488 Tires on Ferrari California?

Rear tyre diameter will give you problems with the TC. The offset of the 488 rear wheels are also 15mm less, and the rim is 1 inch wider. Couple that with a 305 section tyre and you have a wheel that sits way out past the lip. I believe that 15mm spacers will set your stock rears flush, so adding an extra 13mm of rim + wide tyre? It's a no-go. On the rim alone it will be like adding 28 mm spacers to your stock wheels. Too little offset.

 

According to my information, the 488 front tire/rim combination is 245x35/20 J9.0 ET44, which is almost identical to the Cali's 245x35/20 J8.0 ET44. So the tires will stick out 13 mm more than the Cali's but I think it should still look alright, just.

According to the same information, the 488 rear tire/rim combination is 305x30/20 J11.0 ET38 vs. the Cali's factory 285x35/20 J10.0 ET52 and this will have the tires stick out 24 mm more than the original Cali 20" combo. That's sticking out 0.95" more so you should check your fenders to make sure they won't rub upon compression under load. Not sure of effects on the wheel bearings but I think you should have the suspension re-aligned if you use these wheels.

If the tires sticks out too far the car may also end up looking a bit funny. I would have someone hold a stick vertically at 1" out from the rear tire and sight down the side of your car. Imagine what the tire will look like to see if you like it. Other than that, if you're good with computers, you can draw a simulated sketch of the wheel well using accurate measurements. It might actually look good but then it might not so you need to visually check. Aside from that you might get a tiny bit of a "rooster tail" effect on the rear fenders with rain and debris kicked up by the tires getting past the rear wheel wells. I have bigger wheels on my car and my rear rims are 15mm further out and look good, partly because my tires only stick out more by 7mm. So be careful.

The scrub radius will also be 17mm more positive but since it's a non-steering wheel, the total effect along with the slightly wider rubber, all else being the same, will likely be a reduction in oversteer or greater understeer which may please some drivers.

Finally, if the rim is not forged, the result will likely be a heavier rear wheel, by about 10%, which is not good. You can check that by weighing the 488 wheels. I have the factory 20" cast rim wheel weights for the Cali somewhere and I recall I did publish them on FChat. Heavier rear drive wheels makes the car feel more sluggish when acceleration. This is why people who want better performance will buy lightweight forged rims.

 

I wont even ask why!

 

Did you end up pulling the trigger on this? I have been contemplating the exact same thing.