Let's say you had a 27mm wide 29er wheel

[eddief]

What would be the narrowest normal road tire that could be installed for smooth pavement riding?

Is there some sort of safe limit? Could I use a 25 mm normal road tire?

[MIN]

bro - of course not. rim can't be wider than the widest part of the tire.

http://www.sheldonbrown.com/tire_sizing.html

[eddief]

guess i need a normal 700c rim built on a disk hub.

[RPS]

bro - of course not. rim can't be wider than the widest part of the tire.

http://www.sheldonbrown.com/tire_sizing.html
Good information, although the chart at the bottom seems a little restrictive to me -- I'm sure I’ve exceeded the recommended on occasions. On 23 MM tires I'm sure I’ve used rims wider than 15 MM (inside dimension); probably still do.

I ran 1" tires (25.4 MM nominal cross section) on 24 MM wide rims (not sure of inside dimension) for years without a single problem, and I expect that combination far exceeds the recommendation in the chart.

On the other hand his warning below makes perfect sense if we plan to hit road debris from time to time.

“If you use a very narrow tire on a wide rim, you risk pinch flats and rim damage from road hazards.”

[MIN]

Good information, although the chart at the bottom seems a little restrictive to me -- I'm sure I’ve exceeded the recommended on occasions. On 23 MM tires I'm sure I’ve used rims wider than 15 MM (inside dimension); probably still do.

I ran 1" tires (25.4 MM nominal cross section) on 24 MM wide rims (not sure of inside dimension) for years without a single problem, and I expect that combination far exceeds the recommendation in the chart.

On the other hand his warning below makes perfect sense if we plan to hit road debris from time to time.

“If you use a very narrow tire on a wide rim, you risk pinch flats and rim damage from road hazards.”

I agree it is a bit restrictive. IMO, you can go a little larger than the tire size for a given rim width per Sheldon but not the other way around.

[RPS]

Personally, if I had the tire clearance and already owned the wheels, I wouldn't hesitate trying 28 MM tires on rims that are 27 MM wide overall. If I ended up with too many pinch flats as Sheldon predicts, I could then change to narrower rims. However, I don't think pinch flats would be an issue for me.

[Tobias]

bro - of course not. rim can't be wider than the widest part of the tire.
I wouldn't be so sure that it can't be. Part of the reason is that the tire will become wider when mounted on a wider rim. A 25 mm tire should end up much wider when mounted on a 27 mm wide rim. I wouldn't want the rim to be wider than the tire after installation, but as long as the tire width is over 27 mm installed I'd ride it. May be more aero too.

In my early days I used 18 mm and 20 mm tires on rims that may have been wider than the tires. It worked OK except for too many flats, plus I learned quickly it was a stupid idea in the first place.