Rear Diff Options - Power Oversteer Found Here
Aug 23, 2017, 02:56 PM
#1126
If the intent of the changing the rake is to alter roll center, I think there may be more value to raising the front than lowering the rear because I think the front roll center is more strongly affected by ride height than the rear. Or maybe raise the front by the same amount the that rear is lowered.
Have you seen my thread about front diffs and their effect on understeer?
Have you seen my thread about front diffs and their effect on understeer?
Aug 23, 2017, 03:52 PM
#1127
EvoM Guru
iTrader: (1)
Neither did mine... but many people have reported a dramatic improvement with this diff. As mentioned a few times this mod could require me to relearn how to drive or it could require additional setup changes. I plan to continue to test and tune.
The one thing I don't really understand is:
1. If I had the grip to exit underfull boost before while driving clean with no understeer.... why does it feel like I've lost rear grip now?
The one thing I don't really understand is:
1. If I had the grip to exit underfull boost before while driving clean with no understeer.... why does it feel like I've lost rear grip now?
Lowering rear ride height increases grip on corner exit. It's a weight transfer thing, not necessarily geometry. Raising the front could arguably do the same, but the car setup cheat sheet I have says to lower the rear.
If the intent of the changing the rake is to alter roll center, I think there may be more value to raising the front than lowering the rear because I think the front roll center is more strongly affected by ride height than the rear. Or maybe raise the front by the same amount the that rear is lowered.
Have you seen my thread about front diffs and their effect on understeer?
Have you seen my thread about front diffs and their effect on understeer?
My car has the TRE max lock. It used to have a tendency to push on power if the car wasn't setup perfectly on corner entry (stock rear diff). With the max lock, getting the car to rotate with throttle is easy.
Aug 23, 2017, 04:58 PM
#1128
I suppose I don't push my car too hard, but I have no problem getting the rear to step out under power, so I'm not surprised that the Max Lock makes it rotate easily with throttle.
Aug 23, 2017, 06:01 PM
#1129
i guess the thread title doesn't lie, lol
it is strange though, how much u are getting. that sounds like my car in the snow
curious how it behaves in off-throttle turn-in. the rear diff should be eitehr doing nothing or even causing a small amount of understeer, though the car as a whole should not - esp if you have the ACD tune. the only way it's that loose on power is for it to be pretty darn loose on turn-in
it is strange though, how much u are getting. that sounds like my car in the snow
curious how it behaves in off-throttle turn-in. the rear diff should be eitehr doing nothing or even causing a small amount of understeer, though the car as a whole should not - esp if you have the ACD tune. the only way it's that loose on power is for it to be pretty darn loose on turn-in
Aug 24, 2017, 07:32 AM
#1130
Curious how it behaves in off-throttle turn-in. the rear diff should be eitehr doing nothing or even causing a small amount of understeer, though the car as a whole should not - esp if you have the ACD tune. the only way it's that loose on power is for it to be pretty darn loose on turn-in
As for the ACD tune ... the only map that seems to keep things subdued is OEM snow mode. I do have aftermarket maps that are basically unusable.
Could the oversteer start from trailbraking... maybe but it never happened before the diff. Race starts a mid track with long corners and therefore I do brake mid corner just a touch. I've found this approach to be faster than breaking before the corner. My plan is to attempt to try a slow in approach to see if that helps.
Could the oversteer start from abrupt power transition.... maybe but that never happened before either. I used to be able to ninja kick the gas pedal to the floor and track out with minimal drama.
Tonight I'm going to add some toe in 1/16th a side and maybe even add more negative camber.
Aug 24, 2017, 09:50 AM
#1132
EvoM Guru
iTrader: (1)
I suspect its more due to roll center than weight transfer. I can't see the physics for how even a 1" change in ride height can affect weight transfer.
I suppose I don't push my car too hard, but I have no problem getting the rear to step out under power, so I'm not surprised that the Max Lock makes it rotate easily with throttle.
I suppose I don't push my car too hard, but I have no problem getting the rear to step out under power, so I'm not surprised that the Max Lock makes it rotate easily with throttle.
My car certainly gets pushed pretty hard.
Slow Evo, remember, you made a drastic change to the rear differential, so it may require some chassis setup changes to account for it. Ulitmately, you will end up going faster because you're going to be the car more grip.
Aug 25, 2017, 12:24 PM
#1133
Keep in mind the more power your car is making the more youre going to have the ability to roast the tires on corner exit.
I too can have massive power oversteer on corner exit if I want to. This is especially the case if the car isnt pointed straight yet. The key is to not simply mash the gas but rather modulate the throttle. If I go around a corner in 2nd and at any point mash the gas the car will tract outward as the turbo spools then boost kicks on hard and car will shoot sideways every time.
from the sounds of it the diff is doing exactly what is is designed to do so you must either change your driving habits or modify the setup accordingly to get it back to where you are comfortable with it.
I too can have massive power oversteer on corner exit if I want to. This is especially the case if the car isnt pointed straight yet. The key is to not simply mash the gas but rather modulate the throttle. If I go around a corner in 2nd and at any point mash the gas the car will tract outward as the turbo spools then boost kicks on hard and car will shoot sideways every time.
from the sounds of it the diff is doing exactly what is is designed to do so you must either change your driving habits or modify the setup accordingly to get it back to where you are comfortable with it.
Aug 26, 2017, 07:03 AM
#1134
Street lessons.... not all alignment shops are the same...
It sucks having to rely on commercial non-performance shops to handle my alignment. I've had the car aligned a couple times over the past month. From not being able to get the car on the ramps because its too low to having shops tell me that they wont adjust camber even with coilovers... its a PITA. Here is the latest adjustments performed. The previous (to this) round of alignments was performed with a request of 0 toe at all four corners.
http://thumbsnap.com/f/srs5YaEU
It sucks having to rely on commercial non-performance shops to handle my alignment. I've had the car aligned a couple times over the past month. From not being able to get the car on the ramps because its too low to having shops tell me that they wont adjust camber even with coilovers... its a PITA. Here is the latest adjustments performed. The previous (to this) round of alignments was performed with a request of 0 toe at all four corners.
http://thumbsnap.com/f/srs5YaEU
Last edited by EVIL_EV0; Aug 26, 2017 at 07:57 AM.
Aug 26, 2017, 11:09 AM
#1135
Street lessons.... not all alignment shops are the same...
It sucks having to rely on commercial non-performance shops to handle my alignment. I've had the car aligned a couple times over the past month. From not being able to get the car on the ramps because its too low to having shops tell me that they wont adjust camber even with coilovers... its a PITA. Here is the latest adjustments performed. The previous (to this) round of alignments was performed with a request of 0 toe at all four corners.
http://thumbsnap.com/f/srs5YaEU
It sucks having to rely on commercial non-performance shops to handle my alignment. I've had the car aligned a couple times over the past month. From not being able to get the car on the ramps because its too low to having shops tell me that they wont adjust camber even with coilovers... its a PITA. Here is the latest adjustments performed. The previous (to this) round of alignments was performed with a request of 0 toe at all four corners.
http://thumbsnap.com/f/srs5YaEU
What are your fender height measurements and what size tires are you running?
Aug 26, 2017, 04:14 PM
#1136
Yes .... added some toe to combat the oversteer situation. The thing is I have no idea how much toe I really need or what can be considered too much. Dallas told me to run about 1/4" total so that's what I'm gonna try.
As for fender height... where did you want me to measure? The car is basically flat with no rake. Wheel gap in the front is a bit more than in the back. Tires are 255-40-17 BFG R1S.
One more question for the suspension gods (sorry to redirect this thread a bit) Prior to the rear diff I was running a Perrin 25mm RSP and after the rear diff I went back to the stock RSB. My thought was I would tripod less with the stock bar but I have no idea what the affect of that would be on the rest of the car. Would it be better to run the aftermarket bar to help keep the car flat or run the OEM bar?
As for fender height... where did you want me to measure? The car is basically flat with no rake. Wheel gap in the front is a bit more than in the back. Tires are 255-40-17 BFG R1S.
One more question for the suspension gods (sorry to redirect this thread a bit) Prior to the rear diff I was running a Perrin 25mm RSP and after the rear diff I went back to the stock RSB. My thought was I would tripod less with the stock bar but I have no idea what the affect of that would be on the rest of the car. Would it be better to run the aftermarket bar to help keep the car flat or run the OEM bar?
Aug 28, 2017, 09:46 PM
#1140
Yes .... added some toe to combat the oversteer situation. The thing is I have no idea how much toe I really need or what can be considered too much. Dallas told me to run about 1/4" total so that's what I'm gonna try.
As for fender height... where did you want me to measure? The car is basically flat with no rake. Wheel gap in the front is a bit more than in the back. Tires are 255-40-17 BFG R1S.
One more question for the suspension gods (sorry to redirect this thread a bit) Prior to the rear diff I was running a Perrin 25mm RSP and after the rear diff I went back to the stock RSB. My thought was I would tripod less with the stock bar but I have no idea what the affect of that would be on the rest of the car. Would it be better to run the aftermarket bar to help keep the car flat or run the OEM bar?
As for fender height... where did you want me to measure? The car is basically flat with no rake. Wheel gap in the front is a bit more than in the back. Tires are 255-40-17 BFG R1S.
One more question for the suspension gods (sorry to redirect this thread a bit) Prior to the rear diff I was running a Perrin 25mm RSP and after the rear diff I went back to the stock RSB. My thought was I would tripod less with the stock bar but I have no idea what the affect of that would be on the rest of the car. Would it be better to run the aftermarket bar to help keep the car flat or run the OEM bar?
. I'd keep with the stock bar on paper at least.And yeah the non track shops usually aren't the place to get suspension work done. Guessing you aren't close to a shop? Might be worth finding one anyway and then marking where the settings are using paint as I've heard some folks do.