New wheel advice please

TDI-line · Dec 21, 2013

Hi guys,

i'd like to change the standard S-line wheels on my A3, but not too sure on the 7.5J bit, as the new ones would be 8J?

Existing wheels are 18" x 7.5J, with 225/40 R18 tyres.

New alloys would be !8" BBS SR in grey, which can re-use the existing Continental tyres.

I know that the 225 is the width of the tyre, the 40 is depth of wall between tyre and ground, and obviously that the R18 is the size of alloy, but really not sure what the J bit is?

BBS SR Grey 18" Alloy Wheels - Wheelbase

Leeber · Dec 21, 2013

I believe that it's the width of the rim in inches. You also need to take care to select the correct offset (of the rims) so as to ensure that they will fit within the wheel arch and not foul on the brakes/suspension.

This link will tell you the range rim widths are acceptable for each tyre size and type in the continental range.

http://www.continental-tyres.co.uk/...ervices_uk/resource_library/bulletin_6_en.pdf

Gazwould · Dec 21, 2013

Don't know what J stands for but it is the width of an alloy in inches.

Much like ET is in mm for offset.

Perhaps someone can enlighten us.

TDI-line · Dec 21, 2013

Thanks for the replies.

Forget to mention, tyre is the same size 225/40/18, and the new BBS SR alloy is 8J, where as the S-line alloy is 7.5J.

So where does this extra 1/2 J go if it's on the same size tyre?

Leeber · Dec 22, 2013

Nowhere, you still have the same tread width so the same area of contact between the tyre and road. It just means that the sidewalls are 1/2" further apart at the bead (the bit that sits on the rim). Most tyres can fit on a range of rim widths. What type of continentals are they (sportcontact 5p, 5, 3?)

TDI-line · Dec 22, 2013

Leeber said:
Nowhere, you still have the same tread width so the same area of contact between the tyre and road. It just means that the sidewalls are 1/2" further apart at the bead (the bit that sits on the rim). Most tyres can fit on a range of rim widths. What type of continentals are they (sportcontact 5p, 5, 3?)

They are Sportcontact 5 225/40/18 Y.

Leeber · Dec 22, 2013

Well according to the link above, they're good for use on rims from 7 1/2 to 9J. I'd be interested to know if there's any discernible difference in the car's handling by using the same tyres on a slightly wider rim.

The link you provided in post 1 doesn't have the 8v listed as an option for these wheels yet, I don't know the correct offset for the 8v or indeed if it's any different to other models. Have you checked this? Does anyone else know?

TDI-line · Dec 22, 2013

Thanks Leeber.

I entered all details for the 8V, and it says it is compatible for the 2012-2014 A3 8V, but i have not checked the offset.

18" Audi A3 2012 to 2014 (Mk3) (8V) Alloy Wheels

Leeber · Dec 22, 2013

I'm sure it'll be fine then, good luck with your purchase and don't forget to post pics!

TDI-line · Dec 23, 2013

Thanks for the help Leeber, this purchase will be sometime in 2014, but at least i know about the J bit now.

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