Im going to renovate one of my rims so I need to put a support under the car in the back end
Where should I put the support thing? on the wheel bar or is there a support frame thats good for this?
For the rear I would jack the vehicle up on the point dead centre under the rear where the 2 strengthening bars join together onto the chassis, using a trolley jack. This will then allow you to put a stand under each sides jacking point and rest it on those. Let the trolley jack continue to take some weight if you wish. That won't go anywhere then
since you're refurbing a wheel and not going under the car, then for a single wheel removal I'd use the jacking point and then just place the stands underneath any solid piece of chassis as it's only an extra 'accident' insurance.
Use a trolley jack and no cheapo scissor type things and you'll be safe.