Tyre width range for rim width

[grantone]

I have an old hybrid bike, rims appear to be ~21mm internal width and ~25mm external width. Plenty of clearance on the forks & stays.

Is there a rule of thumb for working out what min & max widths of tyre would comfortably fit?

[Gompo]

Did you have a tyre size you were considering? If it is an old hybrid bike the clearance on your chainstays/seatstays and forks may dictate the maximum width more than your rims. What bike is it? Photos? Until the late 90s the widest MTB tyres you'd get were 2.5, and generally you wouldn't get more than 2.1.

[benny.c]

I use this from DT Swiss as a starting point but obviously follow specific guidance from the wheel and tyre manufacturer.

https://dycteyr72g97f.cloudfront.net/uploads/WXWXX...

[grantone]

Thanks for the DT Swiss guide sheet, very handy.

The bike is a 2002 Cannondale Bad Boy, currently has 1 inch wide tyres from when I bought it used a few years ago. I found some very small text on the front rim that says 'ERTO 559 x 19c' which I think means it's 19mm internal width?

I don't have any specific width in mind, though I wouldn't mind going wider as I have moved house and will do more (probably most) riding off road now.

Pics of the clearance on the forks & stays.