Field Notes / Issue 14 / June 2026
The plate that broke the second prototype.
Sam Halberd / Austin, Texas / 2,400 words
The second prototype of the A1 Spike snapped clean across the forefoot in the 1,800m of a 5,000m time trial on the Austin oval, in the heat of August, with three of our athletes wearing variants of the same shoe. Two of them held. One of them did not. The pair that broke was the one I was wearing.
The plate that broke was a unidirectional carbon laminate, 0.9mm thick, cut to the lane radius. It had passed every bench test we had run on it. It had survived two laboratory cycle tests at three times the load we were modelling for. It had not survived the heat. The matrix glass-transition was lower than the supplier had told us, and the temperature on the Austin track in August is higher than the supplier had ever asked.
What the failure looked like.
The plate did not crack along the grain. It folded. The forefoot tipped under and the toe spring inverted, and what had been a racing flat became a ramp pointing the wrong way. I felt it as a softening, not as a break. By the time I had finished the lap and walked off the track, the plate was a U-shape inside the upper.
Why we did not blame the supplier.
The supplier had given us their published spec. The published spec was correct. The error was on us, in the heat envelope we had failed to write into the brief. We had specified the plate for European racing temperatures and tested it on a track that hits 47 degrees in August. Lesson written down. Brief re-written. Heat envelope is now line one of every plate spec we issue.
The third prototype used a higher-Tg resin and a slightly thicker laminate at the metatarsal break. It survived the same trial in the same heat. It survived the next four trials. It survived the development cycle. It is the plate in the A1 Spike that is currently on sale.
What we changed in the workshop.
- Plate spec sheet now leads with operating-temperature envelope, not stiffness.
- Every batch is heat-soaked at the published Tg minus 5 degrees before bench testing.
- We field-test in Austin in August, on the date the plate fails or until we are confident it will not.
- We do not accept plates from any supplier without a measured Tg on the actual batch.
What we did not change.
The plate’s lane geometry. The plate’s pin pattern. The plate’s mass. The plate’s price. We absorbed the cost of the new resin into the existing $245 retail. The athletes did not pay for our mistake. No offshore tooling. The whole plate is still cut in Austin, on the same waterjet, by the same operator.
The numbers.
Three numbers from the rebuild that I have written on the workshop wall and that I look at every spring:
12 / 11 / 3
Twelve weeks from failure to working third prototype. Eleven athletes on the pre-release. Three full racing seasons since the third prototype shipped, with zero plate-related returns.
The plate, as a fragment of CAM code.
For the engineers who write to us asking. The plate’s lane-cut radius is one of three values, picked by the customer’s lane assignment when they place the order. The fragment that does the radius pick is in the plate definition file:
plate.A1.spike {
lane: customer.lane | default(2);
radius: lane == 1 ? 36.5
: lane == 2 ? 38.7
: 41.2;
thickness.forefoot: 0.95mm;
thickness.metatarsal-break: 1.10mm;
pins: 6 @ 4mm;
resin.Tg: >= 135C;
}That is the whole specification. The rest of the shoe is bonded around it.
What I tell first-time A1 buyers.
Race the spike. Re-tool the spike. Send the spike back to the workshop when the spike is done. Do not ask the spike to be a daily trainer. Sam Halberd / founder / Halberd Athletics
The A1 is a racing shoe. The A4 is the trainer. The line between them is bright and was drawn deliberately. Two shoes do two jobs. Asking one shoe to do both jobs is how you end up with a plate that has lost stiffness in the heat at the back end of a season because it has been worn for the previous nine weeks of training.
This is Issue 14 of Field Notes from the Austin workshop. Issue 15 will cover the Trail line’s mid-cut hiker tooling. We publish four times a year. Subscribe and we will send you the next one when it is finished.
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