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Old 10-19-10, 12:40 PM   #1
dasding
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aluminum frame flex

I inherited my brothers racing bike when he upgraded; it is an aluminum framed Olmo "equipe" of uncertain age, though I'm guessing not more than 5-10 years. I got it 1 year ago in very nice cosmetic shape with new wheels (aksium) and components (105), and haven't ridden it all that much.

Recently on I ride I noticed that when I was climbing the rear wheel rubbed against the right chain stay. The paint was rubbed off down to the metal at this point, so it makes me wonder if it has been doing this for longer and I didn't notice. It only does it when I'm pushing hard with my right foot. The wheel is true and seems dished properly and is also firmly in the dropouts. I observed that if I stand up on the pedals with the brakes on and push hard, the frame flexes a lot down by the BB, and I can actually make it flex to the point that the stay touches the wheel.

Do Al frames wear out? I don't see any visible cracks... Or is this a normal amount of flex and I just need to run skinnier tires on this frame (I've got 700x23 on now)? It doesn't seem to have much clearance down there to begin with.
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Old 10-19-10, 12:47 PM   #2
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the Oversize diameter frames don't flex.[as much] smaller diameter tube frames do .
measurable deflection.
Yes aluminum frames have a life span, flexible ones shorter than rigid ones.
AlAn of Saccolongo Italy made nice Aluminum frames , Guerciotti bought them and rebranded the stickers.
wonder if Olmo did the same ...
Pictures?

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Old 10-19-10, 01:11 PM   #3
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the Oversize diameter frames don't flex. smaller diameter frames do .
Yes aluminum frames have a life span, flexible ones shorter than rigid ones.
AlAn of Saccolongo Italy made nice Aluminum frames , Guerciotti bought them and rebranded the stickers.
wonder if Olmo did the same ...
Pictures?

BZZZZZZZZZT! WRONG!
But thanks for playing! You get a copy of the BikeForums home game!

All frames flex. Certainly there are stiffer ones that flex less - and often frames with larger tube diameters flex less than frames with skinnier tubes, but not necessarily, and they all flex to some extent. here are plentyh of smaller-diametrer frames that flex very little and plenty of large-tubed frames that flex a lot.

And the 'flex' perceived in a frame does not necessarily equate to a shorter life span. Many frames are designed with a certain amount of flex under normal riding conditions and still last for decades. Many stiff-as-a-board frames will crack after a couple years of heavy use. It all depends on the design of the frame and the construction.
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Old 10-19-10, 01:19 PM   #4
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scratches become stressrisers, and aluminum cranks have snapped , nobody makes Aluminum Springs.
because it doesn't have enough ductile elasticity.
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Old 10-19-10, 01:37 PM   #5
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Show us some pictures of the rear wheel and the part of the frame that the wheel rubs. All frames flex some, if the tire is too close to the stay, it can rub when flexed under load, such as standing while climbing a hill.

Maybe the tires are too large for the frame?

Maybe the wheel isn't centered in the frame or isn't dished correctly?
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Old 10-19-10, 01:43 PM   #6
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I'm not sure if frame rub might be caused by low spoke tension, so I figured I'd ask the techs at the risk of looking like an idiot.

Can it cause the wheel to distort enough to rub the frame? I've taco'd a wheel with low tension while accelerating hard, so it seems possible. Is this a flawed assumption?

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Old 10-19-10, 01:45 PM   #7
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scratches become stressrisers, and aluminum cranks have snapped , nobody makes Aluminum Springs.
because it doesn't have enough ductile elasticity.
Not enough ductile elasticity for a spring, but for the 1 or 2mm between opposites of a bike frame? Certainly. THe frame does not plastically deform under heavy pedalling loads.
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Old 10-19-10, 03:00 PM   #8
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I'll take some pictures when I get home. I checed the dish and it seemed good. It did seem a little closer to the stay in question, but it was snug in the drop outs and there is not any way to adjust it given the design. given that the wheel appears to be dished properly and the wheel is true and it still appears 1 or 2 mm closer to the R stay, it made me wonder if the frame could be bent. Is this a common place to bend a frame? seemed odd to me. Also, do the italians make frames that don't accept 700x23 tires?
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Old 10-19-10, 03:34 PM   #9
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Even the softest aluminium frames such as the original Alans and Vitus 979s aren't so flexible that they rub the wheel on the chainstays. In fact, the stiffest frames have always been the original fat-tube aluminium Cannondales and Kleins. The actual materials are not as important as the design and construction methods.

I believe those Olmo alloy frames have an aluminium main-triangle with carbon back-end? There may be a loose lug that have become unbonded in the back.

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Old 10-19-10, 03:42 PM   #10
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After I rode my Scott race bike with a steel 520 Reynold's frame for well over 60,000 miles, a mechanic said my shifting problem was caused by frame flex.. . My replacement bike was an aluminum framed Klein Quantum Pro.. Some day, I might find myself returning to steel.?
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Old 10-19-10, 04:45 PM   #11
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my original question was probably phrased in a stupid way: I realize that it isn't normal for the wheel to hit the stay, so I guess I'm wondering if

a) it is a common problem with Al frames and a sign that the frame is wearing out
b) can be attributed to a crack somewhere that I need to look for (not quite sure how/where they appear)
c) it could be a problem with the wheel other than dish--like can the wheel flex if the spokes are not tensioned properly.

Last edited by dasding; 10-19-10 at 04:50 PM.
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Old 10-19-10, 04:59 PM   #12
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I would be more inclined to look carefully for a crack at this point. With the frame firmliy held in various attitudes in a sturdy stand flex the rear triangle in various ways and look for signs of any opening or movement in the joints or near to the joints. Likely you'll need to either leave the wheel in the frame to use as a lever or arrange something else as a substitute lever to apply the pressure.

As for the wheel flexing? Of course it does! ! ! Wheels are just like bike frames in that they are made of small amounts of metal arrayed to form a load bearing structure that is largely dependent on the elasticity of the metal. I've see shots of riders sprinting for the finish where the wheels look like they should taco and collapse because they are so distorted by the leaning of the muscular riders crunching for the win out of the saddle with the bikes canted over to around 20 degrees from vertical. Not just the wheels are flexed but the forks and frame on one of them was so radically flexed out of plane from the effort that there was about a 5 degree angle of difference between the front and rear wheels. The picture was REALLY impressive and showed just how elastic our bikes really are if you have a well trained and heavy "racing gorilla" to ride it for the camera....
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Old 10-19-10, 05:05 PM   #13
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Quote:
Originally Posted by dasding View Post
my original question was probably phrased in a stupid way: I realize that it isn't normal for the wheel to hit the stay, so I guess I'm wondering if

a) it is a common problem with Al frames and a sign that the frame is wearing out
Nope on this one. Frames do not get softer as they wear out. If anything, they would get stiffer right before cracking.

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b) can be attributed to a crack somewhere that I need to look for (not quite sure how/where they appear)
This is more likely. Look at where the rear-dropouts attach to the chainstays. Also where the chainstays meet the bottom-bracket shell.

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c) it could be a problem with the wheel other than dish--like can the wheel flex if the spokes are not tensioned properly.
This is the most likely area. Although the actual amount of flex caused by human pedaling-forces are puny, it is possible to flex a wheel by standing and rocking the bike away from vertical, thus using your weight to bend the wheel sideways. Another idea is loose wheel bearings. Rock the rim back and forth between the brake-pads. Do you see and feel movement with a >clunk< at the end of the movement range?
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Old 10-19-10, 05:30 PM   #14
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scratches become stressrisers, and aluminum cranks have snapped , nobody makes Aluminum Springs.
because it doesn't have enough ductile elasticity.
well, now that we know you don't have a clue what you're talking about...

What you meant to say is that it doesn't have a safe fatigue limit that allows it to operate in a highly elastic application.
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Old 10-21-10, 12:35 PM   #15
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thank you very much everyone for the various advice here. I'm starting to think the wheel may be the culprit, and that it really was a little out of dish. I had checked the dish using a park truing stand borrowed from a friend but only just realized that the feelers are a little off-center, hence the dish may be off by 1 or 2mm, which, given the extremely tight clearance on this frame, might account for it. I made my own dish guage with some material from the hardware store just for fun... so now it looks like I need to adjust the dish back over to the left before I can rule the wheel out and start looking for hairline cracks in the frame.

which leads me to a wheel question: does anybody know the recommended R-side spoke tension for a mavic aksium wheel? using my park guage they were up around 160 kg-f, which struck me as high. but I also don't know too much about the spoke tensions in low-spoke-count wheels...I've only built 36 spoke rear wheels. I called mavic twice and left messages but their tech guy hasn't gotten back to me.
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Old 10-21-10, 01:50 PM   #16
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you could be putting too much torque and having the Quick Release slip on the drive side causing the wheel to rub on the chain-stays until the wheel is realigned and tightened.

internal cam QR are the best.
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Old 10-21-10, 03:54 PM   #17
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thank you very much everyone for the various advice here. I'm starting to think the wheel may be the culprit, and that it really was a little out of dish. I had checked the dish using a park truing stand borrowed from a friend but only just realized that the feelers are a little off-center, hence the dish may be off by 1 or 2mm, which, given the extremely tight clearance on this frame, might account for it. I made my own dish guage with some material from the hardware store just for fun... so now it looks like I need to adjust the dish back over to the left before I can rule the wheel out and start looking for hairline cracks in the frame.

which leads me to a wheel question: does anybody know the recommended R-side spoke tension for a mavic aksium wheel? using my park guage they were up around 160 kg-f, which struck me as high. but I also don't know too much about the spoke tensions in low-spoke-count wheels...I've only built 36 spoke rear wheels. I called mavic twice and left messages but their tech guy hasn't gotten back to me.
160 sounds about right, low spoke count wheels need a lot of tension. always use a dish stick
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Old 10-22-10, 10:44 AM   #18
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just found the specs on the Mavic dealer website--not easy to find stuff on there! but yeah you were right, the recommended tension for the rear is 150-165 kg. 80-90 for the front.

so if the tension is up there on the drive side and it was a few mm out of dish, I guess that means the NDS loosened up?
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