Help with Gear ratios....?

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Nearholmer
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Joined: 26 Mar 2022, 7:13am

Re: Help with Gear ratios....?

Post by Nearholmer »

If you do accidentally cross chain from a 30T ring to an 11T cog on a modern setup, it’s inefficient to a noticeable degree, but if you get out of it pretty swiftly it doesn’t seem to do gross harm (presumably it’s inflicting extra wear, but only for a short duration). I accidentally do it on almost every ride at some stage, and although I chew through chains fairly quickly, which is normal riding a lot off-road, I seem (fingers crossed) to be getting decent life out of chainrings and cassettes.

Thank you to Brucey for putting a name to chordal resistance BTW, because I never knew it had a name, but find it very noticeable, more so than cross-chaining resistance except the small-small mentioned above. After challenging sections, I try to come up from 30T to 46T as soon as I can to get away from it.
Brucey
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Re: Help with Gear ratios....?

Post by Brucey »

46/30 special chainrings https://www.ebay.co.uk/itm/193217614002 no affiliation.
Last edited by Brucey on 23 Apr 2024, 6:33pm, edited 1 time in total.
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Nearholmer
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Re: Help with Gear ratios....?

Post by Nearholmer »

Do they purport to reduce this chordal resistance?
Brucey
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Re: Help with Gear ratios....?

Post by Brucey »

Nearholmer wrote: 23 Apr 2024, 11:16am Do they purport to reduce this chordal resistance?
possibly not; their party piece is fitting a 30t ring onto a standard 'road' 110mm bcd chainset, which is a pretty nifty trick.
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rareposter
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Re: Help with Gear ratios....?

Post by rareposter »

PaulK wrote: 23 Apr 2024, 8:48am Sorry didn't mean to start a posting war.
I bet you're regretting asking now aren't you?!

It's fairly standard on here for - on the face of it - simple questions to go off topic with wildly in depth "solutions".

I wouldn't get overly concerned about cross-chaining - it happens and the system can cope with it even if it might not be ideal. However, I appreciate you've just bought the bike and may still be getting used to it so it's worth pointing out that if you're in the 50T chainring and grinding uphill in the 30T biggest cog at the back, that's basically the same gear as being in the 34T little ring and the 19 or 21T cogs at the back. It also allows a bit more leeway if the hill gets steeper to drop one more gear to the 24 easily or as the hill flattens out to go up to the 17.

It kind of comes with practice, it's actually more to do with "reading the road" and learning what sort of hills you're on when you start to find it hard work than the actual exact gear ratio. A lot of it will also depend on how you're riding - are you out the saddle, giving it full gas or just sitting in the saddle spinning away? Neither way is right or wrong; it comes down to personal preference and if you're out for a nice relaxing spin or if you're in the middle of a road race!

Hope you're enjoying the new bike now the weather is finally getting better, good luck! :-)
Pebble
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Re: Help with Gear ratios....?

Post by Pebble »

Brucey wrote: 23 Apr 2024, 11:31am
Nearholmer wrote: 23 Apr 2024, 11:16am Do they purport to reduce this chordal resistance?
possibly not; their party piece is fitting a 30t ring onto a standard 'road' 110mm bcd chainset, which is a pretty nifty trick.
I think mine is 110 BCD and the smallest is 39t. would love to know how they fitted a 30t

not that I would want 30t, (or may be not till i'm in my 70s) but would love a 35 or 36 or may be a 37
Cyclothesist
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Location: Scotland

Re: Help with Gear ratios....?

Post by Cyclothesist »

Brucey wrote: 23 Apr 2024, 11:31am
Nearholmer wrote: 23 Apr 2024, 11:16am Do they purport to reduce this chordal resistance?
possibly not; their party piece is fitting a 30t ring onto a standard 'road' 110mm bcd chainset, which is a pretty nifty trick.
Brucey that's another thing I've had to look up (http://chain-guide.com/basics/2-2-1-chordal-action.html). Never heard of the chordal vibration effect in chains and gears. I'd been aware of the rumbly vibration you get with a small toothed gear meshing with a chain for as long as I've ridden a bike but never thought to question what it is or why. Now I know. Thank you. You should write a book about all this stuff.
Brucey
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Re: Help with Gear ratios....?

Post by Brucey »

Pebble wrote: 23 Apr 2024, 1:18pm I think mine is 110 BCD ........ would love to know how they fitted a 30.....
most manufacturers offer 34t to fit 110BCD. A few offer 33t but with some cranks you may need to file the ends of the spider arms down before you fit a 33t ring, otherwise the chain will hit them. However, 33t is normally accepted as the smallest conventional chainring you can fit.

As I mentioned upthread, both chainrings are moved leftwards in this conversion so that the chain sits alongside the spider arms when it is on the small chainring; this is how they manage to fit smaller chainrings in.

Obviously there is nothing to stop you from using the same approach with larger BCDs such as 130mm, 135mm, and 144mm. However I don't know exactly what you can get apart from rings to fit 110mm x 4 and 110mm x 5 formats.
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maanderx
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Re: Help with Gear ratios....?

Post by maanderx »

Brucey wrote: 23 Apr 2024, 6:14pm most manufacturers offer 34t to fit 110BCD. A few offer 33t but with some cranks you may need to file the ends of the spider arms down before you fit a 33t ring, otherwise the chain will hit them. However, 33t is normally accepted as the smallest conventional chainring you can fit.
Anyone after a 74 BCD 33t inner ring? I've got three (from Spa Cycles) that I'll gladly get rid of.
AKA De Sisti
Pebble
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Re: Help with Gear ratios....?

Post by Pebble »

Mine is 130 BCD (dont know what I was thinking before) And this is a 39t - can't see how I would get anything smaller on, but if there is I would love to know how (even a 37 or 38)
the fixing is just too close to the outer edge
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TheBomber
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Re: Help with Gear ratios....?

Post by TheBomber »

Surely the most economic way is to just buy a 110 bcd chainset with your preferred ratios? The workaround solutions for putting smaller rings on than the design intended are rarely cheap.
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Chris Jeggo
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Re: Help with Gear ratios....?

Post by Chris Jeggo »

maanderx wrote: 23 Apr 2024, 6:21pm
Anyone after a 74 BCD 33t inner ring? I've got three (from Spa Cycles) that I'll gladly get rid of.
Are they inners of doubles or middles of triples? Other details, e.g. condition?
NickJP
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Re: Help with Gear ratios....?

Post by NickJP »

Cyclothesist wrote: 23 Apr 2024, 8:30am
JohnR wrote: 22 Apr 2024, 8:30pm
Although the Ultegra long cage 8000 RD is only rated by Shimano for use with a 34t big cog, I know that it copes OK with an 11-40 cassette, as that's the combination that we're using on our tandem. Thre are several videos on Youtube showing this combination working. e.g.
Cool, though it looks pretty tight on a 40t and he seems very wary of running it in the big chainring. It would suggest a 36t is very doable, and safe for the derailleur. For the price of a cassette and new chain that seems like the one to try first.
Actually, with those Shimano RDs, the top jockey pulley is coaxial with the pivot point of the derailleur cage, so the top jockey pulley doesn't move up or down when you change between chainrings. If it clears the largest cog in the small chainring, it will be fine in the large, provided your chain is long enough.
NickJP
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Re: Help with Gear ratios....?

Post by NickJP »

BikinGreen sell 46/30 chainring combinations that fit on a 110BCD five arm crank (though it can't be used on crankarms with the hidden fifth bolt). They manage this by faffing with the chainring mounting so that both chainrings are slightly inboard (about one chainring width) of where they would normally be:
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Pebble
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Re: Help with Gear ratios....?

Post by Pebble »

does a 110bcd fiit onto the same sqaure taper as a 130?

I currently run 52/39 can you get something as big as 52 onto a 110bcd ?
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