Help With Tuning Tires and Suspension

[Yes'nt]

I've been playing for a little bit and am able to tune ok, with the exception of the tires and suspension. I'm not entirely sure what I am shooting for when tuning these aspect of a car, and when I change them I only make it worse from the default. The settings that are the worst for me are: tire width, tire diameter and rim size. If anyone has any tips on what to do, that would be great.

TL;DR Any tips on tuning the tires and suspension?

[HorseMeat]

Beats me on the suspension, everything I do makes it worse.
Tires are pretty easy though. more width equals more contact patch equals more sticky and less body roll in corners, but also more weight and cost.
Bigger wheel reduces sidewall height and stiffens the tire, at the expense of comfort, but is also lighter.
If you have the width and wheel size you want, diameter larger increase tire profile, diameter smaller reduces tire profile.
In general a car of 3,000 lbs performs admirably between 185 and 215 wide, wider for more sticky sports situations. 65 profile is about normal for 90's family car, 55 by the 00's. anything below 55 is usually considered sporty.14 inches wheel was common prior to the 00's with 15 16 and 17 being more popular through the 00's and 17-18 being commonplace in the 10's
Trucks usually run profiles of 70 or more and widths upwards of 225. Wheels sizes incrase from 14 in the 80's and prior to 18-20 nowadays.
Economy cars like width between 155 and 185, with profiles between 55 and 80, and wheels from 12-15 inchs.
Supercars like wider rear tires, even when they're all wheel drive and are often wider than 305 at the back and 245 or wider at the front, with massive wheels to fit big stonking brakes.

I know it's a lot to take in, but do a few throwaway builds without spending too much time on details, and try out these base rules, you'll find they work well and once you're comfortable you can apply them to cars you care about.

As for suspension? I just use the damn presets, everything else seems to ruin the car, and I don't understand the graphs.

[Yes'nt]

Yeah it is a bit to take it, but I'm glad to have a target to shoot for.