms of machinery.

I want to be the "impact hammer" test guy. sounds like fun.


Also, how do you quantify the best ride? It's sort of like a mixer overlay on your ipod. Is "Concert Hall" the best, or "Padded room" or "flat"? Just having all the info in the world doesn't mean you can make an objective assessment of the best.

right.. what the individual rider determines is the "best" is very subjective. However, what it could do is correlate individual tastes to certain design parameters.

This is the reason that more than one bike is offered.. but it doent mean that we should be blind and just ride a billion different bikes. It may help narrow down selections.

Hold on. I thought you were trying to characterize different materials. Now you're saying it's the totality of all design parameters. Which is it, or do you think the two are the same?

Yes, frame material is a design parameter. My thread was started as a basis to question how much the frame material impacts the vibration transmitted to the rider. During the experiment it is important to ensure you characterize how much the other design paramters influence the ride as well.

basically, if i do the test and dont realize that 1psi of tire pressure impacts the vibration level by X%, i will not be able to come to a good conclusion on the frame material itself. The result could be that a few PSI of tire pressure has 10x more impact to transmitted vibration levels than changing from the best to the worst frame material. But i wont know untill it gets tested..

Have you measured g lately? How about calculate pi? A quick review of material properties and the dynamics of simple tubes can show that tires deform orders of magnitude more than any other component. The effect of springs in series is left as an exercise. Every wheel doesn't have to be reinvented.