Bike flat tires mystery...fellow bikers, please help me solve this.?

Question

Hello,

I have a Medalist road bike with 700x28C wheels. Last week I noticed the air in my tires was a little low...it was about 40psi..so it didn't feel deflated to the point that it would damage my tires, but a little low on air. I kept forgetting to fill it for a few days, then on Friday came home and filled both tires to 70psi (the tire rim is confusing, but appears to be saying min 50psi max 85 psi. Is that normal?? I know my car takes about 35-40psi). I also filled up both tires on my 2nd bike (exactly the same bike, but newer - I rode it like once or twice) to 70psi. Two hours later, I come back, and my front tire on the first bike was completely flat, while the back one was as still full (no noticeable change). The next morning I came back and found the back one was also absolutely flat. I tried filling both of them up, but both lose air so fast they don't even inflate AT ALL. I took out the font tube and found that it had two very large holes - about 5mm diameter, BOTH

Answer 1

Yep....you got a pinch flat.    40psi is way too low pressure to be riding on that size of tire.   You'll need to replace the tube, because pinch flats can't be satisfactorily repaired 95% of the time.  You can try, but they probably won't hold for long.  

Always check your tire pressure every time you ride....use a pump or a gauge, not just by squeezing.   This is really important on narrow tires because of the risk of pinch flats and rim damage.

Answer 2

There is usually a band around the inside rim. It protects the tube from the spokes, the ends of of which go into the rims, through them. Take that band off and run your fingers along the inside rim. I bet you'll find some small projections. The high pressure exacerbated the slow leak you had on the one tire and caused the new punctures. File down any projections or rough points inside the rim, replace the band and tire. Do not over-inflate. since weaknesses in the tube can succumb to the higher pressure (though not solely on the rim side).

Answer 3

40 PSI is too low for a 700x28 and leads to snakebites: double punctures in the tube from the tire bottoming out and pinching on the rim to make two identical, parallel holes. On a road bike, always inflate to the maximum (85 psi in your case) to prevent them.  I'm pretty sure this is what happened to you.

FYI, road bikes really respond well to higher pressure tires. They handle better and are much, much easier to pedal, though they feel a little harsher. 100 psi is common and 120 psi is not unusual. Buy a pair. The single most effective improvement you can make on a bike (short of a new bike) is good tires.

Answer 4

700 x 28c tyres are designed only for riding on the road- if you took them over any gravel with chopped up limestone that might be the possible cause for your puncture regardless of how hard you pumped them up.