Frame Stiffness - What gives?

Discuss light weight issues concerning road bikes & parts.
Huggis
Posts: 4
Joined: Thu Mar 15, 2018 9:45 am

by Huggis

So I’ve been researching which bike to buy to replace my 2006 S-Works Roubaix. I’ve had a few attempts at replacing it over the years (Scott CR1, KTM Revelator) but they don’t feel as lively and that they don’t respond as well to power input via the pedals.

I came across various articles (GCN, CYCLING TIPS) where experts were discussing a change in mindset around frame (namely B.B. stiffness). They concluded that a B.B. stiffness between 40-80 N/mm was the ideal window for most riders with 60 N/mm being the 'sweet spot'. The logic is that energy cannot be destroyed or wasted. On a frame with some flex the power generated during the downstroke is 'stored' and returned in the upstroke. Anyhoo best to read the articles or listen to the podcasts your yourselves.

It made sense to me and explained why my older, more flexible bike, performs better than any new, stiffer bikes that I’ve riddden.



Thoughts, opinions?

https://youtu.be/BH_AL4rxrp8
http://kirkframeworks.com/resources/tec ... rame-flex/
https://itunes.apple.com/gb/podcast/cyc ... 0385901611

Huggis
Posts: 4
Joined: Thu Mar 15, 2018 9:45 am

by Huggis

I should add that I complied some stiffness data from RoadBIKE.de bike tests. Had to learn some basic german however :-)

by Weenie


flostonf00
Posts: 6
Joined: Tue Mar 13, 2018 12:22 pm

by flostonf00

Just dont buy the cr1 it's not stiff anymore i had it and it was bad in climbing......Ktm i dont know...going from s-works to this you will be very sad...

jlok
Posts: 437
Joined: Tue Jun 30, 2015 3:30 am

by jlok

I had KTM Revelator Sky and this was bad. I'd say the ride was wooden feel and you'd need a fair bit of load at the front to make the front end stable. Strange geometries I guess. Swiched to TCR Adv SL Disc and it's totally different. Much better!

Huggis
Posts: 4
Joined: Thu Mar 15, 2018 9:45 am

by Huggis

jlok wrote:
Thu Mar 15, 2018 11:00 am
I had KTM Revelator Sky and this was bad. I'd say the ride was wooden feel and you'd need a fair bit of load at the front to make the front end stable. Strange geometries I guess. Swiched to TCR Adv SL Disc and it's totally different. Much better!
Thanks this is exactly my thoughts also! Funny how on paper it should be a great bike.

Huggis
Posts: 4
Joined: Thu Mar 15, 2018 9:45 am

by Huggis

flostonf00 wrote:
Thu Mar 15, 2018 10:55 am
Just dont buy the cr1 it's not stiff anymore i had it and it was bad in climbing......Ktm i dont know...going from s-works to this you will be very sad...
Hi I sold the CR1 after a couple of months - did not get on with it. I am hoping that a 2018 Roubaix with newer design and FACT 10R frame will be better then my 2006 FACT 9R grade frame. Advances in design, material and manufacturing process 'should' result in a better bike.

flostonf00
Posts: 6
Joined: Tue Mar 13, 2018 12:22 pm

by flostonf00

I oder a fuji transonic sl which has c10 carbon.C5 its their low you can also choose c15.They also have fuji sl for climbing c10 or c15.I would also choose giant tcr advanced its stiff or bmc slr02 or cervelo.

C36
Posts: 191
Joined: Fri Mar 03, 2017 3:24 am

by C36

I had the opportunity to share this few times on the past but not necessary on a post that specific like yours. You have to differentiate two things, the "feeling" and the "real impact" of stiffness.

The "feeling" is heavily influenced by pretty much... anything. During blind test it has been proven several times that I could make you "feel" very different about the same component depending on how I briefed you. Lighter rims or tires FEEL that you accelerate quicker but measuring it, you gain "nothing" (matter of few cm for an Elite in a 200m 0-max acceleration). I have seen few examples of proven faster products not released due to "so-so" feeling from the testers.

Mechanical stiffness DO matter for the performance at least out of the saddle. Lateral defection stores energy but its is not necessarily useful to turn the cranks. You can put the cranks in 6-12o'clock, cause lateral flexion and none of it will be used to turn the cranks... and still spend energy to deform the structure. each time you balance the bike left and right, part of the frame deflection is useless to move the bike forward. I have measured it and without sharing confidential details about the protocol it repeats below 0.01kmph @ 300W. I have in mind 0.2kmph in a 8% slope. You can also note that you develop an higher power peak with a stiffer structure (remember 10w, but would need to review my notes to be sure).

Now for everyday ride... you may prefer how something feel regardless if the bike is faster or not.



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RyanH
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by RyanH

I highly recommend listening to this podcast on it:

https://cyclingtips.com/2017/06/cycling ... ss-matter/

Tl;dr is that on a blind test some were faster on the less stiff bike.
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maxxevv
Posts: 1952
Joined: Wed Feb 09, 2005 4:51 am

by maxxevv

How fast or 'stiff' or 'responsive' a bike feels (without using any measurements) has influences from the geometry of the frame as well as stuff like the wheel and even the grip of the tyre as well as pressure. Heck, even the handles can create an 'illusion' for that matter.

Stiffness numbers do not mean everything unless you have identical geometries and components to compare with.

C36
Posts: 191
Joined: Fri Mar 03, 2017 3:24 am

by C36

maxxevv wrote:
Tue Mar 20, 2018 4:42 pm
...
Stiffness numbers do not mean everything unless you have identical geometries and components to compare with.
Indeed, the reason why we did test with prototypes changing one parameter at the time, keeping all the rest identical.
Regarding blind test being faster with softer components, depending on testers, I did observed something similar... as long as we don't track very accurately the power.

glepore
Posts: 1072
Joined: Thu Mar 28, 2013 4:42 pm
Location: Pa USA

by glepore

It's all in perception. I stiff carbon frame "feels" fast. So does a car with stiff suspension. Mark Donohue proved 40 years ago that sometime softer is actually faster, as you can get and keep the power down earlier or float thru the corners.
With bikes, who knows. Its not instrumented enough. Ride what y'all like, and if you can keep up with your pals AND your fitness is unquestionable, then look to whether your equipment is "stiff" enough or whatever.
I know that I'm pretty much the same speed over 60 mi no matter what I ride so long as its between 5.5 and 7 kg and has good wheels.
Cysco Ti custom Campy SR mechanical (6.9);Cannondale SS Evo Di2 7970 (5.79); Willier Cento Uno Air Di2 9070 (7.0); C40 Mk2 DA 7800 ; Anvil Custom steel Etap;1996 Colnago Technos Record

gewichtweenie
Posts: 152
Joined: Fri Sep 25, 2015 3:12 pm

by gewichtweenie

You improving your fitness level by 5% is going to produce much more result than a frame measuring 5% stiffer

jeanjacques
Posts: 65
Joined: Thu Apr 14, 2016 11:01 am
Location: France

by jeanjacques

"We decided to do a double-blind test with four identical frames, made from three different tubesets.
(...) Not only that, these riders were consistently faster on the more flexible frames."
https://janheine.wordpress.com/2018/01/ ... re-faster/

by Weenie


AJS914
Posts: 1894
Joined: Tue Jan 28, 2014 6:52 pm

by AJS914

That's the same study discussed in the cyclingtips podcast. It's pretty interesting. Most people would kill for an extra 12% power.

It makes me wonder if any pros have ever participated in any similar studies with their bike sponsor trying different layups looking for extra watts.

I've had a bunch of bikes and best ones have a springy, magic feel. Bikes that feel wooden feel the slowest.

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