Shimano nexus sprockets

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uwidavid
Posts: 21
Joined: 3 Jan 2017, 1:19pm

Shimano nexus sprockets

Post by uwidavid »

I have inherited a Tern folding bike. It has a 7 speed (hub) shimano nexus fitted. The problem is that the gearing is far too low - I've only used 5,6 and 7 ever. Now the normal solution would be to fit a smaller sprocket, but a quick look online seems to indicate that the smallest available is 16T (the one on it has 17T so this will make little difference).
Question is there any other make that would fit.
Otherwise it is the chainring and this is a 5-bolt 44T, but it appears that the BCD is 142mm - a very strange size.
Any ideas?
Jdsk
Posts: 9137
Joined: 5 Mar 2019, 5:42pm

Re: Shimano nexus sprockets

Post by Jdsk »

uwidavid wrote: 21 Jul 2021, 12:49pmOtherwise it is the chainring and this is a 5-bolt 44T, but it appears that the BCD is 142mm - a very strange size.
Yes... what's the distance between two adjacent bolts, please?

Jonathan
Carlton green
Posts: 1062
Joined: 22 Jun 2019, 12:27pm

Re: Shimano nexus sprockets

Post by Carlton green »

IIRC Sturmey Archer sprockets use a similar mounting and might fit ... something for the OP to investigate further. A quick look on eBay produced SA sprockets down to 13 teeth.

SJS sell some sprockets for Brompton’s and IIRC some of them have SA type hubs.

Edit. Sheldon has a ref chart for chainwheels : https://www.sheldonbrown.com/cribsheet-bcd.html
Last edited by Carlton green on 21 Jul 2021, 2:40pm, edited 1 time in total.
Jupestar
Posts: 273
Joined: 29 Feb 2020, 3:03pm

Re: Shimano nexus sprockets

Post by Jupestar »

I'd double check that BCD, could it be 144 5Bolt? That used on the track.
uwidavid
Posts: 21
Joined: 3 Jan 2017, 1:19pm

Re: Shimano nexus sprockets

Post by uwidavid »

The distance between adjacent bolts* is 83.5 mm and between non-adjacent 135 mm.
Changing the sprocket would be preferred (I could get away with not changing the chain). The shimano nexus sprockets seem (from pictures online) to have 3 rounded protrusions which other makes of sprocket do not have.

*I say bolts but they are actually screws.
PH
Posts: 10402
Joined: 21 Jan 2007, 12:31am
Location: Derby
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Re: Shimano nexus sprockets

Post by PH »

Sheldon Brown says SA and SRAM sprockets fit but on a Nexus/Alfine you can't use smaller than 16T due to interference, so it seems you're out of luck
https://www.sheldonbrown.com/nexus-mech ... er%20chain.

Do you live in the fens? 44 x 17 seems about right to me, is that about a 30" bottom gear? I need that even for undulating urban riding.
uwidavid
Posts: 21
Joined: 3 Jan 2017, 1:19pm

Re: Shimano nexus sprockets

Post by uwidavid »

I live in East Anglia so yes it is flat.
As I said the bike is a folder so has rather small wheels hence the resulting low gearing.
I do also favour slow rpm and high power for pedaling (maybe not fashionable these days, but that's what I am comfortable with).
Jupestar
Posts: 273
Joined: 29 Feb 2020, 3:03pm

Re: Shimano nexus sprockets

Post by Jupestar »

Very strange BCD.

Do you think the crankset is original? Screws instead of bolts I’ve only seen in low end stuff, I wouldn’t have thought Tern used non-standard stuff like that. Online seem to show current ones have a 130 5Bolt BCD.

Not particularly helpful, but it looks like there is no easy solutions.
uwidavid
Posts: 21
Joined: 3 Jan 2017, 1:19pm

Re: Shimano nexus sprockets

Post by uwidavid »

I thought something was a bit strange. Turns out the screws only hold on a ring that, I presume, is to stop your trousers getting caught in the chain (without using cycle clips). So the pedal end is all one unit. Oh well!
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