@HumanSteamroller; a bit of a brain dump, but hopefully you’ll find it useful and helpful.
There’s a useful wheel size calculator at willtheyfit.com. You input details of your wheel and tyre size, and it’ll calculate any additional wheel ‘tuck’ and ‘poke’ you might get from fitting wheels of a different width and offset. It’ll also calculate the impact on your speedo reading if you change the overall rolling radius of your wheel/tyre size.
You’ve said you’re looking for some new (to you) wheels but I’m not sure if you’re looking to get brand new ones or used/pre-owned ones.
OEM Wheels
If new OEM wheels, some of the Seat dealers such as Horton Seat (seatpartsshop.co.uk) with on line parts and accessory shops sometime have some good offers on genuine OEM alloys. Many VW, Audi or Skoda alloys will also fit the equivalent Seat models. Audi A3, VW Golf and Skoda Octavia will have the same bolt pattern and centre bore size as the
mk3 Leon but always important to check that the width and offset won’t give any fitment issues - the ‘will they fit?’ calculator will
help with this.
For used OEM wheels, it’s always worth checking ‘for sale’ section of the forum. You can also find used OEM wheels for sale on various on line sites such as eBay. Be aware that there will be many replica, non-genuine wheels for sale on eBay, which may be of poorer quality than the genuine item, and may not have been subjected to the same stringent quality tests (TUV certification or JWL if wheels are manufactured in Japan) as OEM wheels. It should be made clear by the seller that they are
OEM Style if they’re not the genuine article. Genuine Seat wheels will also be marked on the reverse side of the spokes with the Seat logo, the part number for the wheel and the wheel size and offset, so it’s always worth asking the seller for a picture of the reverse of the wheels, so you can see if they’re genuine or not.
Non OEM (aftermarket) Wheels
If you’re considering new aftermarket wheels, I’d always go for a reputable brand - e.g. BBS, Ronal, Borbet, AEZ, Alutec, OZ that should’ve been TUV or JWL certified. Bolt pattern needs to be 5x112. Be aware that some aftermarket wheels have quite aggressive offsets, which could give some rubbing issues. Some will also have centre bore measurements that are larger than the Leon’s 57.1. That isn’t too much of an issue, as the centre bore size can be reduced to 57.1 by fitting reducing/spigot rings. Non-OEM wheels may require different wheel bolts if the profile of bolt holes in the wheel is different to the bolt holes in the OEM wheels - it’s
really important that the mating surfaces between the bolts and bolt holes are the same and the centre bore is 57.1 for safety reasons.
With used wheels (OEM or aftermarket), I’d always check with the seller that the wheels haven’t been damaged (buckled or cracked, or had welding repairs) and whether or not they’ve been refurbished. Bear in mind with diamond cut wheels, these can usually only be refurbished twice; refurbishment involves re-cutting the face of the wheel on a diamond cutting lathe, so a layer of metal is removed to get back to a clean, shiny undamaged surface. Refurbishing more than twice can affect the structural integrity of the wheel. I’d personally always choose wheels with a painted or powder coated finish, as these are much more durable than diamond cut alloys, much more suited to winter road conditions and not susceptible to white worm corrosion like diamond cut wheels can be.
Finally, fitting different wheels to those fitted on the factory production line (even if they’re OEM wheels) is considered to be a modification for insurance purposes, so should be declared to your insurer.
