Dakar rally tires must work across sand dunes, rocky tracks, and fast hardpack in the same stage. Tire pressure is one of the fastest adjustments teams can make to change grip, comfort, heat buildup, and puncture risk. Lower pressure lets the tire spread out and conform to the ground, while higher pressure supports the tire and protects the rim.
Choosing pressure is an engineering tradeoff because the best setting for traction is not always the safest setting for speed and durability.
On sand, teams often reduce pressure to enlarge the contact patch so the tire floats instead of digging in. On rocks, they raise pressure enough to resist pinch flats and rim strikes, even if that reduces compliance. On hardpack, they choose a moderate to higher pressure to limit rolling resistance, sidewall flex, and heat.
Engineers use driver feedback, tire temperature, terrain notes, vehicle load, and pressure gauges to choose a setting that keeps the tire within its safe operating range.
Key Facts
- Contact pressure is roughly P = F / A, so for the same vehicle load F, a lower tire pressure usually gives a larger contact patch area A.
- Lower pressure increases tire deformation, which can improve grip on loose sand but also increases sidewall flex and heat.
- Higher pressure reduces sidewall deformation and helps protect the rim on rocks, but it can reduce traction on loose surfaces.
- Rolling resistance generally increases when pressure is too low because more energy is lost as the tire flexes.
- Gauge pressure is measured relative to atmospheric pressure, so a tire at 1.6 bar gauge has about 2.6 bar absolute pressure at sea level.
- Temperature changes pressure approximately by P1 / T1 = P2 / T2 when volume is nearly constant and temperature is measured in kelvin.
Vocabulary
- Contact patch
- The contact patch is the area of tire tread touching the ground at a given moment.
- Sidewall flex
- Sidewall flex is the bending and deformation of the tire sidewall as the tire supports load and rolls over terrain.
- Pinch flat
- A pinch flat is tire damage caused when the tire is compressed sharply between an obstacle and the rim.
- Rolling resistance
- Rolling resistance is the force that opposes motion because the tire deforms and loses energy as heat.
- Bead
- The bead is the reinforced edge of the tire that seals against the wheel rim and keeps the tire seated.
Common Mistakes to Avoid
- Using the lowest possible pressure for all terrain is wrong because very low pressure can overheat the tire, unseat the bead, or damage the rim on impacts.
- Assuming higher pressure always makes the vehicle faster is wrong because it can reduce grip and make the tire bounce over sand or loose gravel.
- Ignoring tire temperature is wrong because pressure rises as the tire heats, so a safe cold setting may become much higher during a long stage.
- Changing pressure without considering vehicle load is wrong because a heavier vehicle needs more support to prevent excessive deformation and rim strikes.
Practice Questions
- 1 A Dakar vehicle places 4500 N of load on one tire. If the tire pressure is 150 kPa, estimate the contact patch area using A = F / P. Give your answer in square meters.
- 2 A tire is set to 1.4 bar gauge before a sand section. The team raises it by 0.5 bar for a rocky section. What is the new gauge pressure, and what percent increase is this from the original pressure?
- 3 A team must choose between low, medium, and high tire pressure for a stage that begins with soft dunes and ends with sharp rocky tracks. Explain a reasonable pressure strategy and the tradeoffs involved.