does anyone knows the tyre pressure for my MK IV DHC who is fitted with Michelin tyres 500 x 18?
The manual quotes (in p.s.i) 28 front, 30 rear for the 6 cylinder cars and 28 all-round for the 1.5L. This is equivalent to 200 and 210kpa respectively. I usually run about 10% higher (about 33/230 here) on any car I have.
You note the tyre size is 5.00/18 but this is smaller than the recommended 5.50/18 for your car. Your size may be running a narrower tread than the correct size and might be more ‘slippery’ in a challenging situation like wet roads, cornering and harsh braking.
There is a 550-18 Michelin “Double Rivet” tire listed at Coker Tire that has images similar to your photo. There is no pressure recommendation showing at Coker. There is a similar listing at Universal Vintage Tire which suggests Load of 1118 pounds @36 psi. These listings were found using a search term “Michelin 550-18”.
Owner Manuals in cars typically suggest a tire pressure for a particular tire that came new with the car and was designed with the tire springiness as part of the overall spring response of the vehicle. If the tire brand or size is changed, the tire pressure recommendation of the owner manual may not provide an optimal pressure. People factor in comfort, tire lifetime, and other factors. Starting with the owner manual recommendation may be good.
Another factor is the load rating, usually given as so many pounds or kilograms at a certain pressure. The rating pressure is that which will give the best service with a load up to that maximum. Coker told me to run at that pressure with their Classic Radials on my 120.