I have the following rim sizes which I need to re-tyre..... and I think the tyre sizes don't relate directly to rim sizes

18 x 2.15 (front) & 17 x 2.50 (rear) These are on me Trumpet.
SO, what tyres are gonna fit those rims ..... in METRIC ( eg: 18 110/100) and imperial ( eg: 18 x 3.25)
Hoping to go to the MAX size fitable coz there's plenty of room
