Tire becoming unseating from wheel while riding!

Brad Marcus

While racing Quassy yesterday, I was at approx mile 45 on the bike. The day was going almost perfectly according to plan. Swim was ok and I was sticking to my power numbers on the bike with better accuracy than I expected. I was coming down a pretty steep and fast hill when I heard an awful rubbing sound from my back wheel. I figured it was a brake pad. I made it to the bottom of the hill and hopped off to find that about 2" of my tire had become unseated (lost the bead to the wheel) and that portion was rubbing against the frame. Once I stopped, the wheel was locked up and would not spin, so you could imagine how much friction there was while I was rolling and it's amazing the wheel didn't lock up in my descent. I pulled the wheel off and in doing so heard the tube POP! Not surprised by this, I tried to remain calm and pulled the tire bag out and began to change it. The story gets long here and I'll follow that up in my race report since I was out of commission for 40-45 minutes, but I still don't know what would've caused this. Does anyone know what in the world would cause a tire to become unseated suddenly from the rim? My wheel looks ok and didn't hit any large holes or bumps that I can remember. I put a new tire on (Conti GP4000s) only 2 weeks ago and have ridden on it prior. I'm a bit afraid of this happening again..... Thanks!

Darren Freeman

It sounds like you might have had an over inflated tire.  I've read that if a tire is over inflated that it puts much more stress on the bead of the tire and rim and can pop right out and cause a flat because it can't contain the tube. Which this seems about right for your case because after you stopped this is exactly what happened.  Additionally, since it did  warm up quite a bit yesterday you may have started out with the right pressure but with the temp increase during the day it caused your tire to become over inflated.  If you are at the upper limit the tire pressure for your weight, the heat increase seems to be the obvious culprit to this occurring.

I recently realized I was over pressurizing my tires and have significantly reduced the pressure in both.  Previously I was inflating both tires to 110 psi but after playing with the pressure now ride with quite a bit less than that.  Yesterday I inflated my rear tire to 100 psi and the front to about 95-97.5 psi.

My suggestion would be to read Sheldon Browns page on Tires and Tubes and then play with the pressure on your tires over several training rides to find the optimal psi.  Sheldon Brown's recommendation is that the front should be about 10% less pressure than the rear tire since it doesn't support the same amount of weight as the rear.

http://sheldonbrown.com/tires.html

 

wills029

Brad, your tire may not have been uniformly seated around the entire circumference of the bead. This can cause the bead to unseat and tube blow as soon as you inflate to pressure, or slowly work loose over course of a few rides. Whenever I replace a tube or reinstall the tire, I visually inspect both sides of the tire at the edge of the rim to ensure a uniform seating of the bead. If not seated properly, you will see more sidewall showing in one section and less sidewall showing across from that section. I also hold the wheel in my hands with the axle, spin it and watch for any fluctuations in the tire profile. Btw, I also use Conti 4000S and 4000S II.

Brad Marcus

Hmmm...I'd guess that Darren's explanation is more probable in this case. Bill's is a possibility, but I think I would've noticed the tire sitting unevenly prior. Every time I move my bike, I always spin the wheels before I ride since the brakes tend to move around a bit and I want to make sure they are sitting properly. As Darren mentioned, it was cold prior to the race , 47F, and warmed considerably on the bike. I think I pumped my tires 107ish on the rear...maybe I should begin trying less pressure.

Thanks guys!

Darren Freeman

No problem Brad.  

As a follow up to what Bill said is it is possible the bead of the tire might not of have been correctly seated.  I didn't know this either until I read it somewhere, but apparently there are indicators on the side of the tire which you can look at to see if the tire bead is correctly seated in the clincher groove.

Steve West

Brad, I had 2 rear wheel blowouts on a training ride where the tire blew off the rim just 2 weeks before IMLP! Sounded like a firecracker going off under my seat. It freaked me out thinking of the screaming decent into Keene at 45+ mph ....

Ended up being the rim tape. My LBS was the one who figured it out where I couldn't. The rim tape slid off center and up to the bead lip. The thickness was just enough to impair how the bead seated. My LBS trimmed the tape so it sat in the center gullet but replacing it with a different width would have had the same result. Hasn't happened since.

Take a look at how the rim tape sits, see if it is up near the bead seat.

robin sarner

Yes check the rim tape.      And see if wide enough.

What is your wheel?

Personally, I would be very doubtful of the pressure theory.      The idea that one needs to not pump up tires, prior to races, due to sun exposure and the possiblity of tubes blowing up, does not stand up to scientific rigor.         I ride tires pumped to near the upper limit, being a big man.    Have never had issues with riding on the lava, in Hawaii, during training trips.      And never have had issues, with pre-pumping, with bikes sitting in transition area with hot temps.

I often have your same problem with my bike on the trainier, even with trainer tires.    I assume just due to the many hours I do indoors.     Friction heat deforming the tire.     I had to switch wheels to one that seem to accept the tire bead deeper.

So the bead seated thing sounds like a possible issue.          

Maybe a faulty tire too.

harrast

I've never had a tire come off, but I've put my bike inside the car after a race and come back to a blown tire twice. I'm not claiming that this would normally be the case if everything is in order with the tire and wheel. I have a feeling my rim tape was marginal and allowed the tube to slip into a spoke hole under the higher temperature/pressure. For the tire unseating, I would subscribe to the poor tire seating theory--could be either a rim or tire issue, or maybe a guardian angel unseated the tire so that you wouldn't get run over by a bread truck later in the race ;-).

Brad Marcus

I suppose any of the above is a possibility. I have Zipp 404's on my Tri bike. When I changed the tube at the race, I did inspect the tape and didn't notice anything out of the ordinary. I haven't been on the Tri bike since finishing the race on Sunday - I took the road bike out yesterday. Tomorrow I plan to do a long ride 5+ hours on the Tri bike and I guess this will put it to the test. But, I rode that same wheel, tube and tire 200-300 miles before the race with no issues. The whole thing is very strange....

Brad Marcus

Follow up: I took my tri bike out for its first ride yesterday after my race debacle. Prepped bike before my long ride and pumped tires to 105lbs rear, 100lbs front. Walked back inside to grab something and as I came back out....POP! Tube blows...same rear wheel. After I removed wheel and started changing it, I realized that the tire had popped off the wheel again slightly!

I decided to toss the tire and try another one, and of course another new tube. I inspected the tire change afterwards and everything looked good. Rode nearly 80 hard miles on it yesterday (on some not so friendly terrain) with NO issues.

I'm thinking that maybe the tire was defective....or I hope so. Otherwise, I'd have to say its a problem with my wheel. Time will tell, but since I'll be at LP training next week, I'll show up with spare tubes and tires. I only wish that I wouldn't have to think about this as I'm zooming down the monstrous miles of descent in Lake Placid but I know it'll be on my mind..

Brad Marcus

By the way, with tire/tube off, I had a really good opportunity to inspect the rim tape as you guys suggested. It was perfectly centered and in great shape...adds to the mystery I guess.