robertj298 

This is all very confusing. I'm trying to figure out what tire pressure I should be using for each of my 2 bikes. None of the charts I read come up with the same figures plus neither sizes stamped on each bike is accurate. So here is what I have. My vintage road bike has tires that are stamped 27"s X 1 1/8 " but in actuality the tire measures 23mm. Tire pressure is stamper 95- 105 psi. My hybrid bike has tires that are stamped 700mm x 28 mm but actually measure 26 mm wide. Tire pressure stamped on it is 115-125 psi. So if I'm 180 lbs and my bikes are 25 lbs. what should my tire pressure be? Thanks Bob

Doug5150

Firstly,,, a given bicycle tire's inflated width depends partly on the inside width of the rim it is mounted on.
When they are tested by ETRTO, ETRTO has their own (secret?) table of which width rim to use according to what the claimed width of the tire is.
So if you use a rim that is wider or narrower than what they use, your 25mm tire may be narrower or wider than 25mm when inflated.

Secondly--use 75 - 100 PS in either tire, if both have hooked-edge rims.
If the vintage road bike has straight-sided rims (without bead hook edges on the inside) then the max pressure is maybe 60 to 80 PSI.

I am not an expert, but I think that straight-sided (aluminum) rims started being phased out on new bikes during the mid-1970's. So if your vintage bike is that old or older and has aluminum rims, you may want to take a tire off and check that...

tFUnK

Start with 90psi front and 100psi rear and adjust up or down from there based on riding experience.