Some very interesting facts about how tyre weight differ per manufacturer and even manufacturer Spec in the same size and also the myth that 20" is far heavier then 19".
If I didn't mention the manufacturer spec (eg RO1, N1, N2..) then it is the standard aftermarket tyre. All tyres here (except Hankook, their good test results are bought...) are on the same high quality level!
tyre size 305 30 20
Conti 6 FR XL: 12,8 kg
Michelin PS4S: 13,8 kg
Pirelli Zero NO (strongly reinforced for Porsche 911! but more grip): 13.1kg
Pirelli Zero RO1 (Audi R8 Gen2) : 12.1kg
Hankook: 13,86kg (smallest width of all, in fact one size smaller wide then all others)
=> weight saving potential 1.76kg per tyre
tyre size: 305 30 19
Conti 6 FR XL: 10,99kg
Pirelli P Zero N2 : 14,3kg
Pirelli P Zero RO1: 13,21kg
Michelin PS4S: 12,669kg
Michelin PSS: 12,56kg
Hankook Ventus S1: 13,262kg
=> weight saving potential 3,3kg per tyre!!!
Tyre size: 235 35 19
Pirelli P Zero: 10.2kg
Pirelli P Zero RO1: 9,87kg
Conti 6 FR XL: 13,427kg (no typo mistake!)
Conti 5P FR AO: 9.8kg
Hankook Ventus V12 evo 2: 10,022kg
Hankook S1 Evo 2: 11kg
Michelin PSS: 9,96kg
Michelin PS4S: 10,22kg
=> weight Saving potential 3,67kg per tyre, but except Conti 6 they are pretty close around +/- 100g. Choice of exact tyre is by rear as much bigger differences
Tyre size: 245 30 20
Conti 6 FR XL: 9,96kg
Michelin PS4S: 10,38kg
Pirelli P Zero: 11,2kg
Prielli P Zero RO1: 9,67kg
Hankook S1 evo: 10,32kg
=> Weight saving potential 1.5kg per wheel
Tyre Size: 255 30 20
Pirelli P Zero RO1: 10.4kg (I am currently running this)
Conti 6 FR XL: 10,67kg
Michelin PS4S: 11,62kg
1) A lot of unsprung weight can be saved by choosing the right tyre brand & model
2) the choice of tyre is led by the rear one as there are the most differences
19" versus 20":
the rear tyre 305 30 20 is actually one size taller and more rumber, comparing to 305 30 19 the "right" tyre would be 305 25 20 (less rubber so less weight). But not interesting for me.
the front tyre 245 30 20 is also one size wider then the direct comparing one 235 35 19. 235 30 20 shouldn't be used front as LOI is spot on and no reserves here, more chamber then OEM due to coilover and you are above the limit.
With the right manufacturer tyre setup the 20" ones (being one size wider front and one size taller rear) are lighter then the lightest 19":
Pirelli P Zero RO 1 in 245/305 30 20 is front 19,34kg and 24.2kg rear, so 43.54 kg or -1.5kg in total lighter compared to the lightest 19" tyre combo one
a) closest is Michelin PSS in 19" with being 19,92kg front and 25.12kg rear per wheel, so 45.04kg in total.
b) in 235 30 20 and 305 25 20 I am sure there is another 1-1,5kg possible, so direct compared sizes its between 2,5-3kg less unsprung weight in 20" compared to 19".
c) the tyre is the most outside part of the wheel so the influence on unsprung and rotational mass is the biggest one on the car! -1kg tyre weight counts more then -1kg wheel weight.