Interesting Youtube vid on vertical compliance

[StressStrain]

Originally Posted by Dude

can we get a TL;DW for those too lazy to watch a video?

TLDW:

A smart guy instrumented 2 bikes with accelerometers and measured vibration while riding. Analysis of that vibration showed that both bikes shook up and down the same way - no difference in the vertical direction. Further analysis showed that the vibrated differently in the lateral direction. Said smart guy hypothesized that this quantified difference in lateral vibration was related to why the 2 bikes felt different to him.

[deluz]

My steel Mercian rides much smoother than my Tarmac SL8.
Maybe its the lateral flex, also the fork is steel and a much bigger rake.
The SL8 does feel like it responds quicker to power input.

[professerr]

Great video and explanations.

So, what is the mechanism by which greater lateral compliance results in a frame feeling smoother to Smart Guy, I wonder.

Could it be have to do with the fact that the frame isn’t exactly vertical as it rolls along? I mean, I recall reading long ago about some motorcycle frames being built with some amount of engineered lateral compliance so they could flex while leaned way over.

Or is it that the loads on a hardtail frame bouncing vertically along through, say, rutted dirt roads are actually significantly lateral?

I wonder what Rob English (Cambridge engineering degree, I recall) thinks about this - he’s gone on for years about how vertically stiff the rear triangle structure is, (hence his super skinny seat stays).

[oldguy00]

Originally Posted by martl

What, 0 vertical compliance from a classic diamond frame can be measured?

Now that is a shocker! if only someone had told us!!11!

But does it corner on rails?

[Dude]

Originally Posted by StressStrain

TLDW:

A smart guy instrumented 2 bikes with accelerometers and measured vibration while riding. Analysis of that vibration showed that both bikes shook up and down the same way - no difference in the vertical direction. Further analysis showed that the vibrated differently in the lateral direction. Said smart guy hypothesized that this quantified difference in lateral vibration was related to why the 2 bikes felt different to him.

Thanks!! ❤️❤️