elieve it or not, tires for big rigs are still available in tube type. This is hard to
believe since we haven't had tube type tires on our cars for nearly thirty years. If you plan
to do much travelling in Mexico, it is almost mandatory to use tube type tires with split
rims. The tubeless tire is very difficult to locate, even in large cities such as Guadalajara.
This was true, however, in 1991. By now, things may have changed. The tube type tires
come in even designations such as, 10-20, or 11-22 and so forth. The tube type tires can
be had as radial, which have an R designation, such as 10R20. Without the R, they are bias
ply tires.The most common tires on big rigs are the radial tubeless style. They come in various load ratings, which are an extension of the load rating of automobile tires. Most big rigs tires begin with load rating "F". This is the equivalent of a 12 ply tire. The load ratings "G" and "H" are 14 and 16 ply ratings, respectively.
The most common tire on a forty foot bus is the 12.5R22.5 size. This tire fits on a 22.5 inch diameter wheel and the equivalent load rated tire on a semi-truck is the 11R24.5 tire, which fits on a 24.5 inch diameter wheel. Truck tires are almost $100 less per tire than bus tires, since so many more trucks are on the road. If you wish to continue to employ the smaller wheel, ie., the 22.5 diameter, you may purchase the 11R22.5 truck tire in a higher load rating and still save almost $100 per tire. However, you will sacrifice a small degree of fuel economy because you are turning your motor at a specific RPM but not traveling over the ground quite as far.
If you plan to upgrade to alloy wheels for appearance, it is suggested you select the 24.5 size. You may then add the 11R24.5 tire, and the savings will help you pay for the alloy wheels. Keep in mind simply buying alloy wheels is not the only expense you will encounter. New wheel studs must be installed to accept the alloy wheels. These studs must be long enough to show about four threads after the lugs have been tightened. These longer studs, as of this writing, are about four dollars each. Multiply this times ten per wheel, times six wheels, and the added cost is over $240 plus tax, plus installation. Installation requires each brake drum be removed; have the old studs presses or beaten out and the new studs pressed in, then re-installed on the axle. Take a sample of your old stud when buying the new studs. There are many configurations of wheel studs in the catalog so don't simply tell the counterman you want a stud an inch longer. Take the old one to be sure you can compare the length and diameter of the seat.
For years, the suspension system of buses have been air bags. This was considered the standard of the industry until the Golden Eagle was introduced in 1958. The Eagle departed from convention by introducing the Torsilastic torsion bar suspension system. This is a suspension system which uses silicon rubber encased within a steel sleeve which maintains an almost uniform torsional resistance throughout its deflection range. For example, a conventional torsion bar increases the load resistance as it bends until the breaking point. Using the jacketed rubber torsion bar of the Torsilastic suspension, the load resistance is almost constant, ie., if it will resist 1 pound at 1 inch of twist, it will resist 1 pound at 2 inches of twist, and so forth. As the torsion bars tend to relax, they may be adjusted to bring back the original ground clearance. When all the adjustment has been made, the torsion bars may then be re-indexed, by removing them and rotating the mounting bolts over one bolt hole.
One of the drawbacks to the air bag suspension system is its lateral stability. In many of the older 96-inch wide coaches with air bags, they tend to lean noticeably while going around long sweeping curves, and they are visibly affected by cross winds. In the newer coaches the air bags have been placed further outboard increasing their lateral stability immensely.
In some of the older Eagles, where the torsion bars have had all their adjustment used up, air bags have been installed over them, with the added advantage of being individually inflated for leveling purposes. Many of the older coaches use a technique of valving air to individual air bags for coach leveling purposes.
The Prevosts also use their air bags for the added advantage of being able to lift their tag axle tires for tight maneuvering or when they need more load on the drive axle. As a final point, when working on your conversion, block up your coach. Do not trust your suspension system, nor trust any jacking system you may have. Wooden blocks are cheap, and I have seen a bus fall off jacks. Fortunately, no one was under the bus when it happened.
