[CptSumTingWong]

I have a e90 330i that is now seeing some track duty now and I'm getting a fair amount of mid-corner understeer. I don't think I want to dial out the understeer by removing rear grip as that seems counter intuitive since I would want as much grip as possible, so I'm looking at how can I increase front grip?

Current setup:
Bilstein B14 coil over
m3 control arms
Dinan camber plates

Alignment is
0 front tow
-3* front camber

.3 total rear toe in
-2* rear camber

Stock wheels running 235/40/18 fronts and 255/35/18 rears

I know the easy answer is get a set of wheels and tires that can run a wider front tire but that's also a fairly expensive option at around $3k for new wheels and tires.

Seems like most of what I found when searching the forum was larger rear sway bar or run square 235 setup on the tires, but both those options seem to only reduce rear grip.

So what other options do I have to increase front grip? Thanks in advance!

[CptSumTingWong]

Some initial thoughts if anybody can either validate or let me know I'm completely wrong...

What if I lower the front or raise the rear. Put a little more of the weight bias forward a little to help with front grip? Right now there's a little over 1/2 inch of rake.

Dial out some rear toe, like .1 total toe in or 0 toe? Might make it twitchy/unstable at high speed and tram line? Not sure that little bit of alignment difference would do anything?

Toe out the front? How much? Will this just eat tires?

I heard increasing front tire pressure helps too, which seems counter intuitive to me, since it seems that would decrease front contact patch and overheat the front? But I've tried that too and didn't seem to do much maybe I need a bigger difference in tire pressure I only upped it by about 2 psi from 28 -> 30 psi cold

[Brian86]

Square tires.

Bigger front bar. (counterintuitive, I know)

Rear toe-out (er... less toe-in, it's a very sensitive adjustment).

Drive differently.

[CptSumTingWong]

Originally Posted by Brian86

Square tires.

Bigger front bar. (counterintuitive, I know)

Rear toe-out (er... less toe-in, it's a very sensitive adjustment).

Drive differently.

How much rear toe would you suggest I try?

When you say drive differently, could you explain what you mean by that? I don't have a lot of seat time in this car, so I'm here to learn. For some background I usually track a different car (mustang). I'm an intermediate driver getting ready to move up to advanced and have about 20 track days over the last 2 years. I'm getting the BMW setup for my wife who's a novice driver with about 4 track days. I've been driving it like a momentum car but I'm not able to carry as much speed through the turns as I'd like to as the front end just starts to push mid-turn especially through the medium and fast stuff. The slow stuff it handles well and rotates well trail braking. I did take an instructor out with me for a session to see if they had any input and we did try a few different lines through a couple turns to see if it would help but the feedback was I'm wringing most of the performance out of the car and need more front end grip. But I'm hoping someone with more experience and seat time in an e90 has more feedback on how to drive it or how to set it up.

[Brian86]

Just a little toe. Go from 0.3 in -> 0.2 or 0.15?

You'll need a good relationship with an alignment shop :P If you don't like it, go back.

Have you had it in the rain? It'll be even more sensitive to rear toe in the wet.

Typically I run rear toe as aggressively as I can, without letting the car get ass'y in the rain, but that leaves it a little pushy in the high speed stuff when it's dry, which is oK, helps keep my underwear clean. (Those s2k drivers are nuts)


Drive differently is a big question that is tough to answer over the internet. Everything is a compromise, and I have no idea what the 'relative' amount of push is.

At a really high level, spend less time doing what the car is bad at. A little less time at steady state when it pushes. Later more gentle brake release, Holding a 1-pedal into the apex can cure it, but then entry -> brake release really is the hardest part of driving fast. Then switch to driving the car off the rear axel with less time at a steady state (bigger front bar will help with this).

It's subtle, as every car is a momentum car. point -> shoot is slow.

[Jaronbwall]

Square tires are life.

[Tambohamilton]

What spring rates are you currently running?

You say you don't want to take grip from the rear, but if that's the most effective way to get the car balanced, it'll still be faster even though you've reduced grip (at the rear axle).

[CptSumTingWong]

Originally Posted by Brian86

Just a little toe. Go from 0.3 in -> 0.2 or 0.15?

You'll need a good relationship with an alignment shop :P If you don't like it, go back.

Have you had it in the rain? It'll be even more sensitive to rear toe in the wet.

Typically I run rear toe as aggressively as I can, without letting the car get ass'y in the rain, but that leaves it a little pushy in the high speed stuff when it's dry, which is oK, helps keep my underwear clean. (Those s2k drivers are nuts)


Drive differently is a big question that is tough to answer over the internet. Everything is a compromise, and I have no idea what the 'relative' amount of push is.

At a really high level, spend less time doing what the car is bad at. A little less time at steady state when it pushes. Later more gentle brake release, Holding a 1-pedal into the apex can cure it, but then entry -> brake release really is the hardest part of driving fast. Then switch to driving the car off the rear axel with less time at a steady state (bigger front bar will help with this).

It's subtle, as every car is a momentum car. point -> shoot is slow.

Thanks! i'll give it a try. I have not had a chance to push it in the rain.

I know it's hard to explain driving style over text on the internet! Unfortunately, I don't see many e90's (non M3) on the track especially with instructors so hard to get someone with lots of e90 seat time and setup knowledge to ride with me and give feedback

[CptSumTingWong]

Originally Posted by Tambohamilton

What spring rates are you currently running?

You say you don't want to take grip from the rear, but if that's the most effective way to get the car balanced, it'll still be faster even though you've reduced grip (at the rear axle).

it's whatever the included springs in the B14 PSS9 kit come with. I think it's around 400 lb/in in the front and 630 in the back.

So maybe i'm misunderstanding or starting with the wrong premise, but if i'm having mid corner understeer, the front is losing traction. If i reduce rear traction, then my front traction stays the same and the rear now allows more rotation or less push, but that means my average corner speed is still the same or lower since the total front traction remains the same and is the bottleneck. It just gives better balance and feel while in the corner but i'm still having to drive within the maximum available traction available at the front. So how is it faster by reducing rear grip?

[Tambohamilton]

Let's say you reduce rear grip by increasing rear roll rate, then your front tyres will produce more grip due to maintaining their neg camber (less body roll), and you can find a balance where front grip is increased marginally and rear grip is only decreased to the point where it matches the (now more grippy) front.

But you probably shouldn't listen to me, because I'd tell you to run a softer front sway with those spring rates, going against 99% of everyone else...

[CptSumTingWong]

Originally Posted by Tambohamilton

Let's say you reduce rear grip by increasing rear roll rate, then your front tyres will produce more grip due to maintaining their neg camber (less body roll), and you can find a balance where front grip is increased marginally and rear grip is only decreased to the point where it matches the (now more grippy) front.

But you probably shouldn't listen to me, because I'd tell you to run a softer front sway with those spring rates, going against 99% of everyone else...

Softening the front sway bar actually makes sense to me, it would add more grip available from the inside tire giving more front end grip...but like you said, everyone wants a bigger bar, not sure anybody actually makes a smaller one!

[Tambohamilton]

What bars do you have front and rear right now?

[Brian86]

You're not really 'reducing overall traction' by tweaking sway bars and springs.

I mean... it is, but to a much lesser degree. (roll centers, camber)

The car still has the same weight, it's just moving to different places. Adjusting relative front/rear stiffness changes the loading on the front/rear tires, so less on the rear means that same amount goes to the front. (mostly)

Yea, the big front bar thing is counterintuitive. But on rear drive/front strut cars it just works. BMW's are happiest when the front inside tire is off the ground and driving off the rear axle


Here is a good question... How low is the car. Don't really know e9x chassis that well, but all the older 3's got jacked up roll centers when lowering them too much. Made them really wonky. Sudden changes in grip as the nose rolled over.

Perhaps there is more margin for that with the e9x's strut rod layout, but I don't really know.

Springs mostly work the intuitive way (soften the sliding end)

[Tambohamilton]

Old 3 series the roll centre moved up as they got lower? That's definitely not the case for the e9x - it goes down unless I'm very much mistaken. There's definitely still good reason not to go too low, though.

[Brian86]

The old "L" arm/strut 3 series roll center dropped as the car was lowered.

The problem is it dropped too severely, it would lower like 2x the distance of the body until it was right about or below the road surface.

Then as the nose would dive/lift, and roll side to side, the roll center would flip between above and below ground which puts some very wonky weight transfer on the front tires.

[Tambohamilton]

It's probably not too dissimilar in the e9x then. It's definitely pretty low at the best of times. I have a 3d CAD model based on fe1rx's chassis measurements somewhere... Don't have the time to play with it nowadays, sadly.

[CptSumTingWong]

Originally Posted by Tambohamilton

What bars do you have front and rear right now?

oem bars. 26.5 front and 13 rear

[CptSumTingWong]

Originally Posted by Brian86

You're not really 'reducing overall traction' by tweaking sway bars and springs.

I mean... it is, but to a much lesser degree. (roll centers, camber)

The car still has the same weight, it's just moving to different places. Adjusting relative front/rear stiffness changes the loading on the front/rear tires, so less on the rear means that same amount goes to the front. (mostly)

Yea, the big front bar thing is counterintuitive. But on rear drive/front strut cars it just works. BMW's are happiest when the front inside tire is off the ground and driving off the rear axle


Here is a good question... How low is the car. Don't really know e9x chassis that well, but all the older 3's got jacked up roll centers when lowering them too much. Made them really wonky. Sudden changes in grip as the nose rolled over.

Perhaps there is more margin for that with the e9x's strut rod layout, but I don't really know.

Springs mostly work the intuitive way (soften the sliding end)

it's lowered a little less than 2 inches, i've got about 10mm of adjustment up or down still available.

[CptSumTingWong]

Originally Posted by Brian86

The old "L" arm/strut 3 series roll center dropped as the car was lowered.

The problem is it dropped too severely, it would lower like 2x the distance of the body until it was right about or below the road surface.

Then as the nose would dive/lift, and roll side to side, the roll center would flip between above and below ground which puts some very wonky weight transfer on the front tires.

Honestly, don't really understand roll center, i'll try to read up on it a bit but that part of the conversation is definitely over my head at this point...I will say i'm not experiencing sudden changes in grip, it's pretty progressive. Good turn in both on brakes and on throttle and then progressive understeer build up until the front end just starts to plow until i start to unwind a bit and then progressively less understeer as i track out.

[CptSumTingWong]

Originally Posted by Brian86

Just a little toe. Go from 0.3 in -> 0.2 or 0.15?

You'll need a good relationship with an alignment shop :P If you don't like it, go back.

Have you had it in the rain? It'll be even more sensitive to rear toe in the wet.

Typically I run rear toe as aggressively as I can, without letting the car get ass'y in the rain, but that leaves it a little pushy in the high speed stuff when it's dry, which is oK, helps keep my underwear clean. (Those s2k drivers are nuts)


Drive differently is a big question that is tough to answer over the internet. Everything is a compromise, and I have no idea what the 'relative' amount of push is.

At a really high level, spend less time doing what the car is bad at. A little less time at steady state when it pushes. Later more gentle brake release, Holding a 1-pedal into the apex can cure it, but then entry -> brake release really is the hardest part of driving fast. Then switch to driving the car off the rear axel with less time at a steady state (bigger front bar will help with this).

It's subtle, as every car is a momentum car. point -> shoot is slow.

We did just have a pretty good rain over the weekend. First time driving the car around with the current settings and commuting normally, actually driving kind of conservatively, the back end is all over the place. Like it steps out making a left at a light doing 15mph. Traction control flashing like crazy with some sliding just getting on an expressway. Granted first rain in a few weeks out here in Texas and extra cold (for Texas in the mid high 30's) so maybe just extra slick roads and not the greatest tires (but not terrible tires?) Toyo extenza hp2 for the street should be ok?

[Tambohamilton]

Is it an XD? If not, I suspect you actually have an 11mm rear sway.

2" is pretty low IMO, especially assuming you're coming from m-sport? I'd go no more than 1" lower than m-sport, personally.

I'd move closer to 0 rear toe, though that likely won't help much mid-corner.

The position of the car's COG relative to the roll centre (well, roll axis) defines how much roll torque is generated by a given cornering load. Roll torque is what the suspension has to counteract to keep the car flat in the corners (maintaining decent camber etc). If the roll centre (and therefore roll axis) height varies wildly with suspension movement, it results in fluctuating roll load on the suspension disproportionate to the change in cornering load...resulting in big changes in grip from small suspension or control inputs.

This roll centre thing is likely why the e9x responds positively to having an oversized front sway bar...but that's not to say that rear bar won't also help in a similar way!

[CptSumTingWong]

Originally Posted by Tambohamilton

Is it an XD? If not, I suspect you actually have an 11mm rear sway.

2" is pretty low IMO, especially assuming you're coming from m-sport? I'd go no more than 1" lower than m-sport, personally.

I'd move closer to 0 rear toe, though that likely won't help much mid-corner.

The position of the car's COG relative to the roll centre (well, roll axis) defines how much roll torque is generated by a given cornering load. Roll torque is what the suspension has to counteract to keep the car flat in the corners (maintaining decent camber etc). If the roll centre (and therefore roll axis) height varies wildly with suspension movement, it results in fluctuating roll load on the suspension disproportionate to the change in cornering load...resulting in big changes in grip from small suspension or control inputs.

This roll centre thing is likely why the e9x responds positively to having an oversized front sway bar...but that's not to say that rear bar won't also help in a similar way!

Sorry, you're right, probably 11mm rear bar, i haven't measured it but it's the spaghetti noodle sized oem rear bar for rear drive m-sport 330i. And i am not lowered 2 inches. I was just looking at what the bilstein coilovers lower and its 30-50mm and i'm set about in the middle. But the 30-50mm is for non m-sport. So I'm lowered about an inch.

Thanks for the explaination, I think that makes sense, still trying to wrap my head around it...obviously suspension setup is not my forte!