Bicycle Mechanics - ok whats going on here

I switched over to 700x28C tire a few weeks ago. Im on my second flat already, but both times the hole where the leak starts was around the valve stem. I made sure to put the tube/tire on properly after looking up the method on a website. I dont understand why it tears near the valve. The sidewall states 120PSI max, so i put anywhere from 115-120 PSI(going by the gauge on the pump, topeak Joeblow sport)

the tubes are bontrager 700x28-32c -1/8-1/4

the wheel is a Bontrager camino 622-32 wheel

this last flat happned over night, i rode yesterday morning several miles, came home and today the tire was flat when i went to go ride...

is it getting pinched? should i not inflate so high, do i need a different wheel?

thanks

Sounds like a bad batch of tubes to me.

I'd try a different brand at least for the near future just so you avoid this issue.

i hope that is all it is. I will keep my speed lower for a couple of weeks just in case, dont want to have a blow out going 25+

Is your tube touching metal where the valve goes through the rim?

If so, cover the metal with something.

Is your tube touching metal where the valve goes through the rim?

If so, cover the metal with something.

+1 for a check. Also, try filing any sharp edges off the hole in the rim. Having said that, if you weren't experiencing problems before switching, it does sound like either a change in technique on your part or faulty tubes may be to blame.

Of course, check the condition of your rim tape and check the hole for sharp edges.

Next, when you install the tube/tire, be sure to inflate about 30%, then push the stem back into the tire (push the stem back into the rim hole so it goes into the tire, but not so much that the stem falls inside the tire).

This assures that the tube around the valve is seated properly inside the tire and helps make sure there are no tube wrinkles around the stem.

I assume that you are also making sure the valve is 90 degrees to the rim and not laying cattywhompus sideways.

Of course, check the condition of your rim tape and check the hole for sharp edges.

Next, when you install the tube/tire, be sure to inflate about 30%, then push the stem back into the tire (push the stem back into the rim hole so it goes into the tire, but not so much that the stem falls inside the tire).

This assures that the tube around the valve is seated properly inside the tire and helps make sure there are no tube wrinkles around the stem.

I assume that you are also making sure the valve is 90 degrees to the rim and not laying cattywhompus sideways.

What's that now?

edit: nice vocab.

thanks all, will try suggestions.

We sell Bontrager and had a run of bad tubes in that same size. Punctured five tubes on a customer's bike, all where the valve stem is bonded to the tube, before we decided to try the next smaller size. Problem solved.

smaller size as in 48mm valve stem or 36mm? My lbs only stocks 48mm. I should find a new tube. So far i have not had a flat with 40+ miles on the new tube i replaced a few days ago. But i have a feeling in few days i will wake up with one.

what are other brands of tube that are good quality, that isnt over 7 bucks

I would like to mention i rode on the 32c tires for about 6 weeks without an issue at all, i kept them at 85 psi at all times. A week after i switched over to the bontrager 28c tire, now i have these slices near the valve..twice now..and a third is probably coming up soon, hopefully not at high speed.*knock on wood*

smaller size as in 48mm valve stem or 36mm? My lbs only stocks 48mm. I should find a new tube. So far i have not had a flat with 40+ miles on the new tube i replaced a few days ago. But i have a feeling in few days i will wake up with one.

what are other brands of tube that are good quality, that isnt over 7 bucks

I would like to mention i rode on the 32c tires for about 6 weeks without an issue at all, i kept them at 85 psi at all times. A week after i switched over to the bontrager 28c tire, now i have these slices near the valve..twice now..and a third is probably coming up soon, hopefully not at high speed.*knock on wood*

Michelin AirComp. Dunno how much they retail for in the US but for £4 over here they're fantastic.

What do you mean by "good quality"? A $4 MSRP kenda tube holds air perfectly fine.

smaller size as in 48mm valve stem or 36mm?
Sorry for not being more specific. Smaller as in 27x7/8-1", or 700cx20-25. These are actually easier to work with under a slightly wider tire, and the smaller cross section means they just stretch a little more.

All road presta tubes that we stock have 48mm stems.

I've personally had good luck with CST lightweight tubes purchased on an ebay store called nicebiketires.

Don't tighten down the valve-stem nut too far, just enough so you don't lose the stem into the tyre when installing the pump. Also only use floor-pump, no hand pumps allowed.

Leave the stem nut off, I haven't run any for years since I discovered the reason I kept busting stems was from tightening the nut because it rattled. Think of all the weight you save too! :)

Are you inflating with a mini-pump? I killed tubes with mine for years before I invested in a stand pump. Haven't had a problem since.