Stepwise multiple linear regression results that correlated initial impact (40.6 cm vertical drop distance) TTD dynamic surface properties and Clegg Hammer measurements (CIV = impact deceleration, DEF = residual deformation) at the racetracks.

Each column includes the stepwise regression coefficient for candidate variables (in rows), and adjusted R2 value for each model. Bolded terms had the strongest correlation for that model. For each depth of surface, the first 2 drops without missing CIV values were included as potential candidate variables. NA = not applicable or not tested due to missing values. ns = not significant (P>0.05). Intercept for synthetic vertical force maximum was not significant (P = 0.29).