DMF 

Got a flat the other day. The bike was just sitting there on the stand. It had good air when I finished the ride and lost it sometime over then next two days. Timing was good as it turned out; I noticed that the (rear) tire (23 x 622) was worn out so I bought a cheap Continental with a wire bead. (My first wire bead. Hate it.) Strangely, the tube was leaking around the base of the valve. wtf?

Inserted new tube in the new tire. Aired it up and rode 20 miles. Two days later I rode another 20 miles and right at the end (on Disaster Hill - another story) the tire went flat. Pulled the tube, cleared the tire (no intrusions), inserted my new spare and tried to air it up. Nope! A passer-by gave me a ride home.

Got the two tubes in the water and found that they are both (apparently) pinch flats - tiny little double holes on the side. I always run with a minimum 90 psi - usually 115 or so - and have *never* had a pinch flat. wtf?

Anyway.

The point of this post is what happened afterwards. I found both leaks and patched both tubes, and both failed - at the patch. Brand new tube of rubber cement. Apparently sticky patches. Clamped for several minutes in a warm ~95F environment. After the first one failed I took extra care with the second. Extra scuffing, clamped between two pieces of metal for 10 minutes. Inserted carefully into the tire.

Two things concern me: first that the patches generally have a larger diameter than the tube cross section so that they literally hang over the edges of the tube when clamped, second that there are little raised casting lines all over the tube, making it hard to get a flat surface around the holes.

Any recommendations? Is there a problem with my preparation? clamping? the patches themselves? I's be confoosed.

Dennis

JOHNinIL

Regarding the larger size of the patch. I just cut it smaller to fit my particular tube, never had an issue.

Regarding the casting lines, don't worry too much. Just scuff the tube before applying the compound and patch.

Bill Kapaun

Are you using a REMA patch kit?

1 Miyata Biker

Patches are designed to be used on any size tube. If you use narrow tubes, you just need to use a scissors to trim the patches to the desired size and keep them in your patch kit. Just make sure to keep them in a rounded shape.

noglider 

1. Let the glue dry. Too long is better than too short.

2. If the edges are not glued down, your patch is likely to fail.

alcjphil

If the glue has properly dried, there is no need for a clamp

prathmann

Agreed. The glue should no longer feel at all tacky before you apply the patch. And spread the glue over an area that's significantly larger than the patch so the edges of the patch are sure to be glued down.

alcjphil

This is why I always carry spare inner tubes on a ride. I frequently ride with a group and would not want to make them wait the extra time necessary to do a proper patch job. And if I rush things because I don't want to make others wait there is a good chance the patch will fail

shelbyfv

You may want to specify what patches and cement you are using. Some folks use regular rubber cement but most prefer specific patch cement like Rema or Slime. I may have misread but it seems you thought you had a pinch flat on a new tube. This seems unlikely, did you use a lever to mount the tire?

scott967

I don't think I have ever had a problem of patch not holding unless I didn't let the glue dry as others comment. I do rough the tube (std butyl tube) and make sure the glue is past the edge of the patch. I have never "clamped" a patch. I typically patch on the side of the road and just use my fingers rolling the tube as needed to make sure the feathered edge of the patch (Rema) is down. Or maybe use the red plastic holder for my plastic levers as a tool for working in the patch. I haven't a problem using a single patch on a snake bite. For me snake bite typically means "time for a new rim strip, or at least better positioning".

I do have a Kenda tube that started leaking (loses air in about 2 days). I pulled it and tried every trick I knew to find the leak but came up empty. I've just been pumping up before every ride and it hasn't gotten worse. I guess when I get tired of it I will pull it and try again or just replace the darn thing.

scott s.
.

FBinNY 

The very 1st step of tube repair is the most important. just about every patch instruction includes starts out the same

1- use sand paper (or scraper) to buff surface to expose fresh rubber (or something like that).

The outer skin of a tube might still have mold release lubricant on it, otherwise it's oxidized rubber. Either way it will resist good adhesion from what ever.

The last step is almost as important,

x- stitch down the edges. You need to work the patch and tube into each other at higher pressure than you can get by just squeezing. Comercial operations use a stitcher which is basically a wheel on a stick. You don't need buy a tool, rolling the bottom edge of a cup, or even the side of a spoon does the job, and a properly stitched patch is there forever.

noglider 

Right. I never use a clamp.

I always carry a tube. The patch kit is for the second flat. Besides, you can't patch a valve stem failure.

noglider 

Francis and I cross posted. He's advocating stitching which is kinda like clamping. I would normally edit away my "never use a clamp" comment, but this time I'll leave it and say I defer to Francis.