So I was patching tubes the other day, a chore I find needs doing every year or so, and I realized something that seems significant, at least to me.

Background - Until the spring of 2006 I was commuting on my fat tire mtb, running 1.5" City Slicker tires. In June of last year I got a road bike and mounted 700c28 Continental Ultra Sport tires on it. The mtb is now the rain/snow bike. My commute is 20 miles RT mostly on nice bike paths, my bike is the only way I go to work.

Anyway, I have had lots of flats on the mtb, mostly from little pieces of wire and various unknown punctures, but in the two seasons on the road bike I have had exactly two flats and they were both my stupid fault.

So, is this just luck or are skinny tires really less likely to flat?

they are...high pressure plus hard casing

I expect you had a lower grade of MTB tires and you do have a good grade of road tires.

Huh, maybe you're right, strange that the mtb tires cost more though...

Tioga City Slicker - $18
Continental Ultra Sport - $14.50

So much for getting what you pay for, the contis are way faster too

A quibble maybe, but 1.5" slicks are wider than 700c-28's, so they were treading a wider path of road. Not enough of a factor to account for the disparity, but it is something.

I have pulled out of tires little bits of wire like from a wire brush and I believe they come from the street sweepers.

I think that wire is used for the steel belts in tires. I ride alongside the highway a lot, and I always see truck tire casings with that thin gauge wire poking out in a tangled web. I've picked that same wire out of my tires a few times, and it's caused several flats.

I've 10 bikes and have used a wide variety of tires. Flatting is more a factor of quality and wear.

I've tried out a bunch of tire combinations, including regular road tires, road tires with tuffy liners, kevlar belted tires with and without tuffy liners (or with 2 tire liners!), and the semi-knobby tires you see on cheap MTB style bikes.

The semi-knobby tires are the ones that keep the tube the largest distance from the pavement (tread depth plus casing is about 8mm) even compared to running road tires with more than one tire liner.

From all this experimenting I've found that the way to completely avoid wire fragment and glass shard punctures is to have the tube further away from the pavement than the length of the piece of wire or glass. kevlar casings or hard plastic liners helped a little but tire thickness or tread thickness really prevented me from getting flats.

EDIT: I have also had most of my flats on rainy days. I have a hard time figuring out why that is true (the idea of water acting as a lubricant and thereby causing more flats doesn't seem like a great explanation to me, because even if water makes it possible for slivers of glass/wire to slide through the rubber a bit better, it seems the water would also make the things more likely to slip off of the tire.

Well, just statistically, if there's x amount of puncturing stuff on the road, a tire that's 1/2 as wide will be 1/2 as likely to hit it.

Mostly the little wire bits come from tires. Steel belted radials, y'know. Mostly when people have blowouts, they can spread the wire bits around. Plus I think some of them also come from frayed cables.

To me it looks like that differences in the amount of flats are caused by the fact that the mtb is used as your rain bike. Rain or wet roads rapidly increases the chances of a puncture, since water acts as a lubricant on the glass shards /metal wires / flint stones / thorns or whatever punctures tyres where you live.
The Continental Ultra Sport aren't known for their puncture resistance either.

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Regards

I've never, ever flatted my knobby MTB tires and they're 1.95". I have flatted my 1.25" Forte Slick City tires 3 times in about 600 miles. I have flatted 700x25 Bonti selects 6 times in 3,000+ miles. When I switched to the Bonti hard case tires on my road bike, all my flat tire woes faded away.

As much as I love skinny tires, I have found that they flat more than fatties. Perhaps it has something to do with the psi both tires are run at. Anyhow that is just my experience.

That's the tire's fault. The Slick City is woefully thin.

1+

I didn't get many flats on my road bike commuter when I was riding it summer through early fall. Now that it is late fall and the rain has come to the PNW, I ride my fixed gear with the same tire (but 25mm instead of 23mm) on the rear as I was riding on my road bike and I am getting flats from punctures all over the place. The last two week have been terrible. I picked up a razor blade which cut my tire in half last week. Monday I got three flats, one in my front wheel and two in my rear; I only carry two spare tubes so I had to patch the last tube in the dark. Turns out it was two rocks and a small piece of wire. Tuesday I got another flat; a construction staple.

All of these were from the weather. It's been very wet the last couple weeks, and on Monday there was a wind storm which blew lots of crap on the road.

It could be a number of factors interacting.

For several years, I worked part-time as a flat-fixer at a dump truck company. Typically, the truck tires were run with 85-100 psi pressure. I can tell you that high pressure does not prevent flats. I've heard people argue that it helps cause them, don't know if that's the case, either. But dump trucks do have lots of flats.

I don't know how you'd go about establishing this in a proper fashion, as you're always going to be comparing apples and oranges (or more properly, apples and pumpkins). They simply don't make the same identical thickness of tire in totally different sizes.

Over the weekend, I rode 35 miles on an organized ride with my 26x2.125" tires- and no flats. But I did pass a half dozen people who were stopped fixing flats.

My tires accelerate their rate of flatting as they age, so if your mtn bike tires are much older than your skinny ones, I would attribute it to that (as well as quality differences if any). My 2" big apples have only flatted twice in ~4k miles, from a drywall screw that drove in up to the head, and then a couple days later from a big piece of glass that found the hole left by the drywall screw. Yesterday and today I accidentally rode over the same broken beer bottle and no problem, though. Whew.

about 90% of my flats also occur during or shortly after a rain. There are several hypothesis' about why this is.

First, try picking up a small piece of glass or wire with the tip of one finger (careful don't get cut). It will probably just fall off. Then try it again after moistening your fingertip. The small object will pick right up. I think this gives many sharp objects multiple chances of puncturing your tire.

Also, glass (or wire, etc) will slice much more easily through rubber while either is wet than they would when dry.

So....since your mtn bike is your wet weather ride, you are destined to get more flats on it, than on your road bike. I don't think it has much to do with expense here, or width of tires.

I have found no correlation between casing size & flat frequency.
It seems much more related to the specific tire.
cheers

Ive run the same Maxxis Hookworms in 26 x 2.50 inches on my bike for the past three years and I have never ever gotten a flat, knock on wood! and I ride the crappy streets of Filthadelphia!

Must be your luck. My road bike got lots more flats than my mtb turned commuter. I blame it on the road conditions, which were different in each case.

For me, it depends in part on which roads I use. I avoid riding on Auburn Blvd because I seem to get nothing but flats on that road. In fact the only flat I have had in the last couple months was on Auburn, when I decided to give it a try because the route is shorter that way.

Years of riding lots of different tires has taught me:

1. The rubber the tire is made of is very important. I am a big believer in continental tires as i think there rubber compound is much more puncture resistant than any other i have tried.

2. Flats come and go, often in waves.

I have a MTB used for commuting, with slicks mounted on it. They are rated up to 100psi and are 26x1.25.

I have experienced many more flats with the pressure pushing 100 than when they are around 60. My reasoning is that when a rock is run over, the tires have no give, and puncture, whereas a lower pressure tire will give the rock some flex, and go around the rock and distribute its force rather than concentrating it. I may be wrong though!

Excessive flats call for Mr. Tuffy tire liner...

You answered your own question in your post. You use the MTB in rain and snow, when debris will stick to your tire and cause punctures.