"Si on fait la course, je suis sûr que tu perdras !"

Translation: If we race, I'm sure you will lose!

[dospescados]

Another way to say this in English is: If we have a race, I'm sure that you will lose.

[lucui4]

Why cant I sau sure instead sur for femmine

[Fred.duo]

Alternative: Si nous faisons la course, je suis sûr que vous perdrez !

[LenReed]

Lots of alternatives to render this English into French: nous/on sûr/sûre, tu/vous. The three choices are independent, so eight ways for you to lose!

[--Roody--]

I imagine all those choices are accepted, as long as you use proper agreement.

[lucui4]

Why not sure for femmenine