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[Mad Max] Why did Max make Furiosa and the many mothers turn back when they could have made it?

After watching Fury Road for the 4th time, I realised something was a bit off about the many mothers and 5 wives travelling when they set off. In a nutshell, I think Max convinced them not to go because he knew they would reach land and wanted to go alone. More info below.

Intro/backstory

In Mad Max: Fury Road when he reaches what's left of the many mothers, they invite him to leave and cross the salt flats with them, saying they have enough supplies for 160 days. Max follows them and stops them, telling them they won't have reached anything by the time the supplies run out.

Speculation about location:

We know this takes place in Australia from past films, and is somewhere on the East Coast because Furiosa says they go east, and the many mothers say if you came from the West you already past it (the green place). It could be near Sydney, since we see clips of the children he led at the end of Mad Max 3 Beyond Thunderdome living in abandoned buildings, and if they walked there then it can't be too far. Regardless, it must be on the East Coast.

Max knows what the world looks like:

Max was around before The Fall, and has seen pictures of world maps. He must also have known that the Americas existed to the East of Australia, since he seems like a bright guy and I would certainly hope that kids would know about the existence of other continents in Australia before The Fall. Max also know distances, as he asks Furiosa to take the war rig half a kilometer away before dealing with the leader of the bullet farm. It follows that he would probably have a rough idea of how far away America is.

Maths:

Assuming they can ride their bikes at 50mph cruising speed for 12 hours a day, then in 160 days they would have covered 96 000 miles, which is enough to go round the world just under 4 times, in which time they would definitely have run into land. It may well be the case that they can't ride for 12 hours a day, so what if its only 8? Thats still 64 000 miles. The distance as the crow flies to Santiago, Chile is around 7 000 miles. Assuming they take an indirect route because the ocean floor isn't flat, lets call it 20 000 miles just to be sure. They only need to average 5.2 miles per hour over 24 hours, while is 10.4 over 12 hours,15.6 over 8 hours, or 62.5 for just two hours, which I'm sure their bikes can manage.

Attention to detail:

I know how much effort is put into every detail in Mad Max films, especially Fury Road. If they spent so much time and effort on parts of the film that we don't even notice, then why would they be sloppy about something as prominent as the script, especially when there was so little of it. They could easily have come up with a shorter time which their supplies would last for, say a week, which would be equally believable. But they said 160 days. Max also guarantees they won't make it after 160 days after leaving them to go and having plenty of time to think about it. The maths isn't hard, average speed x hours travelling each day = distance travelled. He would have had some uncertainty in his mind even if he thought they wouldn't make it.

Why would he lie:

We know he likes to travel alone, and is always searching. Maybe he too is desperate to travel the salt flats in search of a far away land, but he would want to go alone. Sure he could just leave a couple of days after the many mother, Furiosa, Nux and the 5 wives, but he would know that he wasn't fully alone, that he was copying someone else. Maybe his pride gets the better of him and he leads them to a much nearer and possibly superior life than they could find, while he is free to travel alone? I'm not really sure on his motivation and there's likely a lot of things I haven't considered, but it seems obvious that he would know they could make it.

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What are your thoughts on this?

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tl;dr: 160 days is a long time to cross the dried out Pacific Ocean, Max would know this and persuaded Furiosa to head back to the citadel knowing she could make it across the salt.

Side note at the the end he really should have stuck around long enough to take one of their vehicles instead of disappearing into the crowd. I know it wouldn't have been as cinematic but still.
gpt
Going off piecemeal information from the video game and director's own words here.  Max was planning on committing suicide by just going east into the Silent sands iirc the name or the Pacific Ocean.  He knew you'd have to be insanely lucky to hit one of the island chains or land masses between the two continents and that if you headed into Australia proper you'd be facing radiation exposure as well as droughts and god knows what else.  Heading off the coasts was much worse as the terrain is incredibly brutal and wouldn't be a straight line or even passable at most points.  160 days of supplies would get you across but that's assuming you don't lose a bike which takes weeks worth of supplies with it if you can't bring it with you and assuming you could carry enough guzzoline to even travel that far.  160 days could have been just food and water and only 3 days of gas.  Why risk heading into the region max specifically planned to die in when you know there's a better option behind you.