I have an 87 951 that runs 17x8.5 wheels (factory Boxster twists, +50 offset I believe) at all four corners with 255/40s. They fit great with no rubbing, even with 5mm spacers at the front to clear the hubs and ride height of just under 25 inches fender to ground. I do have front coilovers with factory spring perches removed.

I’m looking at some cheap ESM wheels for the street that are 17x10 +50 offset. I would still run 255/40, which would be slightly stretched but from what I’ve read, but still in an acceptable range. What are some thoughts about these fitting at all four corners?

 

Seems likely there would be a fitment conflict at the front given the wheels inside lip will be 19mm farther inboard than the current setup and about 40mm inboard of the factory setup.

 

Right, I was thinking it would be 3/4 of an inch further inboard (and outboard), which jives with 19mm, so I’ll take a look at how much clearance I have. Not sure of the center bore on the ESMs, but safe to assume I’ll need some spacer at the front, so I can take that into consideration. But just thinking out loud, if I go from an 8.5” +50 to a 10” +50 with the same tire, the tire tread should sit in the same place, yes?

These are the wheels, which are sort of a fake deep dish design for late model Porsche.
https://www.ebay.com/itm/26393892134...fb5c%7Ciid%3A1

 

Use the tire comparison selection here. That’ll confirm how the two setups compare.

https://tiresize.com/calculator/

 

Yes, the tread block should be in the same position. The wheel lip and the (stretched) tire sidewall clearance would be the concern on the inboard side
Thanks for the link. It's a good looking wheel, it appears it is also offered in an 8.5" width, ET 45.