After years of engine/drivetrain building I am turning my focus to tires, suspension and handling. My goal is to make a good performing "street" car that doesn't sacrifice comfort or quiet for all out race characteristics, but still needs to handle some intense road racing situations.

My first consideration is: I just put on some big sticky tires, was wondering if there is a way to calculate what tire pressure I should be running. Maybe weight of the car by size? Right now I have 30 psi in both front and rear 265/40-18 (street tires) and 305/35-18 (competition tires). I don't think airing down really does much in a radial tire. And for the most part it will just see normal daily driving. Maybe 30 is too low and it's just wasting fuel with increased rolling resistance? I've read some Corvettes and other sportier cars run as much as 38-42 psi. Seems high and likely to wear out the center of the tire...

My next step is to upgrade coilovers. I have outgrown my "height only" adjustable set and need dampening adjustability as well. The power and sticky tires really tosses the car around now and I'm noticing things I didn't before. Squat in the rear and lift in the front on accel. Vise versa when hard braking coming off of a power pull. Much more noticable body roll in higher speed cornering. Dampening is insufficient to stop tires from contacting fenders on "bad" bumps. Currently I have Tein street basis Z's, Megan front/rear sway bars and front/rear strut bars, and a Cusco underbrace. Also Megan RCA's if that matters.

I did polyurethane bushing which come with the sway bars, but I have not changed the endlinks. Anything that would be worthwhile upgrading there? As far as the coilovers. I am pretty decided on twin tubes for their mild manners. I know mono tubes are better for race applications but may be harsh under normal driving conditions. I don't have a lot of experience with knowing where to put damper settings. I had a set on my drag car that worked best when all the way loose in the front and all the way tight in the rear for launching. Then Id set them both 6-8 click softer from all the way tight for road use. (all my sets have been typical 16 settings) In general, what should a streetcar be set at? More or less depending front vs rear?

I also need to consider camber settings. I have the rear set to factory spec and feel like that's pretty good for me (in most cases) because I mostly do straight line power pulls. Looking at my car, the front wheels are more cambered in than the rears. I'm assuming this probably isn't normal considering manufacturers of sportier cars put negative camber in the rear and not so much in the front? (Look at any BMW). I don't have adjustable camber for the front, so I should probably invest in a coilover that has adjustable upper mounts too yes? I am a little confused why the camber is visually so negative on my fronts. I though the point of RCA's was to fix that angle when lowering? I am only 2" lower front and rear.

 

So after some research I've already placed and order for some adjustable front and rear sway bar links from Figs Engineering. You are supposed to level the bars after lowering which is often overlooked. I definitely don't need any preload that isn't supposed to be there affecting the suspension while cornering. I will install them at the same time that I upgrade coilovers since the work is related.

 

Camber is adjusted via the lower control arms. Adjustable upper arms are also available.

RCAs correct roll center. Roll Center Adjuster

You should use the normal recommended tire pressure as a baseline and adjust from there based on observed performance.

Damping is not the solution to your clearance issue, and only partly to your body roll. If your tires hit your fenders, then the only way to stop that (without improving clearance) is to reduce your suspension travel or impede it with stiff springs (which is why static stance people run really high spring rates). This is generally bad for handling- suspension travel is good, and overly stiff suspension is not.
Damping settings are going to be important for managing squat though.

 

Thanks for the info. I’ve experienced dampening help a lot for clearance issues in the past, just for the fact that it stops the jounce from being able to send the wheels all the way up. On my last car with adjustable coilovers the rear would bottom out with a passenger and large bumps if the dampening was set soft, but tightening the dampers would stop it from being able to travel that much and it no longer contacted. I know it’s not exactly what it’s intended for, but it definitely helps. I’m hoping a set like the Flex Z’s and the adjustable links will really plant the car and stop the squat/dive and lessen body role.

 

I found a sale on a set of Flex Z coilovers and pulled the trigger. I have always liked Tein's quality in looks, longevity, comfort and quiet operation. This line is still made in Japan too. The Flex Z is better in every way except the forgiving spring/dampening the Basis Z is set too for a dedicated street car. The spring rate is higher as well. At this point I will have to sacrifice a little bit of comfort for the stability I need. According to Tein's specs page the Street Basis Z is 560 front and 504 rear and the Flex Z is 672 front and 560 rear. This should help keep the car closer to ride height under various conditions, like adding a passenger etc. and help decrease the change over bumps. Adjustable damping is obviously the biggest factor in performance. Together I should be able to tune out lift/squat, and feel less floaty under hard acceleration, as well as tighter cornering w/ less body roll.

This is all easier said than done of course. I still will need to find a baseline to start out at and dial it in. I would definitely like input and suggestions on how to set up and what to look for, and how to make changes. Engines are my thing, a bit inexperienced in suspension setup. Is dampening typically set tighter front vs rear? Vise versa?

 

According to the instructions you are just supposed to start at 8-10 clicks down from full stiff and go from there (front and rear). I suppose if the car still feels "floaty" I'd stiffen both more. Most information has to do with dialing in by pushing the car through corners and adjusting based on under and over steer. I will likely be looking at overall stability at speed and lift/dive on launch/hard braking. I suspect I'll be stiffer in the rear to aid in keeping my tire to fender clearance open. Front looser for comfort but as stiff as it takes to feel stable and less lift/dive.
Endlink setting is pretty simple. Has to be done with the car at normal operating height, and adjusted till there is no load on the bar. So a drive on lift in my case, or over a pit, or onto 4 ramps. As long as the car is level and the suspension settled.

 

When I installed my coilovers I just set the ***** to 8 clicks from one end (16 settings) and drove the car to find out how it felt. Someone at autocross pointed out that the rear was looking bouncy, so I added some damping to the rear and it seemed to resolve the issue. That was what worked in my very specific use case and combination of parts, which is pretty much completely different from yours.

There are too many variables, especially if they're all changed at once, to say "these are the settings that will work best". So your plan to pick a baseline, drive it, see how it feels, and go up or down from there is the best plan.

 

You should adjust your tire pressure depending on how you are going to be driving, daily driving, run around 35psi, when you want to increase traction, like in a drag race, lowering the rear tires to about 30psi will help your traction off the line, if you were on a road course, running 32 on all 4 corners would be your starting point. You’ll want to see how your car responds to variations in PSI, same thing with the alignment and shock settings. You can increase your acceleration and handling by increasing the camber and Toe angles on each corner, and you should see measurable improvements on a race track, but it’ll shorten the tire life, so you want to decide where you want them set.
Set your shocks on the softest settings and then start adjusting them accordingly, most people set the coil overs to stiff and actually hurts performance when they do. So depending on what you want to do with your car, you can keep track of how it responds to adjustments. In a drag race, you’ll want the rear on the softest setting and the front in the middle. On a road course, you’ll want to stiffen things up depending on the track. Is there a drag strip around your area? Do you plan on drag racing or road racing? Racing is the best way to measure the adjustments so you know what works and what doesn’t, Get a notebook that you can keep track of what adjustments you have done, and how it performs and overtime you’ll be able to dial it in for any occasion.

 

Corvettes and sportier cars, in fact all manufacturers recommend running higher PSI in the tires because it improves fuel mileage, and also most sports cars are on Run-Flats, so traction doesn’t improve if you lower the PSI.

 

So far I've been happy with 30psi in the rears and 32 in the fronts. I also set a decent amount of negative camber in front and rear, but not too extreme. Makes for a stable feeling.