Snout-vent length and tail length were recorded in almost all the racers examined, but other measurements were recorded in relatively few. In many racers, especially the larger adults, tails had been damaged and lacked their terminal parts. Often only the tip was missing, but, of course, such individuals were not usable in the study of proportions of the tail. [Table 2] summarizes information concerning relative tail length in 935 racers of both sexes and various sizes, from northeastern Kansas. Nearly all measurements are from the live snakes; a few are from recently killed individuals.
In hatchlings, the proportions of the tail are not noticeably different in males and females, but data indicate that the snakes' tails are approximately seven per cent longer in males than in females; as growth proceeds, the tails become relatively longer in proportion to the body, in both sexes. The ratio reaches its maximum in young adults, having increased from approximately 28 per cent of the snout-vent length in males and 26 per cent in females, to 31 per cent in males and a little more than 28 per cent in females. In the largest racers, of both sexes, these percentages are slightly reduced. Tail-length is subject to a fairly wide range of individual variation, which tends to obscure the trends determined by sex and size.
Table 2. Relative Tail Length in Male and Female Racers of Different Size Groups
| Snout-Vent Length in Millimeters | Males | Females | ||
| Number of racers | Mean ratio of tail-length to snout-vent length | Number of racers | Mean ratio of tail-length to snout-vent length | |
| 150-200 | 7 | 27.3 ± .833 | 2 | 26.3 |
| 201-250 | 24 | 27.8 ± .490 | 23 | 25.9 ± .479 |
| 251-300 | 9 | 28.8 ± .634 | 4 | 26.6 |
| 301-350 | 20 | 29.8 ± .246 | 11 | 25.0 ± 1.060 |
| 351-400 | 8 | 28.8 ± .530 | 12 | 27.5 ± .404 |
| 401-450 | 6 | 27.8 ± .775 | 5 | 26.3 ± .357 |
| 451-500 | 12 | 29.7 ± .434 | 6 | 26.8 ± .858 |
| 501-550 | 45 | 30.5 ± .283 | 15 | 27.6 ± .284 |
| 551-600 | 76 | 31.0 ± .218 | 35 | 27.1 ± .254 |
| 601-650 | 45 | 29.6 ± .313 | 64 | 27.8 ± .163 |
| 651-700 | 50 | 30.5 ± .241 | 36 | 27.1 ± .350 |
| 701-750 | 72 | 30.5 ± .177 | 45 | 27.6 ± .373 |
| 751-800 | 45 | 30.3 ± .373 | 38 | 27.8 ± .325 |
| 801-850 | 48 | 29.7 ± .274 | 50 | 27.5 ± .205 |
| 851-900 | 18 | 29.1 ± .519 | 35 | 28.6 ± .422 |
| 901-950 | 5 | 29.8 ± .672 | 31 | 26.7 ± .252 |
| 951-1000 | 1 | 29.5 | 19 | 26.9 ± .390 |
| 1001-1050 | .... | ..... | 15 | 25.9 ± .413 |
| 1051-1100 | .... | ..... | 6 | 26.4 ± .725 |
| 1101-1150 | .... | ..... | 1 | 28.5 |
| 1151-1200 | .... | ..... | 1 | 25.0 |
In 88 racers caught in the summer of 1962 the following measurements were recorded: Head length, from tip of snout to angle of jaw; maximum head width; greatest diameter of eye; circumference of neck; circumference at mid-body; circumference at posterior end of body; and circumference of tail-base. Because the measurements were small, and were made in the field on active, struggling snakes, a high degree of precision could not be attained, and the range of error was several per cent, with occasional relatively large errors. Nevertheless, ontogenetic trends are clearly indicated. Most of the racers measured were adults of small to medium size—in the range 500 to 799 millimeters, snout-vent length. Twelve females and seven males ranged from 800 to 1035 millimeters, and seven young (all females) were less than 500 millimeters. In measurements other than circumference of tail-base, significant differences could not be found between males and females of the same size group; therefore the sexes were combined to obtain larger series.
Table 3. Bodily Proportions (Expressed as Ratio of Snout-vent Length) in Racers of Different Sizes
| Size Group | Large (more than 800 millimeters) | Medium (500 to 800 millimeters) | Small (less than 500 millimeters) |
| Length of head | 3.61 ± .036 | 3.82 ± .025 | 5.39 |
| Width of head | 1.93 ± .049 | 2.02 ± .023 | 2.53 |
| Diameter of eye | .56 ± .008 | .63 ± .009 | 1.00 |
| Circumference of neck | 4.71 ± .082 | 5.05 ± .052 | 6.64 |
| Circumference at mid-body | 7.11 ± .238 | 7.66 ± .082 | 8.58 |
| Circumference at posterior end of body | 5.06 ± .113 | 5.03 ± .061 | 5.90 |
| Circumference of tail at base | 4.23 ± .113[1] 4.47 ± .171[2] | 4.22 ± .075[1] 4.66 ± .043[2] | 4.66[1] |
[1] Females.
[2] Males.
[Table 3] shows that as compared with adults, the small young racers have stouter, stubbier bodies, relatively large heads, and, especially, large eyes. Allometric growth seems to continue throughout life and the changed proportions of the adults are accentuated in the largest and oldest individuals.