Caaah

I'm emailing back and forth with Harris Cyclery on some parts I'm upgrading for the Curve. I wanted to upgrade the chainring to 52t, but the guy over there isn't sure which one I need (since Dahon's site doesn't specify). Can any of you guys help? I don't have the bike with me right now, so I can't look at it myself.

Thanks!

Loch

I think the D3 is like the SL in that the chainring is part of the cranks. You would have to replace the cranks in order to change the chainring.

When I first got my Curve SL I tried to put a 53T chainring on and there was VERY LITTLE room. The chain was rubbing on the frame. I gave up with the parts I had and went back to the original 46T. Lucky mine is the 5 speed and this works pretty well.

I'm not sure if there is enough room for a 52T chainring. All I can say is that it is not going to be easy at all to do, if it is possible. If you do it I've love to know how. Problems arise with chain tension adjustment, bottom bracket length, chainline to make sure it doesn't rub, Q-factor on the cranks to make sure your heel doesn't hit the shifter cover, etc.

Good luck. Maybe some day I'll get bored or get a good deal on some parts and give it a go again.

Caaah

So, if that's the case, is there any rear cog smaller than 19t for the Sturmey Archer 8 speed? I know for the 3 speed, smaller Shimano ones can be altered to fit. Is the same true for the 8 speed?

Or would it cause too many problems going to fewer teeth than 19t?

How much bigger is a 52t cog usually?

Caaah

Ok, I learned from Harris' site how to measure the chainring size. It looks like a 144 bcd. Can anyone confirm?

Loch

Take a closer look at the SA 8 speed a smaller rear sprocket is sometimes not as important because I think the first gear is direct drive and the gears increase from there. Something like that I just know that a lot of people like the way the gears are on the SA 8 speed hub because it works well with small wheels.

Some one on the Dahon forum put an SA 8 speed hub on their Curve and I think they were actually talking about wanting to put a smaller front chainring on because of the SA 8 gearing.

The smallest for the 3 and 5 speed is 13T is that what you have?

What exactly are you measuring on for the chainring? Maybe I need to look at the D3 crank does it have a replaceable chainring? The bolt center diameter is the size of the chainring that bolts onto the crank (bcd). This will depend on what cranks you have. The most common for road cranks are 130 mm and 110 mm.

jur

I looked at the 07 and 08 D3 pics at the Dahon site... none of those photos show a raplacable chainring. Perhaps you should post a photo of yours to make sure.

Caaah

I just figured that because it has screws, its replacable. Here's a pic. I measured from the center of one screw to the other. (I found a metric ruler later)

Caaah

With the 8 speed gearing, I was going by the Harris Cyclery calculator, and trying to find something that would give me about 40 inches as the direct drive. The 52/19 set-up gives me 37-112 which would be fantastic. On the 3 speed hub, I NEVER use 1st gear, and hardly use 2nd. The Dahon site puts the 3 speed at 42"/56"/77"--though Sheldon's calculator seems to be telling me 35/47/63 if I'm entering it right.

rhm

The chainring in your photo is permanently affixed to the crank arm; to replace it, you need a whole new crank. Sorry!

Sturmey-Archer makes only 19, 23, and 25 tooth cogs for their 8-speed hub; and I know of no other cogs that fit this size. The 19 is a very thin ring of metal; I don't think anything smaller would be possible.

Aside from that... it sounds to me like you like to use very high gears (I would consider them TOO high). I'm sure pedaling faster would feel very strange to you, at first, but if you can get used to it you will find it more efficient, easier on the knees, and easier on your equipment. So: I know this isn't the answer you're looking for, but I suggest learning to spin.

Loch

Yes, the difference here is the big apple tires. Because these tires are so much taller than a 16x1.5 inch it will give you GI closer to the ones from dahon site. I tested this with rpm and with my gears at 100 rpm I'm pretty close to 17 mph in gear three (on SA 5speed). This is pretty close to what dahon's site specs for the 2007 curve SL.

the 35-349 wheel size is closer to the 305mm wheel with big apple tire. For direct drive using the actual wheel+tire diameter (roughly 16" 406mm) I got a GI of 56.62 which is 16.84 mph @ 100 rpm. This calculator allows you to input the actual wheel diameter but doesn't have internal gear ratios, so I just did the DD gear and compared (https://www.panix.com/~jbarrm/cycal/cycal.30f.html). Using sheldons calculator I got 56.9 GI or 16.9 mph @ 100 rmp with 35-349 wheel size for DD gear.

Hope this helps

Caaah

Ahh...interesting. That does help! So the 8speed would be more like 39-118 with the 46t/19t set up. That's perfect! You guys rock.

One other question--will I need a longer chain to accomodate the larger back cog? How do I figure out what size?

Caaah

I like a little resistance. I'm sure I'll get tired of it eventually, but in first my feet just fall off the pedals. I never stand and pedal at least.

rhm

What's the existing back cog? If it's just a difference of a couple teeth, you'll probably have enough play in the dropouts; the wheel will be a little farther forward, but no problem. If not, you'll only need to add a couple links to the chain. If you don't have the tool for doing that, no worries; a department store such as walmart sells a cheap chain tool that includes a couple extra links.

Caaah

It's 13t. Actually, the last time I took the wheel off, I do remember it being a pain in the butt to get the wheel far back enough to get the chain tight. So maybe you're right, I won't need a new chain. Yay! Getting excited...the new wheel is shipping today...

Caaah

Just wanted to let you guys know that the swap to the 8 speed went well. I'm very happy with the speed increase. The only trick is keeping that darn chain from rubbing the frame. I'm still messing with it, but I'm starting to worry this is the one big flaw of the Curve design. That swoopy frame looks cool, but where it runs almost parallel with the chain, its a big pain in the booty. I won't give up, though!!

Loch

I agree, that's my only gripe too. They just needed to provide a little more room in there.

Good luck.

rhm

You may need a slightly smaller chain ring. What chain ring are you using now, and what rear cog do you have?

By the way, Caaah... would you be willing to divulge what this conversion cost you? I'm just curious, you know, but I'm probably not the only one....

Caaah

I have 46 in front and 25 in back. I have all intents of changing the back to 19 when everyone gets them back in stock. Do you think that will help? Also, I've already added one extra 3mm washer to the axel on the chain side. I had to push the frame open a little to get that on there, so I don't want to push it and put another washer on. However, when I was looking down at the back wheel while stopped, it looked like the wheel was not on perrrrfectly straight (the left side is a smidgen forward), so I'll try getting that back a few mm and see if that helps.

The whole conversion cost me $170 for the new hub, $72 in spokes, $40 in labor, and $25 for the rim. Harris Cyclery did a lovely job, I must say.

Oh, but I should mention that I only paid $350 for Curve, so it wasn't all bad. I might have been able to find a cheaper wheel build, but I know Harris has a good reputation.

Loch

I'll bet the 19T will help.

What kind of rim did you get?

Caaah

I let them pick it...it says xrims on it...??? I think its the same material as the original, so aluminum?

Caaah

The 19t did the trick! And the gearing is fine for this city. I did a 30 mile ride yesterday, and actually used the entire gear range instead of just 4-8. Here it is on Rockaway Beach:

Loch

Very cool !

I'm pretty satisfied with the 5spd SA hub on my Curve SL, but I'm toying with the idea of having a spare wheel with a SRAM spectro P5 hub (slightly wider range and I like how the SRAMs are set up). Trying to round up some good rims etc. hard to find in this size.

Enjoy your Curve D8.