Lessons and advice for managing oversteer/understeer on autox & track days
#1
Lessons and advice for managing oversteer/understeer on autox & track days
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!
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!
Last edited by txg37x; 02-25-2015 at 12:25 AM.
#2
Lexus Defector
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.
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.
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txg37x (03-03-2015)
#4
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.
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.
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.
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.
#5
Registered User
...
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.
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.
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.
#6
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!
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!
#7
I
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.
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#8
What tire pressures do you use for autox/track?
#10
Registered Member
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.
The following users liked this post:
m3clubracer (09-20-2015)
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