Folding Bikes - Upgrading a Curve D3 to 8 speeds

I apologize if this has been brought up before. I did a search, and didn't really find much aside from hub availability.

I'm upgrading my D3 from a commuter to a touring rig, and one of the things I'm considering is upgrading the hub to 7 or 8-speed - essentially transmongifying it into an SL.

Does this involve replacing the entire rim? Obviously the shifter has to be replaced as well. What hubs should I be looking at? (The D3 uses an SRAM hub.)

What's the $$ ballpark here? Is this something I can do on my own for a hundred or two bucks in parts, or is this bringing me halfway to the cost of a new bike?

Thanks!

Shimano Nexus Red 8, 36 spokes = $230 new
spokes = $40 or so

If the current rim is 36 spokes, I don't think you need to replace it. If it isn't 36, then yes you need a new one.

Rebuilding a wheel is rather tricky. Expect to do it wrong at least the first time.

BF member Caaah did this conversion last year and had various problems which you may want to read about. I think this (http://www.bikeforums.net/showthread.php?t=426753) is the thread, but do a search; I'm pretty sure there are other threads where this was discussed.

The main problem is that owing to the Curve's frame design, there is a limit to how large a chain ring, or cog, you can run. Also, if you have to move the chainring to the left to get the chain line straight, you may have to go to a smaller chain ring. Expect headaches. What size chain ring and cog does your C3 have now?

Therefore your only option in an 8-speed hub is the Sturmey Archer --either the older XRF8 or the new and improved model-- and you will likely have to get the 19T cog for it, which will mean a new crank with a 38T (or so) chain ring.

A Nexus 8 speed hub is not a good option because of the way it's geared; the 1:1 gear is comparatively high in its range, so you will end up with several gears that are too low and not enough at the high range, unless you change the chain ring to an expensive large one (60T is available) which will cause the chain rubbing the frame as mentioned. The same goes for a Nexus 7, a Sram i9, a Rohloff, or a NuVinci.

Also, how many spokes does your wheel have? If it's 28, which I assume is the case, you want to find a 28 hole hub, which will not be easy. There is a way to lace a 28 hole rim to a 36 hole hub; it involves several different spoke lengths.

You could lace a 24 hole rim to a 36 hole hub without problems, but I doubt you'll find that rim anywhere.

I think you can make a Sturmey Archer 5 or 7 speed hub work; in fact you may find an old one on ebay with the desired 28 spoke holes. Barring that, you are probably better off building up a whole new wheel with 36 spokes.

A Shimano Nexus Inter-4 hub would work, but will give you only a modest improvement over what you have now.


What's the $$ ballpark here? Is this something I can do on my own for a hundred or two bucks in parts, or is this bringing me halfway to the cost of a new bike?

Unless you find a particularly good deal on a slightly used hub, this won't be cheap. Even if you build the wheel yourself (which you can do, trust me!), you are probably going to spend at least half what a new Downtube Mini would cost.

why dont u sell ur dahon curve for close to resell value and use that money and buy urself the curve sl or any similar model u want instead of wasting time and money and encounter all sort of problems when upgrading a bike?

why dont u sell ur dahon curve for close to resell value and use that money and buy urself the curve sl or any similar model u want instead of wasting time and money and encounter all sort of problems when upgrading a bike?

The whole point of this thread is to ask that very question. It's my decision if this is a waste of time, not yours.

The whole point of this thread is to ask that very question. It's my decision if this is a waste of time, not yours.

ok great...let us know how the upgrade goes.

rhm, thanks for the info. I may well decide this is more than I can spend, but at least I have numbers to go on!

The respected SRAM P5, five-speed hub has an acceptably narrow OLD and as wide an over-all gear range as a Shimano 7-speed (with larger jumps between the ratios, obviously). You'd need to build or source a wheel with this hub, plus the necessary shifter. With the 46 tooth chainwheel/13 tooth cog from the bike's current set-up, you'd have five ratios from ~30 gear inches to ~75 gear inches. Not spectacular, but actually pretty close to the touring ratios recomended by Velocio (http://en.wikipedia.org/wiki/Paul_de_Vivie).

tcs

The respected SRAM P5, five-speed hub

That's actually not a bad idea. And... hey (http://harriscyclery.net/page.cfm?PageID=49&action=list&searchtype=search&keywords=spectro&Brand=388&gobutnsearch=Search")! there's a coaster brake version! Cool!

When the Curve first came out, there was a gentleman who did this and gave a detailed report on the Dahon forums. He even reported spoke lengths and the such.

I built up a wheel for my R20 on a Sturmey-Archer 8-speed hub with an integral drum brake. I found one of these hubs for 80 bux on Craig's list, but I had to cold-set the frame to 135 mm. This was a pretty inexpensive way to go, but it might take a while to find a cheap hub. Bike Tools Etc. has SA hubs for twice that. Other versions of this hub are different widths- you will need to get the right width.

You could probably use your existing rim if you're clever about spoke lengths and mathematics- 28 spokes on a 36 hole hub means lacing all but 8 spokes. The spokes are 14 different lengths, and a lot of care needs to be used when lacing, but you'll need to get custom-cut spokes anyway... I did it once with a 40 hole hub in a 36 hole rim.

When the Curve first came out, there was a gentleman who did this and gave a detailed report on the Dahon forums. He even reported spoke lengths and the such.Kootenay Joe.

If you're going to do this, the only option that makes sense is Sturmey 8, particurly now that the new model is available.

You can get the 28h model to go with your existing rim at www.biketoolsetc.com
While you're at it, order the 19t sprocket to go with the hub.

Then, start planning how you'll replace the crankset/sprocket to get both proper gearing and decent chainline, particularly given that 19t sprocket is not dished and the chainline is very narrow for the narrow-spacing Sturmey 8.