want new bike, quick and dirty way to check frame flex....
02-22-13, 11:27 PM
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want new bike, quick and dirty way to check frame flex....
walk into LBS, look at bike and like it but how do I determine frame flex??
step on pedal from the side?
step on pedal from the side?
02-23-13, 12:10 AM
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and what would that tell you?
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02-23-13, 12:14 AM
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1 Ride bicycle over hard bump
2 If hard bump felt then little flex- if soft bump felt then great flex
2 If hard bump felt then little flex- if soft bump felt then great flex
02-23-13, 02:51 AM
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Once you've done it to heaps of bikes, a fair bit... but it's a mix of frameset, crank and wheel flex so you'd want to be able to judge the stiffness of cranks and wheels by sight and experience, before you could make a vague comment about the frame. Come to think of it, the cranks prolly wouldn't enter the picture unless they were on a stiff frameset and wheels and pretty flexy themselves.
Too simplistic; you can get a sweet ride out of a stiff ally frame with a carbon seatpost, and today's carbon frames can be stiff as buggery under full power but soak up road shock like you wouldn't believe.
Or rather, I think you and the OP are looking at flex differently...
Or rather, I think you and the OP are looking at flex differently...
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Last edited by Kimmo; 02-23-13 at 02:54 AM.
02-23-13, 08:49 AM
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I do a couple things which are really for me to be curious than anything too productive.
1. Put forearm across the top of the hoods, grab bar. Grab seat tube / top tube area with other arm. Twist frame. Stiffer frames will be more predictable in turns. It really measures flex torsionally so has nothing to do with power transmission. I've been really surprised at how flexible some frames are.
2. Crank in forward position, put rear brake on hard, push down on crank. It's really a tirepressure/wheel/frame/crank test but it's basically the "frame stiffness stomp test" that the scientific frame reviewers do. I can't tell minute differences (who can) but any shocking results aka outliers are worth noting.
For me I'm looking for the most responsive frame. I am good riding a SystemSix for 6-8 hours at a time (alum rear triangle, carbon fork, excellent front end control) so comfort isn't my concern - it's whether or not the frame is so flexible I'm going to stop and check to see if my BB shell is cracked (which happened on 2 frames).
1. Put forearm across the top of the hoods, grab bar. Grab seat tube / top tube area with other arm. Twist frame. Stiffer frames will be more predictable in turns. It really measures flex torsionally so has nothing to do with power transmission. I've been really surprised at how flexible some frames are.
2. Crank in forward position, put rear brake on hard, push down on crank. It's really a tirepressure/wheel/frame/crank test but it's basically the "frame stiffness stomp test" that the scientific frame reviewers do. I can't tell minute differences (who can) but any shocking results aka outliers are worth noting.
For me I'm looking for the most responsive frame. I am good riding a SystemSix for 6-8 hours at a time (alum rear triangle, carbon fork, excellent front end control) so comfort isn't my concern - it's whether or not the frame is so flexible I'm going to stop and check to see if my BB shell is cracked (which happened on 2 frames).
02-23-13, 09:00 AM
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02-23-13, 09:23 AM
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Tell the guy at the shop you want a bike that is laterally stiff, but vertically compliant.
02-23-13, 09:24 AM
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It's relative to your weight and power output. If YOU can't feel it flexing when riding hard why would you care if a heavier, more powerful rider can?
02-23-13, 11:29 AM
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If you could easily get a number to quantify that "flex," what would it actually tell you about the frame you tested?
Ride the bike. If the "flex" is too much or too little for your taste, surely you will be able to sense that. If you can't sense a "flex" issue, perhaps it's really a non-issue.
Ride the bike. If the "flex" is too much or too little for your taste, surely you will be able to sense that. If you can't sense a "flex" issue, perhaps it's really a non-issue.
02-24-13, 05:55 AM
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Some touchy posters in this thread. Take it easy.
How much useful information did you provide about the kind of riding you do and what concerns you have for worrying about "flex" ?
How much useful information did you provide about the kind of riding you do and what concerns you have for worrying about "flex" ?
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Last edited by BillyD; 02-24-13 at 07:41 AM. Reason: cleanup
02-24-13, 06:18 AM
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No way to self determine frame flex accurately. Go by reputation of the frame manufacturer. Some bike manufacturers web sites tell a lot about how they design their bikes and some are mostly marketing for the consumers. One that stands out on their engineering is Cervelo.
02-24-13, 06:49 AM
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Why are men always fixated on stiffness? 
Anyway.... Almost any new road bike will be in the same range of stiffness, and significantly stiffer than a bike made ~10-15 years ago. I wouldn't worry about it.
Anyway.... Almost any new road bike will be in the same range of stiffness, and significantly stiffer than a bike made ~10-15 years ago. I wouldn't worry about it.
02-24-13, 07:55 AM
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OP, there's really no standard, reliable way to test for that. IMHO the phenomena is overrated anyway, but to each his own.
Lets squash the personal attacks and stick to positive, useful replies to the question from here on in, please.
Lets squash the personal attacks and stick to positive, useful replies to the question from here on in, please.
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02-24-13, 09:54 AM
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Not true. There were some super stiff frames 15 years ago. In fact I still ride one. Klein made frames still considered stiff by today's standards and I doubt they were the only ones to do so.
Again, its all relative.
Again, its all relative.
02-24-13, 06:59 PM
#21
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Yeah, I guess aluminum was used a little earlier than that. I'm thinking of the heyday of the traditional round-tube steel bikes, where the geometry and compromises for lighter frames resulted in flexier bikes. In contrast, an entry-level aluminum bike today will have larger ovalized tubes, smaller triangles and beefier BB's.
At any rate, unless you're a monster sprinter, these days it's a mere marketing buzzword. Almost any aluminum or CF road bike in a typical LBS will be more than sufficiently stiff to, uh, satisfy the demanding... Good grief. Y'all need to worry about some other aspect of bicycles.
At any rate, unless you're a monster sprinter, these days it's a mere marketing buzzword. Almost any aluminum or CF road bike in a typical LBS will be more than sufficiently stiff to, uh, satisfy the demanding... Good grief. Y'all need to worry about some other aspect of bicycles.
02-24-13, 07:51 PM
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Now, where can I get hi-modulus carbon fiber handlebar plugs and valve caps ?
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02-24-13, 08:10 PM
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