Milouse - I've noticed that some variations of UCD cars can gain or lose power depending on the mileage on them (I think the PFGT is a notable example).
I've decided that, for my database, I'm going to bin all the power/torque ratings for used cars as they muddy the waters somewhat and, since all cars in the game can be acquired through tickets at 0.0 miles, I'm going to only use 0.0 mile ratings as a baseline. What do you reckon (you're of course, welcome to borrow my data for your site)?
I had gathered data about this too and found that...
If we consider:
1. "OH", the car Power/Torque after Engine Overhaul.
2. "RC", the car values as it arrived in garage first time.
RC = OH * 0.95 * (1 - (mileage_impact / 100) ).
The mileage_impact value grew from 0 to 5, and seems to be calculated from UCD mileage with a quite strange "rule" : it stay at 0 under 5 000 KM, then grew from 1 to 5 until around 15 000 KM.
This means that a car that has 18 000 KM on UCD lose as much (5%) power and torque than a car with 300 000 KM).
This also means that although you can do it, you wouldn't win Power after Engine Overhaul on a car bought with less than 5000 KM.
I am yet to find exception to that "rule". I don't think it works for the cars you actualy drive, however.
The data submission form on website ask for both garage car state and mileage in order to calculate the OH values, which are the target* ones with 1 unit error (the site run with mutliple units at once, so units).
(*) : this has been arbitrary choice (that i'm not sure to be the best one) ; a lot of datas does not reach that target yet.
Edit: Because I found this after building database, many cars from UCD didn't take this 0-5% impact into account, so "Ver. 3" cars and below are often lacking power (not mentionning that their data aren't from garage). I'm not satisfied with how power/torque value reliability is explained on website, and have its redesign on my todo list.
Edit2: Important: Two same model cars, one bought on UCD, and the other received as a prize car with 0 km can end to different Power/Torque even after engine overhaul. Which one is the "good" value is hard to say here. (on the two cars I saw this, one has more, other has less power)