When choosing a silicone hose it is essential that you purchase the correct size. Silicone hoses cannot be stretched or shrunk to accommodate errors. If you select a hose, which is too big, you will risk over clamping which will simply damage the hose.
Selecting a hose which is too small will shear the inner side of the hose and could result in pieces of silicone coming loose and working there way into your system. Not good for turbo, radiators or air intakes.
Hoses are sold by internal diameter not external diameter. You need to choose the hose with the internal diameter matching the outdoor diameter of the pipe you are wishing to connect to. The smaller the diameter the thinner the wool, the larger the diameter the thicker the wool. There is a tolerance with the internal diameter due to shrinkage when manufacturer, this is generally +/-0.5mm.
Viper Performance sell high quality silicone hoses and have lots of technical information on their website to help you find the correct product. They often get asked about hose sizing and therefore have produced this video to explain this process.
Within it they reference the issue of misconceptions about silicone hoses; “People think that if they place the silicone hose in boiling water it will stretch. Our polyester reinforced automotive grade silicone will not stretch or shrink due to temperature and therefore immersing in boiling water is pointless.”
Viper Performance offer a lifetime warranty on their silicone hoses, this will however be invalidated if the wrong size hose is used.