Does Stiffness Matter?

[400bhp]

Leaving all the silly childish innuendo aside, I think it probably makes chuff all difference unless you are at the very top of the game where it 'might' have a tiny impact that could be the difference between a 1st or 2nd place in the sprint for the finish line in a race.
For most (and by most I mean 99.9% of the cycling population) it will make no difference, but could hugely affect bike comfort, which will in a roundabout way have an effect on performance. So a 'stiffer' bike may actually have a negative impact.
I say all this assuming we are not including bikes that are so uselessly soggy that the brakes will rub during periods of intense effort (and obviously a set of suitable wheels will be needed too), we aren't including such bikes are we?

Pretty much this. A couple of other points:
I wonder if the mounting of the bike on a static trainer means the effect is over egged? The trainer effectively channels the force the only way out it knows, which is kinetic energy through the back wheel. In the real world, some of that energy could actually be absorbed through you alternate leg for example?

As per later on in the thread, there will be some loss through kinetic energy in the sideways movement. Think of Newton's cradle.

In my head I think where there may be an advantage in a flex frame is on rougher surfaces, where some dampening effect might be of benefit.

 

[Globalti]

A bike frame is not designed to store then release energy like a prosthetic running blade or a competition snow ski, both of which are designed to bounce you back into the next movement in the sequence.

 

[andrew_s]

View attachment 394648 Been looking on Veloviewer for comparisons between 2 of my bikes. Managed to show those bikes for every ride in 2017. Stats as above.
Considering I have done 26% more climbing on average, the 0.6mph faster average speed suggests stiffer is better? Or is it the Aero elements of the frame? Or both?

You haven't done 26% more climbing on bike 1.
The averages are per ride, which is fairly meaningless in this comparison.

Both bike 1 and bike 2 are 52 feet per mile, so climbing will have had minimal impact on the difference in speed.

 

[Alan O]

Coincidentally, I just happen to have read this...

https://janheine.wordpress.com/2018/01/28/myth-4-stiffer-frames-are-faster/

(I've no opinion on the subject, as it's not something I know anything about, but I thought it might be of interest)

 

[bpsmith]

You haven't done 26% more climbing on bike 1.
The averages are per ride, which is fairly meaningless in this comparison.

Both bike 1 and bike 2 are 52 feet per mile, so climbing will have had minimal impact on the difference in speed.

Absolutely. I was looking at the average elevation per ride, and neglected the fact that the the rides were shorter on Bike 2.

Just spotted that in work break and came back to post it up. You beat me to it.

So the stats work out very nicely indeed. For 2017, I appear to have ridden 2 different style bikes of similar weight, but different characteristics including stiffness and aerodynamics.

The stats show that, at my average speed, there appears to be very little difference in speed whatsoever.

Very interesting indeed.

 

[bpsmith]

Actually just mentioned this to a cycling mate and he asked how the figures stack up if I ordered them in top average speed order and removed the group rides.

Of the top 30 fastest rides, only 5 were on Bike 2 and only 1 was a group ride. The top 10 fastest rides were all on Bike 1.

Perhaps there is something in the Stiffness/Aero frame argument?

 

[Smokin Joe]

It's not how stiff the frame is that matters, but how stiff the legs are.

 

[Drago]

Car manufacturers fit flexible driveshafts because they transmit power more efficiently. Not

 

[nickyboy]

Perhaps one should consider the physics of a flexing as opposed to stiff bike.

If the flexing is lateral and there are no heat losses in the flexing process, there is no meaningful energy loss compared to a 100% stiff bike with no lateral flexing

Where you do get a big difference is flexing resulting in vertical movement of the rider. That's why full suss MBs are so inefficient. The rider tends to bounce up and down and that definitely is a major waste of energy in terms of conversion into forward movement

But lateral flexing...I don't think it does anything meaningful

 

[Drago]

There are heat losses in the flexing process, although the numbers will be infintissimal.

 

[I like Skol]

Car manufacturers fit flexible driveshafts because they transmit power more efficiently. Not

What do you think a dual mass flywheel is? And what about the doughnut in the discovery rear propshaft.......

 

[Drago]

DMF is to protect engine electrics from excessive vibration. The old rubber doughnuts etc were cheaper than a proper UJ.

These items exists not at all in the interest of transmitting power efficiently, and in both cases actually detract from efficiency in favour of other considerations.

 

[Alan O]

Car manufacturers fit flexible driveshafts because they transmit power more efficiently. Not

I don't think anyone is suggesting that a bicycle's drivetrain should be flexible.

 

[Drago]

I don't recall suggesting anyone did.