Chain angle vs gears actually used?

[DaveReading]

I've spent a happy afternoon re-indexing the rear derailleur on my tourer, having had to replace the cable, so I thought I'd do the front one too.

I know that you don't use the small/small and large/large chainring/rear cog combinations, but I'm finding other combinations that cause chain rub on either side of the front derailleur. My setup is a 48/36/26 front and an 11-32 8-speed rear. There's no rub in most gears when I'm on the middle ring, nor in the 3/4 highest gears on the large ring and the 3/4 lowest gears on the small ring, so I've still got the full range available. In that case, should I simply ignore the combinations that result in too much chain angle?

That would mean riding mostly on the middle ring (I'm not particularly fast) or is that what most people do anyway?

On a related question, given that the change in gear ratios between adjacent chainwheels is obviously greater than changing up/down on the rear, is changing up on the front and down on the rear simultaneously (or vice versa) a legitimate tactic to ease the transition?

 

[Stul]

..you will find that gears "overlap".....ie on my 21 speed mountain bike I have probably only got 8 completely different ratios....ideally if you have say an 7 speed bike, you should use the large front gear for 7,6,5 on the rear ...the middle ring for 5,4,3 ..and the small front gear for 3,2 and 1.....some gear changers actually have 3 "segments" marked on them to assist this....at least I think this is the case as I am fairly new to this.....

 

[Garethgas]

What you're doing is learning about gears. The fact that you have 21 gears, as you've found out, doesn't really mean you have 21 DIFFERENT gears.
My 21 speed bike has 12 different gears which is about average.
What you actually get is a RANGE of gears where there is a considerable amount of overlap.
Stul (above) is not far off the mark in terms of keeping a good chain line, although, in practice I tend to ride up the cassette until it makes a noise.
Regarding your last paragraph, I think you're right, there's often times where I go up/down on the left shifter and down/up two or three on the right.
That just goes to show how much overlap you have in your gears.

 

[deptfordmarmoset]

Regarding your last paragraph, I think you're right, there's often times where I go up/down on the left shifter and down/up two or three on the right.
That just goes to show how much overlap you have in your gears.

That's usually more of an issue with compacts, in my experience. It should be possible to use even the most unwieldy gear combinations without rubbing but as long as the front dérailleur works smoothly in the big/small and small/big combinations for front and rear, you'll have the full spectrum of gears available to you.

 

[raleighnut]

I've spent a happy afternoon re-indexing the rear derailleur on my tourer, having had to replace the cable, so I thought I'd do the front one too.

I know that you don't use the small/small and large/large chainring/rear cog combinations, but I'm finding other combinations that cause chain rub on either side of the front derailleur. My setup is a 48/36/26 front and an 11-32 8-speed rear. There's no rub in most gears when I'm on the middle ring, nor in the 3/4 highest gears on the large ring and the 3/4 lowest gears on the small ring, so I've still got the full range available. In that case, should I simply ignore the combinations that result in too much chain angle?

That would mean riding mostly on the middle ring (I'm not particularly fast) or is that what most people do anyway?

On a related question, given that the change in gear ratios between adjacent chainwheels is obviously greater than changing up/down on the rear, is changing up on the front and down on the rear simultaneously (or vice versa) a legitimate tactic to ease the transition?

I do that regularly both ways if I'm really tramping on it gives the most even ratio change. But only with brifters it would be too distracting with downtube shifters.
Funny thing is when I have been riding one of mine with downtube shifters for a while and then take out one with bar/barend shifters I find myself reaching down to change gear, especially after a long time on the flat when I've been in my favourite gear (52-18)

 

[Garethgas]

That's usually more of an issue with compacts, in my experience. It should be possible to use even the most unwieldy gear combinations without rubbing but as long as the front dérailleur works smoothly in the big/small and small/big combinations for front and rear, you'll have the full spectrum of gears available to you.

I'm not sure what you mean.
The OP has a triple on the front and so the duplicating of gears will be greater as will cross chaining.
Dropping from large to middle and changing up two or three at the back will give a similar ratio and vice versa.
Or have I misunderstood what you mean?

 

[raleighnut]

Down one at the front and up one at the rear, gives the next/closest ratio. Same the other way round up a ring at the front and down a cog at the rear.
Where's Fnaar when you need him.

 

[TheDoctor]

I think what DM means is that if you can get to the most extreme gears, then you'll be able to get to all the others too.

 

[Garethgas]

I think what DM means is that if you can get to the most extreme gears, then you'll be able to get to all the others too.

That's what I thought he meant too but you won't get the full range (ie 21 gears) as they are duplicated. My 21 speed hybrid gives me 12 gears and my 20 speed road bike gives me 12 too.
The deciding factor is the amount of cross chaining.

 

[deptfordmarmoset]

That's what I thought he meant too but you won't get the full range (ie 21 gears) as they are duplicated. My 21 speed hybrid gives me 12 gears and my 20 speed road bike gives me 12 too.
The deciding factor is the amount of cross chaining.

It's a language thing, I think. If the ratios are duplicated (or as near as duplicated) then you still have the range but only one smooth way of getting the duplicated ones.

 

[summerdays]

..you will find that gears "overlap".....ie on my 21 speed mountain bike I have probably only got 8 completely different ratios....ideally if you have say an 7 speed bike, you should use the large front gear for 7,6,5 on the rear ...the middle ring for 5,4,3 ..and the small front gear for 3,2 and 1.....some gear changers actually have 3 "segments" marked on them to assist this....at least I think this is the case as I am fairly new to this.....

That what I was told by my LBS when I bought my first bike a few years ago. I think for individual bikes the exact gears that don't rub changes but the principle stands.

 

[DaveReading]

Thanks for the responses.

Down one at the front and up one at the rear, gives the next/closest ratio. Same the other way round up a ring at the front and down a cog at the rear.

Yes, that was one of my concerns - whether there were any mechanical reasons why shifting simultaneously on the front and rear wasn't a good idea. But it seems to work fine and, particularly when changing down, doesn't result in such a big change in cadence because the overall ratio step is smaller and therefore smoother.

 

[Nigelnaturist]

That's what I thought he meant too but you won't get the full range (ie 21 gears) as they are duplicated. My 21 speed hybrid gives me 12 gears and my 20 speed road bike gives me 12 too.
The deciding factor is the amount of cross chaining.

I have 18 individual gears on my 9sp triple though there is some cross over in the 42-53" range, for the most part they run in sequence and whilst the other gears are close I have only 5 that you would call duplicates. example 52x24= 56.98" & 30x14=56.36" and whilst both are usable depending what ring I am on I would normally be on the middle 40th ring at that length 40x19=55.37" and 40x17=61.88" as this is the middle of the cassette.

 

[ColinJ]

Nigel - you need to check your table - there are mistakes in it - for example, two different results for 40x17.

It would be clearer if you rounded to the nearest inch, or at most one decimal place. Nobody is going to notice or worry about a fraction of a gear-inch.

You have got me thinking about what ratios to choose for my Cannondale when I convert it to a triple. Low gears are more useful to me than high gears since I do not ride quickly but do tackle lots of very steep climbs. I will stick to a 13-29 cassette and maybe go for 50/40/30 chainrings, or even 48/38/28.

 

[Nigelnaturist]

Nigel - you need to check your table - there are mistakes in it - for example, two different results for 40x17.

It would be clearer if you rounded to the nearest inch, or at most one decimal place. Nobody is going to notice or worry about a fraction of a gear-inch.

You have got me thinking about what ratios to choose for my Cannondale when I convert it to a triple. Low gears are more useful to me than high gears since I do not ride quickly but do tackle lots of very steep climbs. I will stick to a 13-29 cassette and maybe go for 50/40/30 chainrings, or even 48/38/28.

Thanks Colin, I was a tad tired this morning packing the car for the O.H. (its like a military campaign when she goes away), I am just used to working in decimals a bit of the O.C.D. as well I think.
18 gears then not 19 hope this is better.


I am toying with the idea of a 28/38/48 or even a 26 but you would then need to start at 12 on the rear for the 105", I keep playing with ratios in my table from time to time, I was thinking of going to a 13/14/15/16/17/18/20/23/27, but after today I am not to sure.