corrado33

I have a few bikes. More than most I'd say. However, none of my bikes are more expensive than ~$1300. Most are much cheaper than that. (I like to rescue old bikes and I'm a graduate student who doesn't make a lot of money.)

My commuter is a Motobecane USA Record (from bikes direct). It's an aluminum bike. Now, people often talk about the stiffness of bikes, how much they flex when you pedal, etc. So, to a cyclist who hasn't ridden every steel/aluminum/titanium bike produced from 1958 to present, how stiff is "stiff?"

Lets look at my personal example. I (think) I have restless leg syndrome. My legs never stop moving. They just don't. When I'm at a stoplight on my commuter, I'll often bounce my leg on the pedal. I put my left food down with my left pedal down as well, and bounce my right food on the pedal. Not really bouncing the foot, really just moving my knee up and down with my toes still on the pedals. Now, when I do this, I can look down and see the entirety of the bike flexing (what seems like) more than an inch. I'm not pushing on the pedal purposely. It's surely less hard than I push when I'm going up a hill or going fast. Heck, probably less hard when when I'm pedaling on a flat surface. I'm a skinny guy, I weigh 145 pounds, there isn't a lot of mass behind this movement. Now, in my ignorance, I'd consider this bike "flexible," even though it's made from aluminum. Generally aluminum is stiff, but this bike/frame is very cheap. Would you guys tend to agree? How much frame flex should be visible when you TRY to put pressure on the frame?

andr0id

Short answer: You're moving the tire and wheel (spokes) a lot more than you're moving the frame.

Kindaslow

Remember, if it lasts for more than 4 hours, consult your doctor... Right after telling your friends...

corrado33

I agree. However, the movement I'm seeing is when I look straight down over the top tube and look at the bottom bracket. I can see it moving from one side to the other.

Hahaha

Kindaslow

At 145, you should not experience all that much flex. However, you might not be seeing flex, but just movement.

TheManShow

IMHO there is no answer to your question, as stiffness is subjective from person to person. I love to eat hot food, to me there is nothing too hot. To other people Taco Bell is too hot to eat at.

Retro Grouch 

When I was a boy, way, way back when, Bicycling Magazine of all people actually had a fixture built for testing bike frame stiffness. I think that Gary Klein of Klein bicycles made it. They would test bike frames and publish the results. It had only 2 problems:

1. The results didn't correlate with anything.
2. While somebody had to win that meant that every other bicycle manufacturer was a loser. That's not good for advertising sales.

A little later in time, French companies Vitus and Alan produced aluminum frame bicycles. They were real flexy. Today lots of folks say that aluminum framed bikes, by their nature, are stiff.

I think that there's more people talking about stiffness as it pertains to bicycle frames than there are people who understand the topic.

ShortLegCyclist

Frame flex is relevant to me only in the context of loaded touring, so I would recommend you try simulating that to evaluate the flex of your bike or lack thereof.

Load 70-100 pounds of panniers and saddelbags and then take the bike up a fair incline and down at speed.

You should feel a marked difference in the way different bikes behave in that circumstance, not all of which is related to frame flex, but a lot is.

For instance, touring bikes are made with very low bottom bracket clearance for lower center of gravity and better handling when fully loaded.

The Surly Long Haul Trucker supposedly handles better fully laden than naked, for example.

nitewing117

It really does sound like its just the wheels and tires flexing. I've ridden a frame that flexed enough for the FD to get massive chain rub during hard efforts. I've got the build of an offensive lineman though.

jfowler85

Let me ask my wife.

wphamilton

The last time there was a BF "stiff frame" argument thread, I got curious so I grabbed my bike by the seat and handlebar, put my foot on the crank axle and pushed. There was quite a bit but mostly in the wheels and tires so I started thinking of ways to isolate the frame and simulate an actual pedaling force ... but first the question is, if I only knew for sure when pushing it and not while riding how does it matter?

I don't think it matters at all for just pedaling a road bike down the street. Short of the point of brake rub or dropping chains, no difference.

If I started to feel it while riding though, I'd get off and check for cracked welds.

Cougrrcj

My FD 'chain rub' under load was caused more by the crankset/chainrings flexing, and not the bike frame. I switched cranksets and no more rubbing.

As a side note, if your pedal stroke is even (try riding old-school rollers without a front fork mount and you'll see what I mean), even with a 'flexy' frame, you won't notice all that much. Frame 'flex' is often mistaken for side-to-side flex. That's why I love riding rollers. Doing so will dramatically show the errors in your riding technique. A smooth pedal stroke when riding rollers will magnify the side-side motion and once you eliminate that will translate to a very efficient ride. What little vertical frame or wheel flex one may find is what helps cushion the bumps and jolts.

In all honesty, in forty-plus years of serious riding, I have yet to find the cause of a bike frame/fork to be more 'flexy' than primarily a poorly-tensioned wheelset. After that comes the frame geometry (wheelbase, along with fork angle and trail.)

Yes, some of he cheaper entry-level/X-mart BSOs have frames made of questionable materials. Any 'real' bike with bike-grade tubing should be good enough for 99+% of most riders. I recall reading of a frame tubing comparison a few years ago - several brand-new bikes were built identically by the same frame builder except for the frame tubing, afterwhich various 'experts' rode them all. Most of these professional riders couldn't tell the difference.

Blue Belly

wasnt that the SL vs SLX article? Those are both premium tube sets.

Blue Belly

When riding your different bikes, what difference do you notice between them? Except for a couple, most of the flexy bikes I owned or rode, were mostly flexy in front of the seat tube. If you get too much flex behind the seat tube you start having front deraileur & rear brake rub issues. It takes a lot to get a reasonable amount of flex out of those connected triangles.

Cougrrcj

IIRC, there were five-seven different tubesets.

Blue Belly

Ah, didn't see that one. Would be an interesting read.

StanSeven

You're not flexing the frame that much stopped like that. You're likely seeing movement from the wheels (spokes) snd tires.

spdracr39

You are worrying about a non existent problem. It's not Tour de France so just ride.

andr0id

I agree. Once we got rid of square taper axles and went to stiffer cranks, all that out of the saddle FD rubbing went away. This was probably not ever due to frame flex except perhaps on the noodliest of frames.

GP

https://youtu.be/zf5i0O2PNS4

ltxi

Kinda what I was thinkin'.

molten

The title of this thread also applies to SHOES (soles).