28 inch. Sure?
This would be the same ISO as a standard 700C tire, but it is a rare way of stating it.

Or, perhaps you mean 28mm width?

Since it's a rainy day full of cancellations you could kill time reading Sheldon Brown's page
https://www.sheldonbrown.com/tire-sizing.html

Duh, I meant 28 *mm* tire.... that is, next size up from 25mm

Duh, I meant 28 *mm* tire.... that is, next size up from 25mm

I'm pretty sure I have a couple different 28's you can borrow to test.

My SOMA smoothie has fairly tight tolerances. It doesn't fit many 28's but it does fit one of my fav. all-around tires the Conti 4 Season GP which are more like a 27mm. I might have an old worn one of these to test.

Usually front fork crown distance is not a problem, but rear brake bridge and stays can be very tight. Also, the wider your rim, the smaller your OD becomes.

Anyhoo. I've got tester 28's if you want them.
email me 

Just a note. Different brands can vary quite a bit in size and profile even
when given the same size designation. So if you try one brand and it fits closely don't assume another brand will and vice versa.

Thanks for the replies.

Now, I *should* be able to mount 28s on the same wheels I have 23s on now, yes?

yes.

It's not about the tire size, per se - e.g., the 700c rims will easily fit a 28mm tire.  It's the fork and brake clearance that limits the size of tire you can run.  If the 28 didn't work on your bike, you could swap out for a longer reach brake.

I'm curious as to how this turned out, Janet.

I know both of your bikes Janet. You should have no problems with a 28. If you had a short wheelbase crit frame bike, you might have trouble with a 28.