Bring a large pot of salted water to a boil and cook the elbow macaroni until al dente, about 8 minutes. Drain and rinse with cold water until fully cooled, then transfer to a large mixing bowl.
In a small bowl, whisk together mayonnaise, rice vinegar, and sugar until smooth and slightly tangy. Set aside to allow flavors to meld.
Add chopped cucumbers, finely chopped red onions, and grated carrots to the cooled pasta. Toss gently to combine, distributing the veggies evenly.
Pour the dressing over the pasta and vegetables, then fold everything together thoroughly until the pasta is evenly coated and the veggies are well incorporated.
Taste the salad and adjust seasoning if needed, adding a pinch more salt or a splash of vinegar for extra brightness.
Cover the bowl with plastic wrap and refrigerate for at least 1 hour to allow flavors to develop and the salad to chill thoroughly.
Before serving, give the salad a gentle stir to redistribute the dressing. Serve cold, garnished with additional chopped veggies if desired.
