My tires always look sad and limp.

I pump up my bike tires before every ride, both at home and at work. However, after about 2 or 3 km into my 23 km commute, the tires start to look slightly deflated, and this becomes more noticeable as the ride continues.

I’ve replaced the tubes, checked for leaks, and checked the tires for sharp objects, but the issue persists. I even had the same problem on my previous bike. Is it normal for tires to appear a bit limp while riding?

(Road bike with inner tubes, I pump them up about 90psi)