[Closed] Are Alu frames "uncomfortable" ?

That velo news article suggests a measured vertical deflection of .2", about 5mm. That's going to be a noticeable benefit and certainly an order of magnitude more than your'll ever get from frame flex regardless of material.

All my ali frames have been stiffer than the steel frames I've had but my steel frames have all been skinny tubed jobs and the ali have been fatter. Steel inbred replaced by kinesis xc120, latter was definitely stiffer, when the 120 broke I got an mmmbop which was even stiffer, probably not helped by the large diameter seatpost (120 had same 27.6 post as inbred).
My steel Day one cx bike got run over so (nearly) all the components were swapped to a pro 6, the carbon fork is about the same but the ali frame is stiffer (same post both frames).
But frame builders can do various things with tube size and shape so some steel will no doubt be stiffer than some ali.

You think the comfort difference from a seatpost's flex comes from the tiny vertical vector? (which is about 1/6th of the total movement).

Well first of all whatever it is it seems to make a difference, having ridden back to back bikes where this was the main variable

Of course its not like full suspension its just a bit of a difference

Also however small this movement is at least we all agree that its there and can quantified in measurements that can be made with a ruler

the vertical deflection of a frame must be tiny in comparison

I had this

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and then bought this
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and swapped the exact same parts over. Yes i could feel a lot of difference. The sobo is scandium alloy and can be very harsh

So that 'proves' that different frames feel different not that material A is fundamentally different to material B...

FWIW, I've had fun in the past telling people how a frame should feel and then finding that they agree even though according to common wisdom it should feel different. We're massively guided in perception by our expectations.

[quote=Northwind ]

ampthill - Member
Forks and seat posts bend visibly in use.

Er, no. He's arguing that sideways movement doesn't make a difference to comfort (which is logical given that a bump results in no sideways force - if it did you'd fall off every time you hit a bump), whilst fore/aft does.

No, he's using pseudoscience to try and get round the problem that this idea that frame stiffness makes no difference to comfort, is demonstrably cobblers.

[quote=trickydisco ]The sobo is scandium alloy and can be very harsh

😆 that would be thin walled, not particularly large diameter alu alloy tubes, which are renowned for being a bit flexy? Clearly you based your expectations on incorrect information.

[quote=Northwind ]No, he's using pseudoscience to try and get round the problem that this idea that frame stiffness makes no difference to comfort, is demonstrably cobblers.

How are you demonstrating that it is cobblers?

Via the riding of bicycles.

pssssshhhhht........pssssshhhht, frame comfort sorted.

[quote=Northwind ]Via the riding of bicycles.

Ah, that good old scientific methodology of using a sensor with less accuracy than the variation in what you're testing?

hat would be thin walled, not particularly large diameter alu alloy tubes, which are renowned for being a bit flexy?

aracer - Member

Ah, that good old scientific methodology of using a sensor with less accuracy than the variation in what you're testing?

The scientific method of observation and comparison. What precision sensor are [i]you[/i] using exactly, the comfortometer setting on your multimeter?

[quote=Northwind ]The scientific method of observation and comparison.

Which is only as good as the instrument you're using to observe with. Can't remember the exact figure, but I think you need a change of about 5% to be noticeable, which is far more than the difference a frame material makes to vertical compliance.

What precision sensor are you using exactly, the comfortometer setting on your multimeter?

Well I'm not the one claiming to be able to demonstrate something, but mostly using a calculator, structural analysis and tables of materials properties. I've got accelerometers and data logging capability, but have never got round to doing any proper testing - I doubt the results will be very exciting, and those people who are sure they can feel a difference won't believe them anyway.

BTW where do I buy one with that setting? Mine is just a cheap Maplin job.

aracer - Member

Which is only as good as the instrument you're using to observe with

And then you list a bunch of things that dont't measure comfort at all 😕 Weird. Real world testing is the only way to assess comfort. If your tests can't find it, you need to ask what's wrong with them, but fundamentally you can't measure comfort with a ruler. And as pointed out by various people, the whole "all frames are equally comfortable" doesn't survive contact with the real world.

Mrs S & myself both have Rock Lobster hardtails - pretty much the same spec & size, but hers is the alloy one, mine's the steel one.

The steel one does feel comfier, even with the same bits on.
Sorry.

But.......
The seatpost makes the biggest difference, far bigger than the frame material.

Going from an Easton EA30/50 to Thomson made both bikes feel a lot stiffer, a much greater difference than the frame alone..

Lots of comfy ally frames around at the mo it seems, certainly on road.
Maybe designers have only just figured it out properly?
Or perhaps they've been forced to evolve - lots of cheap carbon being sold as 'comfy, strong and thoroughly absorbant'.

Comfort sells these days.

[quote=Northwind ]Real world testing is the only way to assess comfort.

Of a frame? So putting it in a jig and measuring deflections under load would be a totally useless way of comparing two different frames? This real world testing you claim is the only way, does that involve something other than a flawed human being to do the measurements? Because if not, then it really is totally pointless - you can't even do double blind testing with bike frames, as even if you completely disguise them there are differences in lateral deflection (which doesn't affect comfort) which are possible to detect.

I'm fairly sure that the perceived "differences" in comfort riders feel between different frames are actually differences in lateral deflection which their brain then interprets as comfort, despite not making any real difference. So maybe if you want to test which frame "feel" most comfortable it is a valid method, even if the results aren't real.

fundamentally you can't measure comfort with a ruler

You're still disputing the measurement of vertical deflections under load in a jig as a valid way of determining the comfort of a frame? Or do you not accept that it's possible to calculate the results of such jig testing to quite a high degree of accuracy using structural analysis?

And as pointed out by various people, the whole "all frames are equally comfortable" doesn't survive contact with the real world.

In the same way that various people have pointed out that homeopathy works in the real world?

I'm fairly sure that the perceived "differences" in comfort riders feel between different frames are actually differences in lateral deflection which their brain then interprets as comfort, despite not making any real difference.
So maybe if you want to test which frame "feel" most comfortable it is a valid method, even if the results aren't real.

I'm not sure comfort is objective.

If something feels more comfortable, it is, surely?
Lateral flex is there, and affects feel and comfort.
Too remove or ignore it when comparing comfort seems a little illogical?

Deflection testing would be useful in enabling people to determine which factors affect comfort for them - would be very interesting to spread the net and see the varied definitions.
🙂