## 3 Correct Direction of Chinese HSRS Improved Design
### Rational Condition of Wheel-Rail Matching
(**c**) Two-point contact problem on railroad top with stronger dynamic interaction such as central hollow tread wear in Chinese HSR practices. (**d**) Comparison of RRD curves for three typical wheel-rail matching situations. performance of the vehicle/track interaction are large and the decision should not be made lightly. For instance, the profile evolution from P8 to P12 tread in UK HSR practices fully demonstrates the importance of scientifically promoting the limit and construction speeds under the rational condition of wheel-rail matching [42; 43; 44; 45]. Similar to the practices of Japanese Shinkansen rails, UK HSR has not undergone rail grinding treatment, i.e., UIC60E1 with a bottom inclination of 1/20. In order to reduce the RCF failure on rail shoulder at one side of gauge corner, the P8 tread is selected for wheels, by which the stable wear regulation at high conicity is represented in the operation and maintenance of such as the Mark 3 train and EMU trainset [39]. First of all, the Express Rails to London Heathrow Airport borrowed partially from the rapid rail system. The light rails UIC56E1 with a bottom inclination of 1/20 will be matched to the P8 tread, the flange thickness of which is reduced from the original 32 mm to 28 mm, and the flange angle is reduced from the original 76 deg to 68 deg. As a result, the wheel-rail clearance on each side is increased by 4 mm, and \(\lambda_{eN}\approx 0.18\). Secondly, the P8 adopts a specific hollow tread with a larger curvature radius. However, it is still easy to form the local conformal contact (or two-point contact) on the rail shoulder at one side of the gauge corner. Particularly, the railroad damage is difficult to avoid when the curving negotiation has a small radius. As such, the wheel spin singularity forces the tread to gradually generate the uneven power dissipation problem, i.e., the RCF fails on the flange root or rail shoulder, which is the unbearable cost that must be paid during the stable wear stage at high conicity. Finally, the proposal was adopted to replace the P8 tread with the P12 one, so as to implement the economical re-profiling of the wheelset, which has the following four features: (i) The anti-RCF design near to flange root is used to avoid the two-point contact on rail shoulder as much as possible; (ii) The flange thickness is further reduced by 2 mm, which matches to the UIC 56E1 with bottom inclination of 1/20, and \(\lambda_{eN}\approx 0.10\); (iii) Moreover, UIC60E2 with bottom inclination of 1/40 is partially changed in UK HSR to form hammering impacts, but the rail gauge is broadened to 1438 mm, to which the P12 tread with flange thickness of 26 mm is matched, \(\lambda_{e}<0.10\); (iv) So the economic re-profiling option of wheelset is implemented with the assistance of auxiliary technologies such as proper flange grease spraying [46], and the wheelset re-profiling period is extended twice. Chinese HSR practices should not blindly copy these foreign experiences because the Chinese track parameter system has already achieved the technical objective of their improved designs for wheel-rail relationships. No matter the car body instability or the bogie yaw phase margin deficiency, the improper application of anti-roll torsion bar devices has become one of the most common technical problems in Chinese HSR practice, which may be caused by the long-term operation of dedicated lines. Both practices of CRH in China and CTX in South Korea can confirm that the XP55 tread is one of the optimal wheel profile designs to better fit the wheelset change, i.e., \(L=1353\) mm. If the XP55 tread is matched to the rail CN60 KG with a bottom inclination of 1/40, as shown in Figure 3b-d, \(\lambda_{eN}\approx 0.06\), and the corresponding low wear area is also significantly expanded. Under operations at servicing speeds \(\leq\)200 km/h, the wheelset re-profiling period can generally reach 30 \(\times\) 10\({}^{4}\) km.