You have to be acquainted with cmagic:
Here is a description I saved once - but I don't know who wrote this:
1)
A:
In magic data, tyre wear change ONLY human one...as also bump factors. Therefore, You have to change these factors balancing well, in order to avoid to too difficult trend for humans ( if You increase bump factors, or decrease the value for the tyre wear...and the contrary, of course ).
Regarding tyre wear, the string in magic file is the 50th. Pay attention: increasing this value, only human player will have more grip on tyres, but less duration...In default, the best perf tyres are available from the second-third lap; increasing ( for example, from 15350 to 20350 ) ) this value, You will have immediatelly a better grip, but in some laps You will decrease performances tyres. Decreasing tyre wear value ( example: from 15350 to 8350 ) You will have the best tyre wear about on 7-8th lap, and of course the duration of tyre wear is longer.
But, I repeat, this factor affects ONLY human player.
2)
A:
Briefly: some features affect all drivers, some others only CPU drivers, or humans.
Regarding human driver, the only real factor that can improve your performances is the tyre wear, that affect only human drivers. You have to decrease this value ( 8000, or 4000 ), in order to obtain a longer time of performances for your tyres.
Otherwise, You can decrease ace, pro, semipro, etc grip levels ( that affect only CPu drivers ), in order to be faster.
All other factors ( setups, tyres, bhp for each levels, airresistance, etc ) are affecting both human and CP drivers.
You have to work on Physic file...if You want some vantages on CPU drivers.
Q:
you can increase the track grip value which should speed up all cars and then maybe decrease the power factor.
A:
But that track grip affect all cars ( incresing also fuel consumption ). So...You will be faster..but also CPU drivers.
I suggested to decrease drivers grip factors, that affect only CPU drivers, as You remarked, changing also tyre wear, that affect only human drivers.
In conclusion: if You start from a situation where CPU drivers are faster, in my opinion is not convenient to work on factors affecting both drivers ( human and CPU ).
It's better to decrease some CPU drivers factor, or improve some human driver factor....or both.
Maybe this helps