Changing from 1st to 12th

General cycling advice ( NOT technical ! )
drossall
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Re: Changing from 1st to 12th

Postby drossall » 28 Jan 2019, 8:22pm

With down-tube shifters, you could move both levers with one hand :evil:

Brucey
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Re: Changing from 1st to 12th

Postby Brucey » 28 Jan 2019, 8:54pm

AndyK wrote:
ndwgolf wrote:
Airsporter1st wrote:Presumably, the electronic shifters are/could be programmed to take care of this, shifting both front and rears practically simultaneously. If not, why not?

I would be interested to find out some more about that?
Neil

Shimano's Di2 offers this ("Synchronized Shift" mode). You can even customise its shifting choices if you want. I can't say I've tried it.


one comment from those who have tried it is that the combined (double) shift takes about x3 as long as a normal rear shift and you may not necessarily know it is coming. It is still a good idea to back off during the shift, so if you don't keep track of things you may find yourself pausing for long enough for a rear shift but not a double shift. I confess this would drive me absolutely crackers.

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

Mike_Ayling
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Re: Changing from 1st to 12th

Postby Mike_Ayling » 28 Jan 2019, 9:12pm

A Rohloff is so much easier!

Mike

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Tigerbiten
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Re: Changing from 1st to 12th

Postby Tigerbiten » 28 Jan 2019, 10:00pm

ndwgolf wrote:Something got me thinking today so I will ask the crowd. When going up hill while changing gears from say 8 to 1 but once you get to 1 you now need to drop the front ring to the smaller ring........ how do you go about that because you will then be going to the very easiest gear instead of the next gear if you know what I mean??

Neil.

You need to work out where each of your gears are in relation to all the others.

My gear setup is twin chainrings on a Schlumpf HSD and a Rohloff IHG.
Now the Rohloff is really a 7 speed hub with an internal 2.45 step down gear to give me 14 gears.
Now the Schlumpf HSD is an external 2.5 times step up gear to give me 21 unique gears out of 28 total.
There's no point of using the 7 duplicate gears which use the step up-step down combination due to the extra drag.
The step between each Rohloff gear is 1.136 times, so 3 gears is 1.136 cubed or 1.466 times.
So a 38t chainring times 1.466 equals a 55.7t chainring.
I cannot run a 56t chainring due to interference with the chain guard so I run a 55 for an extra 3 gears or 24 unique gears out of 56.
My normal shifting pattern if I'm going through every unique gear is +14 hub -> Up chainring with -3 hub -> +3 hub -> Up HSD and Down chainring with -4 hub -> +4 hub -> Up chainring with -3 hub -> +3 hub.
So I find that the best pattern which uses 2 double shifts and a triple shift .
That's an extreme case but once you remember and get used to your shifting pattern it's easy ........ :D

Brucey
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Re: Changing from 1st to 12th

Postby Brucey » 28 Jan 2019, 10:54pm

IIRC the standard gear ratios on your bike use a 50,34 chainset and a shimano 11s 11-28 cassette. You can see these ratios depicted here


http://ritzelrechner.de/?GR=DERS&KB=34,50&RZ=11,12,13,14,15,17,19,21,23,25,28&UF=2135&TF=90&SL=2.4&UN=MPH&DV=teeth

the greyed out ratios use a chain angle more than 2.4 degrees so are to be avoided, but you can set this control to different values if you want.

You will notice that 34/13, 34/14, 34/15 are all near-duplicate ratios and since these are less efficient/faster wearing than the similar ratios on the big ring, you should avoid using those too.

All these 'avoid' ratios are ones that you can still use, but it is a bad idea to habitually use them; thus I'd (say) use them for a short while (eg on a piece of false flat) if it avoided more double-shifts, but probably not otherwise.

Anyway, weed out the 'avoid' ratios and you have (from a nominal 22 ratios) fifteen ratios remaining which make sense to use. Gear intervals vary from 7% to 13%, which is typical for a set of dedangler ratios.

You can see the ratios that ideally ought to be used in the 39" to 78" gear range in isolation here;

http://ritzelrechner.de/?GR=DERS&KB=34,50&RZ=17,19,21,23,17&UF=2135&TF=90&SL=2.8&UN=MPH&DV=teeth

Above I have removed all the 'avoid' ratios (as well as all the very high and very low ratios) from the calculator which makes it more obvious what you should ideally be doing with the midrange ratios.

You could do the doubleshift at almost any time (using the 'avoid' ratios) but this gearset arguably works best if you doubleshift from 50/23 or 50/21 into 34/17 when facing increasing gradient. Go from 50/23 to 34/17 if you think you are not going to lose much speed during the shift and go from 50/21 to 34/17 if you think you are going to lose an appreciable amount of speed during the shift. The 50-21 to 34/17 shift is going to be a bit easier and a bit faster than lots of other double-shifts, because it only requires two shifts at the back, whereas most of the other doubleshifts require three shifts at the back.

As the gradient eases, you will need to make a doubleshift the other way; normally this is less urgent because in the face of an easing gradient one tends to lose speed during a shift somewhat less.

hth

cheers
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The utility cyclist
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Re: Changing from 1st to 12th

Postby The utility cyclist » 28 Jan 2019, 11:10pm

There's a stretch of road near the end of my ride were I can give it the beans down the short downhill so will be on 50/13 then I'll ease into the slope and soft pedal a stroke or two down to 24/21 bypassing the middle ring and take it easy spinning at 10mph so I can hit the steep camber with a couple of lower gears in hand if I'm feeling particularly tired.
Having STIs helps so you're not having to take your hands off the controls when you're fatigued, but getting the timing of the transition, effort and judging changing terrain is important to make it smoother and smoother means fewer mechanicals.

Just keep practising and see what works best for you.

AndyK
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Re: Changing from 1st to 12th

Postby AndyK » 28 Jan 2019, 11:28pm

Brucey wrote:
AndyK wrote:
ndwgolf wrote:I would be interested to find out some more about that?
Neil

Shimano's Di2 offers this ("Synchronized Shift" mode). You can even customise its shifting choices if you want. I can't say I've tried it.


one comment from those who have tried it is that the combined (double) shift takes about x3 as long as a normal rear shift and you may not necessarily know it is coming. It is still a good idea to back off during the shift, so if you don't keep track of things you may find yourself pausing for long enough for a rear shift but not a double shift. I confess this would drive me absolutely crackers.

cheers

Yeah, I must admit I would hate the idea of the groupset deciding when it's going to faff around with the front shifter. That's one decision I want to make for myself. Better to go for a 1x12 setup and avoid the problem altogether. [ducks quickly to avoid incoming flak :wink: ]

thelawnet
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Re: Changing from 1st to 12th

Postby thelawnet » 28 Jan 2019, 11:33pm

ndwgolf wrote:Something got me thinking today so I will ask the crowd. When going up hill while changing gears from say 8 to 1 but once you get to 1 you now need to drop the front ring to the smaller ring........ how do you go about that because you will then be going to the very easiest gear instead of the next gear if you know what I mean??

.

You need to consider gear ratios.

If you have a 52/36 with a 11-34 11 speed cassette, the cogs are

11-13-15-17-19-21-23-25-27-30-34

The first thing to look at is the gap between cogs.

The 52/11 is a sort of downhill ratio. From 11 to 13 is a 15% drop in speed/difficulty. Around the middle of the range 21 to 23 is only 9%. 27 to 30 is 10%, and 30 to 34 is 12%.

So there isn't a 'bail-out' gear per se, in that the 30-34 jump is not as significant as it sounds, it's similar in effect to changes up the cassette

However most probably you will want to avoid the big/big combination as it's cross-chained, and not very efficient.

So you would probably have changed before that.

As far as the effect of changing from big to small ring goes, 52 to 36 is a 31% change, which is about the same as 3 changes on your cassette.

In other words your cassette and chain rings result in around 14 effective gears to choose from.

If we rule out big/big and little/little, there are 10 gears in the big ring and 10 in the little ring, but with similar ratios between the big chain ring and larger cogs, and the small chain ring and smaller cogs.

If we take the hardest gear on the small chain ring as 36/13, that's almost the same as 52/19.

And then the easiest gear on the big chain ring being 52/30, which is almost the same as 36/21

So this makes your actual usable gears :

52/11
52/13
52/15
52/17
52/19 or 36/13
... (Overlapping gears from big and small rings)
52/30 or 36/21
36/23
36/25
36/27
36/30
36/34

Hence there are 10 usable gears in each chain ring, with 4 fast gears only available in the big ring, 5 slow gears only available in the small ring, and then gears 7-2 in the big ring overlapping with gears 10-6 in the small ring.

In terms of when to change down, it should be before you are in the biggest cog at the back, because as noted that combination is not a great one to use. Also if you see that the easiest five gears require you to be in the smallest chain ring, then when you are going to need those gears then it makes sense to get into the smaller ring a bit earlier.

As far as your bikes goes, with Di2 there are three options, which are:
Synchro shift which automatically changes the chain ring down when you try to shift to one of the larger cogs, and instead of changing to a larger cog, actually changes to a smaller one, since, as mentioned, a downshift on the chain ring is worth three on the cogs.
Semi synchro shift which moves to a bigger/smaller cog in the cassette automatically when the front shifter is changed up/down, but doesn't move the front derailleur when only the rear shifter is used
Manual which only does 'auto trim' (aligning the front derailleur with the chain line)

If you are currently in manual mode, it's quite easy to change to semi synchro, and this will then solve your issue of maintaining cadence , as a change down at the front will come with an automatic change up or two at the back.

If you go full synchro, then this is programmable so you can adjust when to make the change, so for example in the big ring you could use cogs 11-27 and in the small ring, 17-34.

In that case if you were in 36/17, and shifted up, then it would shift to 52/19 (1 downshift on the cassette). And if you were in 52/27 and shifted down, then it would shift to 36/23 (2 upshifts on the cassette)

I would probably see which you prefer between semi synchro and full synchro

thelawnet
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Re: Changing from 1st to 12th

Postby thelawnet » 29 Jan 2019, 12:07am

Brucey wrote:IIRC the standard gear ratios on your bike use a 50,34 chainset and a shimano 11s 11-28 cassette. You can see these ratios depicted here


http://ritzelrechner.de/?GR=DERS&KB=34,50&RZ=11,12,13,14,15,17,19,21,23,25,28&UF=2135&TF=90&SL=2.4&UN=MPH&DV=teeth

the greyed out ratios use a chain angle more than 2.4 degrees so are to be avoided, but you can set this control to different values if you want.


I think the OP has changed them to 11-34 and 52/36, but I could be wrong.

In terms of the max angle, with 2.2° you can't use the hardest/easiest gear at all, which is silly, with 2.3°, two cogs are 'cross-chained', and at 2.5° only one cog is deemed cross-chained. At 3° all combinations are allowed.

The various 1x setups generally require chain angle tolerances of 2.6°, e.g., S-Works Diverge (40x11-40), SRAM 44x10-42, SRAM 32x10-50, Shimano XTR 10-51, etc.

So while the big/big and small/small are quite definitely to be avoided, using the second-biggest and the second-smallest is not such an issue considering that a lot of bikes are being sold with unavoidable bigger chain angles.

(obviously a triple can give better chain angles in highest & lowest gear than a double, which is better in turn than a single)

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Cugel
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Re: Changing from 1st to 12th

Postby Cugel » 29 Jan 2019, 9:08am

drossall wrote:I think about it as the front gear giving ranges. They necessarily overlap. If I know I'm hitting a hard hill and I'm going to want the low range, I may as well get there as soon as possible. In general, the thing to avoid is difficult changes when you're already struggling - partly because it's just harder, and partly because you'll have the gears under load in your effort to get up the hill, and gears change better if you can slacken off the pressure just slightly as they change.


This is the best approach. I think of the chain rings as providers of two or three sets of overlapping ratios: low; medium;high. One selects the range in anticipation of the coming terrain, not when halfway through the terrain - where this is possible.

It does help to know the route, of course. But even if one doesn't, it can often be seen that the road in front is going to be up-hilly, undulating or down-hilly; or that the wind is in-the-face or behind.

In practice I find that the only time I can't pre-select the right chain ring for the coming terrain is when the undulations are short bit severe; or there is some other rapid and frequent change of conditions that require a move between the two or three gear ranges via a front change. But this generally requires a quick chain ring change when on a section that doesn't require my pedal stomping at that moment, followed by a couple of sprocket changes to the right gear: no-load, changes, as you suggest.

Cugel

Nigel
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Re: Changing from 1st to 12th

Postby Nigel » 29 Jan 2019, 11:36am

Cugel wrote:
drossall wrote:I think about it as the front gear giving ranges. They necessarily overlap. If I know I'm hitting a hard hill and I'm going to want the low range, I may as well get there as soon as possible. In general, the thing to avoid is difficult changes when you're already struggling - partly because it's just harder, and partly because you'll have the gears under load in your effort to get up the hill, and gears change better if you can slacken off the pressure just slightly as they change.


This is the best approach. I think of the chain rings as providers of two or three sets of overlapping ratios: low; medium;high. One selects the range in anticipation of the coming terrain, not when halfway through the terrain - where this is possible.



I think that's it - think a little ahead and get the front ring sorted before hitting the wall. Otherwise one has to perfect a double-shift, under load, which is somewhat challenging and likely to loose a lot of forward inertia.


One thing I've suggested to a new-ish rider on a double front is "outer ring for downhill or tail-wind on flat, inner ring for uphill or head-wind on flat". I've translated that to their bike speedometer: below 16kph inner ring, above 22kph outer ring. Between 16 and 22kph it doesn't matter unless a change in speed can be anticipated ahead. ( Or 10mph and 13mph for those thinking in miles. And the bike in question has significantly smaller front rings than typical off the shelf bikes with "compact doubles", so my speeds may need adjusting for different gearing. ).

A triple is similar: "middle ring = normal road with slight ups and downs, small ring = proper hill or very serious headwind, large ring = down or big tailwind".

ndwgolf
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Re: Changing from 1st to 12th

Postby ndwgolf » 29 Jan 2019, 11:57am

Okay update. I have now figured out how to set up my Di2 shifters so that when I go from large to small ring and vise versa it will automatically drop or add 3 cassette gears. Tomorrow I’m out riding so I will give it a go and give you some feedback when I get home.
Neil

Brucey
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Re: Changing from 1st to 12th

Postby Brucey » 29 Jan 2019, 12:20pm

thelawnet wrote:….The various 1x setups generally require chain angle tolerances of 2.6°, e.g., S-Works Diverge (40x11-40), SRAM 44x10-42, SRAM 32x10-50, Shimano XTR 10-51, etc.

So while the big/big and small/small are quite definitely to be avoided, using the second-biggest and the second-smallest is not such an issue considering that a lot of bikes are being sold with unavoidable bigger chain angles.....


I did mention that you can arbitratily set your limits to chainline anyhow you like. Also please note that just because some folk are daft enough to make bikes that require extreme chain angles and other folk are daft enough to buy them still doesn't make it a good idea; it is a much worse mechanical abomination than normal.

cheers
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Brucey
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Re: Changing from 1st to 12th

Postby Brucey » 29 Jan 2019, 12:24pm

ndwgolf wrote:Okay update. I have now figured out how to set up my Di2 shifters so that when I go from large to small ring and vise versa it will automatically drop or add 3 cassette gears. Tomorrow I’m out riding so I will give it a go and give you some feedback when I get home.
Neil


because the gear ratios are not evenly spaced, always adding/subtracting 3 will have a slightly different effect depending on when you choose to shift. This might be either useful or annoying depending on how well you keep track of which gear you are in.

cheers
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thelawnet
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Re: Changing from 1st to 12th

Postby thelawnet » 29 Jan 2019, 1:32pm

Brucey wrote:
thelawnet wrote:….The various 1x setups generally require chain angle tolerances of 2.6°, e.g., S-Works Diverge (40x11-40), SRAM 44x10-42, SRAM 32x10-50, Shimano XTR 10-51, etc.

So while the big/big and small/small are quite definitely to be avoided, using the second-biggest and the second-smallest is not such an issue considering that a lot of bikes are being sold with unavoidable bigger chain angles.....


I did mention that you can arbitratily set your limits to chainline anyhow you like. Also please note that just because some folk are daft enough to make bikes that require extreme chain angles and other folk are daft enough to buy them still doesn't make it a good idea; it is a much worse mechanical abomination than normal.


Well yes of course you can set any chainline angle you wish, I was really observing that the second cog (second relative to the chosen front chain ring) is only mildly cross-chained.