The offset (ET number) will determine how much more or less your wheels are tucked under your wheel arches or protrude outwards. The lower the ET number, the further the wheels will extend outwards. If the offset is too aggressive (a low ET number), you run the risk of your tyres rubbing the wheel arch edge.
So, if the standard wheels on your Leon are 18” diameter, 7.5” wide with an offset of 51 (i.e they are 18 x 7.5j ET51), and you were to fit, say 18 x 7.5j ET 45 wheels and keep the same size tyres, you would have 6mm more clearance between the suspension strut and the inner face of the wheel and the outer face would ‘poke’ out 6mm more than your original wheels.
There’s a very handy offset calculator on ‘will they fit.com’ (
https://www.willtheyfit.com/). If you input the tyre and wheel specs for both your existing and new wheels and tyres, it’ll calculate the impact on clearance between the inner wheel face and suspension strut and any increase/decrease in ‘poke’ of the outer face.
Also bear in mind;
- That if you change your tyre size, this could impact the accuracy of your speedo. The calculator also calculates the % speedo error of fitting different sized tyres.
- Fitting different wheels to those fitted on the factory production line is considered as a modification for insurance purposes, so you’d need to declare the modification to your insurer, and they may charge you an increased premium.