This goes hand in hand with the Roth 5 year ladder conversion.
Credit goes to MadFIentist
Not gonna copy his whole post and examples, but
When you convert from a Traditional IRA to a Roth IRA, you have the option of undoing the conversion before you file your tax return (this is called a Roth recharacterization). That means, you could execute the conversion in January and then rewind the conversion by April 15th of the following year (or October 15th, if you file an amended return) and the IRS treats it as though the conversion never happened.
To build a Roth IRA Horse Race, you’d instead do two different conversions into two separate (and empty) Roth accounts. So in this example, you’d convert $10,000 worth of Total Stock Market index fund into it’s own Roth account and $10,000 worth of Total Bond Market index fund into a separate Roth account (segregating the funds like this will make the recharacterization process much easier). This will result in converting twice as much as you would actually like to convert for the year."
Then you recharachterize the loser back to a Traditional.