21mm internal will be fine up to 35mm, over that and I would go for a wider rim. With a 25mm rim I wouldn't go below a 30mm tire. Are you worried about aero gainz at all? When you say inner tubes for now, does that mean you are tubeless curious?
Have you ever ridden 28c tyre on a 25mm internal rim?
Yes, a tubeless hookless one no less
@broken_777 started
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21mm internal will be fine up to 35mm, over that and I would go for a wider rim. With a 25mm rim I wouldn't go below a 30mm tire.
Are you worried about aero gainz at all? When you say inner tubes for now, does that mean you are tubeless curious?