Help: looking for the perfect crankset to fit with 7 speed Shimano Nexus gear hub

[difo]

Hi all,

I have a technical doubt.
I have a city bike equipped with a 7 speed Shimano Nexus gear hub. I want to use it for short relaxed trips.
I am looking for a single-ring crankset to mount on the bike. I am wondering what is the most suitable dimension for the crankset ring: how many teeth do you recommend, so that I can optimize the gearbox range?
thank you,

diego

[squeaker]

Stuff some numbers in here with gear inches selected.
You'll then need to decide whether you want to walk up steeper hills and have a relaxed top gear (high gear inches) or vice versa.
For reference, my town hack has a gear range of 31 to 87 gear inches (2.7:1 range from an 8-speed cassette) but a Nexus 7 has a range of 2.4:1, so you'd need to compromise at one end or the other. For me it would be the top end, so I'd probably end up with something like 30 to 73 gear inches.
YMMV!

[Brucey]

if you have a crankset already, the first thing to explore is changing the gearing to suit your needs by varying the size of the sprocket at the back. This is normally cheaper and easier than changing the crankset.

Sprockets are available that fit this hub which vary from 13T to 24T. I recommend using a 1/8" chain and sprocket (eg sprocket from sturmey archer and KMC B1 chain) with this hub.

Commonly a N7 bike is fitted with a 38T chainring ( shimano's nexus chainset is this size) and this gear calculator

http://www.ritzelrechner.de/?GR=SNI7&KB=38&RZ=18&UF=2185&TF=90&SL=2.6&UN=MPH&DV=gearInches

I have configured with an N7 hub, 700x35 tyres, an 18T sprocket and a 38T chainring. You can fiddle with the settings to check/alter the gearing you have, eg try different sprocket sizes by dragging and dropping the sprocket indicator.

cheers

[difo]

Thanks to everybody.
I did not think about changing both the sprocket and the chainring. For the sake of curiosity, if I replace a 18 teeth sprocket and a 38 teeth chainring with a 20 teeth sprocket and a 42 teeth chainring, I get almost the same gear ratios. But it is much easier to find a beautiful vintage 42t than a 38t crankset.
Is there any good reason to prefer 18 and 38 to 20 and 42?
Thank you!
Cheers
Diego

[Brucey]

I thought the idea was to change the gear ratios? If not then arguably 42/20 is better than 38/18 in some respects, eg that the parts will last longer because the chain tension will be about 10% less, and efficiency will be fractionally improved.

However if you later want lower gearing, you may run out of available sprockets; 24T was only made by SRAM and they have packed in making hub gear stuff at all. The largest from other makers is (IIRC) ~22T. You can still buy a new 24T sprocket at present but in a few months, maybe not.

cheers

[difo]

I thought the idea was to change the gear ratios? If not then arguably 42/20 is better than 38/18 in some respects, eg that the parts will last longer because the chain tension will be about 10% less, and efficiency will be fractionally improved.

However if you later want lower gearing, you may run out of available sprockets; 24T was only made by SRAM and they have packed in making hub gear stuff at all. The largest from other makers is (IIRC) ~22T. You can still buy a new 24T sprocket at present but in a few months, maybe not.

cheers

Sorry I was not clear at the beginning.
My post had actually two purposes:
1. understand what are the most recommended combinations of procket / chainring for the Shimano Nexus 7 speeds
2. (I did not said this at the beginning) I am looking for a vintage crankset and it is far easier to find a 42 teeth chainring than a smaller one with 38 teeth (vintage style).

Anyway thank you for your indications, now I have a clearer idea about what I can do.
cheers

diego

[thirdcrank]

There is a Shimano Nexus chainset:-

https://www.sjscycles.co.uk/chainsets/3 ... er-170-mm/

I see that the current version there is available with 33 or 38T

Mine - of a much earlier vintage - came on a complete bike with 33T and an 18T sprocket. I was immeasurably fitter then than I am these days, but that's not saying much. I don't live in the Alps nor even the Yorkshire Dales but that gave me a range low enough to come home with a week's shopping up the hill - Scotchman Lane - traditionally used by local cycling clubs for their club hill climb, in reasonable comfort using the second-to-lowest gear. I've only ever used the lowest gear for really slow uphill manoeuvring. The top gear is big enough for getting a move on, bearing in mind it's a roadster, not a road bike. It never occurred to me to go for something higher because it's always handy to have something in reserve. For comfort cycling, freewheeling downhill rather than pedalling is hardly a big deal. OTOH, struggling or having to climb off just because your gears aren't low enough can be a nuisance. Even if you live somewhere flattish, you can still have strong headwinds.