Google "bicycle shifting technique", for example: http://coachlevi.com/cycling/complete-beginner-guide-to-bicycle-gears-shifting/ You should NEVER run cross-chained (big-big or small-small). The drive train performs best when the chainline is as close to straight as possible. Excess sideways stress on the chain will wear it out prematurely and decrease its normal efficiency. To demonstrate this for yourself, put the bike in the same combination of gears you're having a problem with. Get behind the bike and look straight along the top of the chain. As you can see the line of the chain is a mild zig-zag where it is parallel to the bike at each gear but needs to angle across the drivetrain in between. On some bikes the chain might even come in contact with the next larger chainring when used this way. The big-big combo uses up all available chain length and the rear derailleur will be pulled toward the front of the bike, sometimes so far that it is in danger of being snapped off. THERE IS NO UPSIDE TO CROSS-CHAINING. As you can see, the rear derailleur is probably not long enough to **** up all the slack this gear combination creates. There are other combinations that would yield the equivalent gear ratio without either stressing the drivetrain or dropping the chain. The basics of shifting are these: 1) The big ring and right side of the cassette in back are for speed. 2) The small ring and the left side of the cassette are for high torque, lower speed Ancient bike wisdom for beginners: If your legs ache, shift down. If your lungs ache, shift up.
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Google "bicycle shifting technique", for example:
http://coachlevi.com/cycling/complete-beginner-guide-to-bicycle-gears-shifting/
You should NEVER run cross-chained (big-big or small-small). The drive train performs best when the chainline is as close to straight as possible.
Excess sideways stress on the chain will wear it out prematurely and decrease its normal efficiency.
To demonstrate this for yourself, put the bike in the same combination of gears you're having a problem with. Get behind the bike and look straight along the top of the chain. As you can see the line of the chain is a mild zig-zag where it is parallel to the bike at each gear but needs to angle across the drivetrain in between. On some bikes the chain might even come in contact with the next larger chainring when used this way.
The big-big combo uses up all available chain length and the rear derailleur will be pulled toward the front of the bike, sometimes so far that it is in danger of being snapped off.
THERE IS NO UPSIDE TO CROSS-CHAINING.
As you can see, the rear derailleur is probably not long enough to **** up all the slack this gear combination creates. There are other combinations that would yield the equivalent gear ratio without either stressing the drivetrain or dropping the chain.
The basics of shifting are these:
1) The big ring and right side of the cassette in back are for speed.
2) The small ring and the left side of the cassette are for high torque, lower speed
Ancient bike wisdom for beginners: If your legs ache, shift down. If your lungs ache, shift up.