I'm restoring my dad's old Jeunet racing bike from the seventies.
First thing I did was buy two new tires. The old ones looked still OK, but wanted to take no risk with 40 year old rubber. The new tires have exactly the same size as the old ones, and a pressure limit of 6.0 bar.
To make sure, I also bought two new inner tubes.
Then I started pumping the rear tire. The aim was 4.5 bar. It exploded at about 4.3 bar! The tire was thrown off the rim, but undamaged. The inner tube showed a large gash at the valve. I checked the rim for any spokes or other sharp objects that might be protruding into the tube, but couldn't find any.
Then I tried pumping the front tire, this time I put in earplugs. SAME THING! Explosion.
Could someone please tell me what's going on?