So I had my first autocross today in the FC... Well, first autocross ever, aside from Mazda's "Rev-it-up" and "Zoom Zoom Live" promotional events.

So firstly here's the setup:
1986 GXL, recently rebuilt LSD.
-Cheap Bendix or Raybestos brakes (Came on the car, will replace when they wear out. Have Hawk Blues and SS lines.)
-Öhlins coilover setup. (Non-adjustable ride height, adjustable rebound dampers.)
-Suspension techniques REAR sway bar with stock links.
-Stock front sway bar. (I have the ST front, but was told that if I put that on, it'll understeer more.)
-Falken Ziex tires on rear, stock size 205-60R15
-Hankook Optimo tires on the front. Wrong size, 195-65R15. (Bought vert wheels with four Falken tires, but two were no good. Too much camber wear on both and a nail in one. Used tire shop didn't have anything correctly sized available and these were cheap.

I tried multiple air pressures throughout the day. I think I got as low as 17 PSI on the front so that I could use about 3/4 inch of the sidewall as additional contact patch... I didn't go below 22 on the rear. Those Falkens are still rather nice.

Most of the time I found that I'd understeer into everything, even though I was going into turns like most other drivers. People commented that my car looked like a FWD out there for some reason.

Others commented on my steering input. (Still have to figure out which rack I have... I suspect I have the one with the shitty ratio.)


Anyhow, I'm leaning towards the crappy tires on the front. But what else can I do to eliminate the understeer?

 

Try switching front and rear tires. I bet the under steer is gone and oversteer has replaced it

Next try both skinny tires on one side and the fat tires on the other side.

Then just for grins, put one skinny tire on the front and one on the back for some really erratic vehicle dynamics.

See how silly this sounds? Get the right tire size, try again.

 

couple suggestions;

enter the turn slower, its really really hard to do...

whats your alignment look like? grassroots motorsports did a t2 (when it was new!) and they found a bunch of grip/time in setting up the alignment. i have mine setup at zero toe and as much camber as i could get out of the front, and its way better. much less understeer.

have you tried playing with the shocks? softer = faster weight transfer

tire pressure. if you want it more tail happy run more pressure in the rear. ideally you'd find optimum front PSI and then run a ton in the rear to get it to rotate better. we've done it with our honda...

http://farnorthracing.com/autocross_secrets.html

if it has a 2 line PS pump, like it should have if its a gxl, then its 15:1 steering rack.

 

Maybe you are running too much positive camber on the fronts or too much negative camber on the rears? Get some correctly-sized Ziex tires for the front, install the ST sway bar, and recheck your camber settings. Try that setup on the next autocross with standard tire pressure.

In theory, a stiffer front sway bar will increase understeer due to weight transfer, but it will also reduce positive camber which decreases understeer. I would try the bar and see how it works with the rest of your suspension. My car handled much better with both the front and rear Eibach sway bars installed.

You could also add some rebound to the rears if your understeer is most noticeable on corner entry.

If all else fails, post in the Race Car Tech subforum where there are actually a few real racers. Edit: Or ask Mike/Paul above, lol.

 

I'm going to go out on a small limb here and say its never going to handle right with that tire setup no matter how much you play with it. If you are dead set on not getting new/better tires, try running the 195s on the back, but be prepared to disconnect the rear sway to try to mitigate some of what will surely be serious, rapid, oversteer.

Quick story: when I first started auto-crossing I was on a 205/225 stagger with RE750s or something like that. Car would understeer like a pig everywhere, even on corner exit. Not fun. Part of it was surely driver error, but certainly it was a setup problem too.

Also, you're lucky you didn't unseat a bead running that low of a pressure. Last time I checked the Optimos were all touring tires.

 

These front Hankook Optimo tires are junk tires for me to get the car around... I picked the car up a month ago out of some guy's front yard for $250 because the timing belt in my DD went and I'm busy cleaning up that mess.

Change of all coolant hoses and oil and a charged battery and she fired right up first try.

Stock tires were dry rotted so I picked up the Vert Wheels that had bad camber wear on the two tires... Hankooks were $20 for the pair with about 9/32's of tread on them. Needed to pass inspection.

Then I bought the sway bars and suspension and started dumping money into what was supposed to be a temporary daily driver.

Anywho... I don't really care about the wrong front tires and will probably swap them around and disconnect the front sway bar end links for a fun night in an empty parking lot some time. Hence the experimentation with dangerously low tire pressures.


Now here's a kicker. I mentioned getting R Compounds to one of the other drivers there. They suggested I stick with crappy tires, as while R Compounds will be more sticky, I won't learn to enter the corners with more control...

Could I use these thin tires as a teaching tool?
Or should I grab up the Craigslist $200 1999 Mustang GT wheels with 225-50R16 Toyo Proxies RA1 tires?

 

You should stick to street tires for at least a season or 2. R comps can hide alot of bad habits. The skinny tires aren't necessarily a good "teaching tool" either since a crappy tire isn't going to handle like its "supposed to" in a performance situation, and when you step up to a real street tire, like the XS or Star Spec, you are going to have to re-learn to drive all over again. This is especially true in your case since you have the coilovers, which will really overwhelm a regular street tire. Sell sways, pick up a set of Azenis or something (I think the 205/50/15 is only like $75 a tire) that will take the abuse, and have fun learning.

 

^ Sell sway bars?! NO way.
They're what took away the cushy feel that I hated about the FC and gave me that Go-Kart feel that I so love about my FB.

I'll shop around for some Azenis Tires.

No tire shop around me (Tires Plus, NTB/Merchants/Tire Kingdom, etc) has any good selection. I've always wanted to order from Tire Rack and have my own mounter and balancer. I like my tires match mounted to the wheels anyhow, which nobody seems to do anymore. It was my standard when I used to be a tire monkey.


And two posts above, where I said crappy tires... I meant street tires, but NOT the wrong sized ones I have now.

 

The sways made that much of a difference for you? What are the spring rates on the Ohlins?

 

^

Unfortunately, I can't find any concrete info about the setup. It's like Ohlins never manufactured it. I can't find an application on their website or even a part number on the springs...

It feels like my friend's GTUs with 375/390 lb springs (Eibach/Ground Control coilovers, Tokico Illumnas) I think... I'll have to call him and see.


He rushed me to put the suspension on. I was gonna clean and repaint the springs and replace the rubber caps on the ends of the springs at the pillowball mount and base.

I also may wanna pull the front camber in a little. I'm running around 3 deg negative.

 

Just a thought.

Camber works if the car rolls enough during cornering to make the tire "flatter". If you are running these stiff sway bars as you say...yes you may have too much camber for the speeds you are running.

 

for me gripping is easy, stance coilovers set fairly stiff with 235 and 245 tires works well for me

as far as fixing yours retry with good tires should change a lot and gert a better assement of what is going wrong if anything and you will get a lod better feel for the road

 

He only has a rear sway, which would help out with understeer, if anything.
Do you have a camber adjuster, ala Mazdatrix? How's the alignment?


remember, Slow in, fast out! Also, the later you brake, the more you'll load the front wheels for the corner's entrance.

 

Alignment was good before I put the new suspension on... I don't believe rear camber has changed. Front obviously has.

I have individual camber adjusters that I need to install, but I do need to find a good deal on the center link before I go tearing apart everything out back. I'll do polyurethane bushings while I'm in there and check teh condition of my DTSS bushings.

That's another one of my problems. I brake up to and in the turn, and when the car understeers, it's reflex action for me to turn the wheel further, which isn't too good.

 

I don't think the camber is your problem. FCs tend to like as much as they can get. I'm at -3* now and the only reason I haven't gone for more is to attempt to save my street tires. Do you know what your toe is at?

It might be worth it to pull the springs out and physically test them. Its gonna be really hard to troubleshoot your handling (once you get decent tires) without some spring numbers.

Unrelated: I just got back from trying out my 650/500 setup and it is an absolute demon through the slaloms now!

 

How do I test the springs? Pull them from the shock assembly and measure length and see how much weight it takes to compress them one inch?



Also, my girlfriend, who drive neither car regularly (So it's an unbiased and unconditioned judgment.) said my car feels like it takes more steering wheel input to turn the car the same amount... This'd be between my car and my friend's 1989 GTUs (As mentioned above, it has Ground Control coilovers with Eibach springs and Tokico Illumna shocks, rolling on Kumho Ecsta Supra 712s that day.)

I have the S4 GXL and he has the S5 GTUs... Both should have the 15:1 rack, and with power steering, both should be 2.7 turns lock to lock. I'm fairly certain that neither rack has been swapped out.

 

the gxl should have a rack that says fb55 or fb78 or something like that on it, FB01 is the manual, and FC01 is the single line 18:1 power rack from the 89+.

there are two ways to measure spring rate.

1. pull em off the car, take it to a shop, have them do it. there is a local shop here, price was reasonable.

2. there is some local guy who has a floor jack/bathroom scale setup, you compress spring one inch, look at scale, you need the fat guy scale (300+lbs), and compressing the spring more than an inch seems like a bad idea...

 

^

Label dead in the middle of the rack, right? Or should I look elsewhere?
Time to get out the degreaser.
I bought this from the original owner and while well cared for, it's still 24 years old.

 

i tend to like more pressure in the front tires, though i'm running non staggered tires on staggered wheels. i have approximately -2* camber in the front, -1.7* rear. i do have some understeer but it's due to driver error. tires made the most difference, i got BS RE-01R's. stock sways and tein coilovers which i will get corner balanced when i switch my rack.

 

you have optimos in the front??

Probably one reason as to why you are understeering. You'd need sticker tires in front or else the load will be too much and you will understeer. Always start with tires first before anything else.

if you want some cheap and nice grip tires, tirerack is having a closeout sale on Hankook RS2 tires.

 

if you get some 17s I'll sell you my 225/45/17s Azenis for dirt cheap Theo

my rears are gone and I want some XSs or star specs lol