Cross Chaining - good or bad.

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fredN4
Posts: 60
Joined: 14 Oct 2012, 8:21pm
Location: 30200 France

Re: Cross Chaining - good or bad.

Postby fredN4 » 23 Jul 2020, 7:23pm

pwa wrote:
fredN4 wrote:
Brucey wrote:
avoiding chain rub on the FD is the least of your worries when cross-chaining

cheers

gotta say I've been cross chaining for donkeys on double FDs, Campag mostly, and Shimano. Cant say I am down the shop every year or so having to buy new parts, if ever.

It is supposed to reduce your efficiency though. More of your effort goes into overcoming friction in the drivetrain and less makes it through to actually pushing you forward. So it is still best avoided if you can.

most of my effort goes into climbing, by which time I "might" not be cross chaining.

scottg
Posts: 843
Joined: 10 Jan 2008, 8:44pm
Location: Highland Heights Kentucky,, USA

Re: Cross Chaining - good or bad.

Postby scottg » 23 Jul 2020, 7:33pm

Cross chaining is very bad....
Trivelox coming soon to a bike shop near you.
I like the early picture of Brucey in the advert.

Im19360624Cy-Tri.jpg
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Deutsche Luftschiffahrts-AG
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Brucey
Posts: 41373
Joined: 4 Jan 2012, 6:25pm

Re: Cross Chaining - good or bad.

Postby Brucey » 23 Jul 2020, 8:33pm

this graph shows the measured efficiency of various gear combinations in the absence of chain misalignment, for 53-39 chainrings and 11-28 11s cassette. The middle sprocket (#6) in this cassette is 17T.

Image

I.e. the chainwheel was deliberately perfectly aligned with the relevant sprocket for each test. These losses are primarily 'chordal' losses, i.e. they vary with the size (number of teeth) of the chainwheel and sprocket. You can see that for any given gear ratio you are better off by 1-1.5W using the bigger chainring and the relevant sprocket, whenever this is possible. It is expected that with a 'compact double' the difference seen would be greater.

However once you factor in the chain line seen in the actual setup on a bike the data looks different (apologies for the small scale of the image, it was the only one I could find on the internet, but you can still see what is going on)

Image

This graph shows the original data together with two 'V' shaped plots with data obtained with the cross-chaining set as it would be found on the bike. You can see that the cross-chaining losses add to the chordal losses so that you can be up to 2W worse off in any one gear combination. In fact the cross-chaining losses are a much stronger effect than the difference between the chordal losses in the data seen, such that you are better off with a better aligned small chainring-small sprocket combination than a larger chainwheel-sprocket combination that is badly aligned.

The takeaway from this is that if you want the best efficiency in this setup, you should choose sprocket-chainring combinations such that

a) the smallest sprocket you should ever use on the small chainring is 17T; any smaller than that and there is a better gear ratio (of similar size in gear inches) using the large chainring. This allows you the six largest sprockets and forbids the smallest five.
b) the largest sprocket you should use on the big ring is 21T. This allows you the smallest eight sprockets and forbids the largest three.

So if you were to choose on the basis of chainline alone, you might forbid four of the sprockets leaving you with seven permissible ones per chainring, but with these measurements the data suggests that you would be better off using one extra gear on the big ring than that.

Image

If cross-chaining were really 'harmless' then you would expect chordal losses to dominate such that (say) you would always be better off on the big ring, regardless of chainline: it just ain't so.

Note that the worst chainline permitted in this 2x11 setup is not as bad as the chainline encountered in a 1x11 or 1x12 setup. Also note that if you wanted to make the least efficient transmission possible in the higher gear ratios, you would choose a small chainring, small sprocket (eg a 10T), and a bad chainline. This is exactly what you get with a 1x setup..... :roll: To rub salt into the wounds the smaller chainring/sprocket combinations always wear faster, especially if you are dishing out a fair amount of power. If you routinely cross-chain the usual result is that the chain wears a lot faster than normal; often the shift quality goes down the pan because the chain becomes so worn and laterally flexible it can no longer be pushed around by the RD.

SRAM can bleat all they want about cross-chaining 'being harmless' but it just ain't so.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Jdsk
Posts: 3804
Joined: 5 Mar 2019, 5:42pm

Re: Cross Chaining - good or bad.

Postby Jdsk » 23 Jul 2020, 9:15pm

scottg wrote:Cross chaining is very bad....
Trivelox coming soon to a bike shop near you.

How it worked (the sprockets moved):
http://trivelox.cambrianmoons.com

Jonathan

irc
Posts: 4804
Joined: 3 Dec 2008, 2:22pm
Location: glasgow

Re: Cross Chaining - good or bad.

Postby irc » 23 Jul 2020, 10:37pm

Though cross chain from a 1x system isn't as extreme as big big on a triple. In any case on a 1x system that is in the right gear range most time will be spent in the middle than the cogs either end.

I think 1x9 for example is a decent setup for a city commuter. Enough gear range. Lighter. Simpler. Though the more extreme 11-42 etc must start losing some of the advantage. If I was building a bike for touring where I want a really low gear and a moderately high gear a triple still wins. I tend to use my tourer as a 1x7 on the flatter sections. Only going onto the bike or small chainrings for proper hills.

pwa
Posts: 13251
Joined: 2 Oct 2011, 8:55pm

Re: Cross Chaining - good or bad.

Postby pwa » 24 Jul 2020, 8:12am

fredN4 wrote:
pwa wrote:
fredN4 wrote:gotta say I've been cross chaining for donkeys on double FDs, Campag mostly, and Shimano. Cant say I am down the shop every year or so having to buy new parts, if ever.

It is supposed to reduce your efficiency though. More of your effort goes into overcoming friction in the drivetrain and less makes it through to actually pushing you forward. So it is still best avoided if you can.

most of my effort goes into climbing, by which time I "might" not be cross chaining.

There was an interesting little trial of drivetrains a while back (sorry, I can't remember who did it) and it compared different systems. 1x11 turned out to have an efficiency level similar to Rohloff internal gear hubs, so lower than a normal well maintained multi chainring derailleur system. But without the low maintenance benefits of Rohloff. I imagine that poor result was down to the extreme angles of the chain in some gears. So while you may not be doing too much harm to your components by cross chaining, you are probably wasting some of your effort.

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Sweep
Posts: 6703
Joined: 20 Oct 2011, 4:57pm
Location: London

Re: Cross Chaining - good or bad.

Postby Sweep » 24 Jul 2020, 8:41am

I like sram chains but it's depressing that they appear to have let the marketeers take over from the engineers and product quality teams.
Just wonder what they are going to try to tell us next?
Sweep

bgnukem
Posts: 508
Joined: 20 Dec 2010, 5:21pm

Re: Cross Chaining - good or bad.

Postby bgnukem » 24 Jul 2020, 12:54pm

25 years ago when I bought my Dawes I remember thinking that Shimano's then-new 'compact drive' MTB transmissions were just a way of ensuring parts wore out faster, but the 1x transmissions are shocking.

Once the chain wears most cyclists will probably not replace it quickly enough (i.e. at ~0.5% wear) and it will then destroy the chainring and cassette, so quite probably the life of the transmission will be determined by the life of a single chain, as replacement with a new chain will not be possible on the worn 'ring and cassette sprockets.

Lousy efficiency too. It's just a pointless 'innovation' driven by the need to market 'new' things to clueless, brainwashed fashion victims.

Unfortunately, compact doubles seem to be the only other game in town for most road-biased bikes at the moment.

Brucey
Posts: 41373
Joined: 4 Jan 2012, 6:25pm

Re: Cross Chaining - good or bad.

Postby Brucey » 24 Jul 2020, 2:46pm

my sliver of hope which I am clinging to is that it will be possible to take modern parts and modify/use them make an acceptable -or even better- transmission.

Glimmers of hope include that by using clever materials you can make a narrow chain that lasts reasonably well, even if you have to pay for it.

I don't mind big sprockets too much; they can be made fairly lightweight and -for any given gear ratio- allow you to use a larger chainring which means better efficiency and lower wear. In this respect the low gear chainring/sprocket sizes in a lot of 1x systems are acceptable. Once that chainring becomes one of a pair (or even three) and is offset so the chainline is tolerable, it almost makes sense on the low geared side of the cassette.

What doesn't make so much sense, whichever way you cut it, are the tiny sprockets on the other end of the cassette. They are always a source of inefficiency and high wear rate. BITD I was pretty happy with 52/14 as a top gear and I've never strayed beyond 50/13 on my touring bike. So whilst I've had bikes with 12T and 11T sprockets fitted, I've never been happy actually using them; they don't even run smoothly even when everything is brand new; they would be the first part to be ditched simply because they are not very useful; all they do is increase wheel dish for no real gain.

So one idea is that it may be possible to shorten a wide range 10s or 11s cassette to 8 or 9 sprockets, simply by deleting the smallest ones, leaving you with a cassette that starts with a 14 or 15T sprocket on a shortened freehub body. Then run a 39-53 or 42-52 chainset, or maybe a triple of some kind. As it happens 8s or 9s shifters pull an amount of cable which is comparable to 11s shifters, so it may be possible to make rear indexing work with a simple mod (or a shiftmate) using a shortened 11s cassette , 11s RD, and 8 or 9s shifters. The wheel would have much reduced dish, better chainlines, and all the gears you might ever need.

a couple of schemes using this approach are depicted here

http://ritzelrechner.de/?GR=DERS&KB=39,53&RZ=15,17,19,21,24,28,32,37,42&UF=2185&TF=90&SL=2&UN=MPH&DV=gearInches&GR2=DERS&KB2=36,52,42&RZ2=15,17,19,21,24,28,32,37,42&UF2=2185

In both cases you can have a hard-wearing 'tapping along' gear on the big ring with high efficiency and a perfect chainline; the doubleshift onto smaller chainring(s) is not large and can be carried out 'in anticipation' of a steeper climb whilst the gradient is still moderate, and even with a 110BCD you can get fairly low gears if needs be.

The maths says that such an arrangement is likely to be at least 1W more efficient most of the time vs a 'modern' setup, because there are gains in both chordal efficiency and reduced cross-chaining losses. The maths also says that this gain results in net higher speed even if you are carrying 0.5kg extra up a 10% gradient, leave alone the rest of the time. Also NB I doubt the increased weight will amount to that, not least because the rear wheel can be built lighter than normal, being less heavily dished.

So this -to my mind- is a better 'way ahead' than the ever-increasing width/dishing in rear hubs, with more and more sprockets of ever-decreasing sizes. Importantly it is pretty much within the grasp of anyone who is prepared to think outside the confines of the available parts (that are being forced down our throats) and do a little modification/adaptation.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

bgnukem
Posts: 508
Joined: 20 Dec 2010, 5:21pm

Re: Cross Chaining - good or bad.

Postby bgnukem » 24 Jul 2020, 4:57pm

Brucey wrote:my sliver of hope which I am clinging to is that it will be possible to take modern parts and modify/use them make an acceptable -or even better- transmission.


What doesn't make so much sense, whichever way you cut it, are the tiny sprockets on the other end of the cassette. They are always a source of inefficiency and high wear rate. BITD I was pretty happy with 52/14 as a top gear and I've never strayed beyond 50/13 on my touring bike. So whilst I've had bikes with 12T and 11T sprockets fitted, I've never been happy actually using them; they don't even run smoothly even when everything is brand new; they would be the first part to be ditched simply because they are not very useful; all they do is increase wheel dish for no real gain.

So one idea is that it may be possible to shorten a wide range 10s or 11s cassette to 8 or 9 sprockets, simply by deleting the smallest ones, leaving you with a cassette that starts with a 14 or 15T sprocket on a shortened freehub body. Then run a 39-53 or 42-52 chainset, or maybe a triple of some kind. As it happens 8s or 9s shifters pull an amount of cable which is comparable to 11s shifters, so it may be possible to make rear indexing work with a simple mod (or a shiftmate) using a shortened 11s cassette , 11s RD, and 8 or 9s shifters. The wheel would have much reduced dish, better chainlines, and all the gears you might ever need.

cheers


My approach recently has been to stockpile decent used 7/8/9-speed Shimano MTB triple mechs, Rapidfire pod shifters, rear hubs and Spa Cycles chainsets with a view to running 7/8-speed indexed shifting for the next 20+ years or so. I'm sure some other un-anticipated part/s will then disappear and I'll have wasted my time....

I've often had hire bikes in Majorca or wherever where I'd wanted to ditch the top 3 sprockets from the cassette and move the whole thing over on the freehub body for better chainline and no pointlessly-high gears! Currently I only use 7 sprockets on the rear of my bikes although they are either 8- or 9-speed transmissions, spaced out as close to the dropout as possible, with short (103 or 107mm) BB axles and triple chainsets to give a decent chainline on 3-4 usable sprockets with each chainring.

Like the idea of bigger cassettes but the largest lockring/serrated top sprocket combo I've found for the Shimano cassettes I've had over the years has been 13T. Have recently stockpiled some 13-28 7S cassettes but even 13-up cassettes are getting pretty thin on the ground so if there's a way to bodge a suitable lockring, truncated 9+ speed cassettes as you suggest would be of interest in future I think,,,,

reohn2
Posts: 40129
Joined: 26 Jun 2009, 8:21pm

Re: Cross Chaining - good or bad.

Postby reohn2 » 24 Jul 2020, 6:16pm

Cross chaining is only bad if you want to preserve drivetrain life,and care about energy loss.

I'm in lurv with triples because I'm a nerd about gears,I'm old,decrepit,and riddled with osteo arthritis,and anything I can't pedal over 25mph is useless to me.I've played with Alpine doubles for quite a while now and found them lacking,and so came back home to triples.

Here's the deal for a a perfect drivetrain for the average touring human with little crosschaining than absolutely necessary,
13,15,17,19,21,24,28,32 9sp cassette.Or 10sp 13,15,17,19,21,23,26,30,34 cassette,with a 22/32/44t or 24/34,46t chainset.
These combinations give the average to fit human rider enough high and low end for the vast majority of terrain with reasonable gaps between ratios.Should these ratios be too low a 26or28-36or 38-48or50t chainrings will offer the same wide range/close ratios with little time cross chaining than absolutely necessary.

My 2d's worth.
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Brucey
Posts: 41373
Joined: 4 Jan 2012, 6:25pm

Re: Cross Chaining - good or bad.

Postby Brucey » 24 Jul 2020, 6:27pm

that is a pragmatic choice, bearing in mind that 13T smallest sprockets can be readily achieved/obtained. However provided larger sprockets can be fitted/used, (which isn't certain in every case I grant you) the things that make a 13-up cassette better than an 11-up cassette may apply to a 14-up or 15-up cassette too....?

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~