More gear problems......

[boydj]

Get used to using your front mech and plan ahead to avoid using big/big. Even with the limit screws properly adjusted the big/big combination can be problematic and it's not as efficient as the same ratio using the small chainring.

 

[Adam4868]

Think Ill make do with the other 19 gears !! My winter bike has compact with 12/25 cassette and no problems.My new (good bike) has standard chainset and 11/28 cassette.Like I say it's only one gear.....

 

[Ajax Bay]

the big/big combination can be problematic and it's not as efficient as the same ratio using the small chainring

I thought that but recent came across this persuasive research, suggest that avoiding large/large is not an efficiency issue (my comment: but it is probably a wear and certainly a 'nowhere to go' issue). See this extract:
"Experimental results indicated that the efficiency of the chain drive varied . . . It was found that chain-line offset and chain lubrication have a negligible
effect on efficiency under laboratory conditions. Calculations of frictional loss resulting from offset indicate that this loss should be small compared to
those produced by other mechanisms. This was verified experimentally."
But note that more generally (and away from the large/large extreme) you're better off in the large ring as, for the same gear length, it'll be more efficient as the larger sprocket is more efficient eg 50/21 is more efficient than 34/14.
"Tests of efficiency for the derailleur type chain drive . . . factors affecting the efficiency include the sizes of the sprockets in the drive and the tension
in the chain. It was found that larger sprockets provide more efficient transfer of power while smaller sprockets proved to be less efficient."

From: "Human Power" Number 50 Spring 2000
TECHNICAL JOURNAL OF THE IHPVA
Articles
On the efficiency of bicycle chain drives
James B. Spicer and others . . . . . . . . . . . . . . . . . . . . . . . . . 3

 

[Adam4868]

I thought that but recent came across this persuasive research, suggest that avoiding large/large is not an efficiency issue (my comment: but it is probably a wear and certainly a 'nowhere to go' issue). See this extract:
"Experimental results indicated that the efficiency of the chain drive varied . . . It was found that chain-line offset and chain lubrication have a negligible
effect on efficiency under laboratory conditions. Calculations of frictional loss resulting from offset indicate that this loss should be small compared to
those produced by other mechanisms. This was verified experimentally."
But note that more generally (and away from the large/large extreme) you're better off in the large ring as, for the same gear length, it'll be more efficient as the larger sprocket is more efficient eg 50/21 is more efficient than 34/14.
"Tests of efficiency for the derailleur type chain drive . . . factors affecting the efficiency include the sizes of the sprockets in the drive and the tension
in the chain. It was found that larger sprockets provide more efficient transfer of power while smaller sprockets proved to be less efficient."

From: "Human Power" Number 50 Spring 2000
TECHNICAL JOURNAL OF THE IHPVA
Articles
On the efficiency of bicycle chain drives
James B. Spicer and others . . . . . . . . . . . . . . . . . . . . . . . . . 3

Now I know why gears confuse me !

 

[Ajax Bay]

They don't need to. All those pieces are saying is that, actually, extreme chain angles (ie the circa 2.75 degrees large/large for a double10 speed) have a negligible effect on efficiency and that, given the choice, for a particular ratio, you're better in your large chainwheel (limited by the advice to avoid the largest two sprockets).
Have a play with this gear calculator. I've set it up for the OP's winter bike, but it can be changed and changed again, till it's time for a ride instead of mucking around on here.