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Old 08-20-09, 03:39 PM   #1
McQz
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Seat stem mounted rack for Carbon seat stem?

Can the seat stem type rack be safely mounted on a CF stem? We really like our Roubaix and Ruby, but it would be nice to be able to take a trip to the library with them without wearing a backpack. OTOH, if it isn't recommended, we'll continue to wear the occasional backpack.
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Old 08-20-09, 04:31 PM   #2
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I did a 5 day trip where there were riders with seat post mounted racks on carbon posts. They did wrap the post with an old tube to prevent scratches and they didn't carry a lot of weight.
Another guy had a ton of weight in his, but he had an alloy post.

All of the women in this pic have carbon posts with racks.

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Old 08-20-09, 05:28 PM   #3
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I've used and loved a post style rack on all of my/my son's previous steel/alloy posted bikes. I don't load them down more than 5-8 # or so but find their utility impossible to live without. For me it's a place to carry snacks/ lunch, wallet, windbreaker, fishing rod. ..... Makes a nice rear fender when riding in wet conditions too. I don't mind adding the 20 oz or so for that kind of utility.
FWIW, I just ordered one of these ( yesterday)for my new carbon posted Giant TCX.
http://www.nashbar.com/bikes//Produc...2_216833_-1___

I don't expect any issues as long as I protect the carbon with tape/tube material . Of course, I don't plan on carrying anywhere near the 25# capacity either.
I'll let you know more when it comes in.

p.s. The only downside I've found to these is that if you have one and your riding partner doesn't , you end up carrying all the gear! :-)
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Old 08-21-09, 02:06 PM   #4
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Carbon seat post and bolting anything onto requires a bit of care- so DON'T overtighten. Check the thickness of the post aswell- if it feels thin then don't do it. And to take as much strain off the post as possible- mount the rack as low down as possible on the post

Personally- I would rather buy a cheap ally post and not take the chance,
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Old 08-21-09, 03:19 PM   #5
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The lbs that sold me my Madone said not to and ,untill reading this thread, I believed them. But, I sure did miss it for all of the reasons stated. A few weeks ago, I purchased one of those triangular shaped bags ( I think it was through Nashbar, might have been Performance) that wound up fitting backwards and mounts to the top stem and the rear stem (below the seatpost). I really like it, it holds a fair amount, not quite as much as a rack mounted bag, but still can hold snacks, jacket, loaf of bread etc. I can even unzipp it while riding for a towel or snack or for an extra water bottle as it does make it so that only one bottle holder will work on the bike. Doesn't bother me while pedaling, has nice side illumination stripes, and seems to be aero.
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Old 08-21-09, 05:24 PM   #6
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personally- i would rather buy a cheap alloy post and not take the chance,
+1
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Old 08-21-09, 05:51 PM   #7
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Personally- I would rather buy a cheap ally post and not take the chance,

+1

There's a reason they don't make carbon touring bikes.

If you put a lateral force on your carbon fiber seat post I'm reasonably certain you're exceeding the manufacturer's recommended performance guide. And while there is, no doubt, a safety factor built into it the seat post, I don't even like to contemplate what broken carbon fiber would feel like below the waist.
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Old 08-21-09, 06:23 PM   #8
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I think I'm beginning to see the light I'll wear a backpack when I want to run errands on the road bike. That way I won't be waddling around in bike shoes too much either.

I can always fall back on the Stumpjumper, which has a rack already in place. For that matter, we still haven't gotten rid of the Giant FCR. Maybe I'll just hang onto it for around town trips.

I seem to have read something about N+1
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Old 08-21-09, 06:34 PM   #9
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[QUOTE=Monoborracho;9534003]+1

There's a reason they don't make carbon touring bikes.[QUOTE]

Yes, and the reason is cost versus return. There would be no reason to try to save weight by building a CF touring frame, although I'm sure it could be built as strong as needed.
There are carbon 6 inch travel mountain bikes, carbon long-travel forks, etc.
I know that it's probably not the best idea to use a rack on a CF post, but my friends that have done it have had no problems.
I have never used a cf post, but I have broken 4 alloy posts. I have never tried a post mounted rack as I have a touring bike.
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Old 08-25-09, 01:47 PM   #10
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Well mine is here and installed. The post hast rack has 4 bolts on the clamp so I felt pretty good about tightening it uniformy on my carbon seat post. ( With a double layer of electrical tape under it for cut protection.) It's holding firm with only moderate tightening. I'll be surprised if there are any problems. My CF seatpost is decently thick and CF is strong stuff if you don't point load it. ( They build missle capsules out of it !)
FWIW: The rack as delivered weighed 590gr. The bag attaching hardware another 130gr. The (removable) bag was another 600gr (and 12"x7.5"x7.5"). Not exactly feather weight but versitile and worthwhile for my needs.

I can post pics if desired.


p.s. Nice rack too, BTW.

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Old 08-25-09, 06:39 PM   #11
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Originally Posted by stapfam View Post
Carbon seat post and bolting anything onto requires a bit of care- so DON'T overtighten. Check the thickness of the post aswell- if it feels thin then don't do it. And to take as much strain off the post as possible- mount the rack as low down as possible on the post

Personally- I would rather buy a cheap ally post and not take the chance,
+1 on being careful not to over tighten. That said I have been using one on a CF frame for the last 7 months with no problem, 15kg weight limit on mine (brand is called Inline).
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Old 08-25-09, 07:12 PM   #12
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Originally Posted by WeeHooker View Post
Well mine is here and installed. The post hast rack has 4 bolts on the clamp so I felt pretty good about tightening it uniformy on my carbon seat post. ( With a double layer of electrical tape under it for cut protection.) It's holding firm with only moderate tightening. I'll be surprised if there are any problems. My CF seatpost is decently thick and CF is strong stuff if you don't point load it. ( They build missle capsules out of it !)
FWIW: The rack as delivered weighed 590gr. The bag attaching hardware another 130gr. The (removable) bag was another 600gr (and 12"x7.5"x7.5"). Not exactly feather weight but versitile and worthwhile for my needs.

I can post pics if desired.


p.s. Nice rack too, BTW.

I'd like to see a pic or 2 of the rack - the bike too...
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Old 08-26-09, 06:40 AM   #13
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+1

There's a reason they don't make carbon touring bikes.

If you put a lateral force on your carbon fiber seat post I'm reasonably certain you're exceeding the manufacturer's recommended performance guide. And while there is, no doubt, a safety factor built into it the seat post, I don't even like to contemplate what broken carbon fiber would feel like below the waist.
+100 if the seat post fails you will wish you had hemorrhoids.
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Old 08-26-09, 11:58 AM   #14
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There could be a lateral force of 200 lbs at the collar on the bottom of the seatpost if you hit a bump in the road. I don't see how a 10 lb loaded rack would cause a problem.

I would sand down any sharp edges or corners on the clamp first.

Wrapping the post, and tightening just enough so the rack doesn't slip, would be good ideas.

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Old 08-26-09, 05:49 PM   #15
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It's eight miles to the grocery store, and I've done some runs with a backpack. It really isn't that bad. I guess the disadvantages are hot, uncomfortable, and higher center of gravity -- right?
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Old 08-26-09, 10:40 PM   #16
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I am with the guy who said buy a cheap alloy seatpost for the rides with a seatpost attached rack. I am an engineer and if you look at the clamping needed to prevent the seatpost from moving from side to side it will eventually break a carbon post. The other thing is that there are a variety of carbon posts and this just makes the crotch roulette time variable but certain.
I ride with a rack mounted to the seat post which I can move from my road to MTB and to Cross bikes. I use a carbon seat post on my road bike and it is a simple task to switch it out. Not worth the risk...unless you are contemplating a vasectomy then you might just save some money. Gee I forgot this is the over 50 group. DON'T DO IT.

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Old 08-27-09, 04:41 AM   #17
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mcoz, here you go.







the straps and platforms holding them bolt onto the basic rack and are not used/installed unless you opt for teh bag as well.

Deanster04, I'm also a mechanical engineer with 24 years in the business and significant experience in composit use. Your statementabout certain failure is misleading and unqualified. If the seat post is built well (i.e not to thin walled) and installed with a rubber/taped sleeve and uniform tightness, I see no reason to worry about post failure as long as the rack is installed with consideration and used responsably. Agreed a carbon tube is weakest in a tortional state but the trick is to assure you don't grip it like a vise. As mine is set up, the lower lip rests on the frame to reduce any bending action in the Y axis and it will give and slip over the tape if torqued strongly in the z axis.
That said, to each their own.
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Old 08-27-09, 08:45 AM   #18
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...I'm also a mechanical engineer with 24 years in the business and significant experience in composit use...
What is a composit?
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Old 08-27-09, 10:16 AM   #19
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mcoz, here you go.







the straps and platforms holding them bolt onto the basic rack and are not used/installed unless you opt for teh bag as well.

Deanster04, I'm also a mechanical engineer with 24 years in the business and significant experience in composit use. Your statementabout certain failure is misleading and unqualified. If the seat post is built well (i.e not to thin walled) and installed with a rubber/taped sleeve and uniform tightness, I see no reason to worry about post failure as long as the rack is installed with consideration and used responsably. Agreed a carbon tube is weakest in a tortional state but the trick is to assure you don't grip it like a vise. As mine is set up, the lower lip rests on the frame to reduce any bending action in the Y axis and it will give and slip over the tape if torqued strongly in the z axis.
That said, to each their own.
Not a point worth arguing. I stand by what I said. You are a highly qualified person who knows exactly what you are doing. If you are willing to do the setup for everyone who wants to do it then ok but, in my experience most people who work on bikes don't use torque wrenches and operate by the principle of tighter is better and as you know that is a formula for disaster on carbon. You are highly competent and probably understand metallurgy, composites, and torquing so cycling is easy for you to push the limits however...I won't use carbon for anything other than its intended use. Just be careful when you give advice to nontechnical people it can be dangerous. I really mean this in the most friendly way.
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Old 08-27-09, 11:49 AM   #20
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What is a composit?
It's what an engineer gets when we don't hit the spell check one last time

Deanster, your right, no argument or disrespect intended from this end either. Just pointing out that nothing is cut and dry. Your also absolutely right about varying abilities and risk associated with them. ( I spent the first part of my career writing repair procedures for military personnel of widely varying capabilities.) For the record, I offer no intended "blanket" endorsement of the product or install. Just offering that it works for me with the cautions noted.
IMHO,Nobody should attempt repair or alteration of anything beyond their capabilities/knowledge/comfort zone.

Over and out.
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Old 08-27-09, 11:55 AM   #21
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looks dangerous to me
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Old 08-27-09, 06:27 PM   #22
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How many reading this thread have ever had a carbon seat post break for any reason??
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Old 08-27-09, 08:37 PM   #23
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How many reading this thread have ever had a carbon seat post break for any reason??
I was wondering the same thing. I've broken the alloy posts and I saw a friend crash when he broke one, but I don't remember hearing about anyone breaking a CF post, even those using racks.
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Old 08-28-09, 01:04 AM   #24
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I was wondering the same thing. I've broken the alloy posts and I saw a friend crash when he broke one, but I don't remember hearing about anyone breaking a CF post, even those using racks.
Afew years ago and there was a spate of C.F.Posts and Handlebars breaking. I was into Mountain bikes at the time and I only noted that these were on MTB's- so may not have any relevance to Road bikes.

However- I used to be a fibre glass laminator and I can tell you that any Fibre glass- Kevlar- or Carbon Fibre product has a great deal of strength in it- but it is liable to break for no apparant reason at any time. Could be a production fault but more likely to be the result of a knock or hit- some time previously. A hard enough hit- and it need not be that hard- and the material starts to delaminate internally. This cannot be seen externally so is very difficult to check visually- until it breaks.

I do have C.F. and even have a C.F. bike and don't worry unduly about it breaking- but If I hear any creaking on tightening- or it gets a hard enough hit- It will be changed.
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Old 08-28-09, 10:14 AM   #25
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It's what an engineer gets when we don't hit the spell check one last time

Deanster, your right, no argument or disrespect intended from this end either. Just pointing out that nothing is cut and dry. Your also absolutely right about varying abilities and risk associated with them. ( I spent the first part of my career writing repair procedures for military personnel of widely varying capabilities.) For the record, I offer no intended "blanket" endorsement of the product or install. Just offering that it works for me with the cautions noted.
IMHO,Nobody should attempt repair or alteration of anything beyond their capabilities/knowledge/comfort zone.

Over and out.
I'm with you...but, composit is a good pun for seat posts don't ya think?
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