Don't buy a car if it's not for necessity, it's better to save assets in BTC because if BTC will increase drastically then you can buy that car for only half of the current car price
What do you mean, bro? The car value will be decreasing or our funds will multiply on Bitcoin investment? The car value sometimes is also fluctuated, it can increase or decrease in the future. Regarding the Bitcoin asset, there is no guarantee that it can multiply our money and there is no specific time to take the profits. If having the car uregently, you are better to convert your Bitcoin to fiats immediately.