Solved - problem with out of round 700c40 tires

Apr 1, 2014
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Picked up a couple like new CST 700c40 tires and replaced old cracked 700c45 tires. Reused the tubes. Used wheels have some runout but not bad. The smaller tires were difficult to mount tube seemed to big a diameter when I put them inside the new tires and excess length tube may have bunched up in a spot. After mounting both tires have a flat spot.
The witness line they cast above the bead is sunken below the rim for maybe 6" and that's where the flat spot is.
I have inflated and deflated them several times, worked my way around the bead by hand several times, dropped them sharply on the floor several times around the whole diameter trying to get the tire to seat correctly. This has always worked for me in the past. I'm thinking either the tires are made wrong or my tubes are too big to work with the smaller tires. I don't remember what the tubes I'm using are labeled for size. I notice they seem to cut off at 32mm for smaller size?
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Last edited:
Apr 1, 2014
3,230
3,722
65
Wisconsin
Rating - 100%
10   0   0
Removed the valve stem and dismounted the tire. Surprised to find this. The tube was twisted!
IMG_1894.JPG

It was hard to get all the air out of the tube and the tube which is marked 700c45 when it had enough air to loosely hold its shape interfered with the 700c40 tire bead.
With no air in the tube I placed it back in the tire after lightly coating the inside with talcum powder making sure to keep the tube seams lined up to avoid twist. Tire installed easily with no air in the tube. after inflating to 20 psi and deflating and reinflating to 70 psi the tire runs true now!