How do I correct my understeer?

cu260r6 · 06-19-2016, 11:49 PM

I have a 128i that was awfully spongy after 70k miles on the non-sport suspension, so I upgraded to stiffer springs that dropped each end about 1 in. and koni orange shocks. The car corners much flatter and has a much higher overall G limit, but it also has significantly greater degree of understeer.

Any suggestions on how to remove this tendency to understeer and return to the more neutral handling of the stock setup?

Dackelone · 06-20-2016, 01:50 AM

Koni Orange shocks ? Did you mean Yellows ?

Sway bars are what you need. The non M-suspension 128i's did not have a rear sway bar. That's why BMW included them in the Performance suspension for the 128's. After sway bars.. you could go to a square tire/wheel setup. But sway bars is where you should start.

tuj · 06-20-2016, 02:21 PM

Or add more front neg. camber.

cu260r6 · 06-20-2016, 04:32 PM

Yes, the Koni orange shocks are essentially a less stiff, non adjustable version of the Koni sport shocks (yellows).

To which end of the car would you suggest adding a sway bar? Physics would seem to dictate that by adding a front sway bar you flatten the front in corners and increase the grip of the inside front tire, but I have heard conflicting opinions on this.

Increasing/decreasing the camber of the rear isn't my first choices as this is my daily driver and I don't want to be going through tires that much quicker.

Dackelone · 06-20-2016, 05:10 PM

Quote:

Originally Posted by cu260r6

Yes, the Koni orange shocks are essentially a less stiff, non adjustable version of the Koni sport shocks (yellows).

To which end of the car would you suggest adding a sway bar? Physics would seem to dictate that by adding a front sway bar you flatten the front in corners and increase the grip of the inside front tire, but I have heard conflicting opinions on this.

Increasing/decreasing the camber of the rear isn't my first choices as this is my daily driver and I don't want to be going through tires that much quicker.

You will need to install front AND rear (matched)sway bars. I believe the non M-sport 128i do not have a rear sway bar. And the front bar is very thin. This is why when you order a BMW Performance suspension for the 128i the kit includes new sway bars.

Read this article on what TC Kline did...

The ultimate handing machine: 128i ?
http://www.1addicts.com/forums/showthread.php?t=575027

and this one is really just for reference on 128i's in general.

128i: Simple Fun, Great Price! ...in Bimmer Magazine...
http://www.1addicts.com/forums/showthread.php?t=734600

cu260r6 · 06-21-2016, 02:39 AM

Much appreciated, thanks.

Fume · 06-21-2016, 01:24 PM

Does anyone know what makes the car understeer to begin with? Is it just the stock alignment settings (I believe the rear wheels have more negative camber than the fronts stock) and the staggered wheels?

tuj · 06-21-2016, 01:51 PM

Quote:

Originally Posted by Fume

Does anyone know what makes the car understeer to begin with? Is it just the stock alignment settings (I believe the rear wheels have more negative camber than the fronts stock) and the staggered wheels?

*big front sway / small rear sway
*staggered tire setup
*little camber in front
*no camber recovery under roll (thanks McStrut!)

Dackelone · 06-21-2016, 02:21 PM

Quote:

Originally Posted by tuj

*big front sway / small rear sway
*staggered tire setup
*little camber in front
*no camber recovery under roll (thanks McStrut!)

You forgot tire age & brand/design and or miss matched tires.

John_01 · 06-21-2016, 11:29 PM

Understeer is partly due to staggered tire sizes, but most of it is to do with the inadequacy of the MacPherson strut front suspension. The big problem is there is not enough negative camber on the front. The static front camber is close to zero. Other cars may gain negative camber as they roll in cornering, but there isn't much of this characteristic on the 135i front suspension. BMW have done a respectable job with the multi-link rear suspension on the 1 series, but it would have been really nice if they had a good double wishbone setup on the front to compliment it.

tuj · 06-22-2016, 07:07 AM

John_01 +1 you nailed it. Double A-arm much better for camber recovery in roll.

jafo1701 · 06-23-2016, 12:48 PM

Quote:

Originally Posted by Fume

Does anyone know what makes the car understeer to begin with? Is it just the stock alignment settings (I believe the rear wheels have more negative camber than the fronts stock) and the staggered wheels?

BMW designs their cars to have slight understeer for safety reason. They figure most people can control a little understeer. Better then the other option of having oversteer which most people cannot control. BTW when I changed over suspension from stock on my 135i, my first track day I had a lot of understeer. I changed 3 things. Stiffened up the suspension, got a bigger swaybar, the one one the M3. I put a bit of Toe out on my front tires, be careful with that. Changed things entirely, car is neutral with just a bit of oversteer when I want it. I also have other M3 swapped over on my car.

E82MSport · 06-27-2016, 01:07 PM

Curing understeer mid-corner - stab the clutch and apply full throttle. This should eliminate all understeer and put the car into an oversteer condition. Problem solved.

Maybe this isn't the best way on a second thought...

cu260r6 · 06-27-2016, 06:55 PM

Quote:

Originally Posted by jafo1701

BMW designs their cars to have slight understeer for safety reason. They figure most people can control a little understeer. Better then the other option of having oversteer which most people cannot control. BTW when I changed over suspension from stock on my 135i, my first track day I had a lot of understeer. I changed 3 things. Stiffened up the suspension, got a bigger swaybar, the one one the M3. I put a bit of Toe out on my front tires, be careful with that. Changed things entirely, car is neutral with just a bit of oversteer when I want it. I also have other M3 swapped over on my car.

Which sway did you enlarge? Front?

jafo1701 · 06-28-2016, 09:36 AM

Quote:

Originally Posted by cu260r6

Which sway did you enlarge? Front?

The front with the standard E92/90 M3 one, not the convertible one that tapers I'm towards the middle.

MightyMouseTech · 06-28-2016, 09:40 AM

Staggerd tires are fine, but the front tires are not nearly wide enough.

Wider front tires, more front camber, and a stiffer front bar to limit roll.

Will be much better.

Iron Man · 06-28-2016, 10:08 AM

Quote:

Originally Posted by Dackelone

You will need to install front AND rear (matched)sway bars. I believe the non M-sport 128i do not have a rear sway bar. And the front bar is very thin. This is why when you order a BMW Performance suspension for the 128i the kit includes new sway bars.

Read this article on what TC Kline did...

The ultimate handing machine: 128i ?
http://www.1addicts.com/forums/showthread.php?t=575027

and this one is really just for reference on 128i's in general.

128i: Simple Fun, Great Price! ...in Bimmer Magazine...
http://www.1addicts.com/forums/showthread.php?t=734600

You are correct, the non-sport 128i does not have a rear sway bar. The BMW sport package includes both front and rear sway bars for it.

06-19-2016, 11:49 PM	#1
cu260r6 Private 25 Rep 81 Posts Drives: 428i Join Date: Dec 2012 Location: CO iTrader: (0)	How do I correct my understeer? I have a 128i that was awfully spongy after 70k miles on the non-sport suspension, so I upgraded to stiffer springs that dropped each end about 1 in. and koni orange shocks. The car corners much flatter and has a much higher overall G limit, but it also has significantly greater degree of understeer. Any suggestions on how to remove this tendency to understeer and return to the more neutral handling of the stock setup?
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06-20-2016, 01:50 AM	#2
Dackelone European Editor 10523 Rep 22,992 Posts Drives: N54 e82 Join Date: Feb 2010 Location: Bayern, Germany iTrader: (1)	Koni Orange shocks ? Did you mean Yellows ? Sway bars are what you need. The non M-suspension 128i's did not have a rear sway bar. That's why BMW included them in the Performance suspension for the 128's. After sway bars.. you could go to a square tire/wheel setup. But sway bars is where you should start. __________________ Dackel's European Delivery Museum Guide
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06-20-2016, 02:21 PM	#3
tuj First Lieutenant 49 Rep 379 Posts Drives: '13 135i Join Date: May 2013 Location: Stamford, CT iTrader: (0)	Or add more front neg. camber. __________________ Living the 1-life since 2013.
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06-20-2016, 04:32 PM	#4
cu260r6 Private 25 Rep 81 Posts Drives: 428i Join Date: Dec 2012 Location: CO iTrader: (0)	Yes, the Koni orange shocks are essentially a less stiff, non adjustable version of the Koni sport shocks (yellows). To which end of the car would you suggest adding a sway bar? Physics would seem to dictate that by adding a front sway bar you flatten the front in corners and increase the grip of the inside front tire, but I have heard conflicting opinions on this. Increasing/decreasing the camber of the rear isn't my first choices as this is my daily driver and I don't want to be going through tires that much quicker.
	Appreciate 0 Quote

06-21-2016, 02:39 AM	#6
cu260r6 Private 25 Rep 81 Posts Drives: 428i Join Date: Dec 2012 Location: CO iTrader: (0)	Much appreciated, thanks.
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06-21-2016, 01:24 PM	#7
Fume First Lieutenant 52 Rep 374 Posts Drives: '19 Porsche 718 Cayman GTS Join Date: Jul 2013 Location: Seattle iTrader: (1)	Does anyone know what makes the car understeer to begin with? Is it just the stock alignment settings (I believe the rear wheels have more negative camber than the fronts stock) and the staggered wheels? __________________ New Car: 2019 Porsche 718 Cayman GTS \| Stock for now Old Car: 2013 BMW 128i \| 6MT \| BMW Performance Grills \| CDV Delete \| SSK \| Performance Exhaust \| M3 RSFB \| TCKR DA
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06-21-2016, 11:29 PM	#10
John_01 Colonel 232 Rep 2,643 Posts Drives: E90 325i, E82 135i Join Date: Mar 2009 Location: Sydney, Australia iTrader: (0)	Understeer is partly due to staggered tire sizes, but most of it is to do with the inadequacy of the MacPherson strut front suspension. The big problem is there is not enough negative camber on the front. The static front camber is close to zero. Other cars may gain negative camber as they roll in cornering, but there isn't much of this characteristic on the 135i front suspension. BMW have done a respectable job with the multi-link rear suspension on the 1 series, but it would have been really nice if they had a good double wishbone setup on the front to compliment it.
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06-22-2016, 07:07 AM	#11
tuj First Lieutenant 49 Rep 379 Posts Drives: '13 135i Join Date: May 2013 Location: Stamford, CT iTrader: (0)	John_01 +1 you nailed it. Double A-arm much better for camber recovery in roll. __________________ Living the 1-life since 2013.
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06-27-2016, 01:07 PM	#13
E82MSport First Lieutenant 130 Rep 351 Posts Drives: 08' Crimson 135i Join Date: Sep 2013 Location: Rochester Hills - MI iTrader: (0)	Curing understeer mid-corner - stab the clutch and apply full throttle. This should eliminate all understeer and put the car into an oversteer condition. Problem solved. Maybe this isn't the best way on a second thought... __________________ Ohlins Road & Track Coilovers / Apex ARC 8's 245/255-35 MPSS / Wagner Downpipes / Wagner EVOII Intercooler / ER Charge Pipe / Forge DV / PowerFlex RSFB / PowerFlex Differential Bushings / MFactory 3.46 Torsion LSD / MHD Flasher
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06-28-2016, 09:40 AM	#16
MightyMouseTech Major General 4338 Rep 6,196 Posts Drives: 13 135i 6MT LeMans Blue MSport Join Date: Feb 2013 Location: Ottawa, Canada iTrader: (0)	Staggerd tires are fine, but the front tires are not nearly wide enough. Wider front tires, more front camber, and a stiffer front bar to limit roll. Will be much better.
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