Industry Tire Sizing
Here is the industry tire sizing reference information:
DennisKirk.com - Tire Sizes Explained
The front rim on the CBR250R is 2.75" X 17".
The rear rim is 4.00" X 17".
The allowable tire width range for the front tire is 110 to 140.
That does NOT necessarily mean that a tire wider than 110 is better. There are many other considerations.
The allowable tire width range for the rear tire is 150 - 160.
I'm not sure why Honda paired the factory 4.00" rim with a 140 tire. I do know that there is less than .500" clearance between the factory IRC tire and the chain. A 150 tire is going to reduce that distance to .25" - .30". A 160 will probably rub the chain.
I'm planning on upgrading to a set of Michelin Pilot Road 3s in the future. I will stick with a 110/70 front because they offer that size, but I will have to go to a 150/70 rear as they don't make a 140/70.
I have to wonder if Honda decided to go with 140/70 in the rear based mainly on the extremely low pricing they set on the to compete with the Ninja 250?
Teakdust