Chainring, 5 arms, 58 mm BCD?

[Blackredgold1964]

Hi All,
I am looking for a chainring with 58 mm Bolt Circle Diameter, 5 arms and between 34 and 40 teeth. 42 is the current size, on Stronglight cranks, around 15 years old. I run this with a Shimano alfine 11 spd hub and 34 teeth sprocket, as far as I know the largest there is. I'm looking for a smaller chainring to make pedalling on tour with luggage easier.
Any suggestions welcome.

Regards

Blackredgold1964

[gaz]

I'd begin with double checking the BCD.

5 hole 58mm was briefly a standard for MTB inner rings, typically around 20-24T and usually matched with 94mm middle and outer positions. Inner rings in that tooth range remain readily available.

I don't recall Stronglight making a chainset to that pattern, in any case 42T on 58mm would be rather unusual.

In the 90's Shimano's 400CX chainset had a 58mm inner and middle with a 32T ring in the middle position. Even if spare middle rings were available at the time they'd be like hen's teeth to find today.

[andrew_s]

58 bcd 5 arm was for Shimano Compact Drive, introduced in response to Suntour Microdrive some time back in the late 80s/early 90s.
It was the inner ring for a triple that was typically 22/32/42, with outer and middle on a larger bcd, maybe 96 mm.

If you think 58 mm is hard (try SJSC), try getting hold of a Microdrive inner chainring (56 mm). I ended up having to file the holes in a 58 mm ring oval.

[Blackredgold1964]

Hi gaz and andrew_s,
Thanks very much for your replies, especially the link to the Sheldon Brown site. Schoolboy error, apologies for the confusion, the BCD is 86 mm and fortunately Spacycles sell Stronglight chainwheels in the range of 28-38t, in steps of 2 teeth. https://www.spacycles.co.uk/m2b2s149p40 ... -38t-inner.

Now, ideally I'd like two extra bottom gears. As far as I understand from the Sheldon Brown site https://www.sheldonbrown.com/alfine-11.html#range the Alfine 11 gears come in steps of around 14%. If someone knows what teeth would give me another 2 gears at the bottom (and loose two at the top) then please let me know. The current chainwheel is 42 teeth. I know there are ways to work that out, but maybe someone on this forum knows …

[Brucey]

38/20 compared with 32/20 input ratios on A11 compared here

http://www.ritzelrechner.de/?GR=SA11&KB=38&RZ=20&UF=2170&TF=90&SL=2.6&UN=MPH&DV=gearInches&GR2=SA11&KB2=32&RZ2=20&UF2=2170

38/20 is the lowest recommended input ratio before the torque is allegedly excessive. However folk do use lower input ratios than that, and I think 32/20 might suit you better.

You can adjust all the parameters on the screen, BTW.

cheers

[Tigerbiten]

Now, ideally I'd like two extra bottom gears. As far as I understand from the Sheldon Brown site https://www.sheldonbrown.com/alfine-11.html#range the Alfine 11 gears come in steps of around 14%. If someone knows what teeth would give me another 2 gears at the bottom (and loose two at the top) then please let me know. The current chainwheel is 42 teeth. I know there are ways to work that out, but maybe someone on this forum knows …

With a 14% step up, divided the chainring by 1.14 for 1 gear down or 1.3 for 2 down.
So 1 gear down is around a 37 tooth chainring and 2 down is a 32 tooth one.

Luck ..........

[thirdcrank]

Hi All,
I am looking for a chainring with 58 mm Bolt Circle Diameter, 5 arms and between 34 and 40 teeth. 42 is the current size, on Stronglight cranks, around 15 years old. I run this with a Shimano alfine 11 spd hub and 34 teeth sprocket, as far as I know the largest there is. I'm looking for a smaller chainring to make pedalling on tour with luggage easier.
Any suggestions welcome.
...

If I've read that correctly, that's 42 x 34. Is that correct? Apart from anything else, I'm surprised to read that a sprocket that size is available for a hub gear.

[RickH]

Now, ideally I'd like two extra bottom gears. As far as I understand from the Sheldon Brown site https://www.sheldonbrown.com/alfine-11.html#range the Alfine 11 gears come in steps of around 14%. If someone knows what teeth would give me another 2 gears at the bottom (and loose two at the top) then please let me know. The current chainwheel is 42 teeth. I know there are ways to work that out, but maybe someone on this forum knows …

With a 14% step up, divided the chainring by 1.14 for 1 gear down or 1.3 for 2 down.
So 1 gear down is around a 37 tooth chainring and 2 down is a 32 tooth one.

Luck ..........

According to the ratios I have in a spreadsheet (I can't remember where I got them from but the Sheldon Brown link above agrees), 1st is 0.527 & 3rd is 0.770 (The jump between 1st & 2nd appears to be twice as big as all the others).

In order to make 3rd gear the same as first by changing the chainring the size you need, by my calculation, is 42 x 0.527 / 0.770 = 28.75. So a 28 would give you a 3rd gear slightly lower than the current 1st (~3%) & a 30T would give you a higher one (~9%).

[Cyril Haearn]

One should not go beyond the limit teeth ratio suggested by the manufacturer, doing so would invalidate the guarantee and would surely put more strain on the system so it might fail sooner, right?

Do manufacturers recommend different ratios for light or heavy riders?

[Brucey]

really it depends how hard you push on the pedals. On normal road gradients if you seek lower gears, possibly you are not pushing that hard on the pedals, so you are not so likely to overload the hub even if you have a very low input ratio.

BTW the existence of a (strict rather than recommended) minimum limit is a point of controversy; in the early days of A11, a member of a US forum had it in writing from shimano that there was no lower limit in the input ratio that they could use if they wanted to.

cheers

[Blackredgold1964]

A collective thank you for all your responses. Very helpful and I now ordered a 3o T chainring.
Brucey: useful, that gear calculator.
Tigerbiten and RickH, thx for the claculations
Cyril Haearn: I wondered about any limitations myself but could not understand what might be wrong with having so unusually low gears. However, as brucey pointed out apparently there’s nothing wrong, so I bought the 30 T chainwheel.
thirdcrank: yes, 34 teeth from SRAM is the biggest sprocket I’ve seen. I’ve changed to that size on another 2 bikes with Alfine and SRAM hubs gears as in general I find bikes ‘overgeared’. My family prefers smaller gears.

[Tigerbiten]

The risk with a very low first gear is that if you suddenly jump on a pedal with full force then you'll over torque it and bend something internal.
But there's normally a bit of leeway in the recommendations.
I've been running the Rohloff on my bent trike around 10% below their recommendations for around 7 years now.

But it is done at your own risk .......

[Blackredgold1964]

Thanks, Tigerbiten, for clarifying.
Regards
Blackredgold1964

[Cyril Haearn]

The risk with a very low first gear is that if you suddenly jump on a pedal with full force then you'll over torque it and bend something internal.
But there's normally a bit of leeway in the recommendations.
I've been running the Rohloff on my bent trike around 10% below their recommendations for around 7 years now.

But it is done at your own risk .......

You are straining it a bit more, but I understand Rohloff hubs are exceedingly robust, reliable and long-lived

[Blackredgold1964]

Dear All,
A late response, I know, but just to let you know that the tiny, 30 T chainwheel worked very well on my tour through the mountains of lower Bavaria, Bohemia and along the hilly route along the Vltave into Prague. 2 panniers, with 6 kg each, and I only had to dismount once on a 16% incline.