GuyBoden
Guru
- Location
- Warrington
I have a Shimano biopace triple too, we're both so very fashionable.
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matticus
Guru
"non-round" chainring fans should listen to this:
View: https://audioboom.com/posts/7696811-contador-basso-biometrics-and-ducks
(can probably skip the 1st half if I recall correctly?) Be warned - not a lot of praise for Biopace :O
I'm not remotely interested in the things (nor in the Contador/Basso bikes), but the rest of the episode is interesting!
Pale Rider
Legendary Member
I have a Shimano biopace triple too, we're both so very fashionable.
I agree.
When we met for a @ColinJ century ride, I thought: "Hey, that Guy guy is a cool dude."
andrew_s
Legendary Member
- Location
- Gloucester
PROBLEM :- Half step gearing as in the OP isn't workable.
There are no current front mechs which will shift reasonably between chainrings with such a small size difference. 10-tooth difference is as small as you'll find, and many (or even most) want a 12-tooth difference.
The basic problem is that if the mech is normally positioned, the inner plate of the mech hits the side of the inner chainring before change is complete, so you've got to raise the mech up the seat tube so there's a big gap between the outer mech plate and the large chainring. and doing that wrecks the quality of the shift. Non-indexed shifters will work, at the cost of an increased chance of dropping the chain, but indexed shifters are unlikely to be usable.
Apologies if this point has already been made.
There are no current front mechs which will shift reasonably between chainrings with such a small size difference. 10-tooth difference is as small as you'll find, and many (or even most) want a 12-tooth difference.
The basic problem is that if the mech is normally positioned, the inner plate of the mech hits the side of the inner chainring before change is complete, so you've got to raise the mech up the seat tube so there's a big gap between the outer mech plate and the large chainring. and doing that wrecks the quality of the shift. Non-indexed shifters will work, at the cost of an increased chance of dropping the chain, but indexed shifters are unlikely to be usable.
Apologies if this point has already been made.
Is Shimano Ultegra "current"? Here's someone using it for half step plus granny https://www.crazyguyonabike.com/doc/page/?page_id=281937
Tigerbiten
Guru
I've raised that point in the past about a half step setup and was proved wrong.
There are no triple derailleurs that will work with a half step setup as they all need at least a 10 tooth difference.
A double derailleur is a different story they don't have to cope with as big a chainring difference so their back plates are a lot shallower.
Ideally you would want to go into a bike shop and measure the difference between the front and back of the cage.
You need 2 mm per tooth difference, so around 6-8 mm is ideal but a slight bigger difference will work.
If you cannot measure any, then go for the one that looks best based on their picture.
It may be more tricky finding a derailleur that not only has a small difference but also matches a smaller than standard chainring size.
Luck ............
So, is the half-step+granny in https://www.crazyguyonabike.com/doc/page/?page_id=281937 a hoax?
Thanks!
Tigerbiten
Guru
No, it uses a double derailleur.
Modern triple derailleurs have a deep inner plate that helps lift the chain off the inner chainring.
But this depth is not vital for how it works, so a double derailleur will still work with triple chainrings.
Just maybe not so crisp.
Luck ...........
Ajax Bay
Guru
- Location
- East Devon
No not a hoax, but an article by an extremely experienced (crazy) guy. If you want to be esoteric, don't expect it to be 'easy'. More fun if you have to work for it. Alternatively just adopt my earlier recommendation to meet an optimised balanced compromise of the criteria/context described in the OP.
Thanks for everyone's input so far :-) Now have a plan for what I hope is a workable half-step 2x11 with almost granny built in :-)
Reviewing what I want:
Matching this up to the requirements
http://www.gear-calculator.com/?GR=...,48&UF=2215&TF=90&SL=2.6&UN=KMH&DV=gearInches
Reviewing what I want:
- Currently have 36” low gear, want a couple of lower steps with a bottom around 24”
- Used to up to 17% steps when accelerating – and that’s fine
- For cruising, want half steps so I can get closer to the “ideal” ratio
- Would like a top of about 100”
Matching this up to the requirements
- Bottom of 22.6” and 3/4 others under 36”. Step of 23% to reach 22.6” is quite large but that’s less important low down.
- Accelerating up either chainring is 17% max and usually a bit less
- Half steps 10% max and mostly 8% or less
- 97.2” is close to the desired 100” and the 106” top probably won’t get a lot of use.
http://www.gear-calculator.com/?GR=...,48&UF=2215&TF=90&SL=2.6&UN=KMH&DV=gearInches
Tigerbiten
Guru
In theory yes, in practice no.
From Sheldon Brown's gear calc, which shows cassettes which are possible to buy.
Unless you can make them, 33-39-48 sprockets don't exist in 11 speed.
In 11 speed, cassettes go either 11-12-13-14, 11-13-15-17 or 10-12-14-16.
So to get 11-12-14-16 will take two cassettes to make, so double the cost.
Or you start with a 10-12-14-16 and swap the 10 lockring to an 11.
You also need to find out the minimum chainring difference for a front derailleur which fits your large chainring.
All the spec sheets show the maximum difference but not the minimum.
If you cannot find a find front derailleur that works with your chainring size, then this is all theoretical.
Luck ............
From Sheldon Brown's gear calc, which shows cassettes which are possible to buy.
Unless you can make them, 33-39-48 sprockets don't exist in 11 speed.
In 11 speed, cassettes go either 11-12-13-14, 11-13-15-17 or 10-12-14-16.
So to get 11-12-14-16 will take two cassettes to make, so double the cost.
Or you start with a 10-12-14-16 and swap the 10 lockring to an 11.
You also need to find out the minimum chainring difference for a front derailleur which fits your large chainring.
All the spec sheets show the maximum difference but not the minimum.
If you cannot find a find front derailleur that works with your chainring size, then this is all theoretical.
Luck ............
Ajax Bay
Guru
- Location
- East Devon
I don't think you quite comprehend the practicalities.
https://www.chainreactioncycles.com/shimano-slx-m7000-11sp-rear-derailleur/rp-prod148563
https://www.wiggle.co.uk/sunrace-ms8-wide-ratio-cassette-11-speed?
You will need to keep changing the front derailleur to achieve the reduced steps between available gears: and that's just not going to happen. So you may as well go for a 1x11 (or 12).
https://www.chainreactioncycles.com/shimano-slx-m7000-11sp-rear-derailleur/rp-prod148563
https://www.wiggle.co.uk/sunrace-ms8-wide-ratio-cassette-11-speed?
You will need to keep changing the front derailleur to achieve the reduced steps between available gears: and that's just not going to happen. So you may as well go for a 1x11 (or 12).
Ok, it used to be possible buy any size of sprocket (well, between 14-32) and you unscrewed the smallest sprocket with a chain wrench and all the others came off. Assembly was the reverse of disassembly. Is it not possible to buy and fit a few non-standard sprockets to a modern cassette?
Sorry, I'm getting really confused now. In an earlier post you said:
So, I could use a double derailleur with two closely spaced rings plus a tiny granny and that would work. But if I never selected the granny or simply didn't fit it, it would not work? You also seem to be saying that front changers have a significant limitation "minimum chainring difference" which all the manufacturers refuse to publish??? What am I not getting? Thanks!
Sorry, I wasn't clear. I don't always need the reduced steps. Two scenarios:
- Mixed terrain (often around here) Accelerating up the gears just using the rear mechanism. Accepting up to 17% steps. I do that on the old bike and it's fine.
- Flat or steady terrain (rare around here) Having got up to roughly the right cruising speed on one chainring alone (See #1), make small adjustments to the ratios using one or both mechs. to get optimum cadence.
Tigerbiten
Guru
You can but ............
First:- You need to find somewhere that sells individual sprockets and see if they have the size you want. But if you cannot see a sprocket in a cassette then it's probably not made.
Second:- Individual sprockets tend to be expensive. It can be cheaper to combine two cassettes to get the one you want vs buying a single cassette and a couple of sprockets to make the one you want.
It's not that they refuse to publish the "minimum chainring difference", it's more they see no point as 99.99999% of the time they know it's not needed.
They know most cyclist want to maximize their gear range, big numbers sell hence they publish that data.
So they design their derailleur to work well at that difference.
They also know that a small percentage won't maximize their range so they also take that into account with the shape of the derailleur cage.
But as the number of sprockets on a cassette has increased then the "need" to half step your gears has decreased.
So the depth of the back plate has probably increased to improve shifting with the "standard" range
So if you're pushing the lower limits of chainring difference, it gets a very 50-50 if a derailleur will work in a half step setup.
So it's possible, but maybe only one or two derailleurs out of the whole 10/11 speed range may be able to do it.
If that's the case then you may have to match you chainrings to the derailleur.
If the only derailleur that works is sized for 50t chainrings then a 42/39 double won't work.
But a 50/47 will.
But that also means your cassette will have to start at 13t or 14t if you want around a 100" top.
And so you're back to the old 50/47/30 half step and granny setup if you want a sub-30" first gear .......
Luck .............
