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Folding Bikes Discuss the unique features and issues of folding bikes. Also a great place to learn what folding bike will work best for your needs.

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Old 01-12-09, 11:24 PM   #1
crackerdog
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2009 Downtube Mini review

This is my first folder so I am not comparing to other folders, in fact I haven't ridden on any others. I am quite surprised by how much fun a little bike is, now I understand the enthusiastic ravings here. I tell everyone I had to get a small bike to match my dog, a Corgi mix with short legs.
I have steep hills here so I am going to switch the front gear for lower gearing so I am glad that this bike has mostly common bike parts. The only real problem I have is the seat tube. I am 6'1'' and 200 lbs and the tube is pulled out to the safety line and after only a week, the tube is bending and since it is Aluminum, that is a large problem. I wish they would sell a solid rod version for tall people or a tube or rod that would slide up inside to stiffen the tube. I will have to go out and have one milled to fit which seems expensive and time consuming since I am in the suggested load range, in fact the max load rating is 215 lbs. The folded size is also wrong on the site which says 10 x 20 x 29. It is in fact, 14 x 22 x 29 and that's if I remove the seat post. That's pretty far off. The seat is better than I expected, since most bikes come with really crap seats. This would be fine for someone who doesn't ride much, it is too cushy for me but a good choice for the average American. The Sturmey Archer 8 speed internal hub works flawlessly so far, though I had to get used to not pedaling for a second to shift. The chainring didn't line up perfectly with the rear gear until I moved it inside on the crank, now it is aligned perfectly.
For the money, it is a great bike and once I have the seat post stronger, I will give it a real workout and speed test. I am going to order a Butt Buddy to keep the seat post further down in the frame which should help until I can get to a milling shop in a larger city.
I would like to see suggestions for products that will fit the Mini on the website. Fenders, racks, etc. and the tech stuff like chainring size, width of hub spacing, diameter of seat tube, etc. so I could more easily upgrade. I live in a small town and have to order this stuff on the web and the local bike shop doesn't know much about unusual bikes.
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Old 01-12-09, 11:51 PM   #2
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You could make your own telescopic post for extra extension. You only need:
- A seatpost whose outer diameter matches the inner diameter of your original seatpost
- An extra seatpost clamp

You can then chop and cut a slot in the original seatpost, and clamp the new seatpost on top of that. If your original seatpost is 34mm, the inner post would normally be 27.2mm.

A solid rod would definitely not be a solution as it would be too heavy. I also remember several BF members having problems with their Butt Buddies, specifically the elastomer going AWOL during use.

Congrats on your new folder. Remember that one is never enough
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Old 01-13-09, 06:13 AM   #3
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Cane Creek Thudbuster as an alternative to the Butt Buddy. Available in several lengths including xtra-xtra-long, short travel or long travel, and several stock diameters, and there are also shims available.

What's the O.D. of the 2009 Mini seatpost? Do you have metric calipers?

Last edited by timo888; 01-13-09 at 06:20 AM.
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Old 01-13-09, 07:46 AM   #4
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Yesterday evening I was fiddling around with some bits of scrap metal I have in my basement (I know, I know...) and found something interesting. The lower part of a Razor scooter handlebar stem is an aluminum tube that is wider at the bottom to thread onto the fork, and narrower at the top where the upper part of the handlebar stem fits into it. The upper part of that lower tube seems to be exactly the same diameter as the seatpost of a Downtube Mini. This got me thinking. So then I tried inserting the upper part of the Razor handlebar stem into the inside of the Mini seatpost; and that fit, too, though not as snugly as one might wish. Still, these facts got me thinking as follows.

You could cut a section 6" or even 8" long, from the lower part of the Razor handlebar stem, together with a longer section, perhaps 12" long, from the upper part of the Razor handlebar stem, and bond these together with the Mini seatpost with an epoxy. This would make your seatpost longer, heavier, and presumably stronger.

I can't predict exactly how strong it would be, of course. In my own case (I am 6' tall) I normally ride with the post hyperextended by an inch or so, even with the Butt Buddy. If I extended my seat post as described, I could get rid of the Butt Buddy (and good riddance to it, BTW) and hyperextend the seatpost by 3" or so. The Razor extension would still be completely inside the Mini's frame, so though it would be supporting both the frame the seatpost, it would not be directly supporting me. I'm thinking it would work.

But, of course, I haven't tried it yet.

What do y'all think? I know, I know, someone's going to say "", but I think the additional aluminum would give more additional strength than, say, a piece of wood.
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Old 01-13-09, 07:48 AM   #5
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has anyone got a pic of a thudbuster on a DT mini, or experience of fitting one?
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Old 01-13-09, 08:05 AM   #6
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has anyone got a pic of a thudbuster on a DT mini, or experience of fitting one?
Every time I've looked at the thudbuster website, they didn't have posts as long as the one that comes stock on the Mini, so it wasn't an option.
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Old 01-13-09, 08:22 AM   #7
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yes, that was my experience, and the butt-buddy is now not only hard to source, but apparently breaks up after a while.

I am just about OK with seat tube length on my 2009 mini - which I have to say is my folder of choice at the mo'. Wouldn't mind an extra inch or two though.
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Old 01-13-09, 11:21 AM   #8
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The OD on the Mini seatpost is 25.4 mm. I also couldn't find a Thudbuster that would fit.
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Old 01-13-09, 11:38 AM   #9
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Sorry, I thought it was 30+mm like the usual suspects.
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Old 01-13-09, 11:41 AM   #10
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I found a length of steel pipe that just fits up inside the seatpost. It doesn't add too much weight to it especially considering what would happen if the aluminum snaps off suddenly. I'll just put a touch of silcone at the end so I can remove the steel if I need to. Of course, if the aluminum bends any more it will trap the steel in there forever. I think I will leave a 1/2 inch of the steel exposed so I can grab it with a tool if needed.
So the Butt Buddy isn't worth getting, huh?
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Old 01-13-09, 12:52 PM   #11
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The OD on the Mini seatpost is 25.4 mm. I also couldn't find a Thudbuster that would fit.
This is new. Are you positive regarding the outside diameter?

If you search the forum, there is a big Downtube Mini thread that discusses lots of mods.
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Old 01-13-09, 01:00 PM   #12
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I know, I know, someone's going to say "".


Play the lottery tonight.
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Old 01-13-09, 01:04 PM   #13
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Yes, it looks like it is 26 mm but the Downtube site says 25.4mm.
I forgot to mention that the brakes were opposite from my other bikes, so I switched them.
I just found out when I shortened the chain to try out a 42 chainring that the right rear hub nut is stripped. The axle threads are fine, thank goodness.
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Old 01-13-09, 01:27 PM   #14
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Sorry, I thought it was 30+mm like the usual suspects.
Correct, it used to be 30.4 mm. In fact the Downtube website still indicates 30.4.

Last edited by rhm; 01-14-09 at 06:43 AM. Reason: typo
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Old 01-13-09, 01:32 PM   #15
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Quote:
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I found a length of steel pipe that just fits up inside the seatpost. It doesn't add too much weight to it especially considering what would happen if the aluminum snaps off suddenly. I'll just put a touch of silcone at the end so I can remove the steel if I need to. Of course, if the aluminum bends any more it will trap the steel in there forever. I think I will leave a 1/2 inch of the steel exposed so I can grab it with a tool if needed.
So the Butt Buddy isn't worth getting, huh?
If the aluminum bends with the steel pipe in there, you're not going to get it back out no matter how hard you pull on it. But the seatpost bending is not your only worry; if you hyperextend the post, there may not be enough post inside the frame to fully support that, so you may in fact end up with a damaged frame.

The elastomers on my Butt Buddy vanished several months ago; one day I looked and they'd gone walkabout. I fixed this by wrapping nylon twine around it; quick and dirty fix that it was, it's still holding. Of course this disabled the BB's cushioning effect, but I didn't care about that. Aside from that, it's not clear that the BB is available anymore.
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Old 01-13-09, 02:01 PM   #16
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Yes, it looks like it is 26 mm but the Downtube site says 25.4mm.
I forgot to mention that the brakes were opposite from my other bikes, so I switched them.
I just found out when I shortened the chain to try out a 42 chainring that the right rear hub nut is stripped. The axle threads are fine, thank goodness.
Too bad ... that would mean you can't chop the seatpost anymore ...
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Old 01-13-09, 06:15 PM   #17
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If you're worried about not getting enough extension out of your post then you might try one of these:

(bad cryptic pun intended )
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Old 01-13-09, 09:22 PM   #18
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I have enough extension if I bring it right to the max length, that is to the safety line. It is just I don't like the idea of aluminum bending after only a week using the bike and only for short trips. If it were steel, I would just see if it got worse but aluminum has a bad habit of failing suddenly. This is the only part of the bike that isn't great and of course only applies to tall and heavier riders.
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Old 01-13-09, 10:00 PM   #19
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Crackerdog - welcome to the club! I also have a 2009 mini, although I am short enough that I have no issues with the seatpost extension. If you search the forum, I think that jur did some seatpost reinforcements that worked OK for him.

Re: the Downtube website. Don't trust the numbers on the downtube.com product descriptions; some are not accurate. The downtube.com forums have message threads requesting various measurements along with responses from Yan - I'd trust these more (but still verify vs. my own bike!)

Sources for racks, fenders, etc. I have had good luck with fenders and racks made for the Dahon Curve D3. The rack will mount with p-clips, and the fenders will mount easily. No issues so far. I think the Mini deserves its own wiki, or at least a Mini FAQ.

Enjoy your new bike!
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Old 01-14-09, 06:59 AM   #20
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Quote:
Originally Posted by crackerdog View Post
I have enough extension if I bring it right to the max length, that is to the safety line. It is just I don't like the idea of aluminum bending after only a week using the bike and only for short trips. If it were steel, I would just see if it got worse but aluminum has a bad habit of failing suddenly. This is the only part of the bike that isn't great and of course only applies to tall and heavier riders.
You are right to be concerned. If you are within published weight limits and did not overextend the post, and the post itself was not defective, either the weight limit needs to be revised or the post needs to be of heavier gauge for heavier riders. I'd encourage you to contact DT if you have not already done so. It's the post that should be subjected to the post-mortem, not the rider.
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Old 01-14-09, 07:13 AM   #21
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Quote:
Originally Posted by crackerdog View Post
I have enough extension if I bring it right to the max length, that is to the safety line. It is just I don't like the idea of aluminum bending after only a week using the bike and only for short trips. If it were steel, I would just see if it got worse but aluminum has a bad habit of failing suddenly. This is the only part of the bike that isn't great and of course only applies to tall and heavier riders.
Crackerdog, do you mean the post is flexing, or that it has become permanently bent? I know the post flexes a bit, but mine remains straight at rest.

Also, have you checked the diameter of your post? I'm still not believing the 25.4 thing.

Edit: I get it now. The inside diameter of the Mini seatpost is 25.4 mm; the outside diameter is 30.4

Last edited by rhm; 01-14-09 at 12:20 PM.
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Old 01-14-09, 07:20 AM   #22
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I was under the impression that aluminium flexes and breaks rather than bends (if tempered for bike component usage).
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Old 01-14-09, 07:24 AM   #23
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If the post is permanently bent then I would contact Downtube (Yan) for a warranty replacement right away.
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Old 01-14-09, 11:43 AM   #24
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If I lay a straight edge along the post, there is a gap of approx. 2mm. So the post is bent and of course it does flex when riding. I will contact DT with the problem. Thanks for the suggestion of accessories that fit the Dahon Curve D3, I will check those out.
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Old 01-14-09, 12:14 PM   #25
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Originally Posted by crackerdog View Post
If I lay a straight edge along the post, there is a gap of approx. 2mm. So the post is bent and of course it does flex when riding. I will contact DT with the problem. Thanks for the suggestion of accessories that fit the Dahon Curve D3, I will check those out.
Calipers that can measure O.D. and I.D. are an inexpensive tool and can help make sure you get parts that fit, especially when actual spec is not accurately reflected in published literature and on websites.

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