Load, haul & blast Glossary Global
TKPH explained: tyres, heat and haul speed
TKPH is a tyre's heat limit in tonne-kilometres per hour. Site TKPH = mean tyre load × average speed × K1 × K2; it must stay below the tyre's rating.
Definition
TKPH
TKPH (tonne-kilometres per hour) is a tyre's working limit: the load and speed it can carry before heat build-up damages it.
Contents 8 sections
Work out the site’s TKPH from the mean load per tyre and the average cycle speed, correct it for haul length and heat, and fit a tyre whose rated TKPH is higher than the site figure.
Michelin describes TKPH as an expression of a tyre’s working capacity, set by the maximum internal operating temperature the tyre is allowed to reach. Tyre ratings are set at an ambient temperature of 38 °C (Michelin Technical Data, Earthmover Tires, 2022-23, p. 166, read 25 Sep 2026). The rating depends on the tyre’s size and type, so the same size can carry different ratings for different compounds.
TKPH formula
Basic site TKPH = Qm × Vm
Qm (mean tyre load, tonnes) = (Qc + Qv) ÷ 2, where Qc is the load per tyre laden and Qv the load per tyre empty
Vm (average cycle speed, km/h) = L ÷ H, where L is the cycle length in km and H the cycle duration in hours
Real site TKPH = basic site TKPH × K1 × K2
The tyre is suitable when its rated TKPH is higher than the real site TKPH. When the tyre’s figure is lower, Michelin classes the tyre as unsuitable for the application (p. 167).
Mean tyre load
Work out Qm for the front and rear axles and use the higher of the two. Michelin assumes tyres on the same axle share the load equally. On two-axle dump trucks, the loaded weight (empty weight plus payload) sits 33.3% on the front axle, on two single tyres, and 66.7% on the rear, on four twinned tyres. Empty, the front axle is almost always the heavier, so the highest Qm is nearly always on the front (p. 166). Weighbridge figures for your own trucks beat the standard split.
Average speed
Vm is distance per hour over the whole cycle: cycle length divided by cycle duration, loading, dumping and waiting included. Michelin specifies the reference cycle as “the one with the highest average speed” (p. 167). A short, fast waste haul can therefore set the figure even when most tonnes go on a longer ore haul.
Corrections for haul length and heat
K1 applies to cycles longer than 5 km. Selected values from Michelin’s table (p. 169):
| Cycle length (km) | K1 |
|---|---|
| 5 | 1.00 |
| 6 | 1.04 |
| 8 | 1.09 |
| 10 | 1.12 |
| 15 | 1.16 |
| 20 | 1.19 |
| 30 | 1.21 |
| 40 | 1.22 |
| 50 | 1.23 |
K2 corrects for ambient temperature (TA) against the 38 °C reference (TR):
Above 38 °C: K2 = 1 ÷ (1 - 0.40 × (TA - 38) ÷ Vm)
Below 38 °C: K2 = 1 ÷ (1 - 0.25 × (TA - 38) ÷ Vm)
TA is “the maximum temperature in the shade” during the site’s hottest period (p. 167). Hotter than 38 °C pushes the site TKPH up; cooler brings it down.
Worked example: a rigid truck on an 8 km haul
When site TKPH is higher than the tyre’s
Michelin gives two routes (p. 167):
- Change the tyre. Check whether another tread pattern or type with a higher TKPH can be used. In Michelin’s own example the same 37.00 R 57 size is listed at 848, 1,018, 1,145 and 1,272 TKPH depending on the compound, and the choice between the suitable ones is then made on how abrasive the roads and loading areas are (p. 168).
- Change how the truck works. Reduce the load, reduce the speed, or run fewer cycles in the same period.
The second route costs production: a slower cycle means fewer loads per shift, and a lighter load means fewer tonnes per trip. Price that against the cost of heat-damaged tyres before choosing, and recalculate whenever the haul length or payload changes, or the hot season arrives.
Common questions
What temperature should I use for the TKPH calculation?
Michelin says to use the maximum temperature in the shade during the hottest period at the site. Its tyre ratings are set at 38 °C, and the K2 coefficient corrects the site figure up or down from there.
Does the average speed include loading and waiting time?
Yes. Michelin divides the cycle length by the full duration of the cycle in hours. Use the reference cycle with the highest average speed, because that is the one that works the tyres hardest.
Which axle’s tyre load goes into the formula?
Whichever axle gives the higher mean tyre load. On a two-axle rigid dump truck that is nearly always the front, because the front carries a third of the loaded weight on two tyres and is almost always the heavier axle when empty.
Sources
- Michelin Technical Data, Earthmover Tires, 2022-23 edition, pp. 166 to 169. Michelin. Read 25 Sep 2026.
- Michelin reference documents page, listing the earthmover technical data book. Read 25 Sep 2026.
