Tire help!!
 

I have 700✖38c 40-622 tires on my fixie I want to put thinner wheels on what is the thinnest or skinniest tire I can put on this rim ? Please help

Might be helpful to know what the rim is rather than the tires.

+1

Recommended reading: http://www.sheldonbrown.com/tire-sizing.html#width

How would I measure them

What concerns you is the inside rim width. It isn't critical since each would accept a range of tire widths, so if you don't want to remove the tire first, you can measure the outside diameter and subtract 5mm to allow for the wall thickness. This isn't precise, but is plenty accurate enough for your purposes, or as we say "good enough for government work"

The chart you are looking for, USMC17, is near the bottom of the page. But look on the chart as a recommendation rather than a gospel. Mountain bikes regularly use 54 to 57 mm tires on 17 mm rims. Granted the pressures are lower but that's due to the terrain more than the tire limitations on the rim.

Hi,

The real question is why do you want thinner tyres and what tyres do you
currently have, and why do you think thinner tyres will help matters at all.

rgds, sreten.