Touring with my nexus is great except planning routes around big mountains especially here in the US SW. So I got this crazy idea to upgrade my down shift with a double crank. The chain rings I'm thinking of seem crazy but is it possible.
24/44 double crankset. it'll cost my left nut but might be worth it considering I live on my bike. The numbers seem to jive with max. Ratios of the nexus. HUGE jump in sizes but doable?? Any thoughts? It'll be on my monster Cross check

I haven't tried it on a Nexus, but I did that with my Nuvinci. I worked fine except that I had trouble finding a front derailer that worked because the chainline was pushed out further than most derailers wanted to go. Nexus chainline should be a little closer.

24 sounds really low. I'd be worried about how the hub would handle the torque. Depending on your cog size.

I ended up removing my front derailer. I would manually move the chain. Ride around town on the big ring, push it to the small ring when I was loaded up. Then I got lazy. Haven't used the big ring in a long time. Running 18/36 on my Alfine 8, same as I was on my Nuvinci. High end is missing a little. Low end could be a little lower, but for the most part it's fine. But I have no mountains.

Now I'm moving to bike with horizontal dropouts. One aspect of that I'm looking forward to is ditching the tensioner. Once that happens, there's no chance to use the big ring.

Long term I'm considering a Speed Drive: a bottom bracket based 2-speed set up. Once chainring, but still possible to switch to high gear. Until then, I think I'm good with the set up I have. But, yeah, mountains could change that.

So, sure, you can do it. I would make sure your high end and low end are useable. Might be worthwhile to bring the rings closer together in size rather than to have one ring you just never use.

I have no comment on the Nexus, know nothing about it. But I have a triple on two of my touring bikes that is a 52/42/24. So, I know that shifting between 24 and 42 chainrings is possible. Yours is not much different. I use a chain catcher to keep the chain on the rings, it might help on downshifts. The upshift from the 24 to 42 is a bit slow, but I usually can make that shift within about 30 feet of distance. Need a friction shifter. I am using a vintage Suntour front derailleur.



You could buy a triple and put a bashguard in the outer position. Or - - on one of my bikes I got perturbed that bashguards cost so much, so I bought a cheap chainring and cut all the teeth off it with a saber saw and then spent about 15 minutes on it with a file. It is now a pretty good looking bashguard that has 52T stamped on it. So, if you bought a triple, you could convert the outer position to a bashguard. I later sprayed the bashguard with black paint, but in the photo you can see it before I sprayed it.

FSA Metropolis/Patterson drive might be an option for you.

Just putting a small chainring on may exceed the torque limit of the hub, but the Patterson achieves that with a separate gearing system in the crankset.

FSA Metropolis Patterson two-speed crankset - Patterson Bike

Interesting!

I'm intrigued. I wonder if I can replace the stock Shimano Nexus crankset on my Breezer Uptown 8 with this Patterson Transmission. The product page for the Patterson says it will fit 68 mm bottom bracket, which happens to be the size of the stock bottom bracket ([FSA 7420 Cartridge-Style).

The Patterson would improve the usable gear range of this bike considerably, as the stock crankset is only 38T. It's fine for climbing the hill to my house, but the small size limits my ability to take advantage of descents, especially going down 15th St (in DC, just pas t the Washington Monument) towards E. Basin Dr. (right by Jefferson Memorial). Cyclists there like to pedal hard on the evening commute to encourage motorists to stay in the lane they're supposed to be in (left lane to get on I-395 - right lane goes to E. Basin Dr. and the connecting path to the 14th St. bridge MUP).

You could definitely do it with the right chain tensioner. It should be cheap too if you already have a rear derailleur to use. You'll just need to hack it a bit so that it doesn't move ( longer adjustment screw?)

Here's a vintage BMX with a single cog in the rear, 2 speeds on the crank



The chainring difference of 20t is probably not going to work. But I see some people online claiming to have 15t or 16t chainring differences that work with shimano derailleurs. I tried an 18t difference on an Ultregra triple FD and it didn't work for me. YMMV

Interesting post, I've been wondering about using big 50 or 52 chainring on touring triple. 22-tooth small-big chainring difference AFAIK usually spec'ed as max & wow, you blow past that w/28-tooth diff. Is design of vintage Suntour different enough from current Shimano etc trekking/MTB FD's that it works better? Using 48/36/26 x 11/34 (559 mm wheel) gearing that's OK but not great. Top gear is too low but I still need to shift from middle to big chainring a lot. Don't like using 36-tooth chainring w/smaller cogs due to higher friction & noise. Was working on a friend's Trek city bike & noticed it had a front chain catcher even though it had stock gearing.

I agree it could be done. Getting it to work really well might be a challenge. You'd need a front derailleur and a rear derailleur, and you'd have nearly all the problems associated with derailleur systems. You would preserve some of the benefits is the hub gear, mainly the ability to shift while stopped.

Now I'm not going to pretend the problems with derailleur are a big deal, but the whole point of the hub gear is to do away with them. It seems to me that if you're going to have derailleurs anyway, skip the hub gear (unless it's the old three speed with two cogs, I like that system).

In the case of the Nexus/Alfine hubs, rear sprockets are available over such a wide range (16t-23t are readily available, larger can be found with some effort) and chain rings come in nearly all sizes as well(depending on the crank, of course) that you should be able to gear any bike so it has a gear low enough, or high enough, for where you're riding. Hub gears always involve certain compromises.

Yes, but there is a limit to how small a chainring and how large a sprocket can be used due to torque limitations on the hub, so while in theory you could gear an Alfine lower using any combo, in practice doing so would void your warranty and potentially break the hub.

Yes, that is true, regardless the number of chainrings.

Not as tidy looking as the stock 28t, but bigger chainrings are available thru the Seller of those Patterson metros
28/'45'

Schlumpf speed drive is another 2 gear ratio overdrive transmission .. they offer a 110 5 bolt spider model. for 34t or larger chainrings..

34/'54'

This is true of the Nuvinci. They have published limits. I can't find that info for Shimano gear hubs. I can find "recommended ratios," but no lower limits. Still, the fact that they don't publish limits doesn't mean you can't over-torq your hub. That's why I wonder about the feasibility of a really low range, but in terms warranty, I don't know what the limit is, if any. It seems like it Mountain Bike Land the Alfine 8 has a pretty good reputation among people wanting to use a gear hub, so I figure it must be somewhat robust, but that still doesn't mean it will hold up to serious under-gearing.

As it turns out, somebody already tried a Patterson Metropolis + Shimano Nexus 8 combo three years ago:

The Hub Bike Co-Op Blog: Let The Patterson Transmission Enhance Your Commute

I contacted the coop to ask if that bike is still around and if they still like that combo. I got this email reply:

One of our mechanics rocks this set-up, but usually doesn't start riding it regularly until winter time. He's been using it for at least two seasons (maybe 3) and continues to love it.

I'm guessing it's the same bike that was shown in the blog, which says something good about the durability of the Patterson.

I have not used a current Shimano front derailleur, so I have no clue how to answer your question. The old Suntour has two flat sides whereas I think many of the newer front derailleurs have some weird shapes bent into them to try to lift the chain better for shifting. The reason I am using the Suntour is that it is high normal, it shifts the opposite direction of other derailleurs. I push the shifter all the way forward and it goes into high on both front and rear derailleurs, I do not have to think as hard when I shift. I have been using Suntour fronts almost exclusively (exception, on one bike I use Campy) since the early 70s for that reason. Not all old Suntours are high normal, only some of them are. About 10 years ago I found that a local store had some take offs (they had taken them off new bikes to fit other derailleurs) at a good price that I think are from the 1980s, I bought a lifetime supply of those Suntours, still have a couple more that I have not put on bikes yet - no, I am not selling any of them.

With the 52/42/24 front and 11/32 eight speed cassette rear, I can't use the smallest chainring (24) and also use the smallest two cogs on the cassette (11 and 12) because the XT derailleur will not take up all the slack. So, I have more than exceeded the capacity of the rear derailleur cage. But I would not used those gears anyway as they are too cross chained, so not a problem. The Campy crank came with 30t granny, the 24 was an aftermarket.

With that big of a jump from 42 to 24, I just assumed I would need a chain catcher, so I put one on. I do not really know if it is necessary.

I have a Sachs 3x7 on my Bike Friday, works great. Three speed hub with 7 speed freewheel. It's kinda the same idea. I've thought of a 7X2 setup like you have, you could just use a chain tensioner in the back or an old derailleur with high and low locked out to exactly line the pulleys up. Should work, theoretically, just get your chain alignment set up.