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This weekend went to ax school to learn more about my car. Exercises were the skid pad which was going around in a big circle and to learn over/understeer. Chicago box, which was a chicane turning exercise, and a figure 8 which was hairpin turning exercise.
My car was very sensitive to steering and throttle inputs, meaning I could feel in the steering wheel and in my seat when she was pushing, slipping, or about to loose it and spin out. Compared to the other drivers, my buddy and I (we shared my car for the weekend) spun out more than the rest due to driver error lifting off the throttle at the wrong time. We were all beginners in the class so started to wonder if there was something going on with the car besides driver error...
From the suggestion of the head instructor I reduced the air pressure at lunch and notice the back end is less tail happy.
Besides tires and pressure what else impacts oversteer?
I have the following
1. Pss10s 6/7 damper setting (Does damper setting do anything?)
2. M030 arbs
3. 8.5/10 wheels with hankook rs3s. Summer compound tires. They are date code 2010 and are about done and old. Hot they are 33/36 psi
4. RS spec alignment with 4.5 KT caster value and aligned and corner balanced at a reputable shop.
5. Elephant RS rubber on all bushings
6. Solid subframe bushings for the rear
This weekend went to ax school and learned more about the feel of my car. Did a bunch of exercises around car control with a skid pad. Exercises were going around in a big circle and learning over/understeer. Chicago box, which was a chicane turning exercise, and a figure 8 which was hairpin turning exercise.
She is very responsive to steering and throttle. Meaning I can point her in the direction and she will immediately respond. The rear end though takes much more finesse as I can easily get the rear end to come around if I liftoff throttle suddenly and not stay on the gas and push her through. I am sharing my car with a friend who is a better driver than I am and we have similar driving experiences.
We reduced the air pressure at lunch and the back end is less tail happy.
Besides tires and pressure what else impacts oversteer?
I have the following
1. Pss10s 6/7 damper setting (Does damper setting do anything?)
2. M030 arbs
3. 8.5/10 wheels with hankook rs3s. Sticky 140 compound tires. They are date code 2010 and are about done. Hot they are 33/36 psi. The front is 1/2" wider than stock. I will be switching to new Continental extremes on lighter 18s and a 8" front when these are done.
4. RS spec alignment with 4.5 KT caster value and aligned and corner balanced at a reputable shop.
5. Elephant RS rubber on all bushings
6. Solid subframe bushings for the rear
Thanks!
that kt spec, is it in degrees or 4.5 on a guage?
if it's from a Motorsports gauge that's high and will certainly make the rear end react a lot faster than most would want, though A/X is a whole tuning world of it's own.
The factory delivered all Cups and RSR w/ 2 on the guage, which is ~+3° 30'
That's where I'd start, go higher on the gauge to speed the rear up go lower to slow it down
Also a little more camber is a good thing for cornoring
Is the wheel change something related to A/X? 8.5s are very useful for allowing you to stay on the gas longer and earlier, i'd also try a little less rear air pressure, we usually look for ~ 33f/34r hot, but again in A/X you don't usually get hot quickenogh to matter
911s definitely have a tendency to lift throttle over steer, but 993s set up like yours should be less sensitive especially at lower speeds, but they can snap spin if you are clumsy w/ the gas and brake, old tires don't help this at all.
Samurai I’m running very similar specs to you and my backend is very stable. I can go into a skid pad and do abrupt throttle on/off in 1st gear and the rear will not lose traction. I’ve only had one instance where I felt the rear letting go in a way that made me nervous, but it was kind of an extraordinary situation, in a corner, trail braking late, off camber lump unsettled the chassis.
I’m running 235/265 on 8.5 and 10 inch wheels. I also run 225/265 on stock 8 and 10 inch wheels and can feel a bit of understeer creeping in.
On my sticky tires (re71r) I run cold pressures of 29/30. I find if I ran much higher my rear would get kind of greasy.
I think the most likely problem is the alignment. I’m running slightly more camber in the rear than the front: 1.2 front, 1.7 rear. Which helps to keep the rear in line. I’m running 3.5 on the motorsports gauge, being very careful to keep it even on both sides.
I wonder if you had your alignment checked, if something might be slightly off? Either a camber issue or a KT issue in the back. After going through a bunch of alignments back to back I can tell you that these cars are very sensitive to correct alignment.
I would not change anything on the car until you repeat the exercise with new tires. Brand new tires in different sizes will have an impact on the car's balance, no question. Also, the behavior you describe sounds like a great handling 993 to me. Here's a example of a 100% street 993 (PSS10s, otherwise stock) in an oversteer situation. Notice how you have to give it more throttle as the back end starts to let go.
I have always been a big track guy, however over the past few years have done a bunch of AX and spent alot of time learning how to set the car up more effectively. It is a totally different setup that for a track.
There cars are very sensitive to tire pressure and swaybar settings on an AX course. I have found that to stop the oversteer you need to disconnect the rear swaybar, and ge tthe rear pressure close to the front, I would suspect around 34PSI.
Also as Bill mentioned, if 4.5 is on the MS gauge is on the high side making the rear more reactive. I run the car around 2.5 on the MS gauge when on the AX course.
You will want to keep the front's as 8.5" is you intend doing more AX, you want to be running 235's on the front on an 8.5.
I tried AutoXing my 993 for two seasons and I would kill for more oversteer to try and make it competitive out there. As it were I bought a Corvette instead and save the 993 for track days and ice cream runs.
I would not make any conclusions based on skid pad excersices especially if you are new to performance driving. On wet skid pad first time around, it seems like rear snaps, but in a reality it’s ofter driver’s delayed recognition that is at play and in wet things happen very quickly. I think we all have been there.
Old tires!! these things cant be giving you any good grip... I did a track day on old tires a few years ago and the car would just let go (spin!)
Managing weight transfer is a big part, so good engine mounts, sway bars etc to keep the car stable so you can control the rotation of the car. Lifting to get the car to rotate is a good technique, but you need to be smooth and use the gas to get the car to sit.
Thank you all. Your comments were very helpful yesterday.
I worked with the head instructor to dial in my car. We first reduced the rear tire pressure further from 36psi to 34psi, the front was kept at 33psi. He showed me how to read the tires by looking the outer tire edge for wear and how hot the tire was on the inside vs. outside. Once we reduced the tire pressure the tire felt warm consistently on inside and outside and the melted rubber/scuffing went all the way to indicator arrow. Notice there is a ring from the day before and the second day post the pressure decrease. The front was already at the limit. I am running 1.2F camber and 1.7R camber. Thanks Bill V/Steven!
Overall I had better times the second half of the day through better driving. I did have a few spins due to driver error of turning sharply and being late on my brake to gas transition. Once I figured out how to hard brake, coast (to settle the suspension), turn, and then gas I was starting to get the car to push (understeer) as I gassed it through turns. Had a few fishtailing moments and learned to use check turns to correct like the video. Thanks @mpruden!
I had about 15 runs and my times got better and better, but was not as good as the others. I had a chance to do time keeping and noticed my times were generally on top for the "air cooled" drivers, average with the 996/997 drivers, and 2 seconds slower than the newer Caymans/Boxsters and the 991s. At the end of the day the head instructor concluded my driving wasn't the root cause and so I should dump my tires with some fresh ones as all of you suggest. Luckily I have a second set of wheels with some fresh continental extreme sports to try on the next event or if I can find an empty parking lot in a business part to try some skid pad exercises maybe sooner
Comments below to your questions...
Originally Posted by Bill Verburg
that kt spec, is it in degrees or 4.5 on a guage?
if it's from a Motorsports gauge that's high and will certainly make the rear end react a lot faster than most would want, though A/X is a whole tuning world of it's own.
The factory delivered all Cups and RSR w/ 2 on the guage, which is ~+3° 30'
That's where I'd start, go higher on the gauge to speed the rear up go lower to slow it down
That is the motorsport value. I just checked my rear alignment and noticed it has not moved (I painted indicator lines right after the alignment). I know the KT is set to 4.5 as I watched the tech set it that value on both sides. I had no idea 4.5 is too high so will reduce it to what you and Steven suggest as I would rather concentrate on driving than have an active rear end.
Originally Posted by mpruden
Disclaimer: I know nothing about autocross.
Notice how you have to give it more throttle as the back end starts to let go. https://youtu.be/IW1CVo0GP2c
Thanks for sharing. It was very counterintuitive to give more gas than less to get the rear end to hook up in oversteer. I had a few fishtailing moments and remember one of the older instructors said there is a german word for it and the only way out is more gas and easy on the check turns.
Originally Posted by Railmaster.
Long shot but do You have old engine mounts? Maybe RS mounts will improve handling?
Yes, I replaced the motor mounts with RS ones.
Originally Posted by element
Old tires!! these things cant be giving you any good grip... I did a track day on old tires a few years ago and the car would just let go (spin!)
Managing weight transfer is a big part, so good engine mounts, sway bars etc to keep the car stable so you can control the rotation of the car. Lifting to get the car to rotate is a good technique, but you need to be smooth and use the gas to get the car to sit.
T I R E S !
phil.
Thanks. I did notice my times were decent when I was smooth on the brake and gas transitions. The instructors wanted me to drive more aggressively and be on the gas more and brake harder and longer. As you can imagine learning to do that while turning got me in trouble a few times lifting off at the wrong time and get me into a spin. Hopefully my new tires will help me further.
Originally Posted by NYC993
^oh i missed that....def get proper tires first before making any judgements.
i posted before...functioning LSD was biggest contibutor to understeer (i.e. reduction of over steer).
I don't have a LSD. It is an open diff. One of my upgrades for later!
Even if they weren't 8 years old, I'd look for better tires that the Hankooks. You get what you pay for in rubber, particularly in AX or on track days.
04-29-2018, 01:38 PM
How to reduce oversteer?
