Abstract: A steel wire which has an excellent fatigue limit when made into a spring is provided. A chemical composition of the steel wire according to the present embodiment consists of, in mass %, C: 0.53 to 0.59%, Si: 2.51 to 2.90%, Mn: 0.70 to 0.85%, P: 0.020% or less, S: 0.020% or less, Cr 1.40 to 1.70%, Mo: 0.17 to 0.53%, V: 0.23 to 0.33%, Cu: 0.050% or less, Ni: 0.050% or less, Al: 0.0050% or less, Ti: 0.050% or less, N: 0.0070% or less, Ca: 0 to 0.0050%, and Nb: 0 to 0.020%, with the balance being Fe and impurities. In the steel wire, a number density of V-based precipitates having a maximum diameter ranging from 2 to 10 nm is 500 to 8000 pieces/?m2.

Abstract: A testing machine for a tire on an imitation road in which a tire to be tested is urged against a crawler with the aid of a cantilever arm connected through a crosshead to a lifting and lowering disc engaged with screw threaded rods rotatably mounted in a machine frame. The crawler is composed of an endless chain and a road surface forming rods detachably mounted on the endless chain and replaceable by new rods made of different kind of material. In the crosshead are incorporated slip and camber angle setting mechanisms. Provision is made of load cells such as a strain gauge operatively connected to a tire supporting shaft, driving and driven shafts of the crawler and a guide rail of the crawler and for detecting a vertical load subjected to the tire, a torque for driving the crawler under various load conditions and a transverse component of force subjected to the crawler when the tire having a given slip angle or a camber angle is urged against the crawler.