So what is offset? Good question, well its very simple wheel offset is the distance from its hub-mounting surface to the centre-line of the wheel. Simple explanation of this is to describe 3 general types of offset.
Positive offset: Where the hub-mounting surface is towards the front aka face of the rim.
Zero offset: Where the hub-mounting surface is where the wheel centre-line is.
Negative offset: Where the hub-mounting surface is towards the rear of the wheel.
You will find the offset of your wheels with a stamp (ET) somewhere on the rim on most wheels, otherwise you should see them on a sticker. If still no luck... Congratulations you are about to learn how calculate offset on your wheels! It is just a simple mathematics calculation.
Offset = Backspace - (Width/2). This will give you offset in inches, then multiply that total by 25.4 to get the normal measurement in mm.
We put the wheel face down and put a piece of wood across the back of it to achieve a flat surface. We then measure down to the hub-mounting surface. The measurement reads 5\". Therefore the backspace is 5\". We then measure the overall diameter of the wheel (lip to lip) and it reads 8.5\"
Now here is the fun part, we put them into the formula:
5\" - (8.5\" divided by 2) = 0.75\"... Then 0.75\" x 25.4 = 19.05 round this figure = an offset of +19mm.
Congratulations you are now as smart as an online calculator.
Now you are all getting pretty sick of words right? Well here are some pictures after all a picture is worth a thousand words .
Stock rims - 16x6.5 +39 (205/50/R16 Advan tyres). Stock body with minor lowering via Eibach Pro-kit, no significant alignment settings.
G.Max - 17x7 +42 (205/45/R17 Kumho 712 tyres). Same suspension setup with trial fitting of a body kit notice the rear wheels... This is what people nickname offset fail.
5Zigen - 17x7.5 +35 (225/45/R17 Bridgestone RE01). Here\'s a friends/old members car, the car had mild camber settings and was lowered with coilovers. (Closer to a decent fitment).
SSR SP1 - 17x7.5 +30 (215/45/R17 Bridgestone Potenza GIII). This picture shows how the rears are filled much nicer than the stock and also the G.Max wheels. (Still not ideal). This was still the same setup as the G.Max wheels.
SSR SP1 - 17x7.5 +30 (215/45/R17 Bridgestone Potenza GIII). This picture shows the fronts too, the same setup was used as per the previous picture.
SSR SP1 - 17x7.5 +30 (215/45/R17 Bridgestone Potenza GIII). This picture shows the changes to the stance with the same wheels. This picture was taken after coilovers and all my other suspension upgrades... Alignment here was at ~ -2.2 deg front, and -1.7 rear.
Work Meister - 17x8 +23 (Falken Ziex 215/45/R17 tyres *small footprint*). This was the same suspension modifications to the above SSR picture however alignment settings here were at ~ -1.9 deg front, and -1.4 deg rear. Please note these tyres have quite a small footprint thus the tyres were stretched more resulting in a further dramatised look on the amount of offsets.
Work Meister - 17x8 +23 (plus 5mm spacer effectively 17x8 +18) (Bridgestone Potenza RE001 215/45/R17 tyres *large footprint*). These are recent pictures the new tyres are alot larger in footprint than the Falkens so most the stretch is now gone. Camber is at -2.0 deg at the front, -1.5 deg at the rear.
Work Meister - 17x8 +23 (plus 20mm bolt on spacers effectively 17x8 +3) (Bridgestone Potenza RE001 215/45/R17 tyres *large footprint*) Camber is at -2.5 deg at the front, -2.2 deg at the rear.
P.S. One more thing to note none of my configurations needs rolling of the guards up until the fitting of the RE001 tyres. Since then I had to roll the inner lips of the rear guards (pictured) no more rubbing has been happening.
Edited by NoOg_sTaR, 19 March 2010 - 02:44 AM.