So you bought some old crusty steel wheels and want a quick way to remove all that nasty rust?
Get yourself 2 gallons of good 'ol cheap pool acid from the local big box store. I think it was 7 bucks at my Home Depot. Pour both into a plastic garbage can or other receptacle that is big enough to lay a rim in on its face. A 30 gallon trash can was perfect for a 14 inch rim, probably a 15 too.
NEXT STEP IS DANGEROUS-- better way is to measure amount of water it takes to cover rim and use that amount to get your acid/water mix right. Adding water to a strong acid is dangerous and can cause a boiling action that may cause a splash---pool acid is diluted already so it should not flare up when water is added but it is bad practice. Remember Acid to water!
Place rim in bottom carefully while wearing some heavy rubber gloves or use a hook to lower it in. Wear safety goggles so if you drop it in, the splash won't get your eyes!!! You an always put rim in empty bucket and add 1 water and 1 acid, up to you. Then add water and acid in equal parts so it just covers the rim lip, you'll want it completely covered. Put top on can and let it sit overnight or until you can see it working. I had to let it sit for 2 days but your mileage may vary.
Once it's clean, remove it carefully and hose it down in the grass as the acid will etch concrete. Avoid hose backsplash as it may still be caustic. After a good washdown, you may want to run a brush over it to loosen and stubborn rust spots. After it's all rinsed off, you can dunk it in a bath of water and baking soda to further neutralize any residual acid.
After this, it may flash rust pretty fast so I sprayed mine down with penetrating oil like WD-40 to prevent flash rusting until I could get them painted. Bare steel will rust unless treated.
Evaporust ( Get it here: Amazon.com: Evaporust) is a great post treatment but it's rather expensive to submerge a rim in so pool acid did it for me. Just spray it on and let it dry, no further rinsing needed prior to paint.