Audax Bike (Spa?) with Tourer Gearing & Double vs. Triple

[Freddie]

Is there good data for chain efficiency at differing angles. I suppose a triple allows you the same spread of gears, but with shallower angles than a double, but does this produce meaningful differences in drivetrain efficiency?

[Freddie]

But what about the downshift? You can't make the outer plate any deeper than it already is, since has to completely clear the outer ring. So the mech will always be working at a severe disadvantage when it comes to deflecting the chain off the middle ring, because it can't possibly get as close to the action as it really needs to be! And the middle to inner shift is THE MOST IMPORTANT shift a tourist ever makes, it's the "Goodness me this hill is steeper than I expected" shift, the leg-saving "{FFE - family-friendly edit } give me some lower gears" shift and the "Oh no I've left it too late" shift! So it's no good when the only way this shift works is with the pedals spinning fast with zero pressure on them, because neither of those things are going to happen on an unexpectedly steepening hill!

What is wrong with using a 3 speed hub (+ cassette) to achieve what the front mech does? In theory you have instantaneous changes on the downshift you describe, are there any problems in practise? I suppose remembering to briefly stop pedalling when shifting the 3 speed hub could be confusing, but other than that...

The front mech has always struck me as a very slow and agricultural changer, most of all precisely when you need it not to be (in the situation you described).

[NetworkMan]

Is there good data for chain efficiency at differing angles. I suppose a triple allows you the same spread of gears, but with shallower angles than a double, but does this produce meaningful differences in drivetrain efficiency?

Yes, some info and discussion here. Also Bicycling Science, third edition, Wilson et Al.
viewtopic.php?f=5&t=132147

[Bmblbzzz]

But what about the downshift? You can't make the outer plate any deeper than it already is, since has to completely clear the outer ring. So the mech will always be working at a severe disadvantage when it comes to deflecting the chain off the middle ring, because it can't possibly get as close to the action as it really needs to be! And the middle to inner shift is THE MOST IMPORTANT shift a tourist ever makes, it's the "Goodness me this hill is steeper than I expected" shift, the leg-saving "{FFE - family-friendly edit } give me some lower gears" shift and the "Oh no I've left it too late" shift! So it's no good when the only way this shift works is with the pedals spinning fast with zero pressure on them, because neither of those things are going to happen on an unexpectedly steepening hill!

What is wrong with using a 3 speed hub (+ cassette) to achieve what the front mech does? In theory you have instantaneous changes on the downshift you describe, are there any problems in practise? I suppose remembering to briefly stop pedalling when shifting the 3 speed hub could be confusing, but other than that...

The front mech has always struck me as a very slow and agricultural changer, most of all precisely when you need it not to be (in the situation you described).

Doesn't Tigerbitten otp have a 10-speed cassette on an 11-speed hub... with a front triple as well?

[Tigerbiten]

I opted for twin hub gears, Schlumpf HSD and Rohloff, with twin chainrings to get my range of gears.
It's Mick F who has a triple and SA hub with a 9 block on one of his bikes.

I looked into that combo but with only one hand the three controls would have been too cramped on a single handlebar.
Plus that combo also didn't give me the gear range wanted , 10"-> +130", without going for a very wide range cassette which gave irregular jumps between the gears.

With my combo, one of the controls is under my heels, so I only need two on my handlebar.
And very regular jumps, 13.6%, between all 24 unique gears.


YMMV ........

[CXRAndy]

I have a Kinesis Tripster V2 ATR with a a triple crankset 48/36/26. I use XTR triple Di2 front derailleur with Di2 hydraulic road shifters.

Its great all-rounder for touring, climbing mountains

I use a 11-32 cassette for general riding and a 11-40 cassette for mountains. gear inch range 18"-115"

[pwa]

I have a Kinesis Tripster V2 ATR with a a triple crankset 48/36/26. I use XTR triple Di2 front derailleur with Di2 hydraulic road shifters.

Its great all-rounder for touring, climbing mountains

So that is using drop bar levers but still managing a tourer type (48/36/26) chainset? Sounds useful.

[CXRAndy]

Yes. drop handle bars

[Brucey]

Is there good data for chain efficiency at differing angles. I suppose a triple allows you the same spread of gears, but with shallower angles than a double, but does this produce meaningful differences in drivetrain efficiency?

cheers

[pwa]

Yes. drop handle bars

Nice. I have a mistrust of electronic stuff on bikes, but apart from that, very nice. Attractive frame too.

[CJ]

What is wrong with using a 3 speed hub (+ cassette) to achieve what the front mech does?

Efficiency, dear boy, efficiency.

[CJ]

Is there good data for chain efficiency at differing angles. I suppose a triple allows you the same spread of gears, but with shallower angles than a double, but does this produce meaningful differences in drivetrain efficiency?

There is a lot of bad data, and only one good study that I am aware of, done on a very elegant rig (the only one I've seen that I can believe truly capable of measuring the tiny - but physiologically significant to the puny human engine - differences in losses between competing bicycle transmissions) by a German university on behalf of Fichtel & Sachs in the 1980s. This found that small tooth-count sprockets (13 or fewer) were much worse than any amount of out-of-line running. It also found that hub-gears were indeed less efficient than derailers (Fichtel and Sachs had just bought Maillard and Huret, so made both at that time, so the person paying the piper had an honest interest in an honest tune) except in direct-drive of course. I have all the references somewhere, but nobody pays me to know this stuff any more so I'm afraid I simply can't be bothered looking it up.

In a nutshell: derailers are better than internal gears unless you have energy to spare or are mechanically incompetent. And more teeth is always better. And provided you're not much further out of line than an old-school single-ring 6-speed, you shouldn't really worry about that factor. So a double is pretty much state-of-the-art efficiency wise, so long as the big ring aligns as close to the centre of the cassette as it can be and you don't use the small end of the cassette with the inner ring (which you won't need to, and in that case will be reminded not to by the chain making an awful noise against the outer).

[Brucey]

Nearly all tests I have seen have been carried out at constant torque, which is a very bad simulation of 'the human engine'. If the % losses vary with torque load then any constant torque testing is going to contain errors. Thus you might be OK comparing like with like, but otherwise there is likely to be some doubt.

Some things that are worth reading from the IHPVA archives

http://www.ihpva.org/HParchive/PDF/hp50-2000.pdf

http://www.ihpva.org/HParchive/PDF/hp51-2001.pdf

http://www.ihpva.org/HParchive/PDF/hp52-2001.pdf

but all of these tests/reports have flaws of various kinds.

cheers

[keyboardmonkey]

I have all the references somewhere, but nobody pays me to know this stuff any more so I'm afraid I simply can't be bothered looking it up.

Ha ha. Fair enough

[CJ]

And in reply to the suggestion that the Audax and/or Touring bike is dead (sorry, but I don't visit here often nowadays), I would say that it's more like the roadies have come around to our way of thinking! For now they are adopting bicycles they call road bikes or gravel bikes that have tyres of similar breadth to that which we always held to be optimum for audax or touring respectively! And since UCI were dragged kicking and screaming into acceptance of disc brakes, these road and gravel bikes do not have any reason to skimp on tyre/frame clearance. Yes, there is often room to fit a proper mudguard!

The one area (apart from gears, still stupidly high on all off-the-shelf bikes) where the roadie still has to learn some common sense is front centres. There is no good reason for this dimension to be so short as it remains on a modern road bike, to the detriment of basic road safety. A bicycle already has a worse braking performance than almost every other vehicle on the road, not because its brakes are bad (nowadays they aren't) but because its centre of gravity is high in relation to its wheelbase, so it tips over forward before it slides. The roadie's obsession with a short wheelbase thereby runs counter to basic road safety. A modest lengthening of the front would do no harm and some good to the all-round performance of the bicycle. It would still tip over before sliding, but at a quicker rate of deceleration. If the UCI are really interested in safety they should legislate on that. A simple rule that the tyre miss the rider's toe by at least 1cm would make bikes that can be raced faster in safety and that Joe Public can fit a mudguard onto without kicking it to bits - or worse!