All depends on the offset of the wheels your running at the moment. 8J means 8 inch width.
Believe the standard wheels are of offset ET42 to ET45 depending on wheel you have.
Best thing to do is take the wheel off and on the inside of the spokes all the info should be stamped, for example 8Jx18 ET45
I ran 8Jx19 ET35 which had plenty clearance, ET35 on the 8" width wheel will sit 10mm closer to arch than ET45.
If you measure from the face of you wheel (not tyre) to flush with your arch then you will be able to gauge what width spacer you will get away with.
This is a handy calculator
http://www.1010tires.com/WheelOffsetCalculator.asp
I now run 9Jx18 ET52 alloys with 20mm hubcentric spacers all round, that equates to an offset now of ET32 and the alloys run bang on flush with arch, looks really aggresive, need to raise the coilies tho as at the mo I have around 5mm clearance to the tyre but it is screwed right down.
If your offset ET45 you could get 15mm spacers on, should run flush with the arch. If the offset is lower then 15mm i would guess would be to much.
Ideally you want to get the hubcentric spacers that bolt to the hub first then your wheels bolt to the spacers, ones with longer bolts imo are a bad idea as the longer bolts are subject to alot of stress.
Venom motorsport have a sale on there spacers just now, I got mine from them, eibach ones with the steel inserts for extra strength is what i went for. I tried various cheaper options and tbh they were disappointing and I lacked confidence in them, the ones that bolt to the hub with the steel inserts are far superior and the car feels slightly more sure footed than before.
Hope that helps bud:thumbsup: