Autocross rear toe question (Boxster)
04-22-2012, 08:57 PM
#1
Drifting
Thread Starter
Autocross rear toe question (Boxster)
I'm having issues controlling oversteer. Once the back end breaks loose, it just keeps coming around. I don't like that, I'd like to be able to lift, let the car rotate, and plant it back with the throttle. I just checked and it looks like I have about 1/8 rear toe out. Would toe in make oversteer easier to control with throttle? If so, how much? If not, what else could I do to improve handling?
2004 986S. Only suspension mod I've made is a GT3 front swaybar. Presently not set quite as stiff as it was the day my avatar photo was taken
2004 986S. Only suspension mod I've made is a GT3 front swaybar. Presently not set quite as stiff as it was the day my avatar photo was taken
Last edited by sjfehr; 04-23-2012 at 07:42 PM.
04-23-2012, 12:34 AM
#2
Intermediate
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Toe out in the rear is a bad thing for any car on the street. Toe out in any Porsche is not a good idea for even autox. No wonder your back end is breaking loose. If you are in stock class and just cant find anything to break understeer, rear toe out is a method of last resort.
The question should probably be more, of how much toe in to do. I don't really know whats best for setting for a boxster, but I would think you need at least +1/16" toe in just for reasonable stability. Toe out in the rear is just going to create unpredictable handling. It naturally makes the rear end want to slide out as you load it up in a corner, because the wheel with the weight is pointing out while your front tires are steering in. The car will rotate, but you are also going to be fighting with it the whole time.
As a rule of thumb, regardless of car, your rear total toe should always be large number (toe in is positive) than your front. Toe out in the front is a great idea for crisp turn in and steering response.
The question should probably be more, of how much toe in to do. I don't really know whats best for setting for a boxster, but I would think you need at least +1/16" toe in just for reasonable stability. Toe out in the rear is just going to create unpredictable handling. It naturally makes the rear end want to slide out as you load it up in a corner, because the wheel with the weight is pointing out while your front tires are steering in. The car will rotate, but you are also going to be fighting with it the whole time.
As a rule of thumb, regardless of car, your rear total toe should always be large number (toe in is positive) than your front. Toe out in the front is a great idea for crisp turn in and steering response.
04-23-2012, 06:44 AM
#3
Drifting
Thread Starter
I've got about 3/16" toe-out in the front, 1/8" toe-in in the rear. -.75 front camber, -1.2 rear camber. I can't complain about turn-in, though I wish I had more negative front camber to deal with understeer. It does seem to wear a bit hard on the front tires, though. It's easy to get oversteer right now, but hard to control it. I'd love to be able to drive this like a go-kart and just plant the throttle to stop rotation.
I'm limited to SCCA stock-class rules, so -.75 is the max camber I can get front, though I can still add more rear negative camber.
I'm limited to SCCA stock-class rules, so -.75 is the max camber I can get front, though I can still add more rear negative camber.
04-23-2012, 07:38 PM
#5
Drifting
Thread Starter
Porsche went to enormous lengths to make a mid-engine sports car with near perfect 50/50 weight distribution, and then specced out wheels, tires and alignment that makes it understeer like a FWD. Porsche's recommendations are not intended for performance, they're intended to keep trophy wives out of ditches. It's sad that we need to add all sorts of GT3 components to get the performance it should have came with from the showroom.
In short: I adjusted the front alignment myself (loosened the bolts and slammed them to the stops) which gave max negative camber and a little toe-out, but I haven't touched my rear alignment since being set to Porsche spec, which is a large part of the problem. What should it be for performance?
In short: I adjusted the front alignment myself (loosened the bolts and slammed them to the stops) which gave max negative camber and a little toe-out, but I haven't touched my rear alignment since being set to Porsche spec, which is a large part of the problem. What should it be for performance?
04-24-2012, 01:25 PM
#6
Burning Brakes
I run zero toe in the rear of my 02 Boxster S. It really helps with corner exit on throttle to reduce understeer. I do run -2.1 rear camber as a result of the toe setting. If the car is still too lively, consider a front sway bar adjustment so perhaps one hole stiffer on your GT3 bar but toe out in that car isn't going to work well on national size/speed courses.
04-24-2012, 10:32 PM
#7
In my experience, the 986S works best with about -2 to -2.5 degrees rear camber, and near zero to slight toe-in (maybe 1/10" per side).
Your front GT3 sway bar should help reduce understeer to a point due to decreased roll, but once you go over a certain stiffness, understeer takes over again. you may want to disconnecting the rear bar, but I would fix the alignment issue first.
Good luck
Your front GT3 sway bar should help reduce understeer to a point due to decreased roll, but once you go over a certain stiffness, understeer takes over again. you may want to disconnecting the rear bar, but I would fix the alignment issue first.
Good luck
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04-25-2012, 08:19 AM
#9
Burning Brakes
I never mess with the toe in the rear in my 911, the only time I did reduce the toe, the car became unstable under braking at higher speeds. I think the rear in these cars is well planted, the front is what needs lots of help, the understeer is ridiculous and its more pronounced in our US. spec cars...
05-21-2012, 09:10 PM
#11
Any update? Where are your specs now? Any events?
FWIW, coming from a modded '78 911 to a Boxster, I was shocked how hard it was to get the rear of the boxster to rotate with a lift. Especially if running, say, 275 rears like I was. The 911 was friendly to the "lift, aim and go" approach, the Boxster, much less so. iirc, about -.8 front and -1.4 rear camber, 1/8th toe out up front, and slight toe-in on the rear.
FWIW, coming from a modded '78 911 to a Boxster, I was shocked how hard it was to get the rear of the boxster to rotate with a lift. Especially if running, say, 275 rears like I was. The 911 was friendly to the "lift, aim and go" approach, the Boxster, much less so. iirc, about -.8 front and -1.4 rear camber, 1/8th toe out up front, and slight toe-in on the rear.
05-21-2012, 09:13 PM
#12
Burning Brakes
Any update? Where are your specs now? Any events?
FWIW, coming from a modded '78 911 to a Boxster, I was shocked how hard it was to get the rear of the boxster to rotate with a lift. Especially if running, say, 275 rears like I was. The 911 was friendly to the "lift, aim and go" approach, the Boxster, much less so. iirc, about -.8 front and -1.4 rear camber, 1/8th toe out up front, and slight toe-in on the rear.
FWIW, coming from a modded '78 911 to a Boxster, I was shocked how hard it was to get the rear of the boxster to rotate with a lift. Especially if running, say, 275 rears like I was. The 911 was friendly to the "lift, aim and go" approach, the Boxster, much less so. iirc, about -.8 front and -1.4 rear camber, 1/8th toe out up front, and slight toe-in on the rear.
05-22-2012, 10:41 PM
#13
05-24-2012, 07:10 PM
#14
Drifting
Thread Starter
Any update? Where are your specs now? Any events?
FWIW, coming from a modded '78 911 to a Boxster, I was shocked how hard it was to get the rear of the boxster to rotate with a lift. Especially if running, say, 275 rears like I was. The 911 was friendly to the "lift, aim and go" approach, the Boxster, much less so. iirc, about -.8 front and -1.4 rear camber, 1/8th toe out up front, and slight toe-in on the rear.
FWIW, coming from a modded '78 911 to a Boxster, I was shocked how hard it was to get the rear of the boxster to rotate with a lift. Especially if running, say, 275 rears like I was. The 911 was friendly to the "lift, aim and go" approach, the Boxster, much less so. iirc, about -.8 front and -1.4 rear camber, 1/8th toe out up front, and slight toe-in on the rear.
