Bicycle Mechanics - To let down, or not let down.....

My bike shop guy told me i shouldn't leave my tires pumped up hard (150psi) all the time because they will stretch and become deformed. So after each ride I let them down to about 50 or 60psi.

I have noticed that my Conti GP 20mm tires do get a bit "out of round" after a couple of thousand miles, so is this true, or is the guy yankin' my chain?

I have noticed that my Conti GP 20mm tires do get a bit "out of round" after a couple of thousand miles, so is this true, or is the guy yankin' my chain?

I think he's lanking your chain. Tires don't stretch. Tubes in tires don't stretch. A tire is not round after 2000 miles because it's wearing out. To test it yourself, leave a tire on a spare wheel pumped up while you ride another wheel for 2000 miles.

But I have noticed the tires become much easier to get on and off when they age a little, so, doesn't that mean they stretch?

I dunno

Uhh, tires do stretch, most definitely, kevlar bead more than wire bead. As Fat Hack
notes, tires "get easier" to install, and it is not because the rims shrink. Does it matter that they stretch? Nope, they will wear out or get cut long before it is any
significance. Tubes stretch enormously, just check a new tube out of the box against a tube inflated to 100#+ just once (inside a wheel please or you will get a balloon before you get to 10#). Simple example: take a rubber band and stretch it a bit, relax it and compare with another similar band unstretched.
One other aspect of this is whether you are doing the tire, bike or you any good by going to 150#
inflation pressure. Very few tires are rated to this pressure, and the benefits of riding at this pressure are miniscule. Try 120# just as an experiment for a few rides and see if you can stand a lower pressure. Your pump will last longer also. Steve

One other aspect of this is whether you are doing the tire, bike or you any good by going to 150# inflation pressure. Very few tires are rated to this pressure, and the benefits of riding at this pressure are miniscule. Try 120# just as an experiment for a few rides and see if you can stand a lower pressure. Your pump will last longer also. Steve

The 20mm Continental Grand Prix is rated to 150psi; the 23mm are rated to (i think) 120psi.

I read all the science a couple of years ago about contact patch, etc, so I tired 23mm tires, but I hated them -- felt like I was riding 'postie tires' -- couldn't stand seeing the front tire spread across the road every time I got out of the saddle.

What gets me is that they don't use 23mm tires pumped up to 115psi when they do a time trial, they use something 21mm Vittoria tubular pumped up to 160 or so.