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Will clamping an alum alloy frame on the top tube damage it?

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Will clamping an alum alloy frame on the top tube damage it?

Old 07-25-20, 10:29 AM
  #1  
Chuckles1
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Will clamping an alum alloy frame on the top tube damage it?

Have been clamping lightly on the balance point of top bar for two years, since I got a work-stand. In fact my cyclocross, now road bike, lives on the stand whenever I'm not riding it. Makes it so easy to clean and examine the tires, check the brake pads are straight, degrease the wheels, tweak the indexing, etc.

Can't see any problem, but have read on the forum it's a no-no. Has anyone actually had a frame failure from clamping an alloy frame on the top bar? If so, how did it fail? Bend? Crack? Other?
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Old 07-25-20, 10:41 AM
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I just clamp the seat post and avoid any worries.
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Old 07-25-20, 10:42 AM
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As long as you're always careful to use the lowest clamping force possible, your should be fine. The only frame I ever saw damaged was a Reynolds 531 steel frame---a customer in a bike shop clamped his bike in the middle of the seat tube but didn't realize that the clamp was set for clamping seat posts. Flattened the tube into what would have been an aero shape if the orientation had been front to back rather than side to side.
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Old 07-25-20, 12:06 PM
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No good professional mechanic would ever do it, to put it in perspective. The tubes are butted and are extremely thin in the middle. If clamped gently, then certainly the weight of the bike and minor cleaning and adjustment won't do any harm, but it's a bad habit, because you absolutely could damage the bike if you needed to apply real force to the bike.

I'm assuming you're doing this because there's not enough seat post exposed to clamp it? That is definitely the standard for professional mechanics. If the post is too short we usually indicate the original height with tape and raise the post--takes really very little time in the context of a tune-up, but is admittedly annoying for a quick flat change or the like. Using the stand like you are for storage probably isn't a terrible idea, but I'd advise you to keep it wiggle-room-tight.

As for failure mode, they bend inwards and crack parallel to the tube.
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Old 07-25-20, 01:45 PM
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Depends entirely on the bike. Have a 90's possibly 80's era aluminum Cannondale and have zero issues not only clamping the top bar, but transporting it on a car rack hanging from the top bar. It weighs 60# with the mid drive kit.

Not much chance of hanging this one by a seat post. Good to know about extending the post, only have an inch or so exposed, but couldn't imagine holding it there long enough to mount even with the quick release on the PCS4 stand.
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Old 07-25-20, 03:54 PM
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I had a 'screwed & glued AlAn, those tubes were thick wall Cannondales are thin wall ..
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Old 07-25-20, 07:10 PM
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My answer is only if you clamp it too tightly. Andy
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Old 07-26-20, 10:22 AM
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What's the best place to clamp for bleeding brakes?

Thanks for the replies, all. I have the clamp set loose, just closed enough so the bike won't wiggle loose and fall off while lubing chain or whatnot. Clamping on seat post for everyday use is impractical, as I've got a seat bag that would have to be removed. From what I'm hearing, crushing the tube is the issue, so I'm going to keep on the way I'm doing it.

I've never bled hydraulic disc brakes, but will want to some day. I gather you need to tip the bike at various angles during the process. Is the seat post the place to clamp for that job? And I take it you mean seat post, not seat tube?
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Old 07-26-20, 10:31 AM
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Originally Posted by fietsbob View Post
I had a 'screwed & glued AlAn, those tubes were thick wall Cannondales are thin wall ..
I honestly think you would have trouble crushing the tubes of my cannondale with a vice.

I'm guessing newer bikes are different from the older ones.
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Old 07-26-20, 03:57 PM
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Originally Posted by Chuckles1 View Post
I've never bled hydraulic disc brakes, but will want to some day. I gather you need to tip the bike at various angles during the process. Is the seat post the place to clamp for that job? And I take it you mean seat post, not seat tube?
For those times when really firm clamping is necessary, some folks will remove the seatpost with the saddle and replace it with a "junk" seatpost kept for those special occasions.

As for bleeding the brakes... cars and motorcycles aren't tipped at various angles, so I don't see why a bicycle should need to be when performing this service. AFAIK, "bleeding" isn't the same as "draining".
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Old 07-26-20, 04:31 PM
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I can vouch from personal experience that it is possible to crimp the top tube of a 90's Cannondale with a repair stand. Not too long after that, the bike got really noodly, but I never confirmed whether or not there was actually any crack under the paint. Could have been totally unrelated.
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Old 07-26-20, 04:53 PM
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I took a closer look today and tapping on the tube does sound like it is thin walled. The tube has such a solid feel and like I said, just drove 3000 miles with it hanging on a car rack.

Can't imagine what I would have to do to crush it, seems like it would have happened by now
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Old 07-26-20, 05:14 PM
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Originally Posted by sweeks View Post
For those times when really firm clamping is necessary, some folks will remove the seatpost with the saddle and replace it with a "junk" seatpost kept for those special occasions.

As for bleeding the brakes... cars and motorcycles aren't tipped at various angles, so I don't see why a bicycle should need to be when performing this service. AFAIK, "bleeding" isn't the same as "draining".
When was the last time you bled bike brakes? I typically do so several times a week, and I can tell you that being able to reposition the bike somewhat is useful.

Usually you don't necessarily need to do much more than angle the handlebars up, but the fluid volumes are like an order of magnitude lower for a bike than even a motorcycle, so even amazingly small amounts of air effect performance. Also the actual caliper mount positions vary somewhat significantly so sometimes the fluid path may be poor in practice and require manipulating the position of things.
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Old 07-26-20, 07:03 PM
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Originally Posted by cpach View Post
When was the last time you bled bike brakes? I typically do so several times a week, and I can tell you that being able to reposition the bike somewhat is useful.
Heh... never! I defer to your greater experience. In my defense, I *did* say "I don't see why...", leaving open the possibility that I was ignorant of some relevant detail.
Thanks for the correction!
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Old 07-26-20, 11:03 PM
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Originally Posted by Chuckles1 View Post
Have been clamping lightly on the balance point of top bar for two years, since I got a work-stand. In fact my cyclocross, now road bike, lives on the stand whenever I'm not riding it. Makes it so easy to clean and examine the tires, check the brake pads are straight, degrease the wheels, tweak the indexing, etc.

Can't see any problem, but have read on the forum it's a no-no. Has anyone actually had a frame failure from clamping an alloy frame on the top bar? If so, how did it fail? Bend? Crack? Other?
I have been following your exact same process for at least four years on a Specialized Crosstrail Hybrid aluminum frame. I lift the bicycle up with both hands and place it on the horizontal bottom clamp. I then tighten the top clamp down on the top tube. The bicycle weights around 35 pounds. So, if I measure the bottom clamp area(4 inches by 1 inch), 4 square inches. And then divide 35 pounds by 4 square inches, you get around 9 pounds per square inch(PSI) on the bottom of the top tube. I can apply more force with my hand/fingers on the top tube and I get no flexing. Now add in the clamping force, which is light and I do not believe you are going to damage the top tube. And I hope the two welded joints at each end of the top tube can handle a 35 pound force upward on the top tube.

I use a bike rack that holds the bicycle by the top tube. It has a smaller contact area of about 1 square inch at two places on the bottom of the top tube. So, that makes it around 17.5 PSI at those two areas, plus the jarring as you travel down the road. I have not had any deformation of the top tube and I have driven over some very rough roads. And the two top tube joints show no signs of cracking or fatigue.

I say keep on doing what you have been doing, because I am....
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Old 07-27-20, 02:34 AM
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Originally Posted by dsbrantjr View Post
I just clamp the seat post and avoid any worries.
Until you happen to have a carbon or dropper seatpost. I'd rather clamp the top tube rather than one of those.

I just put a rag between the frame and clamp and us as low clamp force as possible to keep the top tube from sliding around. Never had any problem.
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Old 07-27-20, 12:20 PM
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I would think that there is a possibility of damaging a frame tube by clamping on it. That said, and although I "should" clamp on the seat post, I've been clamping on the top tube of my Cannondales for a number of years. I use a Feedback sports stand and it seems easy to control the clamp pressure.

My seat is too low to use it and I'm too lazy to go through the process of removing it, install old seatpost, making adjustments, and re-installing my seatpost. This also lends itself to real world dinking around where I'll tweak and ride and sometimes tweak and ride, (too much free time), and then take in the spoils of my victory around the neighborhood.

It is an interesting observation about top tube mount car racks and all the rigors that are subjected to the top tube in transit.

John
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