Help with Gear ratios....?

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Cyclothesist
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Re: Help with Gear ratios....?

Post by Cyclothesist »

Pebble wrote: 24 Apr 2024, 10:37am 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 ?
The square taper will almost certainly be the same JIS taper. Different chainsets have differing spindle length requirements to keep the chainline within spec. The chainset info should include a recommended BB spindle width.
Spa cycles have 52t zicral outer rings for 110bcd.
Last edited by Cyclothesist on 24 Apr 2024, 11:08am, edited 1 time in total.
slowster
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Re: Help with Gear ratios....?

Post by slowster »

By way of example, Spa's 110mm TD2 and 130mm RD2 chainsets are both designed for JIS square taper axles. Moreover, I believe that the only difference between them is the BCD, and otherwise the two designs are so similar that for a given axle length they both give the same chainline. In contrast the 110mm XD2 chainset is a different design, and needs a slightly shorter axle than the TD2/RD2 to give the same chainline.

https://www.spacycles.co.uk/m8b17s109p0 ... /Chainsets
rareposter
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Re: Help with Gear ratios....?

Post by rareposter »

TheBomber wrote: 24 Apr 2024, 9:02am 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.
As discussed earlier in the thread, it's about the least economic way given the BB (and the need for adaptors), the need to drop the front mech down (more adaptors) and the fact that the OP specifically stated he didn't want to change the chainset.

Plus it's unlikely to be the sort of thing that a relative newbie would have the tools or experience to do so that's a visit to a bike shop and a significant labour bill whereas changing a cassette (and resetting the gears), even if you take it to a shop, is a 15-minute job.
Cyclothesist
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Re: Help with Gear ratios....?

Post by Cyclothesist »

NickJP wrote: 24 Apr 2024, 10:07am
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.
Thanks Nick. Having a chain long enough to stop the derailleur being ripped off in big big is essential. Even if you make a conscious effort to avoid cross chaining it is going to happen at some time by accident. That's just life and being human. The second consideration is what happens at the other extreme of cross chaining - little little. If the chain is so slack at that point that the derailleur cage rotates back beyond 8 o'clock position so the returning chain rubs on the bottom of the derailleur cage that's another potential snarl up waiting to happen. Operating well within those 2 extreme scenarios is dictated by the total capacity of the derailleur (Shimano says 39t for an RD7000GS ). The question is how conservative is Shimano being?

I've just watched the video you linked to upthread again. There are 2 important points that went by me first time:
1. He says to avoid big-big and he's adjusted the derailleur so it won't easily do that - not sure that's really feasible without hobbling little chain ring-big sprocket combination.
2. He's using an unspecified MTB crankset so the chainring difference may be less than the 16t of a compact double.

For these reasons if I were the OP I'd give 11-36 on a GS cage a go, remembering to measure and fit a new longer chain. I'm sceptical that 11-40 is going to work well with a road chainset.
Brucey
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Re: Help with Gear ratios....?

Post by Brucey »

Cyclothesist wrote: 24 Apr 2024, 12:02pm....... Operating well within those 2 extreme scenarios is dictated by the total capacity of the derailleur (Shimano says 39t for an RD7000GS ). The question is how conservative is Shimano being?........
the actual capacity can vary with exact chainstay length and chainring choice, because chain shortening can only be done in 1" increments. So you will always get the biggest capacity from the RD when the chain is only just long enough to shift into, then run, in big-big. Under these conditions, up to 2 teeth can be added to the total capacity, because that is about what MrShimano has to allow for, bearing in mind that the same mech has to work with any frame or chainring choice.
If you run out of total capacity, slack running in small-small is nearly always a lesser evil than being unable to select big-big when a new chain is fitted even if big-big would only ever be used accidentally.
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Brucey
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Re: Help with Gear ratios....?

Post by Brucey »

NickJP wrote: 24 Apr 2024, 10:19am 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).......
I think it will work just fine if you are prepared to remove or relocate the chain peg and to do what is necessary with the fifth bolt mounting (which is usually just add some spacers).

edit in this casce you might have to make a new bolt; still very doable though.
Last edited by Brucey on 24 Apr 2024, 4:39pm, edited 1 time in total.
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TheBomber
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Re: Help with Gear ratios....?

Post by TheBomber »

rareposter wrote: 24 Apr 2024, 11:11am
TheBomber wrote: 24 Apr 2024, 9:02am 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.
As discussed earlier in the thread, it's about the least economic way given the BB (and the need for adaptors), the need to drop the front mech down (more adaptors) and the fact that the OP specifically stated he didn't want to change the chainset.
The OP already has a 110 bcd chainset - this comment was for pebble who is looking to fit a smaller inner ring to a 130 bcd chainset, when there is a widely available alternative for all bottom bracket types - a 110 bcd chainset.
NickJP
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Re: Help with Gear ratios....?

Post by NickJP »

TheBomber wrote: 24 Apr 2024, 3:24pm
rareposter wrote: 24 Apr 2024, 11:11am
TheBomber wrote: 24 Apr 2024, 9:02am 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.
As discussed earlier in the thread, it's about the least economic way given the BB (and the need for adaptors), the need to drop the front mech down (more adaptors) and the fact that the OP specifically stated he didn't want to change the chainset.
The OP already has a 110 bcd chainset - this comment was for pebble who is looking to fit a smaller inner ring to a 130 bcd chainset, when there is a widely available alternative for all bottom bracket types - a 110 bcd chainset.
You can get triplizer rings for 130BCD that replace the 130BCD inner chainring and have additional tabs to allow a 74BCD ring to be fitted. So you can either convert a 130BCD double to a triple, or fit a chainguard in place of the outer ring and have a double with smaller rings. That would be cheaper than replacing the existing crankset.

eg: https://www.xxcycle.com/1896-148415-str ... e-sh-.html
Cyclothesist
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Re: Help with Gear ratios....?

Post by Cyclothesist »

NickJP wrote: 25 Apr 2024, 3:40am
TheBomber wrote: 24 Apr 2024, 3:24pm
rareposter wrote: 24 Apr 2024, 11:11am
As discussed earlier in the thread, it's about the least economic way given the BB (and the need for adaptors), the need to drop the front mech down (more adaptors) and the fact that the OP specifically stated he didn't want to change the chainset.
The OP already has a 110 bcd chainset - this comment was for pebble who is looking to fit a smaller inner ring to a 130 bcd chainset, when there is a widely available alternative for all bottom bracket types - a 110 bcd chainset.
You can get triplizer rings for 130BCD that replace the 130BCD inner chainring and have additional tabs to allow a 74BCD ring to be fitted. So you can either convert a 130BCD double to a triple, or fit a chainguard in place of the outer ring and have a double with smaller rings. That would be cheaper than replacing the existing crankset.

eg: https://www.xxcycle.com/1896-148415-str ... e-sh-.html
Interesting and useful for Pebble, but not applicable to the OPs FC-7000 chainset. That Stronglight adapter is for a standard 5 arm spider. The FC-7000 has a 4 arm spider 110bcd.
Brucey
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Re: Help with Gear ratios....?

Post by Brucey »

Cyclothesist wrote: 25 Apr 2024, 9:14am.......Interesting and useful for Pebble, but not applicable to the OPs FC-7000 chainset. That Stronglight adapter is for a standard 5 arm spider. The FC-7000 has a 4 arm spider 110bcd.
sometimes a longer BB spindle is required when a tripleizer ring is fitted, sometimes not.
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853
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Re: Help with Gear ratios....?

Post by 853 »

Pebble wrote: 24 Apr 2024, 12:07am 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)
You can buy and fit a 38t chainring to a 5 bolt 130mm BCD chainset - I've been using one on a Shimano chainset for years. But that's the lowest you can go without doing the sort of modifications already mentioned. Both Spa Cycles and SJS Cycles sell them.

The bolts are very close to the edge of the chainring, but I haven't had any issue. If you're a big, powerful, rider who grinds their way up hills then it may not work well for you.

https://spacycles.co.uk/m8b0s210p3386/S ... -Chainring

https://www.sjscycles.co.uk/130-bcd-5-arm/?teeth=38
Pebble
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Re: Help with Gear ratios....?

Post by Pebble »

853 wrote: 25 Apr 2024, 12:34pm
Pebble wrote: 24 Apr 2024, 12:07am 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)
You can buy and fit a 38t chainring to a 5 bolt 130mm BCD chainset - I've been using one on a Shimano chainset for years. But that's the lowest you can go without doing the sort of modifications already mentioned. Both Spa Cycles and SJS Cycles sell them.

The bolts are very close to the edge of the chainring, but I haven't had any issue. If you're a big, powerful, rider who grinds their way up hills then it may not work well for you.

https://spacycles.co.uk/m8b0s210p3386/S ... -Chainring

https://www.sjscycles.co.uk/130-bcd-5-arm/?teeth=38
So there is - I thought 39 was the lowest, Thankyou

I know 39 to 38 will be imperceptible ( only 2.6% less) but in 20 months time I will be 2.6% older! Hopefully they will cancel each other out without me ever noticing
Brucey
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Re: Help with Gear ratios....?

Post by Brucey »

I think that anyone handy could make something to do the same thing as the bikeingreen chainrings do, provided they can drill and tap a few holes accurately and do some basic metalwork.. Using this approach, it should be possible to fit ~35 t to 130 mm BCD cranks, ~37t to 135 mm cranks, and ~39t to 144 mm BCD cranks, in double format.

I suggest the work is done bearing the following things in mind;

1) it makes very good sense to use M6 bolts to replace the original chainring bolts, not least because standard M6 washers will fit right in the original chainring bolt holes. Using button-headed stainless bolts reduces the key size to 4mm, but IMV it is still big enough to secure the chainrings.

2) 'deflectors' need to be made and fitted to the big ring; these ensure that the chain is always thrown over the ends of the spider arms when shifting onto the small chainring, but without finding a place where it can get stuck en route.

3) when a prospective new chainring is under consideration, look for one that has pretty solid arms from ~122 mm dia. out to ~138 mm dia. since this way, the holes can be drilled and tapped for the M6 bolts and there is still room for spacers to be fitted. I think this means the new chainring needs to be 110 mm BCD or smaller if you plan on using 130 mm BCD cranks.

4) the inner chainring sits.~2 mm further leftwards than before, so you need to increase the FD stroke commensurately. Some indexed shifters will permit this, but others won't.There are various different ways you can do this, but you might lose the trim clicks at one end of the stroke. If so, I suggest you use a FD with a wider cage, and learn to live without them.
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maanderx
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Re: Help with Gear ratios....?

Post by maanderx »

Chris Jeggo wrote: 24 Apr 2024, 9:43am
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?
Please accept my apologies. :oops: I have just checked and the 33t middle rings are all 110 bcd,
whilst the inners (26t) are 74 bcd.
AKA De Sisti
gxaustin
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Re: Help with Gear ratios....?

Post by gxaustin »

[/quote]

Cross chaining on a 2x11 is irrelevant, the system is designed to run all 11 cogs in the big ring. Assuming the chain is long enough and the gears correctly set up, you'll get all cogs with no issues.
The only one to avoid is small-small. Some electronic gear systems specifically prevent you selecting that gear when in normal riding mode, it'll only permit it in adjustment mode.

But big-big is fine.
[/quote]

And yet my Di2, in synchro shift mode, prevents this from occuring.
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