txg37x

iTrader: (1)

I've done numerous track days/ autox in the past year in my G37x sedan, and I'm trying to get the car balanced out. Since first starting as stock, I've made several changes and have noted the differences. I am in no way an expert at this stuff. Hell, most of the problems I'm having are probably because I'm still inexperienced at this autocross and track stuff. Please feel free to comment and tell me where I'm completely wrong. Hopefully this thread and your comments will help me and others who want to track and autox their G.

Stock with all season tires, the car pushed hard in turns with severe understeer. Tires were already old, but wore down to belts after about 2 hours of total track time- running 30 minutes at a time. I admittedly pushed the car too hard. In fact, it went into limp mode not wanting to downshift or go into higher RPMs. I recommend not running so long at one time unless you upgrade to oil & transmission coolers.

My first upgrade was Hotchkis sway bars - front at stiffest and middle for rear- and Hankook Ventus v12 tires. The car was much, much more balanced, but still had noticible push at limits. This setup felt perfect for street.

Hotchkis at stiffest front and rear led to noticible oversteer on normal driving yet it felt the best when pushed at the limits. This gave me the most competitive times.

After lowering on swift springs, things started going wrong. Car felt stiffer and had less body roll and movement from braking & accelerating which felt good at first; however, the balance of the car seemed to change considerably. It was fun to do four wheel slides, but at the limit, understeer came back in full force. Because of the lowering, I'm have around -2 camber all around which should be good.

Adding a front strut tower brace seemed to increase understeer even more. More push through the turns, but for street driving the strut bar did seem to help make sharp, lower speed turns more precise when extra speed didn't push completely.

I bought Michelin Pilot Super Spors for my stock 17" rims - 245/45/17 to be used for track/autox only- I thought this would save $ and perform better, but they seemed to perform worse than my 245/40/19 Hankook V12s. The PSS are rated much better, but I guess the larger sidewall on the 17"s allowed the tire to roll over more? Maybe they were worse since they were brand new? I still need to play with tire pressure. Any recommendations for tire pressure?

I have track day coming up this weekend, so I will loosen the front sway bar to the loosest setting. This should make the car more neutral and hopefully prone to oversteer and better able to apply throttle during the turns. I will also run some laps without the strut bar to see if it affects anything. This will also be my first time to track/autox with 20mm H&R DRM spaces. From what I've read, the wider track will only make a negligible if any difference in performance. After the swift drop, I had to get spacers to make the wheels look normal again.

Lastly, I bought the two GTSpec rear subframe braces to stiffen the back up, so hopefully I can put the front sway bar back to the stiffest setting and still feel balanced. I don't think they'll arrive by the trackday this weekend, so I'll update the post once I get a chance to test them out.

Again, I'm just learning all this stuff, so please post to share your expertise!

Black Betty

iTrader: (60)

Sounds like you are figuring it out. I was going to suggest softer front sway bar setting if you are pushing into the corners but you seem to have figured that out. As far as tire pressures, you have to play around with them and see what suits your driving style. Here's a link to a very basic understanding of how to adjust pressures to achieve various handling changes.

http://www.tirerack.com/tires/tirete....jsp?techid=58

As far as your tires, since they are vastly different sizes its kind of comparing apples to bananas. In what aspect are they worse? I have had those same two tires in the exact same size and for me the PSS are noticeably better performers than the Hankooks in every way, wet and dry.

Good luck and have fun.

vqsmile

I'm guessing that those 17" PSS tires were mounted on a narrow rim (pinched), thereby allowing more sidewall flex.

txg37x

iTrader: (1)

Thanks for the link BB. I had read that info from tirerack before, but it was a year ago and I apparently forgot it! It put me back on track with PSI. The reason the PSS felt worse was that they pushed more in turns than the Hankooks on same suspension setup. As you mentioned, the two sets are different sizes and as VQ mentioned fit differently on the rims, so maybe that's why the PSS pushed so much more. It could also be that when I ran them, I dropped my pressure down to 36 all around as opposed to the 42 I had been running with the Hankooks.

I'm still learning more stuff about this everyday, and I had no idea how much of a difference tire pressure makes. That may have been the major reason the PSS felt so much worse. Now I understand why the hardcore guys are checking their tire pressures after each lap.

VQ, the 245/45/17 PSS were mounted on 7.5" rims. According to tirerack,7.5 is still within recommended range for the tire size- albeit the minimum width. Could this still be an issue? Is there a sweetspot for tire width to rim width?

Today's runs were on a track, so the speeds were higher and the turns were a lot wider compared to typical autox courses. With the Hankooks at F42/R39, strut bar removed, and sways still at stiffest, the car felt great. Some push and some oversteer. I think the car felt more balanced this time around since the less sharp turns minimized the brutal understeer I feel on the tight autox courses.

vqsmile

Yes, it is definitely an issue when tracking your car. Even though it is technically within the minimum FOR STREET USE, that tire would be far better if were on a 9" rim. In fact, I would bet that if you ran those 245's in a back-to-back comparison with a 225 width on your same 7.5" wheels you'd find the narrower, but more appropriately fitted tires, would yield better lap times over all; the sidewall flex matters that much! This won't always hold on an autoX course, but out on a track it seriously adds up.

As for minimizing push/improving turn-in, have you practiced any with a trailing brake? Likewise, lifting the throttle a tad on a high speed sweeper will also help turn in. Basic stuff.

txg37x

iTrader: (1)

VQ: Thanks again man. I wish I had known that before dropping the $ on the PSS. I just figured the more rubber on the ground the better. Lesson learned, haha.

I have practiced with trail braking and it's definitely helpful on the track for kicking the rear end out to bypass some front end push, but with the slower, tighter, and narrower room for error on autox turns, I don't think I can pull it off. I honestly haven't even tried. I just don't think I have the skills to do it without getting squirrelly and nailing some cones. I will do my best to try it at least once for the next autox just to see how it goes.

Thanks again for yalls help. I hope others see this and get inspired to take their sedans to the track or autox!

John B

Tire pressure, tire pressure!! Add or subtracting a few pounds depending on temps will make an greater improvement than just buying all this other stuff minus sway bars. I use PSS on sport 18's and I never have a problem with understeer.

txg37x

iTrader: (1)

I take it you have a RWD? I have an X, and it adds an extra ~180lbs up front. The weight along with the front wheels pulling considerably change the dynamics on tight turns. RWDs have to fight to keep the rear end from swinging out on mid turn throttle, while it's nearly impossible to get the X to kick out without upgrades and/or trail braking.

What tire pressures do you use for autox/track?

m3clubracer

^^^ This is what makes a ton of difference!

m3clubracer

You should really save some money and get a track day at your local track. It's expensive, but really worth it. Also search for others with a G35/7x who tracks/auto-xs it and find out their setup. for the track the setup will be different even the car control will be also, but your confidence/fun level with increase exponentially. Your tires will thank you too, but your brakes won't! If you find someone let me know as it will help others.

micafd3s

iTrader: (2)

save up for coilovers... get them corner balanced and youll be happy you did..

4DRZ

iTrader: (7)

If you are just starting out with track days seek out the instructors to help you with technique. Money spent on good instruction is far more valuable than money spent on modifications to the car.

m3clubracer

Yeah, you'll go way faster and learn more.