RP XXX Guidelines for Outset Single Wheels Rev Feb 10, 2006 

# TMC Recommended Practice
RP 6XX VM RS XXX 

## Guidelines for Outset Wide Base Wheels for Drive, Trailer and Auxiliary Axle Applications DRAFT FOR TASK FORCE REVIEW – 9/28/09 Text in blue has been added or changed from the February ’09 draft This draft in cludes changes discussed at 9/14/09 Task Force meeting in Raleigh

- In the load tables, changed from 1.0” outset to 1.13”

- Below the tables, simplified the statement on “Effects on other components” PREFACE The following Recommended Practice is subject to th e Disclaimer at the front of TMC’s Recommended Maintenance Practices Manual. Users are urged to read the Disclaimer before considering adoption of any portion of this Recommended Practice. PURPOSE The purpose of this Recommended Practice (RP) is to prov ide guidelines for selection and specification of wide base tire/wheel applications for drive axles and trailer axles. SCOPE The scope of this RP is limited to single wide base outset wheels on drive, trailer, and auxiliary (e.g, dolly, tag, or pusher) ax le applications. Singled inset wheels are not included in the scope of this RP. REFERENCES/GLOSSARY RP -222 Users Guide to W heels and Rims INTRODUCTION Replacement of standard dual wheels on drive axle and trailer applications with single tire/wheel appl ications can adversely affect the loading on the axle end. This can alter the stresses in the bearings, spindle, hub, axle housing, and reduce the load carrying capability. The anticipated life of the axle end may also be affected. In some applications, it is permissible to operate an outset wide base wheel on the wheel end without significantly affecting the anticipated life, if the maximum load is reduced. The amount of load reduction depends on the wheel outset.Guidelines for Outset Single Wide Base Wheels

RP XXX Guidelines for Outset Single Wheels Rev Sept 29, 2008 For wide base wh eels, either outset or inset is used to describe wheel geometry. Both are calculated as the distance from the centerline of the rim to the wheel - mounting surface. A wheel is inset when the centerline of the rim is inboard of the wheel mounting surface. A wheel is outset when the centerline of the rim is outboard of the wheel - mounting surface as shown in the figure. The axle end load ratings are based on this outset condition , which increases the bending moment (load) on the axle end and correspondingly lowers the rating as compared to dual wheel applications. Some trailer axle manufacturers may recommend a P Type spindle for single outset tire/wheel applications. MA XIMUM LO AD GUIDELINES The tables below show recommended maximum axle load ratings for various wheel outset values on common axle configurations. These recommendations are based on maintaining original fatigue life of hubs, bearings, and axles. Wh eel outset may be verified by contacting your wheel manufacturer. Note that R- Series drive axles are available in three “basic” load capacities: 20,000 lb, 23,000 lb and 26,000 lb. Additional restrictions may apply, depending on factors such as spring center distance and suspension type. For consideration of wheels with outset greater t han 2.0”, consult your axle and wheel end component suppliers. Load point for standard dual application Load point for outset wide base wheels Wi de base wheel outset Standard duals shown in gray
Outset wide base wheelGuidelines for Outset Single Wide Base Wheels

RP XXX Guidelines for Outset Single Wheels Rev Sept 29, 2008 Maximum Loads for Outset Wide Base Wheels – Drive A xles Wheel Outset R Type A xle with 9.5 mm Wall Thickness R Type A xle with 11 mm Wall Thickness R Type A xle with 12.7 mm Wall Thickness R Type A xle Ax le Load Rating (lb) Ax le Load Rating

(lb) Ax le Load Rating

(lb) Ax le Load Rating

(lb) Duals 20,000 20,000 23,000 26,000 1.13” maximum 17,000 20,000 20,000 22,000 1.14 to 2” Consult A xle Manufacturer 17,000 17,000 19,000 Maximum Loads for Outset Wide Base Wheels – Trailer A xles Wheel Outset P Type A xle (Parallel Trailer) N Type A xle* (Tapered Trailer) Ax le Load Rating (lb) Ax le Load Rating

(lb) Duals 25,000 23,000 1.13” maximum 20,000 19,500 * 1.14 to 2” 19, 000 18,000 *


## * Note - some axle manufacturers do not recommend N type axles for use with outset wheels – confirm your application with the manufacturer. EFFECTS ON LIFE OF OTHER COMPONENTS In addition to the primary issue of hub / bearing / axle fatig ue life addressed above, other axle - end components may be affected by use of wide single tires. To assure successful operation, suitable components should be fitted as recommended by the vehicle manufacturer.Guidelines for Outset Single Wide Base Wheels

RP XXX Guidelines for Outset Single Wheels Rev Sept 29, 2008 EFFECT OF WIDE BASE WHEELS ON VEHICLE T RACK AND WIDTH Changing from dual wheels to wide base single wheels can affect significant dimensions such as overall width, inside width, and track.

The effect on these dimensions that will result from a wheel/tire change can be calculated as follows : New Track = Original Track (Dual Tires) – (2 X Dual Wh eel Thickness) + (2 X W ide W heel Outset) New Overall W idth = New Track + W ide - Base Tire W idth New Inside W idth = New Track – Wi de - Base Tire W idth EXAMPLE CALCULATION Original Track as measured : 76.8” Dual W heel Thickness as measured at wheel disc: 0.42” Wi de wheel outset from Wh eel Mfr (Catalog): 2.0” Wi de - Base Tire Wi dth from Tire Mfr (Data Book): 17.2” Then New Track = 76.8 – (2 X .42) + (2 X 2.0) = 79.96” New Overall W idth = 79.96 +17 .2 = 97.16” New Inside W idth = 79.96 – 17.2 = 62.76”