The purchase price of a sorter is negotiated hard and then fixed. The price of the parts that keep it running for the following decade is usually agreed once, in an appendix, and then drifts. Component costs move, currency moves, products are superseded, and the list price of a part that fails in year eight bears little relation to the one that appeared in the original schedule. Buyers discover this at exactly the wrong moment – during an unplanned failure, when there is no time to argue.
The mechanism that prevents the drift becoming a dispute is an indexation clause with a real review process behind it. Neither is complicated, but both have to be drafted deliberately, because a clause that adjusts prices without a way to test them simply automates the drift.
Why Prices Drift
Four forces move spare parts prices, and only some of them are the supplier’s doing. Input costs – steel, electronics, specialised components – follow their own cycles. Currency exposure matters whenever parts are manufactured in one currency and invoiced in another. Product revisions replace a part with a successor that may be priced independently of the original. And mix changes: the parts a machine actually consumes in year seven are not the ones the original schedule weighted most heavily.
That last point is the one buyers underestimate. An indexation clause applied to a fixed basket of parts can be perfectly fair and still produce a bill that rises faster than inflation, simply because the consumption pattern moved toward more expensive items.
What a Review Should Examine
A useful review is not a negotiation about every line item; that is unaffordable administratively. It is a structured look at three things: the index movement applied since the last review, the consumption-weighted cost of the parts you actually bought, and any substitution or obsolescence events that changed the basket.
- Index application: was the agreed formula applied correctly, with the right base month and the right rounding?
- Basket reality: has consumption shifted, and should the weighted basket be re-based?
- Substitutions: which parts were replaced by successors, and how was the successor priced?
- Competitive items: generic parts available elsewhere should not inherit proprietary pricing.
Choosing an Index and a Formula
The index should be published, independently calculated and difficult for either party to influence. Producer price indices for the relevant manufacturing category are usually more appropriate than consumer indices, and for imported equipment the currency question has to be settled explicitly rather than left inside the price. Whatever is chosen, the clause should name the source, the publication and the base month, because most disputes about indexation are disputes about which number was used.
The formula should also say what it does not cover. Price changes driven by genuine product revision, specification change or regulatory requirement are usually handled outside indexation, through a notification and acceptance process, and leaving that boundary undefined is how an indexation clause becomes a general right to raise prices.
Caps, Collars and Cadence
Unbounded adjustment in either direction is unattractive to both sides. A collar protects the supplier from a downward spiral it cannot plan against; a cap protects the buyer from an outlier year. A common structure is an annual adjustment subject to a percentage ceiling, with movement outside the band carried forward or reopened for discussion rather than simply applied.
Cadence should match the review, not just the adjustment. Annual price adjustment with a fuller review every two or three years is a workable rhythm: frequent enough to stay current, infrequent enough that neither party treats it as a permanent negotiation. Anything longer and the accumulated drift becomes too large to discuss calmly.
Technical Background
The published measures used for this purpose are price indices, which track the movement of a basket of prices over time. For manufactured components, producer price indices reflect input costs to producers more directly than consumer measures, while consumer price indices are familiar and widely published but describe a different basket – which is exactly why the clause has to name its source rather than refer to inflation generally.
Benchmarking and End of Life
Indexation does not answer the question of whether a price was reasonable to begin with. Periodic benchmarking of the highest-spend items – against equivalent parts, against other suppliers where alternatives exist, or against the cost of a rebuild – keeps the base honest. It is most valuable when it is transparent: a supplier told which items you are benchmarking, and why, will often explain a price convincingly, and sometimes reduce it.
The long tail is where discipline matters most. As a machine ages, parts become scarce, minimum order quantities appear and the last few years of support get expensive. Planning for that phase – knowing which assemblies will become the constraint and what the options are – belongs with the classification work in the critical spares list. The ownership and replenishment mechanisms that reduce exposure are described in consignment and vendor-managed inventory, and how parts cost enters the lifetime picture is modelled in the total cost of ownership model. Commercial boundaries during the support period are set by warranty and service response terms, and where fitting is outsourced the pricing question connects to the maintenance contract decision.
Frequently Asked Questions
Why do spare parts prices rise faster than inflation?
Because input costs, currency and consumption mix all move independently of the index, and the basket of parts a machine consumes changes over its life.
Which index should the clause use?
A published, independent one appropriate to the components – often a producer price index – with the source, publication and base month named in the contract.
Should adjustments be capped?
Usually yes. A ceiling, sometimes paired with a collar, keeps an outlier year from becoming a permanent step change for either party.
How often should prices be reviewed?
A common rhythm is annual adjustment with a fuller review every two to three years, so drift never accumulates beyond a calm discussion.
Does indexation cover replacement parts?
Normally no. Genuine product revisions should be handled through a separate notification and acceptance process rather than through the index.
What is the most common drafting error?
Referring to inflation generally instead of naming an index, a publication and a base month – which guarantees an argument about the number.
How do I keep the base price honest?
Benchmark the highest-spend items periodically and transparently, and check generic parts against alternatives rather than accepting proprietary pricing.