Touring Gear Ratios for Wimps!

[Brucey]

you seem to be forgetting that with a wide range double there are a load of cross-chained gears (small-small type) that -unlike with a triple- you are forced to use. These gears are expected to have the lowest efficiency. My original estimate of about 1% losses is unlikely to be very far away, and is likely to be comparable (at climbing speeds) to the difference between nice tyres and pretty ordinary ones.

As I mentioned previously one would expect the cross chaining losses to increase over time as the chainring teeth lose their anodising.

I don't think it really matters what size chainring and sprockets are used per se; it is swings and roundabouts here; remember that the (approximate) modus operandi is that the triple in use is basically the same as a double, but with an extra chainring in the middle. The anomalous middle ring results seen in the tests quoted have not been reproduced in other tests, BTW; they have gone more predictably with chainring size and resultant chordal losses. The bottom line is that running cross-chained costs you; with a better chainline even a gear that uses slightly smaller chainring and sprockets is preferable. If the choice is the latter gear vs one that is running small-small and is cross chained, it is a real no-brainer.

Testing of an 11s system probably gives flatteringly low cross-chaining losses, BTW, because 11s chain is typically more flexible than 9s or 8s chain. BTW I am not clear if they used a rear mech or not, but since no test equipment is perfectly rigid, so I would expect the 'slack run' of the chain to be genuinely slacker than the other chain run, even if there is no mech present. The chain is of course not at all subject to side loads in the middle of the wrap round the chainring, so lube will get moved about at this point anyway. I wouldn't worry overly whether there is or is not a mech present in these tests, since the main requirement is that the tests are comparable with one another. Stuff like chain lubrication will vary anyway, and I would not expect it to greatly alter the main thrust of the test results.

As I mentioned earlier it is currently fashionable to pooh-pooh losses that may be accrued by running bad chainlines; I think that to do this is a real mistake.

cheers

[gloomyandy]

you seem to be forgetting that with a wide range double there are a load of cross-chained gears (small-small type) that -unlike with a triple- you are forced to use. These gears are expected to have the lowest efficiency.

Who says you have to use small/small? With the wide range double I use (42/26 chainring and 11-36 cassette), there is a pretty large overlap of gears in the mid-range. So I will basically stay in the "big" ring happily cross-chaining because my understanding is that the higher efficiency of the larger sprockets will exceed the losses due to cross chaining. If I decide that I really need lower gears then I will shift to the small ring and use the larger sprockets on the cassette (from around 40" down). I will very rarely use the smaller 4 sprockets with the small ring, but unlike with many triples if I decide that I want to, for say a short downhill, then I can use them without the chain catching on the mech or other chainrings.

Now many triple users will be muttering about big jumps from one gear to the next, which for some may be an issue, but it isn't for me. I

As I mentioned earlier it is currently fashionable to pooh-pooh losses that may be accrued by running bad chainlines; I think that to do this is a real mistake.

cheers

Yes you did and I accept that that is your opinion. But I'll just leave you with one further set of actual experimental data...
http://www.ihpva.org/HParchive/PDF/hp50-2000.pdf
and the conclusion that they draw from it...

"First, comparing the results here
with those in the long-duration tests,
the effect of chain offset can be estimated.
These data were obtained with
the 52–11 and 52–21 configurations in
the offset condition while those in the
long-duration tests were taken with no
offset. Comparing the data for 60 RPM
100 W tests shows that the offset lowers
the efficiency by, at most, 0.5%
when measurement precision is considered.
Additionally, if the efficiencies are
normalized by efficiencies measured in
the 52–15 configuration (both sets of
data were obtained with no offset),
then it appears that the offset has a
negligible effect on efficiency."

[Brucey]

I agree that if you have enough overlap between gear ranges on different chainrings you can largely avoid running the least efficient (small-small) gear combinations. But IME such setups use small-ish chainrings, small-ish sprockets, and fair sized gaps in cassette to get the overall range. When you use smaller chainrings and sprockets you are paying an efficiency penalty all the time; between cross-chaining losses and chordal losses, I'd expect such a transmission to be about 1% or so less efficient most of the time vs one with larger chainrings and sprockets, better aligned. I'd also expect it to be somewhat less durable, too.

Spicer's paper is interesting but I don't think that the results contained within are to be taken as in any way representative of real-world conditions. May I gently remind you that the same paper suggested that the efficiency of the chain drive was not markedly impaired by running the chain with no lubricant present at all? Also they could not tell a significant difference between chain lubricants in terms of losses. These results are not in any way 'normal' and have been flatly contradicted in more recent tests. This suggests that there was something odd about the test conditions. They don't go into details but I think they used a chain with a (PTFE?) coating on it (other parts too I suspect) and either didn't notice or didn't emphasise this point.

As per previous comments some short duration tests in the lab with a perfectly clean chain will not wear the anodising off the chainring teeth ( and BTW IIRC at that time some Dura-Ace chainrings/sprockets were electroless-Ni plated instead; another coating that doesn't last but offers a friction reduction whilst it is there....) and probably won't (quickly) wear the coating off the chain either. IMHO it is 'extremely unlikely' that the losses they measured reflect those that would be incurred in longer term real-world service.

There are also concerns about the use of continuous drive vs real pedalling conditions. Between smaller chainrings than they used, and real pedalling, I'd expect chain tensions that are about x2.5 higher in (say) your preferred setup @ ~200W power on the 42T chainring and about x4 or x5 higher when you are on the small chainring; this is liable to be a much more destructive condition for the transmission to withstand. Throw in a little dirt and there is unlikely to be the slightest resemblance between the real world and those test conditions.

I think that if you were to draw a useful conclusion from Spicer's paper (which is very relevant to racers that fit a load of new parts before a big race, BTW), it would be that if you use a Dura-Ace transmission (including the chain, especially), it may be reasonably efficient at first, even if you can't be bothered to lubricate the chain properly. However IME this behaviour is unlikely to persist more than a few hundred miles of real-world use, sadly. Most folk buy chains that don't have such a coating on them and don't ever see conditions that are like this.

cheers

[Brucey]

BTW to put my remarks into context, in the past I have put a fair degree of effort into making transmissions as efficient as possible on some racing machines; if you lose a TT by less than 1% then it is exactly the sort of thing that might make a difference. Also when setting up a bike (any bike) from scratch, all else being equal, why choose an inefficient, short lived transmission when there are other possibilities?

However I have equally well chosen a less efficient transmission, with gear ratios that are not ideal if it offers me some other advantage, like robustness, durability, ease of use, or low maintenance, which could be a priority for some purposes. Pragmatism in various forms also can influence your choice, for example if you confine yourself to cassettes that are 'off the shelf' then you might accept a setup that isn't ideal, just to have an easy route to getting the correct parts.

For my own touring bike I have happily used a 3x7 setup for many years that gives me no more than 11 distinct gear ratios, and one of those is arguably 'a bonus ratio' that I might use when running downhill only, not often. I expect I shall need lower gears as time goes on and I might go to a 3x8 or 3x9 system with more, larger sprockets to give me that. The reason I like the setup I have at present is that the gear intervals are fairly uniform ( most shifts don't give a shift that varies more than ~3% from other shifts), the chainlines are good in the most used ratios, and the shifting itself is very simple and easy; there is only one double-shift and that is not too big. [There is in fact intentionally a lot of ratio duplication, which means that I get the best efficiency and a simple shifting pattern; this allows me to best maintain rhythm as easily as possible.]

There is more than one way to skin a cat....

cheers

[pwa]

I must confess that I rarely know what gear I am in, and don't have a set path from highest to lowest. Very often I will plump for a front shift or a rear shift according to whether I want a step or a step and a half. Or at the bottom of a steep climb I might drop to the smallest of the three rings so I won't have to think about that later on in the climb.

The one bit of discipline I exercise is that I avoid extreme chainlines. I glance down occasionally to make sure I'm not about to do a naughty chanline. But each of the three rings seems to work fine on at least four or five sprockets, so it is not something that is on my mind a lot. And frankly, I'd sooner sacrifice 1% of efficiency than have to be thinking about that all the time. I'm not racing.

[Brucey]

it is easy enough to glance at the transmission itself but one point about conventional gear levers (eg DT ones, or Kelly's etc ) is that no matter how absent minded you are, you immediately know what kind of gear you are in by just glancing at the levers or feeling with you hand.

Many other shifting systems don't tell you that, and my experience of road STIs with gear indicators is that they are the first things to get broken...

cheers

[pwa]

it is easy enough to glance at the transmission itself but one point about conventional gear levers (eg DT ones, or Kelly's etc ) is that no matter how absent minded you are, you immediately know what kind of gear you are in by just glancing at the levers or feeling with you hand.

Many other shifting systems don't tell you that, and my experience of road STIs with gear indicators is that they are the first things to get broken...

cheers

It hadn't occurred to me but yes, you are right, STI levers do disconnect you from where your mechs are on the sprockets or rings. Down tube / bar end / Kelly levers are like the hands on a clock, constantly telling you things.

[gloomyandy]

Well I think we are going to have to agree to disagree on this. What I will say is that having ridden many thousands of miles with triples (of various configurations) and now thousands with my 2x10 setup I much prefer the 2x10. In my experience of these systems I haven't seen much difference in wear rates (and I do track these pretty closely) and my conclusion is that people fret far too much about cross-chaining and the impact it may have. My 2x10 system uses SRAM components and they have been a strong proponent of using all of the gears in a system so perhaps that makes a difference. I find it interesting that CJ seems to have adopted a very similar setup on various bikes so perhaps there might be something in it.

Enjoy your triples!

[Brucey]

like I said before there is more than one way of skinning a cat...

- and there is more than one cat to be skinned, too.

Efficiency is not the only priority and anyway will vary net with the duty cycle. For example I've toured in places where you really need just two gears, mainly, because you are riding on the flat or you are climbing, and the roads are engineered so that the climbs pretty much all have the same gradient. If these correspond with nice efficient gears then the rest of it doesn't really matter...

cheers

[pwa]

My missus and I cycle together sometimes. I have my bar-end lever operated 3 x 9 and she has an STI operated "Alpine double" that I concocted for her. We both manage very nicely, though she has a slightly higher bottom gear that is not ideal when carrying panniers. Neither of us is in a hurry to change our set-up.

[meic]

For example I've toured in places where you really need just two gears, mainly, because you are riding on the flat or you are climbing, and the roads are engineered so that the climbs pretty much all have the same gradient. If these correspond with nice efficient gears then the rest of it doesn't really matter... :wink

Have they abolished wind too?

[Brucey]

Have they abolished wind too?

er, the local diet would suggest otherwise...?

cheers

[bretonbikes]

I was wondering if anyone would know the answer to the following-


I want to buy a new touring bike but I am struggling to find one which I like the look of and has gearing low enough to allow me to climb hills whilst loaded up. A lot of my fellow cyclists seem to suffer the same problem so I am interested to see if there is anything I am missing. .

At the minute I tour on an old mountain bike with a triple with 44t/32t/22t chainrings and an 11t-32t 9 speed cassette. Lowest gear (22t chainring, 32t on cassette, 26" wheel) works out a little under 18". I'm looking for a disc braked drop bar bike with a similarly low gear, but I'm drawing a blank. Even with a road triple (typically 50t/39t/30t) and a wide range cassette (e.g. 11t-32t), the lowest gear (30t chainring, 32t cassette, 27"/700c wheel) works out a shade over 25", so significantly higher and there is no way I am getting up some of those hills out there.

The "obvious" solution seems to be to use a mountain bike triple, but most drop bar bikes I've seen spec'd in this way come with bar end shifters, which I'm not keen on. I'd prefer an STI-type brake/shift lever. Is it possible to use a mountain bike triple crank with a road triple STI brake/shift lever or will the indexing be forever out? All solutions gratefully received.

Personally I'd think hard about going to 26" wheels as it makes lower gearing easier. With modern slick tyres they fly along and it means that you can use a full sized chainset with say a 12-36 rear sprocket and combine lower wear with a sun 20" gear. The Ridgeback Expedition I reviewed a while back (link on here) is a prime example of how well this can work.

[BigG]

The difference between the rolling diameters of 26" wheel/tyre combinations and their 27" equivalents is almost negligible. A 26' wheel with a 559-50 tyre is only 3% smaller than a 27" wheel with a 622-28 tyre. This is equal to about 1 sprocket tooth at the bottom end of the cassette.

[Brucey]

if you use the same section tyre on a 622 rim vs a 559 rim, the latter wheel is about 10% smaller, and the gears are all 10% lower too.

There are a few combinations of road STI shifter, road triple FD and MTB chainset that have been persuaded to work, but it is a bit hit and miss TBH; the chainline is the biggest single problem. An easier solution is to use a square taper triple chainset (as per Spa cycles) which can be run at a road chainline and fitted with small-ish chainrings.

BTW if the chainrings are too small a road triple FD may clout the chainstays, so 24,36,46 is a sensible compromise. If configured as a 3x9 setup you can have a 36T biggest sprocket which gives you a gear of ~16" if you are using 32-559 tyres.

NB IIRC Surly disc trucker is available to accept 559 wheels in up to medium sizes.

cheers