Converting Dahon 6-speed to internal gear hub with coaster brake?

[az2008]

Hi, I picked up a Dahon Dream[1] on craigslist for *free*. It's in poor condition, stored outside for awhile. Needs some rehab. The seller gave it to me for free because the folding latch's pivot mechanism is broken. One of the tabs welded onto the frame (which the pivot goes through) broke off. I'll have a 3/4" square (by 1/8" thick) piece of steel welded on. I was excited to receive a project bike. I've wanted a folder for awhile. So, this works well. I get to make my own bike starting at zero cost. Learn more about components, repair, etc. in the process.

The biggest change I want to make is: replace the tourney derailer with an internally geared hub. The rear dropout is 126-127mm.

1. I see Sturmey Archer 3 and 5 speeds in that size.
2. Prowheelbuilder.com in Las Vegas sells custom length spokes. I can get really short ones.

I also want to get a hub with a coaster brake so I can remove the rear V-brake, cleaning up the appearance of the bike.

I'm inspired to do these changes because 1), I saw a KHS Manhattan iPed and liked its simplicity. It has a 3-speed IGH with coaster brake. Very clean look. The only thing I didn't like is that it's a bit small with 12 and 16" tires. It also doesn't fold. But, at that smaller size it doesn't have to. 2) When googling about the "Dream" model, I found a thread on this forum from a guy in Singapore who replaced his derailer with an Alfine 8-speed IGH. (See the footnote below.). That planted the seed too.

My questions:

1. Are there any "gotchas" anyone can warn me about. I'm pretty good at working on bikes. I think I can re-lace the wheel. I'm just concerned whether an IGH and coaster brake are "drop-in" replacements.

2. My area is mostly flat. I think a 3-speed would be fine. Does a 5-speed IGH introduce greater maintenance/failure potential? (does the extra internal cogs and things come at a greater long-term cost?). If there aren't any significant downsides (beyond cost), I think I'd go with the 5-speed.

Thanks

[1] It's a model which was (still is) sold in China, Singapore, etc. It has stickers saying "USA Technology" with red/white/blue flag decals. They really play it up as a USA brand. It seems to be identical to the Boardwalk. It's just not made for the US market. Perhaps it has differences like high-tensile steel instead of cromoly, cheaper components, etc. From what I can tell, a few were purchased by enterprising individuals and sold on eBay a few years back. The one I have was purchased by an American living in China who brought it back to the US. It seems like there's a few in the US. But, not many.

For photos of a Dahon Dream converted to 8-speed Alfine IGH, see this thread. He calls it a 16" wheel. But, my tires say 20".

[Dynocoaster]

Concerning the IGH I would recommend the Sram spectro 5 speed as Bruce Metras has put this on a Moulton. http://www.bikeforums.net/showthread...hlight=moulton

[az2008]

... I would recommend the Sram spectro 5 speed ...

Thanks for the tip. I just noticed the Sturmey 5-speed coaster doesn't seem to be available.

The SRAM Spectro P5 appears to have a over locknut width of 122mm. My frame's dropout is 126-127mm. I'll have to learn more about what that means. (The Sturmey 5-speed with coaster was 127mm. It sounded simple.).

[Sangetsu]

I have a bike which is fitted with a Shimano Nexus 7 speed hub with an integral coaster brake. The Shimano bits are well made, and not expensive, mine has given me three years of reliable service.

[BruceMetras]

Thanks for the tip. I just noticed the Sturmey 5-speed coaster doesn't seem to be available.

The SRAM Spectro P5 appears to have a over locknut width of 122mm. My frame's dropout is 126-127mm. I'll have to learn more about what that means. (The Sturmey 5-speed with coaster was 127mm. It sounded simple.).

The SRAM P5 has a minimum OLN of 122, but you could easily add a 4mm spacer to the non-drive side as there is plenty of axle length.

[az2008]

The SRAM P5 has a minimum OLN of 122, but you could easily add a 4mm spacer to the non-drive side ...

I read about the SRAM P5 last night. What is the "clickbox?" I wanted a trigger shifter, but it sounds like the hub requires a "clickbox" and that only comes with a twist shifter(?). The Sturmey seems simpler in this regard. But, I can't find anyone selling it via Google.

Regarding Sangetsu's post about the Shimano Nexus 7-speed, it has an OLN of 130. Is it possible (advisable?) to spread my frame 3-4mm? I've read about it on Sheldon's site. My frame is steel. It doesn't seem too complicated, nor a drastic movement. On the other hand, the chainstays/seatstays are short due to the 20" wheel size. Is 3-4 mm too much for this size frame?

[Dahon.Steve]

Keep the three speed hub but leave the front brake alone! Unless you plan to use clipless pedals, the coaster brake is asking for trouble. I have a 3 speed bike with the coaster brake and front brake and there are time when you need both!

If you went clipless, then you can stop at any postion. If you don't, there are only two locations during a spin that you can stop in an emergency. Don't let yourself be stuck with this limitation. Keep the front brake!

[puchfinnland]

early shimano nexus 7's has a nice clickbox.
here is one used in german ebay-they are not easy to find and they work on all nexus 7 hubs
http://www.ebay.de/itm/Shimano-Nexus...item4d00ea1c3e

if you find one of these they are really tough and never break! the nexus 7 is the best in my opinion as there is nothing outside the stays to get bent or broken. you might twist my arm for a used one-I have some here in finland.
try ebay.de for used ones

[az2008]

the nexus 7 is the best in my opinion as there is nothing outside the stays to get bent or broken. you might twist my arm for a used one-I have some here in finland.

Since you have experience with these, can you tell me the over locknut spacing of a Shimano Nexus 7 with coaster brake? One of Sheldon Brown's pages says 130mm. The online retailers say 132mm.

Thanks.

[az2008]

In case anyone finds this thread in the future: I spread my frame's rear dropout today from 126 to 132mm. I decided to do it before ordering the Shimano Nexus 7-speed (with coaster) because I couldn't bring myself to order the hub while preoccupied with how the frame spreading would work. And, I thought I should do it before I had the new latch tab welded onto the frame (in case my spreading popped a weld and needed additional repair).

I started with Sheldon's 2x4 method. But, I didn't get a good feeling about it. Maybe because the triangle is so miniature on a folding bike. I felt I was exerting too much force to have a controlled bend.

So, I decided to use a 9.5 by 180mm axle off a department store bike. On one side of the frame I used two nuts (and washers) to tighten the axle on this side. This made it more solid, ensuring the axle won't slip out, etc. See:

PICT0599.jpg

On the other side, I used an axle nut, a washer and a large fender washer to give it a better "bite." See:

PICT0600.jpg

There are a couple more photos below showing different angles:

PICT0601.jpgPICT0602.jpg

The key is to spread it in small increments. Open it 5, back it off and see if that amount of flexing caused a permanent change (bend). Flex it open 10, back it off and check what happen. Do 15, etc. When it starts to affect a permanent change, each additional mm of flex can make a permanent difference. It could be easy to overshoot it. Go in gradual steps looking for small changes.

I was worried one side would "give" more than the other. For example, I wanted 3mm on each side. But, I worried one side might go 4, and the other 2. I used Sheldon's string alignment method. It's perfect. Within .5 mm.

One thing I lucked out with: my fork flanges (the flat area at the end of the rear triangle, where the axle bolts onto) already pointed in toward each other. (Toed in.). Opening the frame made them more parallel to each other. If they were already parallel, they'd probably be pointing away from each other now. (splayed outward.). If that happened I'd probably clamp them (one at a time) in a bench vise and pull the frame a little to bend them straight.

Now I order the hub and get my weld fixed.

Edit: You don't need to use an axle as the spreader. The hardware store sells threaded rods. Lowes has them about 12" long. Probably 3/8" diameter would work. Just 3 nuts, three washers and one fender washer.

[az2008]

Next question: The Nexus 7 is a 36h hub. My Dream's rims are single-walled 28h. I've read that it's not wise to lace mismatched drillings. But, it's not clear if that's more for full-size wheels. (I.e., I've also read that 20" wheels are inherently strong and don't suffer the same stresses. And, the wheel won't be dished because the hub is IGH.).

I've seen this pattern. Would it be reasonable for me to do this? I know I can get an inexpensive double-walled 20" rim with 36 holes. ($25). It just seems like 8 more spokes is overkill. The 28-spoke wheel already looks dense considering the small diameter. I'm not going to ride the bike roughly either.

So, would it be crazy to lace the new hub to the original 28h single wall rim? If the general consensus is to get a new 36h rim, what kind of spoke pattern would make sense for a 20" wheel (keeping in mind that the spokes will be shorter than normal given the Nexus's larger diameter flange)?

Thanks.

[bbmike]

For what it's worth LittlePixel's pattern looks good - my concern would be that radial spokes on one side are un-oposed on the other side. I think it could introduce extra torsion in to the wheel because cross spokes will flex differently than radial spokes. That said, there's a blog which tries to prove that there's very little difference in flex between cross three and radial lacing...

Anyway, if you're already at 28 spokes why not just add 8 more and get better wheel to boot (wider wheel will allow for lower PSI and therefore more cushion). I use crows foot pattern which I like quite a bit. It's easy to lace, true and replace spokes when necessary (the picture is of "dual tone" crows foot - one side silver and another black):

CrowsFoot.jpg

[az2008]

Anyway, if you're already at 28 spokes why not just add 8 more and get better wheel to boot

You talked me into it. I'll also have my original rear wheel in case I ever need to go back to a derailer. (Or, I could sell it.).

[az2008]

Anyway, if you're already at 28 spokes why not just add 8 more and get better wheel to boot (wider wheel will allow for lower PSI and therefore more cushion).

I'm having a little trouble picking a rim. Is it common for folders (20" wheels) to use double-walled rims? It seems like 20" double-wall rims are mostly for BMX(?) (Harder riding?)

The existing rims are single wall, 18.5mm wide with 1.50 tires. I see new Broadways (which look exactly like this Asian market "Dream") come with 1.75 tires. So, I think that's what you're referring to when you speak of a larger tire? Or, would you go wider?

If I go with a 1.75 tire, it sounds like I need a 22mm wide rim. Then the question is whether I should do double wall. (Do Broadways come with double wall? I guess that's what I'm asking about what's common for folders.).

[HGR3inOK]

... The existing rims are single wall, 18.5mm wide with 1.50 tires. I see new Broadways (which look exactly like this Asian market "Dream") come with 1.75 tires. ... Then the question is whether I should do double wall. (Do Broadways come with double wall? I guess that's what I'm asking about what's common for folders.).

When you said "Broadway" did you mean "Boardwalk"? I believe all Dahon Boardwalk models have single-wall rims. "P" model Dahons (Speed P8, Mu P8, etc.) have double-wall rims.

-HANK RYAN-
Norman, Oklahoma USA

[az2008]

When you said "Broadway" did you mean "Boardwalk"?

Yes, that's what I meant. Thanks for pointing out how double-wall rims are an upgrade. Now I know it's not unusual.

I can't tell what's "normal" for a 20" rim. Searches produce a lot of BMX rims that look a bit "sick" (as the younger BMX crowd would say.).

I'm trying to decide between the Sun CR-18 (18mm inner rim width) or Sun Rhyno Lite (22mm inner rim width).

The CR-18 seems like it's just barely wide enough for a 1.75 tire. (I read somewhere tire width should be 1.45 to 2.0 times the width of the rim.). But, my Dream's original wheels are 18mm (internal) and are stamped "1.50/1.75".

The Rhyno's width sounds more suitable for 1.75 tires. But, it looks disproportionately wide compared to what I see in photos for most 20" folding bikes. I'm afraid it will look strange on a folder. (But, it would probably let a tire inflate wider, and be more cushiony.).

Sun's web site says they have the same "effective rim diameter". So, if one didn't work out I could switch to the other without buying new spokes.

[az2008]

the nexus 7 is the best in my opinion as there is nothing outside the stays to get bent or broken.

I agree, the Nexus 7 is great. I'll look for one of those clickboxes you mentioned. I'd like to have a spare.

I laced it to a Sun Rhyno Lite 20" rim. I finally finished this project this weekend. (I can't believe I started May 5 and finished July 29. A lot of interruptions.).

I'll cap this thread with some photos soon. It's been a great learning experience. (IGH, building my first wheel, metal fabrication to repair broken latch tab on frame, etc.). Not bad for what started as a free dumpster bike.

I'm going to give it some time to see if I like this configuration (IGH w/coaster). If so, I'll cut off the rear brake posts, cable guides and derailer hanger. Then have it powder coated. (Maybe have a flat piece of metal welded as a kickstand top-plate. The bike came with a kickstand that mounts to the rear dropout, held on by the axle nut. I don't like that.).

Lot's of fun. Can't wait to take it on the bus.