The internet has not been particularly helpful on this subject, so thought I?d ask you guys for an(other) opinion. I have put new 185/65R15 Michelins on my 68 beetle. I have the original manual and sticker on the inside of the glove box, but that is for the original bias tires. What pressure should I set front/rear for normal driving and ~ 300 lbs for a pair of passengers?
I’d start with the sticker numbers - what does it say? You might find more old Bug lovers over at thesamba.com.
I would start with what was recommended for old bias tires…I suspect the rear tires get a little more than the front…26F-32R something like that?
Start with the original recommendation and adjust as needed.
Do not under inflate them. That can be dangerous (remember the Ford Firestone problems?)
first the tires you put on are over sized. the OE size for a 68 VW bug were bias 560x15 radial were 155r15. recommended air pressure was for an average load 17 psi front and 26 psi rear. this info is from a 1974 tire guide book. it was normally advised to increase that by 3 psi at each end of the vehicle. i wold place them at 26 front and 29 rear’ my experience. in the tire service business since March 1970
Tire Guides says a 1968 VW Beetle originally came with 5.60-15?s or 155R15?s mounted on 4?" rims, inflated to 17 psi front, 26 psi rear.
A 185/65R15 has more load carrying capacity than the original tires, so in theory, you could use less pressure. But, the pressure is already quite low. I am not aware of anyone recommending using less than 26 psi for a passenger car tires ? so I would start there, but mainatuin the front / rear split = 26 / 35 psi.
But you have another problem ? the rim width. A 185/65R15 has an allowable rim width of 5? to 6??. If you are using the original rims, then the tire is going to arch across the tread face and tend to wear in the center. Given that you already are going to use more inflation pressure than what the load calls for, do not expect the tires to werar evenly.