What action is directly linked to the speaker's friend's suggestion?

The action that is directly linked to the speaker's friend's suggestion is purchasing tires. This indicates that the friend likely recommended buying new tires for a vehicle, perhaps because the existing tires are worn out or unsuitable for driving. The context might involve a conversation about maintaining a vehicle, where the friend points out that tires are crucial for safety and performance.

Choosing tires signifies a specific recommendation that aligns directly with the needs of vehicle maintenance, unlike the other options which involve different aspects of vehicle care. For instance, while buying a bike or changing the oil are related to transportation, they do not stem from the suggestion about tires. Refueling the car, while also necessary, does not relate to the condition or performance of tires. Thus, purchasing tires stands out as the most relevant action linked to the friend's suggestion.