Boost information
Boosts are a speed increase mechanic in Mario Kart Wii. Boosts are visually represented by orange flames coming out of the vehicle's exhaust pipes.
Overview
While they are active, boosts increase the vehicle's maximum speed, and cause IV to increase every frame by a constant rate. If bikes are both in a boost and wheelie, the max sped modifiers are added together. Some boosts also grant offroad immunity while they are active, preventing the decrease in max speed and deactivating the slippery road physics.
The length of boosts is tracked by a timer, which decreases every frame. Once the timer hits 0, maximum speed returns to the base value decreasing at a rate of 3 u/f^2, the IV acceleration ends, and the offroad immunity is removed.
There are three main types of boosts: miniturbo boosts, trick boosts, and mushroom boosts. They differ in the max speed modifier, and IV acceleration rate.
Boost properties
| Miniturbo boosts | Trick boosts | Mushroom boosts | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Standstill miniturbo | Miniturbo | Start boost | Respawn boost | Stunt trick | Single flip trick | Double flip trick | Zipper boost | Zipper trick | Mushroom | Boost panel | Flip trick ramp | |
| Duration (bikes) | 30 | 15 - 141 | 10 - 70 | 30 | 45 | 80 | 95 | 50 | 100 | 90 | 60 | 60 |
| Duration (karts) | 40 | 70 | 85 | |||||||||
| Max speed increase | 20% | 30% | 40% (minimum 115 u/f) | set to 100 u/f | ||||||||
| IV acceleration rate | 3 u/f^2 | 6 u/f^2 | 7 u/f^2 | |||||||||
| Offroad immunity | No | No | Yes | Yes | ||||||||
Boost priority
If multiple boosts are active at the same time, their effects do not stack. If the two boosts are the same type, then the second boost simply resets the boost timer, not adds to it. If it is possible to get multiple boosts in quick succession, for example during a double trick, it is better to space out the boosts to avoid wasting frames of boost, instead of getting as many boosts as possible.
If the boosts are of different types, one of them takes priority. Mushroom boosts have priority over miniturbo boosts. Trick boosts have priority over both, despite giving a lower speed increase and acceleration than mushroom boosts. Therefore, overlapping trick and mushroom type boosts should be avoided, as this gives a lower speed boost. (This is not as relevant during a wheelie, because max speed reaches the cap of 120 u/f anyway, but the IV acceleration is still affected.)
Optimal boost distribution
When two boosts can be chained one after the other (for, it is optimal to trigger the second boost midway through the deceleration from the first. As discussed in this document, it is a trade-off between spending more frames above maximum base speed, and starting the second boost at a higher speed to spend more frames at max boost speed.
The optimal speed for releasing the miniturbo depends on many factors: the vehicle combo's speed stat, the max speed modifier of the second boost (boost type + wheelie), and whether the wheelie is active at the end of the second boost. This sheet includes the theoretical optimal speed in all possible cases; in practice, the optimal frame for starting the second boost is whenever IV is closest to the theoretical value.