by Steve Hansen
Now that our Alpines and Tigers are between twenty-five and thirty years old, they are probably not riding on their original 6. 00 X 13 Dunlops any longer. Still for those who may be interested in upgrading their Sunbeam’s shoes, a short primer on some of the considerations involved may be in order.
The original tires on our Alpines and Tigers were the state -of- the-art for their day: Built with the latest nylon or rayon cord construction, they had an aspect ratio of 80, that is the tire’s sidewall height was 80% of its width. Later advances in tire technology brought the so- called “wide oval” bias ply tire (for example “A 78 -13″), with an indicated aspect ratio of 78%, and the first- generation radial ply tires, which introduced us to metric tire width designations (for example” 165SR 13″, where 165 refers to the tire width in millimeters – in this case, just under 6 1/2″. The “S” designation refers to the tire’s maximum speed rating, in this case 112 -MPH. “R” is just shorthand for “radial”).
More recent developments have included the introduction of tires with lower and lower aspect ratios- such as the “70- series” tire (185/70SR 13, for example) and the still wider and lower “60- series” (205/60HR 13). Careful readers will have noted the “H” speed rating of this last example, indicating a safe maximum speed of 130- MPH.
All of the tire sizes I’ve listed can be successfully substituted for the Sunbeam’s original 6.00x 13 rubber provided that wheels of the correct width and offset are used. Wheel width should be obvious, however the term “offset” refers to the distance between the wheel’s centerline and the mating surface where it contacts the hub. Further, offset can either be positive (wheel center line inboard of mating surface) or negative (outboard of mating surface). Standard Alpine and Tiger steel wheels have a positive offset of 1 – 1/8″. It’s important that this original offset be matched or closely approximated when replacement wheels are fitted, otherwise wheel bearing life and static wheel balance can be negatively affected.
Another recent trend in tire/wheel upgrading is the “plus” concept, in which the original wheel diameter is increased by one or two inches (so -called “plus one” or “plus two”). This enables the use of lower aspect ratio tires while approximating the overall diameter of the original tires, to which the speedometer is calibrated. Generally speaking, if a “plus” wheel and tire package is desired, the overall diameter of the lower- profile tire should be within about 2 1/2% of the original. (For those of us who are absolute sticklers for detail and function, a knowledgeable speedometer shop can fabricate a small gearbox to attach to the back of your stock speedo so that its gear ratio can be increased or reduced to match the different diameter of substitute tires!)
According to one major manufacturer of radial tires, the following tire sizes are direct conversions for the 6.00 x 13 originals on our Sunbeams. The italicized wheel rim width represents the rim used for measurements only. It is strongly suggested that candidate replacement tires and wheels should be checked on the car, if possible. Neither the author nor the Editor assume responsibility for verifying proper clearances under all operating conditions!
| Input shaft bearing | 8D-7025 | 13.45 |
|---|---|---|
| Main shaft output bearing | 8D-7065 | .09 ea |
| Reverse idler roller bearings (44) | CODZ-7121-A | .20 ea |
| Cluster gear roller bearings (44) | C4AZ-7121-A | .16 ea |
| Input shaft/Mainshaft rollers (15) | C3AZ-7118-A | 1.75 |
| Oil seal, Input shaft | B7AZ-7A283-B | 5 |
| Oil seal, Tailshaft | C4TZ-7052-A | .32ea |
| Shift arm "0" rings (3) | IA-7288-A | 0.8 |
| Rubber oil seal inside tailpiece | B9AP-7A011-A | 1.55 |
| Gasket set (3 gaskets) | C4AZ-7153-B | 0.05 |