I think it's based on Level, if It costs 20 parts to repair a car, two car team it will cost 40 parts.
For 50 points in reliability it reduces the cost to 12-13 parts. 24-26 parts two car team
For 100 points in reliability it reduces the cost to 2-3 parts. 4-6 parts two car team
Some tracks cause more wear than others if you think back to when Reliability done nothing it cost us 2 or 3 parts after the race for each car.
instead of 40 parts for lvl 20 team it should go to max 20 parts including both cars as one can't produce more than 20 parts
and yes i think there are tracks where the wear are less like what i saw today Monaco only 3 parts each, so it need good thought process
like in a race total possible part consumption =< [60% of team repo + 40%HQ]
tht is if lvl 20 and lvl 20 hq then
12 + 8 = 20 parts consumption, so either we can keep same 20 or can reduce to 19 looking at storing the parts for utilizing when the level of either hq or team repo increases
if lvl 20 and lvl 10 hq then
12 + 4 = 16 parts consumption [consumption of 15-16 parts]
if lvl 15 and lvl 10 hq then
9 + 4 = 13 parts consumption [12-13 parts]
something like this, its an avg example i consider it can be track to track