My bro just gave me some wheels he claims will fit but i have serious doubts my 2008 octavia has 205/55/ZR 16s 6.5J 16 H2 ET 50  Ronals the wheels he has given me are 235/40/18R  8.0J 18H2 ET43 any info appreciated They have decent winter tyres on continental conti winter contact. 

https://papasmith.co.uk/alloy-wheel-fitment-guide/

i am still no nearer -too much infor for my brain to take in - it looks like stud patterns are the same so thats a start - going from 205 to 235 mm i wouldnt imagine to cause a problem its the et 50 and et 43 that concerns me a tad is it offset ie possibility of fouling on caliper or wing .

 

The specification of the standard 18" wheels on the Octavia MK2 are 225/40R18 fitted to 7.5Jx18 ET51 5/112 57.1 rims.

 

Outside diameter of tyres

225/40R18 637.2mm

235/40R18 645.2mm (1.3% bigger outside diameter compared to 225/40R18)

 

As you can see in the chart below, the 235/40R18 8J wheel has an actual inflated width of 235mm, ie. it is the same as its "235" nominal width. The 225/40R18 7.5J wheel has an actual inflated width of 224mm, ie. 1mm less than its nominal "225" width.

 

So the 235 tyre when fitted to an 8J rim is 11mm wider than a 225 tyre fitted to a 7.5J rim.

 

Because the ET43 offset, moves the centre of the tyre 8mm further out in the wheelarch compared to ET51, there will be 2.5mm more room on the inside...with the front tyres in the straight ahead position...and there will be 13.5mm less room on the outside...because of the 8mm difference in offset and the 5.5mm difference in actual tyre width.

 

The actual width of an inflated tyre is measured from outside of one sidewall to the outside of the other sidewall, measured at the widest point. 

 

Actual inflated width of tyres

225/40R18 fitted to 7.5J rim 224mm

235/40R18 fitted to 8J rim 235mm

 

Like the Octavia MK2, the Octavia MK3 also uses 7.5Jx18 ET51 5/112 57.1 rims.

 

Octavia MK3 7.5Jx18 ET51 5/112 57.1 alloy rims shown in the Skoda accessory catalogue

https://eshop.skoda-auto.cz/cs_CZ/alu-kola/c/alloyWheels?sort=priceAsc&q=%3AscoreDesc%3AcarType%3AOctavia%2BIII%2B%282017%2B%29%3ArimDiameter%3A18#

 

Edited 14 May, 20242 yr by Carlston

Will they fit and totate without fouling on anything though - tyres are only 30mm wider  does the face of the wheel sit closer to the hub face  ?  its all too technical for my failing mind i expected a yes they will fit and not have any noticeable issues or NO they are unsuitable because they will rub on X   Y  and speedo will be way out due to larger diameter

You will be fine, I have set of ronals with the same specs. Check my profile cover photo if you want to see how they fit. With 17x8 et37 I could run about 10-15mm spacer and it would be flush with the fender.

 

Edited 17 May, 20242 yr by siiiim