Wa `alaykum as-Salamu wa Rahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Dear brother, thank you for your question and for your commitment to Islam’s rulings concerning you financial affairs.
Interest-based car loans are not permissible in Islam, especially in cases like yours where car is not a pressing need or a necessity of life.
Responding to your question, Prof. Dr. Monzer Kahf, Professor of Islamic Finance and Economics at Qatar Faculty of Islamic Studies, stated:
Interest-based car loans are prohibited in Islam. Allah Almighty prohibited interest (riba) with the strongest word in the Qur’an and there is no necessity for a car to warrant breaking this strong prohibition. You can live without a car for years and even forever.
For the other point, it is permissible to accept any contribution, given voluntarily, to family expenses by your wife.
Allah Almighty knows best.