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Largest cassette on a 20" Dahon?

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Largest cassette on a 20" Dahon?

Old 01-22-24, 02:51 AM
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OK, additional question: My old Dahon does not have a conventional rear derailleur hanger. I thankfully was able to find a claw-mount RD that holds under the axle nut. The claw is riveted to the derailleur. But for all the derailleurs noted above, none are available in claw mount. Mine is a steel frame that does not have the recesses for the later derailleur mounts (I think #27 someone said?) So... does anyone make a simple claw mount to fit under the axle, that has the conventional threaded hole to mount a typical derailleur? If I was still working, I could make one in a half hour in any of the machine shops present at my former employers. Ah, I see they are common on amazon, usually called derailleur hanger plate. I'll leave this up, may help someone.
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Old 01-22-24, 03:09 AM
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Dang, that SLX 7000 GS is expensive, well, at least to me, $63. My claw-mount Shimano Tourney TX 6/7 speed (I use on 7, may work for 8) was $13 retail at the LBS. One of the advantages of using ancient designs. But darned it has been durable and flawless shifts. I won't be in a hurry to switch to a 42 low gear, the 50/34 11-30 21" low is adequate for local hills, steep but not too long. I'll want to try a bike with that 15 inch gearing before I did the change, only needing if I tour in mountains, and I still don't know if that is preferable to walking the bike up periodically. Standing on the pedals, I think that is too low.

This is a really good thread, good knowledge for me. Especially helpful to you folks that don't want the complexity of a front derailleur (not normally complex, but was a bit to add to my folder). But I'll tell ya something: I don't often drop the chain off the chainring, but when I do, instead of greasy fingers, a quick shift on the front derailler pops the chain right back on. And that alone was worth the upgrade.

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Old 01-22-24, 04:44 AM
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Originally Posted by CrimsonEclipse
So, the answer is 50T

That's impressive. How close to the tire is the derailleur in the lowest gear? And is the cage parallel with the gears, or does it skew outboard (away from the wheel) slightly toward the lower pulley? Mine does that slightly, and I haven't corrected it as it gives me more clearance to the tire. What derailleur? If that's the original Dahon and all you had to do was swap the shifter along with the cassette, I'll flip.

I'm guessing your crank is a 52, I'm gonna go do a gear calc on that setup right now. No wait, I don't need to; a 52x50 is gonna be damned close to a 34x32, I currently have a 34x30 low. That's very close total range to my 50/34 11-30 (and next time I replace the cassette, I'll change out the freehub body and go from 11-30 7 speed to 11-34 8 speed). I'd say I still prefer my setup, but you don't have 5 duplicate gears in the middle of the range.

That's how a Mariner should come from the factory, right there.

Last edited by Duragrouch; 01-22-24 at 05:01 AM.
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Old 01-22-24, 08:59 AM
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Originally Posted by Duragrouch
That's impressive. How close to the tire is the derailleur in the lowest gear? And is the cage parallel with the gears, or does it skew outboard (away from the wheel) slightly toward the lower pulley? Mine does that slightly, and I haven't corrected it as it gives me more clearance to the tire. What derailleur? If that's the original Dahon and all you had to do was swap the shifter along with the cassette, I'll flip.

I'm guessing your crank is a 52, I'm gonna go do a gear calc on that setup right now. No wait, I don't need to; a 52x50 is gonna be damned close to a 34x32, I currently have a 34x30 low. That's very close total range to my 50/34 11-30 (and next time I replace the cassette, I'll change out the freehub body and go from 11-30 7 speed to 11-34 8 speed). I'd say I still prefer my setup, but you don't have 5 duplicate gears in the middle of the range.

That's how a Mariner should come from the factory, right there.
It's now a 52t oval front and with a 50t granny, it comes to around 19 gear inches, which is enough for all inclines I deal with.
The derailleur is very close to the tire when in granny mode so a 1.95 tire is likely the limit, does not sway toward or away from its track, and is a cheapie Ltwoo SRS clone I paid $30 for.

I had the weird Dahon derailleur that mounted to the frame but the frame also had a fitting for a normal hangar, so installed a #27 hangar, derailleur, and 10 speed cassette. New shifter came with the derailleur but I prefer friction thumb shifters.

Also installed a BMX 24mm crankset and bottom bracket.

Pictures when I have a chance.
(can't have people throwing tantrums with old media)
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Old 01-23-24, 12:01 AM
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Originally Posted by CrimsonEclipse
It's now a 52t oval front and with a 50t granny, it comes to around 19 gear inches, which is enough for all inclines I deal with.
The derailleur is very close to the tire when in granny mode so a 1.95 tire is likely the limit, does not sway toward or away from its track, and is a cheapie Ltwoo SRS clone I paid $30 for.

I had the weird Dahon derailleur that mounted to the frame but the frame also had a fitting for a normal hangar, so installed a #27 hangar, derailleur, and 10 speed cassette. New shifter came with the derailleur but I prefer friction thumb shifters.

Also installed a BMX 24mm crankset and bottom bracket.

Pictures when I have a chance.
(can't have people throwing tantrums with old media)
You rock dude (or buddy, looking online, that is the choice for fem equiv of dude). "Lighter than air, stronger than steel, cheaper than dirt." (mechanical engineering mantra)

Last edited by Duragrouch; 01-23-24 at 12:15 AM.
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Old 01-25-24, 01:00 PM
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Originally Posted by Duragrouch
You rock dude (or buddy, looking online, that is the choice for fem equiv of dude). "Lighter than air, stronger than steel, cheaper than dirt." (mechanical engineering mantra)
I always used "dude" as gender neutral so no worries.

New pics of a slightly dirty drivetrain. Additional pics of the tire clearance and chain line a bit later.


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Old 01-25-24, 03:14 PM
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Originally Posted by CrimsonEclipse
Additional pics of the tire clearance and chain line a bit later.
..no need to, it's all in the picture.
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Old 01-25-24, 08:27 PM
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(above) Yeah that's mighty close. A flat tire may cause derailleur and chain damage.
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Old 01-25-24, 10:07 PM
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Originally Posted by Duragrouch
(above) Yeah that's mighty close. A flat tire may cause derailleur and chain damage.
True, but it's a Marathon so....

and if I'm still riding on a flat, it'll be in a lower gear
:j
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Old 01-25-24, 10:08 PM
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Originally Posted by splithub
..no need to, it's all in the picture.
Lateral tire to derailleur clearance.
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Old 01-26-24, 08:08 AM
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OK people, let's stick to the topic and not get personal.
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Old 01-27-24, 02:41 AM
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Very relevant quote from Bikepacking.com review of Bike Friday All-Packa (20" wheels but swinging rear triangle folding):
The All-Packa comes in a 1x or 2x version. The 2x option is a reflection of the fact that the bike won’t accommodate the very large cassette ranges that are common nowadays on 1x drivetrains. That’s because the derailleur cage has to be relatively short to not put it completely in jeopardy. The biggest cassette gear will therefore be a 40. The one they sent me has a 42 chainring, yielding a combo that I found reasonable for loaded trips, but that for many won’t cut it going up the steepest pitches. On the other end, the 11-tooth small gear met my ambitions for going fast enough on the flats and downhills, but I could imagine some people finding it limiting. Clearly, that would get worse with a smaller chainring. A 2x therefore makes good sense. I can report, too, that having a front derailleur on one of my other Bike Fridays makes chain management when folded a little easier since the derailleur keeps the chain somewhat scooped up.
So 50/34 x 11-40, with 20"x1.75", gives a gear inch range of 15.9 - 84.9, that's yummy. (The All-Packa comes with 2.4" tires, so gearing will be a bit higher. Sheldon Brown gear calc did not have a tire option over 20"x1.75".)

Last edited by Duragrouch; 01-27-24 at 02:54 AM.
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Old 01-27-24, 03:45 AM
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Originally Posted by Duragrouch
So 50/34 x 11-40
...requires a long cage derailleur
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Old 01-27-24, 12:47 PM
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Originally Posted by Duragrouch
Very relevant quote from Bikepacking.com review of Bike Friday All-Packa (20" wheels but swinging rear triangle folding):


So 50/34 x 11-40, with 20"x1.75", gives a gear inch range of 15.9 - 84.9, that's yummy. (The All-Packa comes with 2.4" tires, so gearing will be a bit higher. Sheldon Brown gear calc did not have a tire option over 20"x1.75".)
Did a recalc of my numbers:

(I previously stated I had 1.95" tires: I actually have 1.75" width tires)
20(406)x 1.75 50T x 52-11 yields 20-92 gear inches.
20(406)x 2.4 50/43 x 40-11 yields 18-98 gear inches.

This is the beauty of engineering compromise.

Two very different paths each with very similar results and different compromises.

The All-Packa is the no compromise options approach.
Pro:
You want bigger tires? Done!
Best clearance for all terrain? Yep!
Risk reduction (or lawsuit prevention) so it can be sold to the general public? Absolutely!
Con:
More complicated
More expensive

The Franken Dahon is the no compromise path to doing whatever the hell I want while being a cheap bastard.
I wanted more range, I'm NOT going to invest a lot of money on a Dahon.
or adding shifter/cables/derailleur/chainring, even if I did have it lying around.
So I added a 50-11 cassette and long cage derailleur for (I think) $15/$20 respectively and achieved my goal.
Pro:
Cheap (seriously, $35!)
Works for my use, paved rail trails and descent climbs.
Con:
Tire width over 1.75" might have derailleur to tire sidewall rubbing
Ground clearance
Triggering weak willed wannabe bike salesman.

Honestly, this whole project is really just an engineering experiment just to see how far I could push the envelope.
I found the edge, this is a far as I want to go.
So now I push back, seeing how short I can make the Jockey Cage (or whatever it's called) and not compromise shifting.

I still have a few derailleurs in the parts and I'll swap them out when I care to and post results.

My guess is I can take off .5-.75" and still work properly.
I'm relatively confident that a 1x 50-11 doesn't need the full long cage length.

Last edited by CrimsonEclipse; 01-27-24 at 12:52 PM. Reason: re-re-re-calculated my recalculations.
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Old 01-27-24, 07:05 PM
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Originally Posted by splithub
...requires a long cage derailleur
Perhaps. My guess is it will need a long cage with pivot slightly down from the top pulley, so when upshifting, the top pulley goes forward in addition to the bottom going backward. The range capacity should still be the same, but may not hang as low. What should not be in dispute, is that a 40 low cog with double crank, should have more ground and tire clearance for the derailleur, than a 50 tooth, but an equal low gear. For larger bikes, 1X is the way to go, because no duplicate gears (my double crankset has 5 gears in the middle which are dupes). So that should yield finer gear steps, a plus. But on a 20" bike, 1X is a heavy lift to get full gear range and good derailleur clearance.
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Old 01-27-24, 07:21 PM
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Originally Posted by Duragrouch
Perhaps. My guess is it will need a long cage with pivot slightly down from the top pulley, so when upshifting, the top pulley goes forward in addition to the bottom going backward. The range capacity should still be the same, but may not hang as low. What should not be in dispute, is that a 40 low cog with double crank, should have more ground and tire clearance for the derailleur, than a 50 tooth, but an equal low gear. For larger bikes, 1X is the way to go, because no duplicate gears (my double crankset has 5 gears in the middle which are dupes). So that should yield finer gear steps, a plus. But on a 20" bike, 1X is a heavy lift to get full gear range and good derailleur clearance.
Looked up a few 20" folder specific derailleurs and surprisingly, not THAT much more clearance.

The best solution is 2x, or internal gear hub which also has significant challenges.
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Old 01-27-24, 07:31 PM
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Originally Posted by CrimsonEclipse
Did a recalc of my numbers:

(I previously stated I had 1.95" tires: I actually have 1.75" width tires)
20(406)x 1.75 50T x 52-11 yields 20-92 gear inches.
20(406)x 2.4 50/43 x 40-11 yields 18-98 gear inches.

This is the beauty of engineering compromise.

Two very different paths each with very similar results and different compromises.

The All-Packa is the no compromise options approach.
Pro:
You want bigger tires? Done!
Best clearance for all terrain? Yep!
Risk reduction (or lawsuit prevention) so it can be sold to the general public? Absolutely!
Con:
More complicated
More expensive

The Franken Dahon is the no compromise path to doing whatever the hell I want while being a cheap bastard.
I wanted more range, I'm NOT going to invest a lot of money on a Dahon.
or adding shifter/cables/derailleur/chainring, even if I did have it lying around.
So I added a 50-11 cassette and long cage derailleur for (I think) $15/$20 respectively and achieved my goal.
Pro:
Cheap (seriously, $35!)
Works for my use, paved rail trails and descent climbs.
Con:
Tire width over 1.75" might have derailleur to tire sidewall rubbing
Ground clearance
Triggering weak willed wannabe bike salesman.

Honestly, this whole project is really just an engineering experiment just to see how far I could push the envelope.
I found the edge, this is a far as I want to go.
So now I push back, seeing how short I can make the Jockey Cage (or whatever it's called) and not compromise shifting.

I still have a few derailleurs in the parts and I'll swap them out when I care to and post results.

My guess is I can take off .5-.75" and still work properly.
I'm relatively confident that a 1x 50-11 doesn't need the full long cage length.
My conversion was amazingly cheap (most parts bought on amazon). The hardest part was trying my best to make measurements and doing the math, to try to get it right the first time. In fact, I've written a treatise on the conversion and the benefit of a fully capable folding bike, because I saw posts on bike forums asking whether a Dahon could take a double crank, and everyone said no, but that was before my (very recent) discovery of the folded subforum, and it's clear, most folks here already know this stuff. A couple notes:
- My initial order of a triple crank, 52/42/30, did not work; The 30 ring was too far inboard, overlapping the bottom bracket (typical, normal), but with the very fat Dahon seat tube, and a front derailleur adaptor (clamp-on, to use a braze-on FD), no way the derailler could go in far enough. It wasn't even close. Plus, the triple crank weighed a ton. I sent back, bought a 50/34 double, which has been a DREAM. Low q-factor, light, hollowtech II style, with external bearings, works fantastic, $75 including bearings, and gets me *almost* as low a gear because of modern wide-range doubles, 16 tooth drop. But I still couldn't get the FD in far enough, so initially spaced the crank out a couple mm with spacers, but with less clamp engagement on the left crank arm, it came loose; I removed the spacers, modified the derailleur to allow it to go closer, and that worked fabulously. Note: BB is 168 and crank designed for that; With a crank designed to fit 168 (with spacers) or 170, crank could probably be spaced out 2mm, and FD not modified; Saw a good SRAM one on amazon, but it was 2-3X the cost.

Shifters $15
Chain (needed to be longer, not because of double crank, but because converting from Dahon compact RD to conventional one, GS length $10
Rear derailleur $13 (local bike shop), claw mount to fit older Dahon frame
Cable and sheath (needed for both front and new rear derailleur) $10
Front derailleur $15
Front derailleur adaptor, I think $30 (bought years ago from ThorBikes)

So $168 + tax total, not dirt cheap (ok perhaps not amazingly cheap) but not bad. I had an older square taper double crank, 52/42, which I used for initial test on the 42 with no derailleur, better, going in the right direction, then ordered the new parts. But the 50/34 was not only wider range, it's so much better in design, especially the external bearings, in being able to adjust preload on those, whereas once a cartridge BB starts to loosen up, cannot correct, and wear accelerates.

Note: That claw-mount GS rear derailleur, not only clears fine, but has the cage extending at least 12mm below the bottom pulley, as a guard, and to keep the chain on if it comes off the crank; If I needed more clearance, that could be easily removed without harming function.

These pics were with 1.5" tires, ground clearance even better with new 1.75". I also made the chain as long as possible, not as short as possible, so RD not wound as tight forward, and space for a 32 or 34 (currently original dahon 11-30). Big/Big, Small/Small:



Last edited by Duragrouch; 01-27-24 at 07:48 PM.
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Old 01-27-24, 07:54 PM
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Originally Posted by CrimsonEclipse
Looked up a few 20" folder specific derailleurs and surprisingly, not THAT much more clearance.

The best solution is 2x, or internal gear hub which also has significant challenges.
I met a guy while on my bike, he was walking, he has a Burke 20 with 1X (pricey titanium 20", folds sort of like a Brompton), and he complained about the 1X, he liked my setup better.

I have thought that perhaps having a chain guard, both for clothes (only circle on crank is very ineffective), or protecting the chainring when folded, is the motivation for 1X on a folder, but only if it even has a chainguard.

Bike Friday New World Tourist came with triple crank for many years, before wide-range doubles were introduced.

Last edited by Duragrouch; 01-27-24 at 08:01 PM.
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Old 01-27-24, 09:05 PM
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Originally Posted by Duragrouch
I met a guy while on my bike, he was walking, he has a Burke 20 with 1X (pricey titanium 20", folds sort of like a Brompton), and he complained about the 1X, he liked my setup better.

I have thought that perhaps having a chain guard, both for clothes (only circle on crank is very ineffective), or protecting the chainring when folded, is the motivation for 1X on a folder, but only if it even has a chainguard.

Bike Friday New World Tourist came with triple crank for many years, before wide-range doubles were introduced.
huh.... never needed a chain guard to protect the chain ring... I had a double chain guard to keep the chain from jumping off on a previous Dahon 20" but that was before the narrow wide was a thing.
My lowered seatpost generally protected the chainring.




Side note, completely off topic (didn't feel like starting a new theread)

Anyone know the exact aluminum the Mariner is manufactured with?
Is it a 6000 series?
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Old 01-27-24, 09:30 PM
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Originally Posted by CrimsonEclipse
huh.... never needed a chain guard to protect the chain ring... I had a double chain guard to keep the chain from jumping off on a previous Dahon 20" but that was before the narrow wide was a thing.
My lowered seatpost generally protected the chainring.




Side note, completely off topic (didn't feel like starting a new theread)

Anyone know the exact aluminum the Mariner is manufactured with?
Is it a 6000 series?
I'll check... my 89 Cannondale was 6061-T6, but that requires post-heat-treatment after welding. Most have gone to 7005 because it doesn't need that IIRC, so less distortion in frame (see link below). I think 7005 is also a bit higher strength. Dahon Mariner, they just call the material "Dalloy Sonus", so no clue, but highly likely 7005 like other bike makers. A big no-no decades ago was 7075, not weldable so often glued into lugs, and it was also more "notch sensitive", susceptible to fatigue failure at a serious scratch.

Thread that talks about 6061 vs 7005, confirms my memory, see post #6:
https://www.mtbr.com/threads/tempera...minum.1053439/

EDIT: Per my memory, 7005 was *specifically designed* for use in bike frames:
https://en.m.wikipedia.org/wiki/7005_aluminium_alloy

Last edited by Duragrouch; 01-28-24 at 12:17 AM.
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Old 01-27-24, 11:56 PM
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Of course, there’s always the option of what I like to call a Cheapskate Rohloff: a Shimano Nexus-7 or Alfine-8 hub, tensioner and double chainset. Range is 20”-90” with an Alfine-8 with an 16T sprocket and a 48-32T chainset, less with a Nexus-7 (to get a 20” gear you’re dropping the top end to about 80”).

Its advantages are as follows:
  • Plenty of ground clearance;
  • Grease lubrication makes for a clean ride, compared with the oil used in Alfine-11 and Rohloff hubs;
  • Ease of maintenance - an annual dunk of the hub innards in grease is all that’s required;
  • 20” wheels enable a low bottom gear without compromising the 1.9 ratio of sprocket - chainring recommended by Shimano;
  • Ease of indexing compared with the fussiness of the Alfine-11 and a greater range than the Alfine-11 with a 1x chainring;
  • Range of shifters - bar end, flat or dropped bar STI, thumb shifters and probably twist shifters are produced by Shimano and Microshift;
  • The option of electronic shifting (possibly, I’m not sure how Shimano Di2 would play with the combo, but all the hardware is there for it at least);
  • Range of dropout widths - Nexus-7 hubs fit 126mm and upwards; and
  • Price compared with a Rohloff.

The principal disadvantage I can see is the additional hassle of getting a wheel built around your hub of choice, and the lack of range compared with a Rohloff’s massive 20”-110”.

Any thoughts?
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Old 01-28-24, 12:12 AM
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Originally Posted by Reddleman
Of course, there’s always the option of what I like to call a Cheapskate Rohloff: a Shimano Nexus-7 or Alfine-8 hub, tensioner and double chainset. Range is 20”-90” with an Alfine-8 with an 16T sprocket and a 48-32T chainset, less with a Nexus-7 (to get a 20” gear you’re dropping the top end to about 80”).

Its advantages are as follows:
  • Plenty of ground clearance;
  • Grease lubrication makes for a clean ride, compared with the oil used in Alfine-11 and Rohloff hubs;
  • Ease of maintenance - an annual dunk of the hub innards in grease is all that’s required;
  • 20” wheels enable a low bottom gear without compromising the 1.9 ratio of sprocket - chainring recommended by Shimano;
  • Ease of indexing compared with the fussiness of the Alfine-11 and a greater range than the Alfine-11 with a 1x chainring;
  • Range of shifters - bar end, flat or dropped bar STI, thumb shifters and probably twist shifters are produced by Shimano and Microshift;
  • The option of electronic shifting (possibly, I’m not sure how Shimano Di2 would play with the combo, but all the hardware is there for it at least);
  • Range of dropout widths - Nexus-7 hubs fit 126mm and upwards; and
  • Price compared with a Rohloff.

The principal disadvantage I can see is the additional hassle of getting a wheel built around your hub of choice, and the lack of range compared with a Rohloff’s massive 20”-110”.

Any thoughts?
Well written! My initial thoughts are, if IGH, in for a pence, in for a pound, go 100% IGH. However, for range of gearing desired, that probably requires the more expensive/finicky IGH hubs that you mention, thus I can see your point of IGH plus double crank as a bargain approach, plus vastly better ground clearance (on 20" wheels) for the rear derailleur/tensioner, you only need a short cage. Well done. Cheapsters, myself included, salute you!
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Old 01-28-24, 12:48 AM
  #48  
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Originally Posted by Duragrouch
I'll check... my 89 Cannondale was 6061-T6, but that requires post-heat-treatment after welding. Most have gone to 7005 because it doesn't need that IIRC, so less distortion in frame (see link below). I think 7005 is also a bit higher strength. Dahon Mariner, they just call the material "Dalloy Sonus", so no clue, but highly likely 7005 like other bike makers. A big no-no decades ago was 7075, not weldable so often glued into lugs, and it was also more "notch sensitive", susceptible to fatigue failure at a serious scratch.

Thread that talks about 6061 vs 7005, confirms my memory, see post #6:
https://www.mtbr.com/threads/tempera...minum.1053439/

EDIT: Per my memory, 7005 was *specifically designed* for use in bike frames:
https://en.m.wikipedia.org/wiki/7005_aluminium_alloy
Saw the "Dalloy" in their specs....
meh. 6xxx and 7xxx (generally) can be welded and heat treated, but some Dahons had 4xxx hinges to make them lighter and welding is a major no-no.

My main hinge is clicking again and I'm just about over it.
I'll take one more wack at clean/lube/adjustment before I donate the damn thing.

Almost tempted to find a BMX frame and transfer as much of the components as possible.
(I'll get around to doing a geometry comparison one of these days/weeks/years)
This is likely the end of my second Dahon phase.
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Old 01-28-24, 12:56 AM
  #49  
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Originally Posted by CrimsonEclipse
Saw the "Dalloy" in their specs....
meh. 6xxx and 7xxx (generally) can be welded and heat treated, but some Dahons had 4xxx hinges to make them lighter and welding is a major no-no.

My main hinge is clicking again and I'm just about over it.
I'll take one more wack at clean/lube/adjustment before I donate the damn thing.

Almost tempted to find a BMX frame and transfer as much of the components as possible.
(I'll get around to doing a geometry comparison one of these days/weeks/years)
This is likely the end of my second Dahon phase.
7005 was designed to not need heat treat after welding, just a low temp bake for "artificial aging".

Hinge of 4xxx, cannot weld? Well how is the hinge attached to the frame?

Hinge clicking: Do you mean loose when clamped closed? Or clicking as you fold it? The latter may indicate a bent hinge pin, but try lubing. There is a thread on here, somebody replaced their pin, pulled pin and reamed hole for a VW door hinge pin.

I have an old cracked Dahon frame, I keep for hinge spare parts if ever needed, but also use it as a wheel truing jig, held in a "workmate", as dimensions are identical to my replacement Dahon frame (which didn't come from Dahon). If you don't want to do that, you're not by chance near Seattle, are you?

The components should transfer to a BMX frame... EXCEPT... the rear dropout OLD may be narrower for fixed gear. And no rear derailler mount, but then neither does my dahon frame (for a conventional derailleur), I use a claw mount under the axle nut.

Last edited by Duragrouch; 01-28-24 at 01:02 AM.
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Old 01-28-24, 01:16 AM
  #50  
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Originally Posted by Duragrouch
7005 was designed to not need heat treat after welding, just a low temp bake for "artificial aging".

Hinge of 4xxx, cannot weld? Well how is the hinge attached to the frame?

Hinge clicking: Do you mean loose when clamped closed? Or clicking as you fold it? The latter may indicate a bent hinge pin, but try lubing. There is a thread on here, somebody replaced their pin, pulled pin and reamed hole for a VW door hinge pin.

I have an old cracked Dahon frame, I keep for hinge spare parts if ever needed, but also use it as a wheel truing jig, held in a "workmate", as dimensions are identical to my replacement Dahon frame (which didn't come from Dahon). If you don't want to do that, you're not by chance near Seattle, are you?

The components should transfer to a BMX frame... EXCEPT... the rear dropout OLD may be narrower for fixed gear. And no rear derailler mount, but then neither does my dahon frame (for a conventional derailleur), I use a claw mount under the axle nut.
Not sure about the 4xxx Dahon. no idea how it was done.

The hinge is tight, but has a small 'click' with a bump or if I hold the front brake and add force in an alternating forward/back motion or lean it off the kickstand.
I've seen it before with similar Dahon frames. they commonly rub in 3 places and the hinge itself is the 4th pressure point. If they don't all take the exact load, one of them doesn't have enough force and will stick just enough to release with a click or a ting.

Solutions include a very small, fine filing (not yet), small piece of electrical tape on one or more of the offending rubbing points, good cleaning (it's due), or checking the pin (i'll get to it)

East coast for now. Looking for a frame?
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