Coupling a sprocket with a nexus 3 speed hub

[theratking]

Is there a certain sprocket size that works best with nexus 3 speed hub?

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[horsefarmer]

Sprocket on the hub or the sprocket on the crank?

 

[us56456712]

Is there a certain sprocket size that works best with nexus 3 speed hub?

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In my experience it mostly depends on the bike frame. Some vintage frames, have beautiful swoopy chain stays and this can cause the chain to rub on the chain stays with some front/rear gear combos. I had a problem with 30 front and 23 on the Nexus with my 1940 CWC but a 28x23 just clears the chain stay drop. The Nexus 3 speed hub has worked for me with a lot of different combos. I think your only considerations would be frame chain clearance, the type of terrain you will be riding for chain wheel and rear cog selection, the correct anti rotation washer for your drop outs and your frame chain stay spacing. I had to cold spread my chain stays and align my drop outs before the Nexus would fit in my CWC. Sheldon Brown's web site has instructions for cold spreading and has a chart to help select the proper anti rotation washer. I like the Nexus 3 speed as it has a wide ratio, shifts like a dream, is easy to adjust and has a powerful coaster brake that always catches with very little back peddling no matter what gear it is in. The yellow anti rotation washer that came with the Nexus works with my CWC.

 

[theratking]

I was initially talking about the sprocket on the crank, but now that you mention it, I'd like to know what configuration with the hub sprocket and the crank sprocket when using the nexus 3.

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[us56456712]

I was initially talking about the sprocket on the crank, but now that you mention it, I'd like to know what configuration with the hub sprocket and the crank sprocket when using the nexus 3.

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I use one of mine for single track with 5.5 inch crank arms so it is geared low as I indicated in the above post (28x23). Is it flat or hilly where you ride? How strong a rider are you? is the bike heavy or light? I ride pretty much every day, at least 5 times a week 9 to 15 miles single track and occasionally 40 mile road bike trip with my wife. We are old so even though we ride quite a bit we gear lower that the young guys. I have a lightweight stripped down old English 3 speed that I run 44x18 and I can go up all our hills on the Lake Superior shore but I have to stand on a few near the top. In some communities up here in the U.P. of Michigan Like Houghton and Hancock this would be too high for me to climb the city hills. In some communities near Lakes Michigan or Huron or at the eastern end around the Ste. Mary's River it is flat so you could go higher. For my heavy full dress cruisers I like 36x18. If you have rolling hills with out big climbs and your bike is heavy a good place to start might be 44x18 or 16 with a standard 6.5 inch one piece crank and 26 inch wheels. If you have 20 inch, 24 inch or 29 inch wheels than this recommendation is no good. 20 and 24 inch wheeled bikes usually have 5.5 inch cranks. I guess with 6.5 inch or 165 to 175mm cranks and 26 inch wheels 44x16 would be good for a heavy bike with gentle terrain with moderate rolling hills. If it is a little steeper than I guess I would try 44x18. Rear cogs are pretty inexpensive so you could try several until you found one to your liking. 16 tooth cogs are a little hard to fine but Ebay usually has them. If your bike is lighter, you are young and strong and it is flat and not in a windy area then you could try something like 50x16. If you don't like the 50x16 replace the rear cog with a higher number up to 22 or 23. It seems to me like the middle gear on the Nexus is like one speed coaster gearing and high is an overdrive . I might be wrong, but this is what it feels like to me when I compare my single speed cruisers with similar gearing to the nexus. Another factor is your weight. Climbing is all about strength to weight ratio. I weigh 153 so I can climb better than the otherwise faster but heaver old timers I ride with as I weigh much less. Also your height and leg length are factors. I have a 29 inch inseam and that is apparently rare now as the only place that makes jeans that short is LL Bean.

 

[horsefarmer]

Lots of great info from us56456712.
Here is a handy online gear ratio calculator:

http://kstoerz.com/gearcalc/compare/

Results are shown in "gear inches", It's the distance the tire travels per crank revolution, so the bigger the number the taller the gear and the pedal effort goes up.

Using above calculator with a nexus inter 3 IGH - Internally geared hub and 36 tooth crank sprocket, 18 tooth hub sprocket and a 26x2.0 tire,
Gear inches are 1st = 38", 2nd= 51" and 3rd= 70"

As a reference for "Sport Touring" gear inches - Steep hills 27-37
Medium hills 32-42
Flat 37-47

Of course, your personal style, terrain and fitness will determine what ratios work best for you. Maybe calculate gear inches for a bike you like to ride now and take it from there.

 

[Bicycle808]

Some good advice here, along with oddly specific suggestions.

For all intents and purposes, "gear inches" are, as @horsefarmer suggested, probably the easiest metric we have as far as planning purposes go. So, is 36x18 a good gear? Yeah, it's fine, although it's lower than i'd use for on-road use. But, i'm a guy who rides every day and i live in a flat area. Ppl who don't ride as much, suffer from knee problems, or who live in the hills might think it's perfect. Very young, fit riders will likely want to try something much higher. But, let's get back to gear inches...

In terms of direct drive, 38x16 is equal to a theoretical 52 gear inches. The direct gear on a Nexus 3 is the 2nd gear; the low (1st) and high (3rd) will be about 38gear inches and 71 gear inches, respectively. We know this because we take 73% of that 52" direct drive to find the low gear, and we take 136% of 52" to find the high gear. (This is Nexus-specific; other 3 speeds are geared differently.)

So, in the end, this is all math. A 38x16 combo will yield the exact same ratios as 32x16, 44x22, or anything else that is equivalent to a 2:1 direct-drive ratio. If you want to have a 38"/52"/71" range, look at what front sprockets you have on-hand, and then order a rear sprocket that has half as many teeth. It's that simple. IF you want to go a bit higher, go right ahead. Incidentally, Shimano strongly suggests keeping the 2:1 direct ratio as the lowest possible ratio; the high-torque that comes with ratios <2:1 could theoretically pulverize the planetary gear system in your Nexus. That's just Shimano's suggestion; in the real world, ppl like @us56456712 have been running lower ratios offroad, and many folks don't have any problems. (Then again, many folks do...) Bottom line: if you're running lower than 2:1 and you kill the hub, that's your fault, and NOT Shimano's.

My general advice on 3speed gearing is, find the gear you like to run for a singlespeed set-up on the same terrain that you intend to ride your 3speed bike. Duplicate the exact same gearing. That way, you're in the most efficient & durable gear for most of your cruising (2nd), and you'll have a low gear for climbing (1st) and an overdrive for downhills or just ridin' hard...

HTH
Rob

 

[us56456712]

Some good advice here, along with oddly specific suggestions.

For all intents and purposes, "gear inches" are, as @horsefarmer suggested, probably the easiest metric we have as far as planning purposes go. So, is 36x18 a good gear? Yeah, it's fine, although it's lower than i'd use for on-road use. But, i'm a guy who rides every day and i live in a flat area. Ppl who don't ride as much, suffer from knee problems, or who live in the hills might think it's perfect. Very young, fit riders will likely want to try something much higher. But, let's get back to gear inches...

In terms of direct drive, 38x16 is equal to a theoretical 52 gear inches. The direct gear on a Nexus 3 is the 2nd gear; the low (1st) and high (3rd) will be about 38gear inches and 71 gear inches, respectively. We know this because we take 73% of that 52" direct drive to find the low gear, and we take 136% of 52" to find the high gear. (This is Nexus-specific; other 3 speeds are geared differently.)

So, in the end, this is all math. A 38x16 combo will yield the exact same ratios as 32x16, 44x22, or anything else that is equivalent to a 2:1 direct-drive ratio. If you want to have a 38"/52"/71" range, look at what front sprockets you have on-hand, and then order a rear sprocket that has half as many teeth. It's that simple. IF you want to go a bit higher, go right ahead. Incidentally, Shimano strongly suggests keeping the 2:1 direct ratio as the lowest possible ratio; the high-torque that comes with ratios <2:1 could theoretically pulverize the planetary gear system in your Nexus. That's just Shimano's suggestion; in the real world, ppl like @us56456712 have been running lower ratios offroad, and many folks don't have any problems. (Then again, many folks do...) Bottom line: if you're running lower than 2:1 and you kill the hub, that's your fault, and NOT Shimano's.

My general advice on 3speed gearing is, find the gear you like to run for a singlespeed set-up on the same terrain that you intend to ride your 3speed bike. Duplicate the exact same gearing. That way, you're in the most efficient & durable gear for most of your cruising (2nd), and you'll have a low gear for climbing (1st) and an overdrive for downhills or just ridin' hard...

HTH
Rob

I like the Nexus 3 speed so much that that I wouldn't mind pulverizing it. I would get another. It has lasted way longer than I thought it would. I was reluctant to even try it after reading others experience on the MB forums. I only weigh 150s so That might be part of it. I do stand a lot though.

 

[Bicycle808]

From what i've learned about Nexus hubs and offroad is, it seems like maybe QC is a bit irregular. Seems like some of the hubs are completely bomb-proof, whereas others blow-up immediately. The same seems to be true for the 7- and 8-speed versions, although the 8 speeds are reputably the most stalwart off-road....

The cool thing about a Shimano hub versus something like a NuVinci or a Rohloff is, in the even you kill one, it's cheap and easy to just buy a new hub and move the new hub's guts into the existing hubshell. No need to re-lace the wheel. (TBF, the same can be said of Sturmey-Archer and SRAM.) The really fancy hubs aren't nearly as serviceable m(in fact, you're not s'posed to crack some of them open. They're sealed-for-life) plus the cost of a Rohloff is enough to make you keel over if you blow one up.

From what I've read, NuVinci hubs can survive offroad, even with low ratios... but the lower you go, the less efficient they become. The mtbr folks who run'm offroad have reported good reliability, and good support from Fallbrook (the distributor of the NuVinci hubs). If you kill the hub, you send it in and they send you a new one. But, i'd be PO'd if i had to re-lace more than once every couple years....Still, I think I'd like to try it out. The stepless CVT concept intrigues me.

 

[us56456712]

From what i've learned about Nexus hubs and offroad is, it seems like maybe QC is a bit irregular. Seems like some of the hubs are completely bomb-proof, whereas others blow-up immediately. The same seems to be true for the 7- and 8-speed versions, although the 8 speeds are reputably the most stalwart off-road....

The cool thing about a Shimano hub versus something like a NuVinci or a Rohloff is, in the even you kill one, it's cheap and easy to just buy a new hub and move the new hub's guts into the existing hubshell. No need to re-lace the wheel. (TBF, the same can be said of Sturmey-Archer and SRAM.) The really fancy hubs aren't nearly as serviceable m(in fact, you're not s'posed to crack some of them open. They're sealed-for-life) plus the cost of a Rohloff is enough to make you keel over if you blow one up.

From what I've read, NuVinci hubs can survive offroad, even with low ratios... but the lower you go, the less efficient they become. The mtbr folks who run'm offroad have reported good reliability, and good support from Fallbrook (the distributor of the NuVinci hubs). If you kill the hub, you send it in and they send you a new one. But, i'd be PO'd if i had to re-lace more than once every couple years....Still, I think I'd like to try it out. The stepless CVT concept intrigues me.

Yeah, the NuVinci is quite the engineering marvel. I spoke to a bike mechanic on the phone that does a lot of internal gear repair. Both my Bendix manual 2 speed rebuilds had a lot of rear travel before the brake caught and low was kind of noisy and the brakes were a little grabby. He gave me some test hints and it seems this is normal. Anyway he was really bragging up the Nexus 5 speed. He thought that was the best, but he is probably looking at all aspects including rebuilding. Anyway, that is his favorite. He said they were tough. I can't find it with a coaster brake though and it looks like they are all gone for now. I think they are around $200, but I can't remember as it was the beginning of the summer when I looked. I believe it was the guy at Memory Lane Classics, but it could have been someone on the west coast that does a lot of internal gear repair. My old brain can't remember that I have a water bottle on my bike and I could die of thirst.