Hi,

70 psi ? That is more than I've currently got in both my 1.75" tyres total ....
Its moreorless equivalent to running 23mm tyres at 140psi - that is high.

The front must be rock hard and I presume very uncomfortable
and probably feels awful on anything other than smooth tarmac.

I'm gravitating towards the maximum rear pressure 3bar/43psi on my tyres
for the rear, even though I'm average weight, and 2bar/29psi for the front.

(Swalbe recommend 45 psi for road 1.75" tyres and a bit more for small wheels.)

That is 60%/40% weight ratio. A bike guru has said he has never measured
any form of racing bike with a static ratio less than that, (though the alleged
ideal is 55%/45%), so you can be pretty certain on a folder it is a lot more,
but big bumps can load up the front somewhat more than the rear, so my
thinking is the front needs to be harder than weight distribution suggests.

I cannot envisage any more than 35psi in the front for 1.75" tyres. I initially
tried 50psi front and back when I got my bike, the front especially was too
harsh and too bouncy off bumps to inspire any sort of roadholding confidence.

FWIW tests showed that thick sidewall cheap heavy tyres, with no particularly
high pressure rating reduced rolling resistances more for higher pressures than
good quality tyres with more flexible walls, the optimum pressures varied
with tyre type, and the optimum pressures are lower for good rolling tyres.

Regarding your question about how thin you can go on small wheels, look
at all the stuff about how fat you can go at lower pressures on big wheels.

If I wanted to ride my folder on a trail or similar, basically worse than tarmac
but not too bad, I'd probably drop to 30psi rear and 20 psi front - tried that
on the road, its OK but somewhat sluggish.

rgds, sreten.

My folder is pretty naff, getting it to work well is a challenge.