Drop testing is the spool industry’s most common informal quality check and its least reliable. Somebody drops one, it survives, and everybody concludes the design is fine. Then winter arrives, or a different corner takes the impact, and rims start cracking.
The problem is not the drop. It is that an unplanned test tells you one thing about one impact, and you then generalise from it.
What drop testing can tell you
Reasonably: relative toughness between two designs. If you drop design A and design B the same way and one consistently fails first, that is real information.
Less usefully: absolute service performance. A drop onto a concrete floor from half a metre tells you something about half-metre drops onto concrete. It says little about being tipped off a truck tail-lift onto frozen ground.
Variables that dominate the result
All of these change the outcome more than the spool does:
- Surface. Concrete, steel plate, compacted dirt and asphalt give wildly different results.
- Temperature. Polypropylene loses impact resistance substantially as it gets cold. This is the biggest single variable and the one most often ignored — we covered the mechanism in our article on cold weather behaviour. A spool tested indoors in summer tells you nothing about February.
- Orientation. Flat on the flange, on the rim edge, at an angle — each is a different test.
- Loaded or empty. A loaded spool behaves differently, and usually worse.
- Age. UV-exposed PP becomes more brittle over time. A new spool is the toughest it will ever be.
A test worth running
If you want to compare designs, hold everything else constant:
- Pick the surface you actually encounter. If it is a concrete yard, use concrete.
- Pick a drop height that reflects a realistic mishap, not the worst case you can imagine. Realistic is a tip-over, not a fall from a loading arm.
- Test at your coldest expected service temperature. If you cannot condition them cold, at least know that your results are optimistic.
- Choose one orientation and use it every time — rim impact is usually the most informative because that is what happens in practice.
- Use five samples per design. One tells you nothing.
- Define failure before you start. Visible crack? Rim deformation? “Still usable” is too vague to compare.
What to do instead of optimising the drop
If you are testing because rims crack in service, probably stop testing and fix handling. Drop testing finds the strongest design among the options; it does not make rough handling safe. The spools that come back broken were dropped, and however tough you make them there is a drop height that wins.
We would rather talk about how they are being dropped than help you specify a spool that survives being abused.
Where it does earn its cost
- Comparing two construction options before committing to a large order
- Validating a rim reinforcement change actually helps — see our piece on rim reinforcement
- Qualification for genuinely harsh duty
- Setting an acceptance standard with a supplier so there is something objective to argue from
What not to ask a supplier for
A pass/fail drop height as a headline specification. Any supplier can quote a number, and it will be conditioned on so many assumptions — temperature, orientation, surface, age, sample count — that comparing one supplier’s number against another’s is close to meaningless.
Ask instead what standard they tested to and under what conditions. A supplier who can tell you that in detail probably ran the test. One who quotes a height with no conditions probably did not.
Our position
We will tell you how our spools are constructed and what we know about their behaviour, and we will run a comparison test with you if you want to make a decision between options. We will not publish a drop rating, because every honest one comes with so many qualifiers that it stops being useful as a headline.