What is TPI and EPI (Threads Per Inch) on Bike Tires

Bicycle tires often have a TPI or EPI rating which stands for “threads per inch” and “ends per inch” respectively. These ratings describe the build on the tire and might allow you to ride with different levels of air pressure for different performance (lower pressure increases traction but might decrease efficiency). Five PSI seems to be a good sweet spot for 4” fat tires operating in snow and something like 15 PSI can be good for gravel and loose dirt. You may have different results based on bicycle weight and the exact softness of terrain. In general, higher PSI is more efficient but decreases surface area and cushion.