seewater

I took my 1987 "American Breezer" out of 13 years of storage recently, and for the time being have "cityfied" it, for daily around town riding that is averaging 60 mi. a week. It's wearing a couple new Schwalbe Marathon Supremes (26 x 2). Rims are fairly narrow old Mavic MA-2's in good condition. And the brakes are the original (pretty aggressive stopping) Cunningham roller cams.

I've had 5 (all front) presta valve stem flats, right where stem meets the tube in less than a month. I have 2 steep residential hills as I leave home. Because the road is so narrow, and has 2 speed bumps, I have to lean on both front and rear brakes pretty hard for safety because of steepness, and cars popping out of driveways. All 5 flats happend going down this residential grade, usually as I hit a slight bump in the road toward the bottom of the hilly area's.
For the first time last night while changing one of these flats, I noticed just how hot the front rim was getting, pretty darn hot. I know tubes are generally constructed differently around the valve than they were in 1987, and I'm wondering if a couple hundred degree's of front rim heat, along with hitting bumps in the road while tube and rim are so hot could be causing the glue/seal to let go around the valve stem as has been happening.

I'm not married to this idea, but it's the only one I have right now. No rear flats at all, and no difference in how I install the rear tube/tire. I've been running the front at 55psi and the rear at 60psi. I'm 6'3" and 210lbs. right now.

Thoughts???
THANKS,
Paul

(san diego)

lubes17319

1st thing that comes to mind is there could be some jagged metal at the valve hole in your rim.

seewater

I will take the tire off and check again (carefully) today. Thanks. I will have another look, but assume it's not because last night I had a little makeshift piece of extra tube installed as a barrier at the stem, but that didn't seem to prevent anything.

Thanks,
Paul

Svr

Sounds like bead creep. The tire/tube is rotating slightly around the rim during braking and shearing off the valve stem. You can make a little ink mark on the tire and rim to see if they've moved relative to each other after hard braking.

lubes17319

^ and that was the 2nd thing to come to mind, but seemed much less likely.

seewater

Bead Creep...Interesting. I'm leaving for a 6 mile ride to the post office, and will mark the tire/rim so I can check it when I get back. I will leave the marks on for a few days, and see how things progress. Might take tube/tire off today and talc up a bit as well.... If it turns out to be bead creep, how can I limit it? This 6 mile ride is a bit of a gamble, I can fix a regular road flat... but am out of new tubes for a couple days while I wait for a shipment, and it's 101 degree's outside right now...LOL Oh well...I'm still young...

THANKS,
Paul

Mr. Cranky

A buddy of mine had the same type of flat at the bottom of a steep hill with extended brake application. The tube was sheared where the stem meets the tube. I like the theory that the heat builds up the pressure in the tube, and then hitting a bump causes an additional spike in the pressure. Think of it this way... if you grabbed the stem from the outside and yanked hard on it towards the wheel center, eventually the tube would fail in the same way. It doesn't make much difference if it's being pulled from the outside or pushed from the inside, the results are similar.

You might try lowering your tire pressure just a bit, alternating usage of the front and back brake so one wheel can cool off while the other is braking, and being sure to avoid the bumps as much as you can (especially near the bottom of the hill when the wheel and tire are hottest). Just my two cents.

seewater

Thanks for the input, and history of your friend. It doesn't have to turn out to be a HOT rim related flat, but until a better theory based on the circumstances comes along, based on what I know, and have seen, a Very hot front rim (from the BIG Cunningham roller cam brakes) is the prime suspect right now. Probably a few more will have some input here, so I look forward topthat as well I've got Michelin airstop tubes coming, and probably will try 1 or 2 Schwalbe tubes as soon as amazon gets them back in stock for $10 shipped.

Thanks,
Paul