4″ wide tyres… If a DH bike had 4″ wide tyres, surely it would be quicker than one with 2.7″ wide tyres? Am I missing something?

4 inch wife tyres would give you loads of grip but also a huge amount of rolling resistance. Hence it would take more force to roll at the same speed and would be slower

so you want to race fat bikes DH…

It’s all a trade off between weight and strength, a 4″ rim and tyre would also weigh loads more than the normal DH setup along with rolling badly and being harder to pick up speed out of stuff. Add in wider frames and all that and it’s probably going to be a pig…

If anything DH tyres a getting smaller in volume these days.
And don’t call me Shirley.

I thought some boffins concluded wider tyres had less rolling resistance, but more aerodynamic drag

Unsprung weight would be so high there would probably be less grip.

Why would having a “low surface pressure” be any use on a modern DH course?

4 inch wife tyres

I’d get lots of resistance if I mentioned those in polite company, might get down the hill quicker as a result

For Gee’s sake I hope Santa Cruz don’t race that. I don’t rate a GT Fury’s chances at keeping up with it

The wife tyres would I suspect be quite noisy too.
I should remember to proof read my posts when using predictive text on my phone.

Tyres are effectively undamped so the riders would have less control. It would also be harder to move the bike from side to side when going round tight corners.

Think off powder skis compared to super g skis. You need a narrower platform so you can switch from edge to edge faster.