Why is it a disallowed play?

[HatterTobias]

I tried to play these cards :

- 3
- 4
- Stress (in the real game I played, I used two regular Stress cards instead, with it being revealed to be a 3 and 4 iirc)
- Stress (it was a special card that lets me cooldown by 3 (getting rid of 3 heat cards from my hand, I had one) during the react phase

with these initial conditions :
- Initial gear was 2 (so the move would've cost one heat)
- I have zero heat in my engine
- It's on a straight part of the track, and I wouldn't have encountered a corner after the play
- It's a GB track (not really an important info)

However, the site didn't let me to do this play because "I do not have enough heat". Sorry, but wouldn't I have just enough heat to spend for making this play?

It's not THAT important but I figure that it could be the difference between 1st and 2nd in some races, as this was intended to be my last play during the game.

[thoun]

You must spend a heat to change more than one gear (2 to 4), and you pay it when changing gear, not at the end of the turn. You can't if you have 0 heat.

[Arjuna92]

You can spend the heat you get from cooldown on boosting though, which will give you the same effect as pushing the gear up by 2 in order to play a stress card - but with some extra flexibility, since you can use it after a different reaction phase effect (such as draft).