[R.G.]

Frustrated with chassis's inability to put power down and looking for feedback / suggestions. The car has a single turbo and is likely being run at ~550hp. Until I can get the rear end issue dealt with any more hp is just a waste. 3rd gear half throttle and the cars rear breaks loose. 4th gear full throttle same issue.

Set up:

Advan AD08R 275/30/19 on
19lb forged rims
-1.8 camber

Bilstein PSS9
Had to compress springs near max to get car high enough to run the Advans as they are thick. Fenders fully shaved

Meagan toe arms
Had these for a few years, is there a chance the bearings are bad?

M3 subframe bushings
Powerflex purple control arm bushings


I've tried running softer compression settings to get the car to squat harder rather then rebound too quick and lose traction but spring set up might be too compressed to allow it...don't know


From least expensive to most
Rear lower bar brace
Rear sway bar upgrade
Custom rear brace fabricated
Replace M3 bushings to solid aluminum
New coilovers
New smaller rim / larger tire set up with less camber. I know the Advan's are not great in the cold (read terrible) might just be the biggest issue?



Really just unsure which direction to go and don't want to throw money at it wthout a gameplan. Any thoughts/feedback would be appreciated.

[feuer]

Rear wheels on RWD tent to toe-in under hard acceleration so maybe try different rear toe settings. When acceleration begins with good grip the wheels move forward, toe changes (more toe-in) and available grip is reduced so wheel spin occurs. Also, check your rear shocks and if they are adjusted and function properly go with stiffer shock mounts.

[The HACK]

-1.8º of camber on a car that struggles to put straight-line traction down?

The more the car squats, the more negative camber you're going to have. The more negative camber, the less grip for straight-line traction. You don't see drag racers run significant negative camber in the rear. Negative camber in the rear is only for guys who wants to go fast IN A CORNER.

Set your rear camber to ZERO.

[R.G.]

Originally Posted by feuer

Rear wheels on RWD tent to toe-in under hard acceleration so maybe try different rear toe settings. When acceleration begins with good grip the wheels move forward, toe changes (more toe-in) and available grip is reduced so wheel spin occurs. Also, check your rear shocks and if they are adjusted and function properly go with stiffer shock mounts.

Will check alignment and see if I can get a bit of toe out in rear. Good tip, thank you.
Regarding shock mounts, you're suggesting stiffer lower shockmounts? Can you elaborate on effect this would have as I'm having trouble visualizing. Regardless thanks for feedback.

Originally Posted by The HACK

-1.8º of camber on a car that struggles to put straight-line traction down?

The more the car squats, the more negative camber you're going to have. The more negative camber, the less grip for straight-line traction. You don't see drag racers run significant negative camber in the rear. Negative camber in the rear is only for guys who wants to go fast IN A CORNER.

Set your rear camber to ZERO.

Would have to go shorter tire or smaller rim / less aggressive offset. Rims are M3 (-25 IRC) spec offset so unfortunately it does not provide me with the room needed to zero out camber. Basically as close to zero as I could muster. Replacing rims is one of the more expensive options unfortunately.

[Julian2485]

Just throwing this out there but what about getting an lsd? Would that help him guys ?

[STR8-6IX]

all good advice. start by adjusting your rear toe/camber. invest in an LSD to help put power down. if you are still not putting down power as well as you like, i think you will have to consider lowering the power.. struggling for grip in fourth gear with good 275 width tires really doesnt sound safe to me.

[feuer]

Originally Posted by R.G.

Will check alignment and see if I can get a bit of toe out in rear. Good tip, thank you.
Regarding shock mounts, you're suggesting stiffer lower shockmounts? Can you elaborate on effect this would have as I'm having trouble visualizing. Regardless thanks for feedback.

The OEM stock upper shock mounts are very soft and take away from the shock effectiveness. Firm mount will allow the shock to do all the work. I run -2,2 rear camber with 275/35-18 on 10" et25 and toe-in/out is more of the problem than the camber. Toe-in will introduce wheel hop as well. I have a differential lockdown for that.

[Fundguy1]

LSD, rear diff lock. I have no issues with 150 more hp than you. But I have an LSD, 305 rears, Bridgestone Potenza tires, rear diff lockdown, and stiff subframe bushings. M3 are not stiff. I have ake black. I have a manual and can chirp 3 to 4 shift at around 90 mph sometimes but past first plenty of grip. First i can spin regardless so for the track I'm swapping to 28" drag slicks on 16" wheels. Other than that no issues.zero wheel hop. The diff lockdown takes care of that. You have 275 mm of tire working. I have 610mm of stickier tire working.

Originally Posted by feuer

Rear wheels on RWD tent to toe-in under hard acceleration so maybe try different rear toe settings. When acceleration begins with good grip the wheels move forward, toe changes (more toe-in) and available grip is reduced so wheel spin occurs.

Everything you are saying here is opposite of the truth; rear wheels on a RWD car absolutely do NOT go toe-in when moving forward...the behavior you are describing is descriptive of the front wheels on FWD cars while in motion.

[feuer]

Originally Posted by Fundguy1

LSD, rear diff lock. I have no issues with 150 more hp than you. But I have an LSD, 305 rears, Bridgestone Potenza tires, rear diff lockdown, and stiff subframe bushings. M3 are not stiff. I have ake black. I have a manual and can chirp 3 to 4 shift at around 90 mph sometimes but past first plenty of grip. First i can spin regardless so for the track I'm swapping to 28" drag slicks on 16" wheels. Other than that no issues.zero wheel hop. The diff lockdown takes care of that. You have 275 mm of tire working. I have 610mm of stickier tire working.

610mm? Wider tires don't provide larger contact patch. They make it wider but shorter which is worse for traction, more lateral stability but faster break away. So your 305s don't help you as much as you think. Yes, you might spin them less but is probably due to increased weight of the tire and the rim. We need to compare the tire PSI as well, less equals larger contact patch thusband more grip.. LSD or not at those HP levels you would spin both wheels regardless. I agree on the rest:sticky tires, diff. lockdown, stiff bushings. Another thing, your is e93, a lot heavier in the rear, especially with top down (some look like a boat when on stock suspension ) so more pressure on the tires back there.

Originally Posted by feuer

610mm? Wider tires don't provide larger contact patch. They make it wider but shorter which is worse for traction, more lateral stability but faster break away. So your 305s don't help you as much as you think. Yes, you might spin them less but is probably due to increased weight of the tire and the rim. We need to compare the tire PSI as well, less equals larger contact patch thusband more grip.. LSD or not at those HP levels you would spin both wheels regardless. I agree on the rest:sticky tires, diff. lockdown, stiff bushings. Another thing, your is e93, a lot heavier in the rear, especially with top down (some look like a boat when on stock suspension ) so more pressure on the tires back there.

I think what you're trying to say here is that "larger contact patch" does not always = better longitudinal traction; I tend to agree with this notion as well because physics:
http://www.autospeed.com/cms/article.html?&A=108915

Be forewarned though; when it comes to tire/wheel theory regardng longitudinal/lateral grip, FundGuy will not be swayed by scientific fact...it's just not his cup of tea I guess.

[feuer]

Originally Posted by FCobra94

Everything you are saying here is opposite of the truth; rear wheels on a RWD car absolutely do NOT go toe-in when moving forward...the behavior you are describing is descriptive of the front wheels on FWD cars while in motion.

You probably correct and I will stand corrected. know toe in/out changes during accelerating and is important to have it dialed in correctly especially for accelerating out of turns. I might have mixed up the two as I started with hillclimbing VW GTI, FWD car, and now track the 335i which is RWD. Thank you for catching it.

[Fundguy1]

Yes and no. I agree to a point. Heres a good link from physics professors on the subject. http://www.physlink.com/education/askexperts/ae200.cfm

Again, I didn't get this setup for drag racing. Its a daily driver setup and similar to what comes on a 911. For drag racing I would use slicks, low pressure, small wheel, big sidewall. Big long contact patch and the sidewalls act like a coiled spring on launch.

As for weight, my setup is almost the same as the oem wheel tire combo. Anyway, the debate about tire size vs traction is out there. But I still stand behind my statement I have 610 mm and he has 275 mm because I have 2 tires working, 2 contact patches, and he has one. The LSD and sticky tires were two biggest increasers that I feel helped me with grip. The 305s aren't overly large for my car weight and size. I don't see them hitting that critical point where the contact patch stops growing and widens laterally and narrows longitudinally. I would run correct tire pressure for handling, wear,and safety reasons unless on a track drag racing.

But again, the concept is debated even between physics professors. Not sure why when for 50 yrs of drag racing, you'd think if a drag racer put on a wider set of tires identically otherwise and ended up getting worse times then they'd revert back. And since for 50 yrs, the millions of guys literally who do this and swear by this should be good prima facia evidence that to a point, wider works. And if the opposite was true you'd see these guys all going more narrow. These guys are so dialed into their cars they know within a couple 10ths what their quarter mile time will be and all other things being equal they typically increase width moderately over factory with positiveresults. So yes, there's a balance and a sweet spot.

Bottomline, get your chassis dialed in, lsd, bushings etc, get your tires more sticky in the 265-305 range, and you should be fine.

[The HACK]

Originally Posted by FCobra94

Everything you are saying here is opposite of the truth; rear wheels on a RWD car absolutely do NOT go toe-in when moving forward...the behavior you are describing is descriptive of the front wheels on FWD cars while in motion.

What he said.

[R.G.]

Originally Posted by Julian2485

Just throwing this out there but what about getting an lsd? Would that help him guys ?

It won't exactly be a game changer in a straight line but something def. to consider.

Originally Posted by 6IX-F10-N52

all good advice. start by adjusting your rear toe/camber. invest in an LSD to help put power down. if you are still not putting down power as well as you like, i think you will have to consider lowering the power.. struggling for grip in fourth gear with good 275 width tires really doesnt sound safe to me.

The car hits very hard and can be scary to drive without DTC if you don't know what you're doing.

Originally Posted by feuer

The OEM stock upper shock mounts are very soft and take away from the shock effectiveness. Firm mount will allow the shock to do all the work. I run -2,2 rear camber with 275/35-18 on 10" et25 and toe-in/out is more of the problem than the camber. Toe-in will introduce wheel hop as well. I have a differential lockdown for that.

I've been looking for a set of solid mounts for the rears this afternoon. Will update with what I find unless you have a good rec.

Originally Posted by Fundguy1

LSD, rear diff lock. I have no issues with 150 more hp than you. But I have an LSD, 305 rears, Bridgestone Potenza tires, rear diff lockdown, and stiff subframe bushings. M3 are not stiff. I have ake black. I have a manual and can chirp 3 to 4 shift at around 90 mph sometimes but past first plenty of grip. First i can spin regardless so for the track I'm swapping to 28" drag slicks on 16" wheels. Other than that no issues.zero wheel hop. The diff lockdown takes care of that. You have 275 mm of tire working. I have 610mm of stickier tire working.

I ran the Potenzas and the AD08Rs are on a different level in warmer weather. The issue is the type of compound they use becomes ineffective in sub 45 degree temps.

I'm guessing you had the M3 bushings prior to the blacks, was it that noticeable of a difference between the two?

Someone mentioned yours is an E93. I've got a healthy list of weight shedding I've done to my E92 and it weighed in at 3300lbs with 1/2 tank of gas and no driver. Not sure what has worked for you will necessarily work for me.

Originally Posted by FCobra94

Everything you are saying here is opposite of the truth; rear wheels on a RWD car absolutely do NOT go toe-in when moving forward...the behavior you are describing is descriptive of the front wheels on FWD cars while in motion.

Interesting, I know little about FWD cars but will remember that.




After a bit more tinkering I began adjusting my front suspension. I went to the stiffest setting up front and softest in the rear. It's 49 degrees tonight as opposed to 34 degrees last night so that made the tires a bit more predictable. After some quick test pulls I can say there was a much needed improvement.
I've ordered a differential lockdown to further prevent any rear torsional play. After some testing with that I'll likely move to a larger rear sway like the E93 M bar. Will report back. Thanks gents.

[Julian2485]

Originally Posted by R.G.

It won't exactly be a game changer in a straight line but something def. to consider.

The car hits very hard and can be scary to drive without DTC if you don't know what you're doing.

I've been looking for a set of solid mounts for the rears this afternoon. Will update with what I find unless you have a good rec.

I ran the Potenzas and the AD08Rs are on a different level in warmer weather. The issue is the type of compound they use becomes ineffective in sub 45 degree temps.

I'm guessing you had the M3 bushings prior to the blacks, was it that noticeable of a difference between the two?

Someone mentioned yours is an E93. I've got a healthy list of weight shedding I've done to my E92 and it weighed in at 3300lbs with 1/2 tank of gas and no driver. Not sure what has worked for you will necessarily work for me.

Interesting, I know little about FWD cars but will remember that.




After a bit more tinkering I began adjusting my front suspension. I went to the stiffest setting up front and softest in the rear. It's 49 degrees tonight as opposed to 34 degrees last night so that made the tires a bit more predictable. After some quick test pulls I can say there was a much needed improvement.
I've ordered a differential lockdown to further prevent any rear torsional play. After some testing with that I'll likely move to a larger rear sway like the E93 M bar. Will report back. Thanks gents.

Which diff lockdown are you going with ?

[Fundguy1]

I wanted a def tech lockdown but they weren't available when i needed it as they were relkcating their facilities and temporarily out of production so I got another. Forgot which. Not as pretty but does the job. No wheel hop. I was worried about breaking axles.

[Fundguy1]

I didn't see the "r" at first glance on your tires. Still, why no LSD? The electronic one doesn't do the job especially for straight line grip.

[feuer]

Originally Posted by Julian2485

Which diff lockdown are you going with ?

Originally Posted by Fundguy1

I wanted a def tech lockdown but they weren't available when i needed it as they were relkcating their facilities and temporarily out of production so I got another. Forgot which.

I have one for sale. BNIB. However, only helps with wheel hop. If your car doesn't suffer from wheel hop there isn't need for one.

[Julian2485]

Originally Posted by feuer

I have one for sale. BNIB. However, only helps with wheel hop. If your car doesn't suffer from wheel hop there isn't need for one.

Which one do you have

[techwhiz]

OP - LSD and lock the diff down.
You are putting most of your power to one wheel.
You need to be putting it to both rear wheels.

The limitation for acceleration is traction. More driven rubber gives you more traction and potential for better acceleration.
Get a LSD before you do anything else.

[Fundguy1]

Originally Posted by techwhiz

OP - LSD and lock the diff down.
You are putting most of your power to one wheel.
You need to be putting it to both rear wheels.

The limitation for acceleration is traction. More driven rubber gives you more traction and potential for better acceleration.
Get a LSD before you do anything else.

What ive been saying all along. Why do you think a GTR gets a good launch? Its not tall skinny tires.