OTR Engineered Solutions has expanded its SolidBoss smooth skid-loader tire lineup with the introduction of a new 31x10-20 (10-16.5) size. (Illustration: OTR) OTR Engineered Solutions, a supplier of off-highway tire, wheel, and track solutions, has expanded its popular SolidBoss smooth skid-loader tire lineup with the introduction of a new 31x10-20 (10-16.5) size, providing customers with another flat-free solution for hard-surface applications.