Tire Works 4

Five and a half degrees negative camber.  Did I do it on purpose?  No, that’s actually as positive as my adjustments allow me, with the parts I chose.  Is it fast?  Maybe not.  My braking sure suffers, but surprisingly, it does seem to make good use of the tires in corners.  Soft, narrow, bubbly tires sure help that happen though.  Do I like it?  Yah.  I like it a lot.

Soft, narrow bubbly tires: look at that outside rear slip over.  For me at least, this goes a long ways towards making driving fun.  Gotta have a good relationship with your car, gotta be able to understand what’s going on and respond.  Yes those are 6J wheels in 185 rubber.  Not that engineers always get things right, but surprise surprise, that’s what Dunlop says I should be running.  I know you think I should be running 9J, or at least some 8’s… but I’m sure you think that hot girl who just lies down and takes it, is something exciting as well.  IMO, both are good for impressing your friends and little else.

The goal of my vehicle set up as I’ve suggested, is not to build the fastest machine possible, but instead to build a driving toy that will help me re-hone my skills, and maximize the amount of fun I can have with a car that isn’t actually “competitively” built for any form of motor sports.

As I started out saying, 5.5 degrees of negative camber.  Seems like a lot, but this photo shows pretty well how I still end up using the full tire.  Of course, throw some body roll in and you can see that the inside tire probably sits at more like 8 or 10 degrees negative mid-corner, and that effectively makes it useless in this situation.  But it practically already is anyways.  With big stiff springs and a massive sway bar up front, approximate calculations say that there is only 50lbs of weight on it  at 1g lateral acceleration.

The big benefit of all that camber is not better overall grip, but camber thrust.  Camber thrust makes things challenging on the street, but it works awesome on the track to help the car turn in hard.  We all have our standards and ideas of what is good, but this car turns in better than anything I’ve ever driven.  Toe-In helps.  I’m running  a little more than an 1/8″.  Talk on the internet says that toe-out is better for turn in and overall grip.  For turn in?  I’m not there.  It can help overall front grip through tight turns where factory ackermann is not sufficient.  There are a couple of reasons that I don’t care about ackermann, but the obvious one is because my inside tire is barely on the ground.  I feel like toe-in gives better turn in and feel, but as an added benefit it helps counter all the instabilities that large amounts of negative camber can cause.

Regarding caster and KPI.  My hope was to minimize KPI and maximize caster.  Thinking about weight jacking, such a set up transfers weight to the outside rear tire under positive steering angle (i.e. turning into the corner), and helps the car break into oversteer should a push develop.  Ideally though, the car turns in hard and neutrally and I have no need for highly positive steering angles.  Should I find myself in a state of high oversteer, the weight jacking effects of caster will transfer weight to the inside rear tire and outside front in countersteer and thus help the car return to a more neutral state AND really help me put the power down.  This does make throwing the car around easy and fun, and even gives you the impression that you’re really fast because you leave your foot on the floor all the time.  It’s a trick however… at least if you let angle and washout get as big as I often do.

The camber changes caused by this caster set up are not as favorable, but that’s largely because my static camber is so high already.  Under positive steering angle, when the car is  possibly in a state of understeer, the outside tire gets more negative camber which at that point is probably becoming a little excessive.  Under negative steering angle, the outside front camber angle becomes more positive, which helps the front of the car wash out and return to a neutral state.

Thoughts for next time?  I have no plans to change anything.  My driving can be a lot better.  Particularly I need to drive a good line rather than let the car turn in and take what ever path it chooses.  If I struggle again, my next step would be to remove the rear sway bar.  Not only would that help the rear stay planted, it would also give me a little more body roll which could help to calm things down further.  It is looking like I might be a match for some cars running in the STX class.  Eventually my pride will return and I’ll actually want to beat them, even if cams and other things have me in SM with really fast cars.  The way I see it though, a GD Impreza with solid footwork, a basic power up and similar rubber in 255 size should be a lot faster than me.

But maybe I’m already making excuses.

All these pictures are belong to Ian Gulinao.  Thanks Ian.  They actually make this way more fun for me.