if you factor out those HUGE grooves ( to counteract the aquaplaning? or is it one of the new "energy saving" low rolling resistance designs- ie a thinner tyre) how much actual rubber is touching the road with that? its like they took a 135 and spread it over a 195 carcass - all groove no tread

And the cracking down the middle groove looks ominous

especially as its not a heritage Michelin

Sorry but I don't fully agree on this one. IIRC from uni the friction coefficient slightly raises with a lower specific pressure (less N/mm² or Stones/inch² ) in the tyre contact area.
As a result a wider tyre should give slightly more grip. I can imagian there is a limit to this effect tough.

If you spent the two years between my age and yours constantly wanking 1, see a therapist 2, I bet you look fairly odd with one arm bigger than the other.

And yeah they look good see sparrows red 2cv. Think I'm gonna go with 165 toyo 350s at the front then 135 toyos at the back.

the larger the contact patch the lower the pressure, Im going back 20 odd years and seem to remember that taking in to account surface area and adjusting for the pressure it was pretty much cancelled itself out or was so minimal an effect it was more practical to just rule it out. Then there was Static friction( sticktion) and Sliding friction

all got too complicated

New that would get taken the wrong way

No it wasn't taken the wrong way, sarcasm doesn't seem to translate into text .

True!

No matter how large a tyre, for a given amount of mass on the tyre at a given pressure its contact area will be the same. That's simple physics.

A wider tyre will simply adjust its contact patch to be shorter longitudinally (front to rear). If the wheel isn't held perpendicularly to the road, for example when cornering, then the contact area will rapidly change shape and the stiffer sidewall of the lower profile tyre may well mean there is much less tread contacting the road, so less grip.

Low profile, wide tyres are a reaction to many modern cars' hugely compromised MacPherson strut front suspension which need stiff anti roll bars to keep it working correctly. These transfer a lot of load away from the inside tyre to the outside one in a corner, so a wide contact patch is needed to maintain cornering ability with only the outside tyres doing most of the work.

The downside is poorer wet weather performance, tramlining, wear on steering, poor ride and snap loss of grip near the limit. As well as higher air resistance as speeds build and extra undamped mass which creates havoc with the suspension (so further reducing grip).

There is no chance of improving a standard 2cv's cornering grip beyond a Michelin 135 tyre on the front. And in my experience, with just the driver and no heavy load in the back, a 125 on the rear grips longer and harder than a 135ZX, which can cause sudden loss of grip in extremis.

With slightly stiffer shock absorbers, correctly adjusted and unperished bump stops, an original chassis and strong shell (not to mention earlier wheel arms) and a pair of 135ZXs on the front, a good 2cv can grip and handle very very well indeed!

The only benefit of a lower profile, wider tyre is that ceteris paribus the rubber compound may be softer since less internal friction and sidewall distortion as the tyre rolls down the road means less heat. But with a car which never goes much over 80mph, a 2cv's Michelin 125s have a softish tread compound anyway.

For road use, anything much wider than 135 is going to slow the car down, both on the straight and through corners. Although with a high payload and stiffer chassis, a 145 tyre of cheaper make can make up some of the loss of grip compared with a Michelin.