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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > how to kill this under-steer



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      05-27-2013, 11:19 AM   #1
longliven54
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how to kill this under-steer

i have had my e90 for a few years now, and mileage was adding up quick. so i picked up a 90 nissan 300zx TT to be my daily driver. i was very happy with my e90's handling up until i drove the 300zx. now whenever i drive my e90, it feels like a big boat hovering around on the road. i feel the e90 understeers a lot and i wish to bring some grip to the front or maybe make the rear slide out more to counter the understeer.
here is my suspension mod list

koni yellows all around
zsp springs from e92 mt(i believe mt e92 have the shortest springs)
dinan camber
m3 front control arms
sp lowering perches
cusco strut bar
megan racing toe
no LSD
245's upfront/255 rears to minimize stagger(pirelli rosso)

i have thought about installing front sway bar, but i have heard it can induce more understeer. UPgrading rear sway bar makes the car fish-tail happy unless LSD is already installed. is there no other way to get more grip upfront to kill this body roll & understeer?
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      05-27-2013, 11:57 AM   #2
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Quote:
Originally Posted by longliven54 View Post
i have had my e90 for a few years now, and mileage was adding up quick. so i picked up a 90 nissan 300zx TT to be my daily driver. i was very happy with my e90's handling up until i drove the 300zx. now whenever i drive my e90, it feels like a big boat hovering around on the road. i feel the e90 understeers a lot and i wish to bring some grip to the front or maybe make the rear slide out more to counter the understeer.
here is my suspension mod list

koni yellows all around
zsp springs from e92 mt(i believe mt e92 have the shortest springs)
dinan camber
m3 front control arms
sp lowering perches
cusco strut bar
megan racing toe
no LSD
245's upfront/255 rears to minimize stagger(pirelli rosso)

i have thought about installing front sway bar, but i have heard it can induce more understeer. UPgrading rear sway bar makes the car fish-tail happy unless LSD is already installed. is there no other way to get more grip upfront to kill this body roll & understeer?
Unfortunately you'll be hard pressed to make the e90 handle like the 300zx. Fact of the matter is the weight is higher, and lawyers f**ked up the handling of cars (the notion that understeer is safer).

Lightening up the front end would help, and with grippier tires it would understeer less. I would focus on increasing front end grip versus loosening up the rear to be honest. You want to increase the cars stability overall, not reduce it. Another thing that can help is by being smoother at turn in. If you snap the wheel it will induce understeer, much like if you mash the gas it will induce oversteer.

Based on your list of mods, I would take your car to a reputable performance shop, one that specializes in racing, not one that specializes in making Hondas look fast, and ask them to check the front end geometry. By changing as much stuff around as you have, it is possible that you have made it worse. What I mean by that is components may be fighting each other (i.e. m3 control arms may not work right with the lowering perches, etc...).
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      05-27-2013, 12:12 PM   #3
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I would say go with a decent set of coilovers that you can adjust the dampening and calibrate the back and front accordingly. Alignment, more - camber up front. Get a thicker sway bar for back and then only change the front one if needed. Tires: go for a square set up.
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      05-27-2013, 12:30 PM   #4
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hmmmm, interesting. never thought that my modifications might be making the car understeer more. i think the big as* intercooler i have might be making this worse.

i completely understand that e90 will never be as tight as 300zx, and i am okay with that. the weight difference is huge. 300zx being more sports oriented than my 4 door people mover. but it is still surprising that a bone stock suspension on 20+ year old car can put shame to "the ultimate driving machine"

if i were to get a carbon fibre hood, would that help or is that going to throw off the front/rear balance?
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      05-27-2013, 12:35 PM   #5
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265 square setup. Result? Still under-steer. So sad. Non M-E90 I am talking about.
It was have a tiny tiny bit of under-steer but much better than before.
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      05-27-2013, 12:39 PM   #6
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Quote:
Originally Posted by sle39lvr View Post
I would say go with a decent set of coilovers that you can adjust the dampening and calibrate the back and front accordingly. Alignment, more - camber up front. Get a thicker sway bar for back and then only change the front one if needed. Tires: go for a square set up.

running -2 camber upfront. reason i didnt go for coilovers was to avoid using high spring rates. even with lowering perches, i am still a little higher of the ground compared to eibachs(which offer the least drop). i need that clearance to go up my driveway. are there any coilovers that offer spring rates close to zsp and also zsp height?

i cant go square setup, as i have staggered rims. thats why i reduced the difference in tire sizes. this setup is a lot better than my previous 235/275

which rear sway bar is suggested without upgrading the front?
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      05-27-2013, 12:47 PM   #7
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Quote:
Originally Posted by longliven54 View Post
hmmmm, interesting. never thought that my modifications might be making the car understeer more. i think the big as* intercooler i have might be making this worse.

if i were to get a carbon fibre hood, would that help or is that going to throw off the front/rear balance?
The intercooler may be a factor. If it is that much bigger it may weigh more, though not likely much. A carbon fibre hood would help reduce the weight significantly.

Like I said, have a shop check all the front end angles (caster, camber, ride height, wheel offset, toe) and have them set it up for the driving you do most. Minor suspension adjustments make a huge difference.

Last edited by silversnl; 05-27-2013 at 01:42 PM. Reason: Because I'm an idiot and got called out (thankfully)
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      05-27-2013, 12:49 PM   #8
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http://www.e90post.com/forums/showthread.php?t=152991
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      05-27-2013, 12:54 PM   #9
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suspension was tuned by a drift suspension tuning shop.
any idea what is the lightest/still good intercooler? i like to maintain sleeper look & carbon fibre hood is going to rice it all up(in my opinion).

the same shop who did the suspension tuning was advicing me to get better/stiffer engine mounts to kill some of that weight transfer. does that make any sense? if so, what are the recommended brands for them?
thanks
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      05-27-2013, 01:10 PM   #10
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Wow...those are some hardcore mods.. So I guess you track the car?
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      05-27-2013, 01:12 PM   #11
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I'd get some Hotchkis sway bars
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      05-27-2013, 01:36 PM   #12
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Quote:
Originally Posted by sle39lvr View Post
Wow...those are some hardcore mods.. So I guess you track the car?
hardcore?? i thought this was the basic stuff..i dont track my car as such, just a lot of aggressive driving in-around town. anyone can go fast in a straight line, i like going fast thru corners/highway ramps. a lot of mountain passes around where i live. luckily enuf many roads are hardly ever used. i go thru about 2-3 sets of rears tires a year blasting up-down the mountain passes
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      05-27-2013, 01:37 PM   #13
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Quote:
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The intercooler may be a factor. If it is that much bigger, and filled with water/coolant it weighs a lot more.
Lolwut?
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      05-27-2013, 01:40 PM   #14
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Originally Posted by Transport3r View Post
Lolwut?
Mah bad. For whatever reason I was thinking radiator (air/water exchange versus air/air exchange).

OP, ignore the original statement I made. The increase in weight from the intercooler would only be from materials, and I would expect aftermarket aluminum I/Cs are lighter than the stock one.
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      05-27-2013, 01:48 PM   #15
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actually, my aluminum one is about 3 times heavier than the stock core. Still it's only a ~10 lbs increase, which is just a 0.6% increase of weight over the front axle. I doubt it'll be noticeable.

I'd check the front camber and rear camber, as those will affect cornering forces on each axle the most. Generally for oversteer, you want to decrease the camber up front. Tightening up the rear axle with M3 subframe bushings and end links should help too.
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      05-27-2013, 02:24 PM   #16
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Quote:
Originally Posted by longliven54 View Post
hardcore?? i thought this was the basic stuff..i dont track my car as such, just a lot of aggressive driving in-around town. anyone can go fast in a straight line, i like going fast thru corners/highway ramps. a lot of mountain passes around where i live. luckily enuf many roads are hardly ever used. i go thru about 2-3 sets of rears tires a year blasting up-down the mountain passes
Not sure if serious...

This thread is hilarious!
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      05-27-2013, 02:40 PM   #17
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Quote:
Originally Posted by doogee View Post
Not sure if serious...

This thread is hilarious!
this thread may be,,,but you are NOT.....lolz
get off my thread
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      05-27-2013, 02:53 PM   #18
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No worries. I'm just here to watch

But seriously. Stop worrying about weight and all the mods. It's not a racecar. You're just screwing the car up more throwing random parts at it.

Want it to rotate better? Have an LSD built for your car and add a bigger FRONT swaybar. Leave the rear alone.
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      05-27-2013, 02:58 PM   #19
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Funny, weight distribution of the 335i is far better than a 300zx so it should be the zx that understeers at its limit, but Im sure the 300kg difference has a lot to do with the 335i giving way first. After all those mods you've done to the front end I'm not sure what you expect to be able to do if you're still having issues....

All I can suggest is that the rossos aren't the greatest tyres, try some michelin pilot supersports. If you are still getting the slip balance front orientated after that, then....
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      05-27-2013, 03:01 PM   #20
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To OP, when I drove my buddy's stock twin turbo z32 300zx I didn't remember it as wanting to oversteer (unless during a turn and boost kicks in hard). Overall i think the 300zx is very neutral yet still tend to understeer. If you go back more to say like a 280zx or 240 then those things oversteered xD.

Anyways. Back to your question. First thing to correct is probably your driving sadly take it to the autox and try to induce oversteer. Although much more difficult than a lot of other cars, its not at all as bad as it seems. (trust me, try to get a old volvo or an audi to oversteer... now those I find hard). Do proper weight transfer and dont be afraid to smash your brakes hard to acheive the desired effect. (of course that is if it's safe and maybe in an enclosed course or track) Take a course with Pro drivers if you have to. Of course, a squared set up, more camber up front, and thicker rear sways all will assist to acheive the effect. But at the end of the day, its how you drive the vehicle that counts. If i were you, there is only one thing that i'll do and with proper technique, it'll for sure get you all the oversteering you want - a LSD (Don't know why you don't want it...). If you're insane, you can also do a clutch kick or e-brake turn, but i highly do not recommend it.

Also, as one of the other members have suggested, changing too much may have a negative effect as well. Dropped car with stiffer suspension sometimes might not be able to get you the needed weight transfer and therefore actually encouraging understeer.

At the end of the day though, whatever you do to your car is totally up to you!Good Luck and have fun!!
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      05-27-2013, 03:02 PM   #21
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I had an E92 with the M3 front bits, SP lowering perches, BMW performance kit and it was well balanced. I tried a M3 rear sway bar and it was too big and made the car oversteer like crazy. Yes I had an LSD and the M3 subframe bushes (I think the bushings aren't worth it). So the SP perches work fine with the M3 bits etc.

Start with the simple things...Tire pressures and adjusting the Koni Sports. To help with understeer you should firm up the rear shocks and/or soften up the fronts. If you are going to buy parts get a square setup with good tires. I had square RS-3s for autoX and it did pretty well considering the weight.
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      05-27-2013, 03:23 PM   #22
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Quote:
Originally Posted by doogee View Post
Not sure if serious...

This thread is hilarious!
That's what I was starting to think....

To OP, what I meant to say with my last post was, I just think you are missing some basic mods. "Harder engine mounts to help with weight transfer"? really? I can see that coming in to play if you are a constant track driver.

I am in the process of killing understeer also, here is my list:
- Coilovers - dampening adjustable (next)
- M3 arms up front (done: helped with understeer mildly, good start)
- M3 rear subframe bushings (done: helped with rear end responsiveness)
- M3 rear sway bar (done: with stock front sway, my car now feels completely neutral)
- M3 front sway (next: still contemplating on it...)
- Better tires (done: PSS)
- Good alignment

Those should take care of making the car feel balanced if you are serious about it..
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