Andy_K 

Last week I got a flat tire (two of them, actually...you might remember me whining). One was a slow leak. When I patched it, I found a cut in the tire but nothing in the cut. So I patched the tube, and put it back on. Thirty miles later, the tire was flat again. Same spot (missed the patch by about a quarter inch), same empty cut in the tire.

Do you think it's possible that an edge on the cut in the tire caused the second (and maybe even the first) flat? I slapped a patch on the tire, in addition to the tube. I don't know if it will have any effect.

I know, I know, get Marathon Plus. I'm actually planning to order Marathon Supremes. I'm just wondering what happened.

dirtyhippy

Sounds like you got a pinch flat, and didn't notice the second hole at first. It happens when you don't have enough pressure in your tube and you hit something, pinching the tube against the rim and causing a pair of holes.

Andy_K 

I think it's unlikely. I was running at the max recommended pressure, and the cuts weren't parallel. Plus, how would that account for the hole in the tire?

ragboy

Don't mess with patch kits. Just slap a new tube on -- it's only $3.

Andy_K 

Updating: I came out to the garage this morning and it was flat again. Maybe my patch failed (it was raining and I didn't wait long for the rubber cement to dry). Or maybe this tire is a tube assassin.

Here's the timeline:

Sunday night: patched the tube pumped it up to 65 PSI (max for this tire)
Monday morning: squeeze-checked pressure and rode 11 miles to work
Monday evening: squeeze-checked pressure and rode 11 miles home
Tuesday: took a different bike
Wednesday morning: squeeze-checked pressure and rode 11 miles to work
Wednesday evening: tire was flat when I came out from work, patched, inflated to 60 PSI, rode 11 miles home
Thursday morning: flat again

imi

Are the cuts on the inside of the tube? same side as the valve, nearest the rim? I've seen this when the rim tape is too soft, the tyre well pumped and the spoke holes too sharp... Good quality rim tape is the answer

Andy_K 

Nope. Cuts are on the outside (tire side) of the tube.

imi

yeah sorry, should have read the op more carefully...
I'd probably just buy a new tyre... in my experience when a good quality tyre starts puncturing it's time to get a new one... 'fraid I can't be of more help...

HardyWeinberg

+1

JeffS

ragboy

Is that the universal symbol for you agree with me?

Andy_K 

I was going to use this one:

Not to be dismissive, but your method would have cost me $9 already this week.

StanSeven

If the cut is large enough for you to ask that question, road debris is likely working its way into the hole causing the second flat. The tube can also partially come through the hole making it easier to flat.

How large is the hole? If it's noticable, just toss the tire.

ragboy

You're riding must be a lot different than mine. All the cyclists I know don't bother with patch kits. They just carry a spare tube.

cyccommute 

It sounds like you still have something in the tire. Run your fingers around in there...carefully...and feel for the pokey bit. Alternatively, run a cotton ball around in there and watch for strands to catch on something. This is safer.

You may want to use something to probe the hole of the cut and see if there is still an object buried in there. If the cut spans several cords in the tire, it may be large enough for the tube to sneak out and puncture. Boot the tire or replace it if the hole is that big.

Andy_K 

I examined the tire closely -- nothing. It felt smooth inside and out. Then I pulled out my trust awl and probed the hole. As the astute reader has guessed long ago, out popped a piece of glass. The glass was small enough not to protrude from either side under examination conditions, hiding completely in the thickness of the tread, but it was large enough, apparently, to poke out and cut the tube under riding conditions.

Lesson learned.

Now when are my Marathon Supremes going to ship?

lambo_vt

Are these high pressure tires?

I would think a sharp-ish edge from a cut in the tire would be enough to puncture your tube. That's why people boot cuts in tires, right?

If it were me I'd try booting it with duct tape or something and would spring for a new tire as a last resort.

jefferee

People boot cuts in tires so that the inner tube doesn't blow out of the cut when it's pressurized.

A tube not contained in a tire can't handle more than a few PSI of pressure before it explodes.

lambo_vt

Right, so if you've got a sizable cut in your tire and you don't boot the tire, it's reasonable to expect that cut to contribute to the tube failing.

RiverShark

Wish I would have read this yesterday. I could have saved you some trouble? Had the same exact problem happen to me last year. And I used almost the exact same fix.

gerv 

I have the same issue this week - 3 flats. I know there is something in the tire or rim, but haven't located it yet. (Or possibly bad tubes...)

woodenidol

Flats suck. I used to fix mine, but I quite doing it. I have a patch kit with me, but thats just a second back up to my extra tube. I was so pissed when I had a stretch of 3 flats over 5 commuting days. Replaced my 23's with 28 gator skins. One flat in four months since. Not bad considering before the change I was hyper aware of road debri, now I dont even pay attention unless its something big.

marcoocram

Patch it. Why throw away good money.

Before you do so, have you checked to make sure your spokes are covered by the rim strip? If not throw that rim strip away and get some rim tape! Why waste good patches on your spokes.

New tube. Ridiculous.

Andy_K 

I'm starting to see there's a certain amount of randomness to flats. I got so sick of flats with my Gatorskins that I replaced them with RiBMos. I think it has more to do with the time of year. People are out breaking bottles, but the street cleaners aren't running yet.

woodenidol

I can understand your sentiment here. I guess my position is, when its dark, cold, or rainy (a good percentage of my communtes in the NW) I found that my patch jobs integrity, was often compromised by difficult conditions for repair. I can see how ideally, one could put on new tube, and then repair punctured tube later in the garage and rotate it in as your spare. I used to do this also. The last time I did it was on a tube I had repaired. Found out I had missed the small second snake bite hole. Repaired again. Found I had done a poor job and patch leaked. Repaired. Tube was good, installed. Still leaking, what the heck. Took it off, found I had then ripped a hole around the presta valve. Doh. Last puncture I repaired. Then again, at a present rate of one punture every four months, Im willing to buy the tubes.

That being said, when I was younger and a bit more frugal, I remember tubes when I was racing a bit that had 4 to five patches on them, and they gave me zero problems. I guess I lack both patience and manual dexterity now.