Tire retreading: model casing acceptance and repeat lives
A retreading opportunity begins with a reusable casing, not simply with a tire sold in an earlier year. Some casings are not returned, some fail initial inspection and others do not pass final acceptance. Repeated lives therefore form a shrinking cohort, and a fleet’s retread demand cannot be inferred directly from its original tire purchases.
The deliverable is a casing-generation ledger and an expected cost-per-distance worksheet. It distinguishes collection, conditional acceptance, final delivery, service distance and residual value. The model is an investment-research example, not an instruction for inspecting a casing or deciding whether any tire is suitable for a vehicle or axle position.
Locate the acceptance stages
Michelin’s retread manufacturing page has an Explore Our 9-Step Retread Manufacturing Process section. Initial Inspection is step 1 and Final Inspection is step 9. Those named stages establish that eligibility and final acceptance are separate evidence objects; the page does not give the invented pass rates or prices used here.
Manufacturer statements describe their own process and eligible products. They do not establish that every returned casing, maintenance history or application has the same acceptance rate. Obtain fleet-specific return records and inspection dispositions before applying an industry narrative to a company’s actual throughput.
Create a stable casing identifier linking the first life, each return, inspection result, retread delivery and subsequent disposal or transfer. A tire casing is the continuing asset; a retread invoice represents one service event. Counting both as new casings would inflate the circulating population and any implied remaining opportunity.
Rebuild the first retread generation
Assume a fictional cohort of one thousand new tires completes its first life. Collection is 90%, so nine hundred casings return. Of returned casings, 80% pass initial inspection, leaving 720. Final acceptance is 98% of those entering the simplified later process, producing an expected 705.6 first-generation retreads.
| First return stage | Calculation | Expected casings |
|---|---|---|
| Originally placed | Defined starting cohort | 1,000 |
| Returned | 1,000 × 90% | 900 |
| Initial acceptance | 900 × 80% | 720 |
| Final accepted delivery | 720 × 98% | 705.6 |
The decimal is a planning expectation, not a physical shipment count. Actual records must contain integer counts and separate rejected, retained, transferred and unresolved casings. Do not round the expectation and label it observed production. Conditional rates must also keep their denominators: final acceptance is not 98% of the original thousand in this case.
For a physical ledger, nine hundred returns minus 720 initial passes gives 180 initial rejections. Later expected rejection is 14.4, and expected final acceptance is 705.6. Together those dispositions sum to nine hundred. The expected hundred unreturned casings are outside the returned inspection population, not additional inspection failures.
Carry only eligible survivors into the next generation
Assume the 705.6 expected delivered retreads complete another service life. The next collection factor is 90%, initial acceptance 70% and final acceptance 98%, all explicitly fictional. Expected second-generation delivery is 705.6 × 90% × 70% × 98% = 435.63744.
The second generation starts from the first generation’s successful deliveries, not from the original thousand. Applying both generations to the original base would create second returns from casings that never passed the first process. A new customer casing bought from outside the cohort belongs in a separate addition line.
Do not infer unlimited repeated lives from one successful retread. Later acceptance can differ with the cohort’s actual condition and usage. If return or acceptance information is missing, show a conditional range rather than extending a constant pass rate forever. Public process descriptions cannot replace the observed transition data.
Calculate a bounded distance-cost case
Assume each new tire costs $400 and delivers 100,000 tire-kilometres in its first life. A delivered first retread costs $180 and contributes 80,000; a delivered second retread also costs $180 and contributes 60,000. These distances are scenario assumptions, not product guarantees. Costs are charged only to final accepted deliveries in this invented commercial agreement.
Add a $10 inspection charge for every returned casing, including rejections. Total expected inspected returns are 900 + 705.6 × 90% = 1,535.04. At the end of the second retread life, assume a $20 residual credit for each of the 435.63744 casings; earlier rejects have zero credit in this case.
Expected cost is $400,000 + $180 × (705.6 + 435.63744) + $10 × 1,535.04 − $20 × 435.63744 = $612,060.3904. Expected service distance is 100,000,000 + 705.6 × 80,000 + 435.63744 × 60,000 = 182,586,246.4 tire-kilometres.
Dividing cost by distance and multiplying by one thousand gives approximately $3.35 per thousand tire-kilometres. The first-life purchase-only figure is $4.00 on the same narrow cost basis. This is a ratio of expected cohort cost to expected cohort distance, not an observed fleet result or the expected value of every possible realised ratio.
Mounting, downtime, financing, fuel effects and replacement tires outside this cohort are excluded. Therefore the number is not complete total cost of ownership. A truck-kilometre is also not a tire-kilometre: multiple tires can travel on one vehicle. Keep the distance unit explicit before comparing a fleet’s operating cost.
Test different acceptance and commercial boundaries
Suppose initial first-return acceptance falls to 60%, with all other first-return assumptions unchanged. Expected accepted output becomes 900 × 60% × 98% = 529.2. The inspection bill still covers nine hundred returns in the stated contract. A lower pass rate reduces service distance and changes inspection cost per successful delivery even if the retread’s quoted price stays $180.
A different contract could charge processing before final acceptance. Then the rejected volume may incur more than the inspection charge used here. Obtain the invoice basis rather than assume the delivered-retread price captures every unsuccessful attempt. Residual credits also need a buyer, eligible condition and payment evidence before becoming actual cash.
Equal acceptance does not establish equal mileage or application suitability. Match service duty, recorded distance and product specification when comparing generations. A selected, well-maintained return population is not automatically representative of all casings a new collection program might receive.
Use the cohort verification sheet
| Input | Obtain | Check |
|---|---|---|
| Starting casings | Serial or asset ledger | No duplicate casings across life events |
| Returns | Collection and transfer records | Unreturned distinct from rejected |
| Acceptance | Stage dispositions | Each conditional denominator and unresolved case |
| Distance | Matched service records | Tire-distance, generation and application |
| Charges | Inspection and retread invoices | Per return, attempt or accepted delivery |
| Residual | Credit agreement and receipts | No double disposal or unsupported cash credit |
When fleet and plant counts disagree, reconcile transit, inventory dates, purchased outside casings and pending inspections. Do not force the gap into rejection. Preserve an unresolved-inventory line until the identifiers connect the two systems.
Update with actual returns, final dispositions, observed service distance, charge changes and residual receipts. Replace expectations with integer evidence for closed stages while keeping later generations conditional. The conclusion should state how much reusable supply was actually accepted, which future lives remain assumptions and what costs the distance ratio includes.
Put generations on a calendar and assign residual rights
The lifetime cohort total is not one year’s factory demand. The first nine hundred returns and the later expected 635.04 second returns occur after different service intervals. Without return dates, adding them describes lifetime inspection opportunities, not simultaneous workload or current-year retread deliveries.
Place actual return dates and pending inspection inventory on a calendar before comparing the cohort with plant capacity. A collection program can increase eligible supply while delivery remains delayed by transport or inspection. Conversely, a plant can process outside customer casings without increasing the surviving population of this original cohort.
Ownership also affects the commercial bridge. If the casing belongs to a fleet customer and the retreader earns only a service charge, the entire residual value cannot automatically be credited to the retreader. A credit applied against a later invoice is different from current cash receipts. Record who owns the casing at each stage, who receives the residual and when any credit is recognised or paid. A technically reusable casing and an economically owned resale asset are different evidence objects.
FAQ
Is 705.6 an actual shipment count?
No. It is a cohort expectation; shipments are recorded separately as integer counts.
Does a retread price alone establish lower fleet cost?
No. Acceptance, mileage, inspection charges and omitted operating costs also matter.