Balanced to understeer during autocross

[rocketrider807]

Would like some advice. Current setup:
20x10 rear, hankook ventus v12. (275-40-20)
20x8.5 front, michelin pilot super sport (255-45-20)
1" lower
Bmr sway bars, full stiff rear, middle front
BMR pro bushing kit

My issue was that at test n tune today, during the morning the car was perfectly balanced and very sticky, but as the day wore on i seemed to lose front grip. I ran rears at a constant 36 and modulated the fronts between 38 and 34 hot trying to help, but nothing made it handle like it did in the morning. Best results were actually at the 34 hot. Tires never felt overheated. They got warm but I could leave my hand on them without being uncomfortable

Anyone have ideas as to what i may be doing wrong? Considering putting the front way bar at its loosest setting to try to help with the "hot" understeer.

[NJ Drive]

When surface temps rise grip usually improves, and the rear tires on a RWD car usually benefit first.

You didn't mention how much front camber you're running either. Did you spray the tires at all during the event?

[tw78911sc]

go full soft on the front or drop some front PSI, add camber, if you have the $$, go to a square setup like the 1LE, 285 all around. Try left foot braking to provoke trail braking.

[rocketrider807]

Originally Posted by NJ Drive

When surface temps rise grip usually improves, and the rear tires on a RWD car usually benefit first.

You didn't mention how much front camber you're running either. Did you spray the tires at all during the event?

Never sprayed, didnt feel like I needed to (again just by touching the tires after each run, heat didnt feel excessive)

alignment that I got about 3 weeks ago, requested specs as close to the "aggressive street" settings that I could get using pretty much all stock adjustments

Front Toe: 0" total
Front Camber: -1 and -1.1 deg
caster: 6 and 5.5 deg (no adjustment available)
Rear Toe: 1/8" total (in)
Rear Camber: -.6 and -.7 deg

Square setup is definitely a priority in terms of planned upgrades, may have to wait til next year though. Not worth it to buy bigger rims and run these tires (they will fit 20x10) and selling tires/rims isnt really cost effective either, just gotta deal with it best I can until it's time for new fronts.

I appreciate the input!

[Norm Peterson]

Just guessing that you got a bit more aggressive and faster as the day progressed, to the point where -1°-ish front camber wasn't enough any more (particularly with those wheel width and tire differences).

Did anybody notice where your outside front tire cambers were in the middles of turns? Or better yet, took pictures?


Norm

[SPCBA]

Mr Peterson is spot on with that camber. My "agressive street" alignment has twice the camber front and back. There is definatly some room in your posted alignment for speed.

[Anthony @ LG Motorsports]

I agree with the posts above, you need more camber front and rear for sure. I don't know if I would go any more toe on the car, if you are not going to swap it between street and track settings.

For sure the car would greatly benefit from a wider front tire, even on our race cars running 305's front and rear we were still fighting a push to some degree depending on the track. Nothing beats more rubber on the ground.

Did you by chance get any tire temps?

[woodside783]

Going with a squard set up will help out a ton will fix just about all under steer problems

[rocketrider807]

Update:
Softening the front sway bar to loosest definitely helped the second day. Still felt like I was starting to lose grip as things got hotter though. Ill assume it's like Norm said, I was just getting more aggressive as I ran.

Never did get temps, I've just got my good ol fashioned pressure gauge. Hand could stay on the tire without burning.

Will definitely try more camber...and also the first competition put the bug in my butt. I can make podium with my current setup but 1st place is going to require superior tread and wider fronts, I'ma bite the bullet and just do it. Considering 20x10 TSWs all around and Hankook RS3. Any opinions are appreciated

[Norm Peterson]

What class are you running in?

Be careful when making mods at autocross - in SCCA, 10" wide wheels will bump you out of the Street and Street Touring classes up to Street Prepared all by themselves.


Norm

[TBone]

I will leave this here for you too.



T.

[kobSS]

^Diggin that graphic - Thanks TBone!

[rocketrider807]

Originally Posted by Norm Peterson

What class are you running in?

Be careful when making mods at autocross - in SCCA, 10" wide wheels will bump you out of the Street and Street Touring classes up to Street Prepared all by themselves.


Norm

TESP. Other mods aside from tires/wheels put me there already (see first post)

[TBone]

Shirley. I mean surely. Dammit I meant, oh hell with it.....



T.