I have a cruiser bicycle, and I prefer the cruiser bike to a mountain bike because there are fewer gears to work with. I'm more comfortable with that, but I'm thinking about replacing the tires with MTB tires so that my bike will be a little more road-worthy.

My commute will be about 5 to 6 miles each way.

I really don't want to replace my cruiser with a mtb, so would replacing the tires suffice?

It will probably work. Most cruisers have 26 X 1.95 (or similar 26 X x.xx) tires that fit standard 26" mountain bike tires without any trouble. If it is an older bike it might have 26 X 1-3/8, which is a different size entirely and mountain bike tires will not work.

So what size are the tires?

But what sort of tires are you thinking of? If your commute is on pavement or smoother dirt then you should get something with less aggressive tread (road slicks or similar) and that can take higher pressure to give you less rolling resistance.

Do you ride off road ?

Knobby mountain bike tires aren't very good on the road, they don't have as much traction, they wear quickly, they are noisy and the rolling resistance is higher then a slick or treaded road tire that can take higher psi.

Sounds like a Repack replica throwback to the 60s to me..
Smoking the grease out of coaster brakes on downhills required re packing.

MTB tires are for Dirt fire roads roads , Loose gravel , not pavement,

but for the mountain bike market segment there are road tread tires ..
still not super easy rolling high pressure but you can get closer.

Schwalbe big apples are wide comfy but easy rolling, I'm told,

I'm running their Marathon Plus tires , adds a very puncture resistant tread design.
559-47

559 is the international standard bead seat diameter measurement rims and tire makers agreed upon.. for the mountain bike 26"

you should get a tire a little wider than your rim, as a minimum... 47 is like 1.75"

My bike is a La Jolla cruiser with 24 inch tires. Now that I know a little more about mtb tires, I may not make the change.

Here in the Phoenix area, the roads are quite smooth and flat. I just thought that mtb tires would be more resistant to sharp debris on the road.

Thanks!

Keep your tires pumped up nice and hard. Read the maximum pressure on the sidewall of the tires and pump up to that. Use a pressure guage and pump up regularily as air seeps out over time. This is the #1 thing you can do to any bike to make it better on the road and more flat resistant.

Nah not really. If you really want you can get hard case tires with a layer of Kevlar to protect against flats. But unless you're running over lots of glass or nails on a regular basis, the inner tubes you'll replace are probably a lot cheaper than new tires.

If you do want new tires, get slicks (or very close) if you never do any serious offroading.

Do the tires have 507 indicated on them? If so, here are some choices:
https://www.biketiresdirect.com/searc...=true&ust=true

I like the looks of the Contis and the Maxxis. I like the slick treads of both Innovas, but they're so dang WIDE!

The Continentals are kinda skinny, so may not work so well if you've really wide rims.

I'd probably wait 'til your current tires are wasted before replacing them, however.

If your main concern is puncture resistance, you could go with slime or Mr. Tuffy.

Thorn resistant tubes .. heavier but a normal type innertube
Mr Tuffy strip overlap causes flats , personal experience speaking, end abrades tube.

I've never suffered a flat from the ends of a Mr. Tuffy. Here's how I run 'em:

1. Run full length for a few days.
2. Cut excess, using overlap indention as a guide. This may leave about a mm exposed, but no problemo.
3. Sand ends smooth
4. Reinstall, ride on and be happy.

I will say, however that I liked Slime when I lived in the Valley of the Sun. Slime handles the millions of goat heads well.