Side-to-side movement of chainrings

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When using the largest 'ring and on the 4th or 5th (of five) rear sprockets, and pedalling at normal speed, I can see 3-4mm of side-to-side movement as each crank is at the maximum drive point. There is no play in the BB bearings and the cranks & 'rings are tight so is this typical or just my Explorer showing it's age/weakness?

 

[ufkacbln]

Trice Explorer?

If so how old?

Could simply be pedaling style. Try spinning instead of pushing big gears.

 

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Err, no, Falcon Explorer 15, about 10 years old but with casette BB.
COuld very well be technique, am working on using more muscles and using more of a 'spin not push' movement.

 

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Thanks for the 'spinning' tip, I was amazed when I tried it how different it felt, how much less movement there was in the chainrings, and most of all how much faster I went! I have also discovered some muscle groups I didn't know existed as they are now aching, but all to the good in the end