OE vs Aftermarket wheels

[Owen B]

Hi all

I am brand new here and have not modified a car for about 18 years, so please bear with me!

I have a 2015 Focus Zetec S tdci in Magnetic grey. It currently has the stock 17’s on. 

I am looking to add some 18’s and some Eibach springs. 

I have narrowed down my wheel choice to two (both 18x8), one is an OE wheel and the other is aftermarket. 

The OE wheels have an offset of 55 and the aftermakets are 45.

I have been on willitfit and I understand the 45 will be slightly further out, but I don’t know how much difference it will make, if any. 

The last thing I want is fit issues.

My 2 questions are,

1) is one going to be better than the other?

2) the OE’s come with 235/40 tyres and the aftermarkets come with 225/45. Which is best?

Thanks very much in advance. 

[YOG]

Wheel Offset Calculator:

https://www.1010tires.com/Tools/Wheel-Offset-Calculator

Visual Tyre Size Calculator:

http://www.kouki.co.uk/utilities/visual-tyre-size-calculator

Wheel/Rim Size Calculator:

https://www.tyresizecalculator.com/tyre-wheel-calculators/wheel-rim-size-calculator

[Owen B]

Thanks very much for those links, unfortunately I’m still none the wiser as to what is better. 🤷🏼‍♂️

[Luke4efc]

Your stock wheels will be 215/50/R17. As soon as you change that to a random tyre size you will probably throw your speedo out.

225/45/r18 will make your speedo 2% out (as the wheel circumference & Diameter is 2 larger). At 60mph you'll be doing just over 61.
235/40/r18 is the tyre size used on Focus 18 inch alloys. The speedo difference is negligible.

I'm not sure what you mean by which alloy is better. It's all personal choice as to what you prefer.

[Owen B]

8 minutes ago, Luke4efc said:

Your stock wheels will be 215/50/R17. As soon as you change that to a random tyre size you will probably throw your speedo out.

225/45/r18 will make your speedo 2% out (as the wheel circumference & Diameter is 2 larger). At 60mph you'll be doing just over 61.

235/40/r18 is the tyre size used on Focus 18 inch alloys. The speedo difference is negligible.

Thanks very much for that. 

Thats Q2 answered then!👍🏼

Much appreciated!