Right. I’ve matched drivability (and can easily exceed it). However, I still haven’t yet found the secret to matching all the other stats (not even remotely close LOL). And my car’s several hundred dollars over budget. Not in the spirit of the contest, but in the spirit of collaborative learning, since this is a demographic and an era I have not played with frequently, I’m going to post my thoughts so far…
[details=Under This Cut]The most important tab for single stat maxxing is the “Detail Stats” view. This is a tab that takes a lot of time to understand… and also one that I confess to not looking at unless I’m beta testing something very specific. The math is also going to change a heap so the specific numbers are going to go mostly out the window come UE4, but the general principle will remain the same.
That’s right, I’m going to go through each and every one of these values, so sit tight.
Base values: these values form the total upon which the Factors modify, so maximising them is your first priority… how you go about this is what will affect the modifier.
Cornering: simply put, the higher the G you can pull, the higher this value is. Smaller cars and better tuned cars with better tyres will score higher. The size of your car matters for many other things, because no matter what people may say to make you feel better, size matters 
Bump Test: I frankly don’t know the algorithm the game uses to test this. What I can say is that the more your wheel and body bounces or wobbles after you hit a bump, the harder it is to drive over bumps… but this value seems to pale in significance to the understeer/oversteer modifier.
Brake Distance: self-explanatory. Short is good, so use good brakes.
Understeer/oversteer: this is denoted by the placement of the white circle on the Steering Low Speed graph, along those red and blue lines, in the Suspension tab. The S and D values tell you your modifier. Maximum values for each is 1. Basically if the yellow line crosses the blue line at the game’s decided point of grip loss, then your D modifier is 1, meaning 0% loss i.e. gently progressive understeer is predictable.
Brake quality: self-explanatory. Each tech point contributes 0.2% to this modifier.
Roll Angle: see the stat box on the suspension tab. Less roll is better.
Driver Assists: also self-explanatory, except for the fact that Power Steering is not included (and I’m pretty sure Launch Control isn’t too). It gets its own category.
Brake Fade: see brake fade stat in the brake tab. Most of us who have built a car in the good ol’ days will know well that brake sizing is a challenge… so you may want to pick a car with potentially big wheels for this challenge.
Wheel Load: I haven’t fully yet worked this out but assume that this is to do with whether there’s enough weight over each end. I notice that cars with ridiculous balances like 75F/25R and vice versa that are very light lose value… but the same balance in a really heavy car doesn’t cost anything. If this drops below +5%, you’ve got some serious weight balance issues going on.
Bottom Out: obvious. Actually, not so obvious. This is how much your springs reach the end of their travel and hit the bump stops (if your car has any). Not, as most of us thought, about how often your bumpers scrape the road. Suffice to say springs suddenly jolting on the bump stops mid-corner/bump is really bad for wheel to body load transfer dynamics. Note that when you lower springs on a car, you’re actually increasing the rate too by virtue of compressing the spring. In computer sims, since we modify the spring rate value directly, think of it as chopping off or adding coils to your spring, as you’ll obviously need to increase the rate yourself if you lower the ride height.
Brake Balance: how closely does your brake balance match the frictional force of your tyres at any given speed, as shown on the brake graph?
Wheel Spin: self-explanatory. Well, the most drivable cars are probably the most boring right…
Power Steering: Note that power steering is good for comfort, utility, offroad, but also adds weight, reduces overall reliability, and sportiness.
Drive Train: This is your layout: transverse/long, FF, FR, MR, RR, AWD etc. etc. Here I’ve picked FR which has a low drivability rating. If I picked longitudinal FF, the value would be 0 but then I’d have to go back and tune the suspension etc. all over again and the brake balance would be impossible to optimise because the weight distribution would get screwed up and right now I CBF.
Driver Height: body matters, and you can’t do much to change this beyond that.
Performance: This is the interesting part. You need enough power that your car can actually move in a… satisfactory fashion. Exactly what this magic number is, I haven’t yet figured out (because switching sections of designer requires more loading times), but it seems that acceleration is the metric by which this factor is measured. I haven’t yet established if this changes with the era, because, well… I don’t make slow cars, and I rarely make old cars 
Engine: This is probably where a lot of magic I haven’t tapped yet works. For example, raising the redline reduces drivability. Having a smoother engine raises it (so using an i6 is actually a good idea, if expensive). What else affects it? Well, I guess I need to find out.
Suspension Options: self-explanatory.
Gearbox: also self-explanatory. Having to row your own is not conducive to easy drivability.
Tyres: This takes type and size and profile into account. Changing relative sizes of your tyres so they are staggered blows your costs out though, so I wouldn’t recommend that to fit this rather tight budget.
Suspension Quality: self-explanatory. Again each tech point is 0.2% modifier.
Footprint: The larger your car (or is it your car’s wheelbase?) the harder it is to cram into small places.
Fixtures Quality: self-explanatory.
Dynamic Response: I am not sure what this does. Anybody? The title implies this is how the car responds to changes in direction but fiddling with the suspension tab and the tyres tab did zilch.
What I’m impressed by here is how everything works together to produce such a strong set of stats, because some of these factors work against each other. For example, safety and utility generally means weight. Practicality means room, and the fact phale’s car weighs in the mid 900kgs means that it’s decently sized (for a 60s car) but the larger the car the lower the base factors will be. And that reliability! Even using cheap options in the engine designer and standard options in the trim that you wouldn’t expect to give you nearly enough safety or comfort, it’s hard to keep the costs within budget. This implies to me that phale’s found a body that gives superior base values… or some surprisingly cheap combination that allows for some sacrifices to drivability… like not using double wishbone suspension, because that kills utility.
Since I have limited time to do more of this, input from others is welcomed.
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