Maybe, in Am English. In Br English it's 'tyre'.
Also, the first 'spare' is not well chosen. If you spare something from doing something, you relieve it of the necessity. You could only 'spare your waist...' from doing something, if you meant to imply* that it had to do it and you spared it the duty: 'I'm passing that way anyway, so you could give me the parcel and I'll drop it in - it'll spare you the effort.'
How about 'so as to avoid getting a spare tyre' [that is, don't mention your waist at all]?
*Edited, to make sense. Sorry if the earlier version had anyone foxed.
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