Is it safe to run 5 mm spacer on stock stud bolt? I don't want much just 5mm out is enough.

 

Yes, 5mm is safe to run on. It adds a bit more stress so instead of doing the recommended factory torque specs add a few more to it. (76 ft lbs recommended factory setting).

 

on a lexus i wouldnt even risk a 5mm slip on. i know my old LS and my homies SC is like this so im sure the IS is the same, but the lexus has short studs so you wont get alot of turns even with a 5mm. on my old LS i ran a 5mm up front without the longer studs and it worked, but, i only had like 3-4 turns which is hella unsafe.

i would either get the spacers with the studs in them, or just get the longer studs if you are going to run the 5mm slip on long term