Thinking 25c on the front and 23c on the rear.

Can be anything dodgy in that can there?

It would be fine but normally done the other way round. More weight goes on the back.

What’s your reasoning?

Why?

I can’t see any problem, other than a remote possibility that you will bump over or up something and the rear tyre might puncture.

I’d go 23 front if I had to; more cushion on the rear.

Having different tyres is bad enough. Having different size tyres will get the Velominati on you.

If you can even spot the difference between a 23c and a 25c tyre, I’d be astounded…

As an ex DH racer this is intuative, but I doubt you put anywhere near as much weight over the front on a road bike, so I wouldn’t think there is much benefit from that point of view

I should have added that I actually have a 23 on the front and 28 on the rear of my commuter. Not intentionally, it it just came like that, but it works well enough not to change.

Virtually zero difference in rolling resistance from 23/25 and even 28. Well compared to the actually noticeable difference in comfort and grip.

You can buy odd tyres – conti attack/force, narrow front, wider rear. out and out race tyres.

changing the width of the front, can make steering feel odd ime. wider tyres make steering feel slower, and you can tell.
Changing the rear will make very little difference, although you may hear that wider tyres are more comfortable

Virtually zero difference in rolling resistance from 23/25 and even 28. Well compared to the actually noticeable difference in comfort and grip.

I’ve read in a few different places now that rolling resistance decreases as you increase the tyre size, up to 28c beyond which other factors counter the effect.

I’ve also read that in a few places. Something to do with the footprint becoming shorter and fatter compared to longer and thinner. If it’s up or down then we’re talking pretty small figures.

It would be interesting to see what pro’s train on. I’m guessing that 25/28 is very common for comfort and puncture reasons. In fact I would wager that pro level riders probably train on more comfortable tyres than your average MAMIL!