Your math is wrong...
A load rating of 88 equates to a max weight of 560kg, Seat OE spec calls for 92 which equates to 630kg.
This tyre is only capable of supporting this load when running at >36PSI according to spec laid out by the European Tyre and Rim Technical Organization.
The recommendation is to ensure the new tyres, even if a different size, have the same or a higher load rating.
It is normal for combined load of the 4 tyres to exceed the maximum weight of the vehicle by about 25% to allow for uneven load distribution or excessive loads when cornering or braking.
Remember that the weight distribution isn't 50:50, and that cornering will transfer the weight to the loaded tyre.
In the case of the Cupra the max gross weight is 1950kg, so running 88's would cut your safety margin to 14.9% compared to the OE 29.2%. That's near enough having the safety margin (at 36 PSI).
Granted it doesn't sound like you will be loading your car up that much...
If you were to blow a tyre and have an accident I don't think your insurance company would look to kindly on it...
It is a breach of Construction and Use regulations to run on tyres that are below the specified Load Index (Road Traffic Act 1988), so if plod was sharp enough it's a fine and 3 points! (and the insurance company will wash their hands of you).
Since the top speed of the unmodified Cupra R (~100BHP down on Pov's) is >155 mph running 168 mph (W rated) tyres also isn't the best if you are tracking it...
^ The above is for information purposes only, it's Pov's life and on a closed track he can do whatever he likes. All the best Pov
