Strongest seat post rack

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Re: Strongest seat post rack

Post by nineball » Jul 28 2009 8:32pm

ya know what...... we, I, you, us , we e-bike guys, are just gonna have to design R own, so keep the Idearrrrs comming
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dogman dan   100 GW

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Re: Strongest seat post rack

Post by dogman dan » Jul 29 2009 6:41am

Those frames kick ass! I like the idea of going retro, and using two shocks in the rear just like the old school motorcycle suspension. Or if monoshocked, there are lots of ways to build a rack into the frame. The seatpost attach idea is lame. Just a few welded on brackets in the right spot would allow a bolted on rack that's far stronger like the example on the tandem.

I'd get cracking if I could weld at all.

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Re: Strongest seat post rack

Post by docnjoj » Jul 29 2009 7:07am

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I'm waiting for this rack so I can carry stuff again. Stein claims 50 kilos and it is bolted to the frame, not the suspension, but I still don't want to put 20 lbs of batteries up that high. It gets tippy, I believe with a trike. Definitely want the weight as low as possible. Rack will be for groceries etc. and some panniers.
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Patriot   10 kW

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Re: Strongest seat post rack

Post by Patriot » Jul 30 2009 12:49am

Doc,

Since you have a Mongoose, similar to mine, you could do what I did. I made an addition to my existing 25lbs capacity Transit rack. It works really well. Since your rack has the same double seat tube support setup as mine, it may work. I made it out of simple 3/4" angle iron. What's really nice is the double tube support prevents it from any possible swaying when riding.


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Re: Strongest seat post rack

Post by Doctorbass » Jul 30 2009 8:38am

Patriot wrote:Doc,

Since you have a Mongoose, similar to mine, you could do what I did. I made an addition to my existing 25lbs capacity Transit rack. It works really well. Since your rack has the same double seat tube support setup as mine, it may work. I made it out of simple 3/4" angle iron. What's really nice is the double tube support prevents it from any possible swaying when riding.


http://endless-sphere.com/forums/viewto ... =6&t=10885


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That is a great idea and nice job for this model Patriot

But the bike i need to put the rack on are different!.. I have 7 bike to modify.. so i need a less complicated way!.. did you saw page 3 of this thread?.. I shown a pics of the similar bike i'll need to put the rack on.

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Patriot   10 kW

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Re: Strongest seat post rack

Post by Patriot » Jul 31 2009 10:59am

Doctorbass wrote:
Patriot wrote:Doc,

Since you have a Mongoose, similar to mine, you could do what I did. I made an addition to my existing 25lbs capacity Transit rack. It works really well. Since your rack has the same double seat tube support setup as mine, it may work. I made it out of simple 3/4" angle iron. What's really nice is the double tube support prevents it from any possible swaying when riding.


http://endless-sphere.com/forums/viewto ... =6&t=10885

That is a great idea and nice job for this model Patriot

But the bike i need to put the rack on are different!.. I have 7 bike to modify.. so i need a less complicated way!.. did you saw page 3 of this thread?.. I shown a pics of the similar bike i'll need to put the rack on.

Doc
:wink:


OOOOOOHHHHHH....

Stupid me.

In that case, since it appears very difficult to build anything easy for that particular frame, then I would suggest using the AXIOM ODYSSEE seatpost rack, which was posted earlier. It does have a 25kg rating, and is the beefiest I found when searching for a strong seatpost rack when building my bike a couple months ago. They use brass bushings and heavy duty bolts for the extra strength. I've seen one before, and they are very stout compared to most others.

Also, if you are loading up that rack, I suggest you try and find a STEEL seatpost to replace the cheap aluminum post that comes with the Cadillac bike.

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ElectricEd   100 W

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Re: Strongest seat post rack

Post by ElectricEd » Aug 01 2009 8:30am

I've posted this piccie before but (brain fade) have forgotten where. I have been using this setup for about 6 months now. The version in the picture had the aluminium tubes bent too much so they eventually fatigued and cracked at the bend. I now have them straightened out much more and the fatigue has stopped. The tubes were from an old TV antenna made back in the middle 60s, so I have doubts as to the quality of the alloy. If they fatigue again I'll get some thicker walled tubing from Alcoa. That should beef it up a bit. The copper tubing aroud the bolt points are to reinforce the aluminium at the high stress points.
This is the cheapest way that I can think of to strengthen a seatpost rack and keep the weight down at the same time.
Rack Supports reduced.jpg
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Re: Strongest seat post rack

Post by TylerDurden » Aug 01 2009 10:33am

For the Costco bikes, I'd use plywood and a tube. (one side not shown for illustration) Pretty much a box-beam.

For super strength, the plywood could have a layer of aluminum (like Bubba's creations).
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BVH   1 kW

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Re: Strongest seat post rack

Post by BVH » Aug 01 2009 5:22pm

ElectricEd, what are using for your seat post/rack clamp pictured above where your support arms land? I need a 1 3/8", nice looking clamp for the same purpose.

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Re: Strongest seat post rack

Post by ElectricEd » Aug 02 2009 2:48am

BVH wrote:ElectricEd, what are using for your seat post/rack clamp pictured above where your support arms land? I need a 1 3/8", nice looking clamp for the same purpose.
Hi BVH,
it's a galvanised plumbing pipe clamp. They are made up from two pieces (exactly the same) that interlock around the seat tube. They are used for clamping water pipe to a "T" that is mounted on a bracket or wall. They come in all sizes to suit either copper or gal water pipe, so you'll have no problem finding one to fit your seat tube. Any plumbing supplier carries them.
I'm sorry that I cant post a picture of it, my camera is out of action at the moment.
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dogman dan   100 GW

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Re: Strongest seat post rack

Post by dogman dan » Aug 02 2009 6:23am

The axxiom rack is pretty nice. It's the one I'm using, with the metal braces. It looked pretty unbreakable to me, but I put on the bacing to help the steat tube stand it more than anything. I pound broomsticks up seat tubes to strengthen them now too. My bent one was bent a lot more before I put a stick inside.

No matter what the bike is like, there should be enough space to put in some kind of short brace between the rack and the point where the seat tube enters the frame, even allowing a little bit of seat height adjustment. All the rack really needs is to have the point where the tube clamp welds to the beam supported since that or the clamp itself seems to be the point of failure. I put my braces on further along simply because it made a great way to attach a fender that way.

A very inexpensive post rack could be cut short, and then a small brace could be put on between the cut rack and the actual rack to add support. At wallmart I was able to buy a steel and plastic rack for about $12 that would be perfect for this, allowing a brace to be added without drilling a hole in the seatpost. I made my bracing out of steel tube simply because I had it in the yard. Aluminum square tube would work great and still be light, and stronger than tv antenna stuff.

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Re: Strongest seat post rack

Post by spinningmagnets » Aug 02 2009 11:21am

G'Day Ed. The plumbing pipe-clamp suggestion is a great idea. There are so many variations, perhaps its something similar to this?
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BVH   1 kW

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Re: Strongest seat post rack

Post by BVH » Aug 02 2009 11:29am

OK, thank you!

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Re: Strongest seat post rack

Post by lcyclist » Aug 02 2009 1:01pm

After breaking a seatpost rack after few hundred miles, I since mounted my battery/controller on the seat post itself.
I fabricated an aluminum plate attached from the inside of the leather battery bag and bolted it using seatpost water bottle clamps.

Since I use a small battery pack (Bosch fatpacks 6AH 36V), mounting the battery this way also gave my bike better handling since the weight of the battery is inline with my weight when seated on the bike. It is a very strong setup; I now have over 2500 miles with this configuration without any problems.
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Re: Strongest seat post rack

Post by ElectricEd » Aug 03 2009 3:51am

spinningmagnets wrote:G'Day Ed. The plumbing pipe-clamp suggestion is a great idea. There are so many variations, perhaps its something similar to this?
I've knocked up a quick drawing of the clamp...
Pipe Clamp.jpg
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Re: Strongest seat post rack

Post by GreenKnight » Aug 03 2009 5:27am

I like spinningmagnets design but I would put the downtubes back on the axles and place a hinge joint near the seatpost.

otherwise

split the load and get some of it up front of the handle bars. This would also improve handling.
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Re: Strongest seat post rack

Post by BVH » Aug 03 2009 10:31am

Thank you EE!

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Re: Strongest seat post rack

Post by gerlewis » Nov 18 2009 10:31am

Hi guys, I now have this same Topeak rack problem, where it sways as I go on a journey!

My idea is to create a better bond between the clamp and the seatpost, either by gripping both surfaces with a keying of somekind, or by using something like threadlock or superglue to create a permanent bond.

Anyone have any thoughts on this, or a recommended bonding agent for rubber-alloy? epoxy resin any good (i have some at home!)

Ger

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Re: Strongest seat post rack

Post by DarthSensate » Nov 18 2009 12:07pm

gerlewis wrote:Hi guys, I now have this same Topeak rack problem, where it sways as I go on a journey!

My idea is to create a better bond between the clamp and the seatpost, either by gripping both surfaces with a keying of somekind, or by using something like threadlock or superglue to create a permanent bond.

Ger
I was just reading this entire thread to see if that had been suggested yet. I have the Axiom Odyssee rack rated at 55lbs cap. and want to make sure it does not rotate on the seat post as others have mentioned.

My plan was to use a drill press and bore a hemisphere into the seat post and a matching hemisphere in the clamp plate of the seat post rack and place a matching diameter ball bearing in the two hemispheres. I don't know if the bearing would be a better idea that a key slot cut with a grinder or not. Seems to me the shearing strength of a small ball bearing would be greater than a key and would require a smaller cut into the post and clamp surfaces without cutting through the metal.

I wasn't going to use the rubber grip stuff that came with the rack at all. metal on metal and galvanic compatibility be damned.

I like the broom stick in the seatpost idea as well.

It occurs to me that many of the Wally World racks are not ovalized tubes and would benefit from a broomstick shoved up them as well. The weak point would then be the weld at the seat post clamp. Welding a cuff around that would do well I think, just as with double butted frame joints.

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Re: Strongest seat post rack

Post by gerlewis » Nov 18 2009 4:33pm

good idea with the ball bearing, what you thinking, 4mm - 5mm?

A grub screw glued in place might do a similar job, though im not sure where on my clamp I could drill a hole to be honest.

I need to do something, as its not up to the job as it stands, swaying this way and that.

Ger

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Re: Strongest seat post rack

Post by rguy56 » Nov 18 2009 4:39pm

There are implications to the seat post itself if the weight gets excessive.

I think it may work well to find two racks that nest well on each other and clamp them one over the other on the seatpost. If you were to do that and add struts between the two, I think the major limitation would be seatpost strength.

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Re: Strongest seat post rack

Post by DarthSensate » Nov 19 2009 12:12am

gerlewis wrote:good idea with the ball bearing, what you thinking, 4mm - 5mm?

A grub screw glued in place might do a similar job, though im not sure where on my clamp I could drill a hole to be honest.

I need to do something, as its not up to the job as it stands, swaying this way and that.

Ger
As small as I have on hand. I don't think it will take much at all to stabilize the clamp laterally on the seat post. As long as the clamp is tightened down really well, its not going to jump the bearing unless you drop the bike. My primary concern is to do as little to impact the strength of the seat post as possible.

I could definitely see a set screw in a threaded hole in the clamp as a workable solution. ... not sure how many threads you could get in the thickness of the clamp's plate.
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DarthSensate   1 W

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Re: Strongest seat post rack

Post by DarthSensate » Nov 19 2009 12:18am

rguy56 wrote:There are implications to the seat post itself if the weight gets excessive.

I think it may work well to find two racks that nest well on each other and clamp them one over the other on the seatpost. If you were to do that and add struts between the two, I think the major limitation would be seatpost strength.
I think the broom/rake/shovel shaft fiction fitted in side the seat post idea would do a great deal to strengthen the post. Got to be good hardwood shaft though and not the crappy yard rake replacements you find at Wally World seasonal. I about tore my arm open on one of those stupid pine shafts when it snapped in half the first day I put it on a rake.

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Re: Strongest seat post rack

Post by ion » Oct 27 2011 9:35pm

I have about 23 pounds on my rack and it was breaking at the first weld off the seat post. I took a steel angle iron measuring 1.25” X 3.25” long and centered it on top over the weld on the new rack. Then I took 4 hose clamps and placed two on one side of the weld and two on the other side of the weld to hold the angle iron to the rack. The rack had a slight angle at the weld but the hose clamps still held the angle iron tight. I used a socket wrench to tighten the clamps and about 10,000 miles of bumps later they still are holding tight with no more cracks in the welds. You could use two angle irons on opposite side but one worked for me. Just make sure the steel angle iron is 1.25” wide and no wider or it might extend over the edges of the rack tube giving it a weaker fit.

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Re: Strongest seat post rack

Post by electr0n » Jan 09 2012 8:01am

I'm looking for a good seat post rack too. I've got it narrowed down to either the axiom odyssee (the seat post only version) or the delta post porter rack. I'm leaning towards the post porter based on more positive reviews. Are these the two strongest seat post racks available right now?

I don't want to spend too much $$$. Anyone know where I could pick up a good seat post rack from within Canada to avoid brokerage fees ? Any other suggestions?

I bought a cheap used full suspension mountain bike to use as my new commuter but I didn't realize I'd have to spend so much on a rear rack and worry about it snapping off while I'm riding.

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