used an Apis today (and only talk about weapon):
T1 : 115 ; to reach 1.0 it decayed by 23.89 ped
T2 : 390 ; to reach 2.0 it decayed by 14.67 ped
T3 : 312 ; to reach 3.0 it decayed by 28.40 ped
T4 : 112 ; to reach 4.0 it decayed by 116... ped
For T1 i spend around 110-120 ped of ammo. From my society it seem pretty common that a weapon with a T1 of around 100 to spend 100 -120 ped of ammo to reach 0.9-1.0
if we consider each following tier as twice as difficult, we might get a trend.
For T2, would I wanted to spend 100-120 ped of ammo, it would have needed to have a T2 of 200. Since at this time, it is 390, it is half of that.
Following with T3, for 100-120 ped (tier@ ~100) of ammo it would have needed a T of 400. Since it is only 312, I spend a bit more than that (all this is based on decay).
Maybe there is a different rule for further tier (4-5-6 then 7-8-9 and finally 10?)
And I think that tools /armor/weapons work differently
2 nd theory:
instead of doubling the decay for each new tier,, just Xtiply the T by 100 :
you have a base of 100 -120 ped ammo spend for tier 1 with a TIR of 100
for T2,you have to get a TIR of 200 to get the normal rate
for T3 you have to get a TIR of 300 to get the normal rate
for T4 you have to get a TIR of 400 to get the normal rate
with that second theory, the numbers seem to corroborate it (like... 25 ped of decay for a TIR of 100 @ T1) the variation would be due to the randomness.
(close to 5 am... forgive my english)