Originally Posted by phantomcow2
Well currently I am using 1.4" RItchey tom slicks for my XC rig when it is on the road. The shop has this tire in 1 and 1.4, well im wondering if there would be a noticable difference (positive and/or negative) by buying a 1 when my current tires wear out
Unless you have laboratory grade instrumentation I doubt you'll be able to measure much difference.
1. At equal air pressures the 1.4's will have slightly less rolling resistance.
2. The 1.0's will have slightly less aero resistance.
3. You'll probably run the 1.0's at higher air pressure if, for no other reason to minimize pinch flats. The higher air pressure will probably neutralize the rolling resistance penalty.
4. If you ride on crushed limestone rail-trail conversions, the 1.4's will feel much more secure.
In real life the differences mentioned above will fade into the background when compared with the effort required to push your torso through the air. The higher air pressure will probably "feel" a little faster because it bounces around more but actual measureable speed will probably be about the same. Higher air pressure will make your bike feel subjectively bumpier.
My advice is to buy whichever size you think looks cooler.