I have been using Enkei PF01 in 18 x 9.5 ET35 and 265/35R18 R-specs for the last 2+ years, with a 25.4mm spacer on the rear and a 12.7mm spacer on the front. I'm not able to exploit a wider rim given our category rules in "Modern Sports Cars".
Spacers are machined concentric to the hub and the 75mm centre-bore of the Enkei wheel and since I used ARP 75mm extended studs I also torque-up the spacer onto the ARP studs and then the wheel also.
This does give a slight risk of a stress riser on the ARP studs with torque reversal between braking and power-down but the length of the studs exposed to torque reversal is modest because we machined the spacers to ensure that the nuts securing the spacer are only 40/thou below the spacer face that the wheel seats to.
Even so, I am not a big fan of spacers, so I've lifed the studs to 100 track days/competition events which at my rate of competition in the Z34 is 4 years.
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