# Newb question about bike flex/stiffness



## mysavers (Dec 1, 2009)

Hi. I got back into road cycling last march, so consider myself a newbie. Just have a few questions about some terms i often read to describe a bike's performance. What exactly does frame flex and stiffness mean? While riding how do i know if my bike has less flex/more flex in terms of its frame, or how can i determine or feel the bike's stiffness. Are these characteristics seen during cornering, climbing, descending, etc? Your feedback will be appreciated as i want to learn more in comparing different bikes' features. Thanks.


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## Kerry Irons (Feb 25, 2002)

*Flex problems*



mysavers said:


> Hi. I got back into road cycling last march, so consider myself a newbie. Just have a few questions about some terms i often read to describe a bike's performance. What exactly does frame flex and stiffness mean? While riding how do i know if my bike has less flex/more flex in terms of its frame, or how can i determine or feel the bike's stiffness. Are these characteristics seen during cornering, climbing, descending, etc? Your feedback will be appreciated as i want to learn more in comparing different bikes' features. Thanks.


Frame flex is not an issue in a modern bike. Your wheels will likely flex a lot more (laterally). You can use the search function and find things like forums.roadbikereview.com/showthread.php?t=199400 Just the length of such threads and the fact that there are such opposed views should tell you that the issue is not settled such that it should be a factor in your bike choice. The fact that most bike tests are done with the wheels supplied with the bike (rather than a "standard" wheel so bikes can be compared) says that bike tests are mostly not worth squat on the subject.


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## PJ352 (Dec 5, 2007)

mysavers said:


> Hi. I got back into road cycling last march, so consider myself a newbie. Just have a few questions about some terms i often read to describe a bike's performance. What exactly does frame flex and stiffness mean? While riding how do i know if my bike has less flex/more flex in terms of its frame, or how can i determine or feel the bike's stiffness. Are these characteristics seen during cornering, climbing, descending, etc? Your feedback will be appreciated as i want to learn more in comparing different bikes' features. Thanks.


If you have to ask, you're probably fretting over a 'problem' you don't have. 

Generally speaking, a 'flexy' frame will have vague steering response and/ or you'll get some chain rub under load due to BB flex, _but_ these 'symptoms' can also be caused by other factors. Conversely, a stiff frame will feel stable at speed and in turns, and you won't feel any flex at the BB. Other factors can contribute to this as well. 

When comparing different brands/ models, it's pretty much impossible to make direct comparisons re: frame stiffness, because independent tests are almost nonexistent. There are TOUR tests conduicted measuring (among other things) STW (stiffness to weight), but many results aren't published because they're conducted at the request of manufacturers. Along with that, and relating to CF frames, makers resort to their 'in house' names for CF grades/ layups used, such as OCLV, 10r, FACT IS, DYAD and on....

Whether the material be alu, steel or CF, the arena you're entering is one of the murkiest in the bike world. You're apt to get a weath of opinions, and that's all they will be. But that's not to say certain materials don't have 'best uses'. They do, but that wasn't your question... yet.


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## Hank Stamper (Sep 9, 2009)

If you're reading reviews and see someone mentions the bike is really stiff it could mean:
A. If feels like I'm riding on just rims over cobble stones.
B. When I sprint all my energy goes to turning the pedals and isn't wasted flexing the frame.
C. When I taking a corner really really fast the bike doesn't feel like it's giving out.
D. All, or a conbination, of the above.
E. Something(s) I forgot.

So you see it could be good, it could be bad. Now the problem is what they are saying may or may not actually have anything to do with bike stiffness despite the bikes performance being attributed to stiffness. Could be the wheels, could be the geometry, could be the fit compared to whatever bike(s) they have been on in the past and are using as their standard of comparision. 
It seems that every bike maker says their frames are stiff, so that makes it even tougher to factor in because everyone and their brother claims the bike is stiff now-a-days so who knows what it really means.

In other words go by how a bike feels to you and not what tests and other people say about stiffness. If stiffness (within certain parameters) even matters at all is another topic to.


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## UrbanPrimitive (Jun 14, 2009)

Opinions opinions opinions. Hank's list and PJ352's post really cover it as far as my experience goes. Unless you're riding a frame made of dead-soft annealed copper it's probable that "frame stiffness" will be experienced as a combination of multiple factors in the bike build. The few independent frame material stiffness tests I've seen measured the difference in terms of thousandths of an inch. The flexy-est frames were still within four thousandths of an inch of the stiffest. Granted, this was testing rear triangle deflection, not lateral, but still you get the idea.

There has been a little discussion about the "frequency" of a frame. That is looking at the total make-up of the frame and components and considering a native harmonic resonance to vibration as a result. Basically looking at the bike like a bell. Most people who talk about this idea consider a resonating bike an unpleasant experience. The idea being that the bike that resonates easily will transfer vibration from the road into the rider more easily. While resonance may not be a direct function of stiffness, material resonance is something that some people debate about (CF doesn't, Yes it does, no it doesn't, yes it does, et cetera). I mention this because it's another grey area in biking technology that borders on the arcane, but is related to the symptoms or promises of a a frame material.

Having muddied the waters even more, happy riding!


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