The 5-grains-per-pound floor (vertical bow) vs What an arrow spine number means: specs compared
Updated 05 September 2026.
9
specs differ
The 5-grains-per-pound floor (vertical bow) and What an arrow spine number means differ on 9 specs: the rule, 70 lb example, why, crossbow parallel, what it measures, reading the number.
| Spec | The 5-grains-per-pound floor (vertical bow) | What an arrow spine number means |
|---|---|---|
| The rule | At least 5 grains of total arrow weight per pound of draw weight | |
| 70 lb example | A 70 lb compound needs a minimum 350 grain arrow including the point | |
| Why | A too-light arrow leaves excess energy in the bow, like a partial dry-fire, and can damage limbs or cams | |
| Crossbow parallel | The same 5-grains-per-pound floor sets the minimum bolt weight on the crossbow side | |
| What it measures | How far a shaft deflects, in thousandths of an inch, under a 1.94 lb weight hung at the centre of a 28 inch span | |
| Reading the number | A 340 spine deflects 0.340 in and is stiffer; a 500 spine deflects 0.500 in and is weaker | |
| Draw weight | Higher draw weight needs a stiffer (lower-number) spine | |
| Arrow length | A longer arrow flexes more, so it needs a stiffer spine | |
| Point weight | A heavier point weakens dynamic spine; adjust one spine group per 25 grains of point-weight change |
Questions and answers
How do The 5-grains-per-pound floor (vertical bow) and What an arrow spine number means compare?
The 5-grains-per-pound floor (vertical bow) and What an arrow spine number means differ on 9 specs: the rule, 70 lb example, why, crossbow parallel, what it measures, reading the number.