It’s a ballache trying to find staggered tyres.

Why is there no easy way of finding both sizes in one shot??

You chaps with 224/40/18 and 255/35/18

What you fitted?

Why do you want staggered tyres?

Fat jobbies up back.

Have always run them, got them now

Bloody hell Viper those are low profiles! OK for a track but on our “great” roads?
Other issues.......will they fit under the wings?
Less cushioning due to small sidewalls making for a harsher ride.
Ground clearance?
I haven’t looked at calcs road speed effect either.
Maybe wider with same profiles as original would be better if you can find some.you’d get the “look” with maintained ride.

It’s what I have fitted here.

35 is only an aspect ratio so the tyre being a 255 means the sidewall is taller than a 40 on a 225 if anything.

Looks good!

I have the same sizes on the Series 2 and last time I purchased I found Michelin Pilot Super Sport in those sizes. I realise they are now replaced with MPS4S in the range so not certain if you can still find fresh ones. Absolutely great grip and feel.

They are certainly more forgiving than the lower profile 19's on the Coupe.

Yeah I love the MPS4S but they don’t do both sizes.

They do in the US, you just need to find someone to import them..

Otherwise its MPS4 (the non-S) version only in those sizes for UK.
Or if you go for 245/40 on the back then you can have Cup Sport 2s, or Cup Sport 2s with build in tyre sensors (called connect).

Re the tirewall size a 255/35 is almost identical in sidewall height to a 225/40, which is why BMW use that staggered configuration on some of their cars. There is a handy online calculator below where you can compare two tyre sizes:
https://tiresize.com/tyre-size-calculator/

Nick makes a good point, often the UK importer will not bring all products in based on historic volumes. I found this out when trying to find some tyres for an R33 GTR a long time ago. I approached them with a couple of other GTR owners and we all bought 2 sets each so they did a special order. It took about 2 months to arrive as they it was a Japanese manufactured item not EU.

The other option is to hit the EU or US web sites and look at the availability.

US - https://www.tirerack.com/content/tirerack/desktop/en/homepage.html

EU and so more chance of shipment
Mytyres, most of the shipments come from france and germany anyway and I believe tyre are a german company from the invoices.
Tyreleader are similar to the above but I have had a couple of bad service attempts with so don't use them anymore.
They both have UK .co.uk sites but can also be found in EU blends which offer tyres I do not see on the UK ones like Blackcircles.

If you can get the Mich Pilot Super Sports they are still pretty good but do check the age of manufacture.