ker thunk, ker thunk, ker thunk...HUN?

[digibud]

Yesterday I took off my studded tires and put on some skinny street tires as our ice is melting in the streets and I can ride without studs. I'm about 4mi down the road and I feel a thump thump thump so I stop, thinking I have some odd flat but the tire is not flat. I had failed to inflate it full enough to pop the bead in place. I took out a C02 cartridge and forced air into the tire till it popped in place, let some air out and took off again. Whoa! In just a minute or two I feel a thump thump again and I stop but now it's the FRONT tire. It's not impossible that I simply didn't notice this earlier but jeez...it was pretty pronounced...I fixed the second tire with more CO2 and was on my way.
Is there ANY way a tire can get a bead to move so as to create this issue? I think it's most likely that I simply didn't feel it as it was the start of the ride; I can't think of anything else so just curious...anyone ever have this happen ... they find a bead not properly seated part way into a ride?

[Kimmo]

Cheap tyres?

[IthaDan]

Low pressure can cause a bead to slip. I'd imagine it'll only happen in a specific spot if you're pretty much holding still and moving the bars quickly (like track standing). Could that be it?

[Bianchigirll]

DID you check to be sure the tube was not caught under the bead before inflating the tire fully, or to your desired pressure? Depending on your pressure it is possible that the tube got caught and the riding forces helped the tire wotk of the rim.

[digibud]

thanks for the suggestions...I think this will remain a mystery. The tires were at 60lb (made to inflate from 40-65) and I wasn't doing any track standing. Oh well. Not a big deal but definitely and odd one.