Tire Pressure Service Shop Dope November 1, 1946

No. 252 November 1, 1946

Tires Wheels Speed

When a racing motorcycle or car Is being groomed for an event on road or track, just as close attention is given to perfect condition of wheels and tires as to engine tuning for maximum performance. Wheel bearings are checked, wheels and tires are checked for out-of-true sideways, eccentricity, out-of-round, and out-of-balance. Careful attention is given to anything found not just right. If a tire tread is found worn irregular to an appreciable degree, tires are transposed or a new tire installed. Inflation pressure is carefully adjusted to the poundage known to be right for weight of vehicle and nature of event.

In other words, engine R.P.M. and horsepower dont mean anything unless the vehicle being driven can be guided with ease and safety at top speed. If, due to faulty wheel and tire condition, a racing vehicle develops wheel hop, shimmy, or some other bad handling condition which makes control difficult at high speed, it might just about as veil be without an engine.

Big twin stock model motorcycles of today are as fast or faster than most racing model motorcycles. Therefore, due attention to wheels and tires of stock motorcycles driven solo at high speed is just as essential as in the case of a racing motorcycle. Too many motorcycle mechanics are pretty much engine and horsepower minded, and as a result are inclined to consider wheels and tires something secondary to be given attention only after something fails, or a rider complains of serious handling irregularities at high speed.

Riders as a general thing do their own tire inflating and a wide variable is found in the pressures to which they inflate. This probably is mainly because no one has taken, the time to impress them with the importance of correct inflation pressures according to load and tire size, and to enlighten them as to the influence this has on good or bad high speed handling. One solo motorcycle will be found with 10 lbs. tire pressure; another with 25 lbs. or more.

Here and there a rider transposes his tires to avoid, excessive irregular wear of front tire tread and to equalize tire wear, but most riders dont make this a practice because they dont realize it is a must, if high speed solo handling is to be kept at its best. The larger the tire size the more essential it is that this practice be followed. A tire kept in continuous front end service long enough to allow tread to wear quite noticeably irregular and peaked, is very likely to set up a high speed weave or shimmy, especially if over-inflated.

When a solo rider complains of bad handling at higher speeds, check as follows and give attention as needed:

1. Loose wheel axle nuts.
2. Excessive wheel hub bearing play.
3. Loosened spokes.
4. Rear wheel alignment in frame and with front wheel.
5. Rims and tires too much out-of-true sideways. (Should not be more than 3/64).
6. Rims and tires too much out-of -round, or eccentric with hub (Should not be more than 3/52).
7. Irregular or peaked front tire thread wear; also determine mileage since tires were last transposed. If mileage is found to be 2500 or more, transpose wheels and tires even though irregular wear or peaking of front tread is not very noticeable.
8. Tire inflation as per inflation pressure chart included with this Shop Dope. DO NOT OVER-INFLATE.
9. Tire and wheel balance, if balancing equipment is available. Static balancing will be satisfactory, if dynamic balancing facilities are not at hand.
10. Steering head bearings for correct adjustment and any indication of pitted ball races.
11. Ride control or shock absorber for normal functioning.
12. Steering damper for good working order and adjustment so that it can be applied easily and gradually to any desired steering friction. If steering damper torque arm is found with more than .005 side lash where the rear end of arm engages frame head, this should be corrected. Every motorcycle rider should be made to understand his steering damper is an important safety appliance with which steering is steadied when driving at higher speeds. It, therefore, must be kept in good working order and adjustment, and it should be used.

With attention given as outlined you will in nearly every case find any high speed handling faults corrected. The possible exception will be the case where there is serious frame or fork misalignment or maybe a tire in extremely bad condition, which should be replaced. REMEMBER, TRANSPOSING WHEELS AND TIRES AND INFLATING NO HIGHER THAN THE RECOMMENDED PRESSURE ARE OF FIRST IMPORTANCE. IN MANY CASES YOU WILL FIND THAT THIS ATTENTION ALONE APPLIED TO A MOTORCYCLE THAT DEVELOPS FAULTY HANDLING AT HIGHER SPEEDS WILL GAIN THE DESIRED RESULT.

The advisable thing to do is to offer your riders this chassis tuneup as a preventive maintenance service to be repeated at about 5000-miles intervals. Strongly recommend that they take advantage of it. If you sell this plan, you can be sure you will hear little more about faulty handling, weaving, shimmy, etc.

The above should be applied to 45 cu. in. models as well as to big twins, especially those equipped with large tires; however, the mileage interval between service jobs can be somewhat longer. Applying to 45 model, transposing tires, of course, means removing tires from wheels, rather than simply transposing wheels with tires.

Wheels and tires should be rebalanced, at least statically, whenever casing and/or tube may be replaced.

TIRE INFLATION PRESSURES

BIG TWIN

45 MODEL

The above tire inflation pressures are based on rider and passenger weight of approximately 150 lbs. each; Package Truck load 150 lbs.

When these loads are exceeded by 50 lbs. or more, increase tire pressure as follows: For each 50 lbs. of overload, increase pressure of rear tire, 2 lbs.; front tire, 1 lbs., sidecar or Package Truck tire, 1 lbs.