Halebopp

I've been riding my cross bike that I just built a fair amount, and am really enjoying it.

However, I'm becoming increasingly frustrated because in the space of a week, I've gotten three pinch flats on my front tube.

I'm only 140lbs, and haven't been riding the psi really low...maybe 40psi at the lowest?

Anyone have any ideas of what could be causing them or what I could do differently?

Thanks a lot.

pretzelface

Bad rim strip?

Halebopp

I suppose it could be, though i've been using these wheels for two+ years on the road with 23c tires and have never had a flat on my front tube.

Andy_K 

How narrow are the rims? How wide are your tires? What size tubes are you using? What's your psi?

pungee

If you are bottoming out with clinchers you are going to pinch flat. Run higher tire pressure.

flargle

What sort of things are you pinch-flatting on? You might have to ride with your weight back more, and use a bit more technique over rocky/rooty/curby things.

badbikemechanic

Obviously you need tubular rims and tyres

Halebopp

32c tires, 28-32c tubes, not sure how wide my rims are. They're kind of semi aero, if anyone can guess from that.

Cynikal 

I'm wondering how true your pressure gauge is. For clinchers I use tubes that have removable valve cores and I add some sealant like Stan's.

crocodilefundy

Sealant is a great idea. your gage could be wrong. 40 psi in cross tires feels firm but you can still deflect the tire a bit.

When you ride over rocks/ roots do you ever feel them hit the rim? if so you clearly are running too low a psi.

brianbeech

Having worked in a MX shop for years, I found that sealant typically, if left alone, would corrode the rim and make it so nasty that you didn't want to mess with it. Is this common on bicycle applications as well, or do you typically change tires often enough that it's not sitting for very long?

crocodilefundy

Assuming one runs normal tubes the sealant should not ever hit the rim. Also if one runs tubless there is a rubber rim strip that covers almost the entire rim. Finally the aluminum rims probably corrode differently than steal rims.

brianbeech

yeah, that's really my question, sorry for being unclear - aluminum vs steel (which is what i saw). Obviously not tubed tires, but in the tubeless applications.

Andy_K 

I think something unseen is going on here. Are you sure these are pinch flats? I weigh 195 and have raced with 700x30 tires as low as 30 psi, and I have never had a problem with pinch flats. All the theory says I should.

I use 700x28-35 tubes, usually whatever I can get cheap from Price Point or Performance. I put baby powder on the tubes before installing them. I don't know how much that matters. I'm sure my riding style is a factor, but I couldn't tell you what I do that helps. I often hit things head-on rather than glancing. That's not so good for my speed but probably helps the tubes.

How careful are you when you install a tube? I generally pump the tire up to abotu 15 psi and then rock it back and forth to try to make sure the tube and tire are seated properly. If the tube is pinched when you install it, it's only a matter of time before it flats.

Thicker tubes could help. Also, check the rim for damage and make sure there's nothing embedded in your tire.