AWD Sway bar

TACP · 11-09-2020, 01:10 PM

I am under the impression that typically a RWD car needs a front sway bar and a FWD need a rear sway bar. HOwever, I have a AWD M235i and looking at getting a sway bar but not sure to get front or rear.
I am not a super aggressive driver yet as I just started Autocross. I had the traction/stability controls turned off and only had minor issues with the rear kicking out on heavy acceleration.
Thanks for any help/advice.

dradernh · 11-09-2020, 02:20 PM

Quote:

Originally Posted by TACP

I am under the impression that typically a RWD car needs a front sway bar and a FWD need a rear sway bar. HOwever, I have a AWD M235i and looking at getting a sway bar but not sure to get front or rear.
I am not a super aggressive driver yet as I just started Autocross. I had the traction/stability controls turned off and only had minor issues with the rear kicking out on heavy acceleration.
Thanks for any help/advice.

In addition to input from here, I recommend asking experienced drivers in your club. Owners who drive AWD cars may be ideal sources of useful info, but I'm guessing that the information you're seeking is also known by many of the drivers who have been autocrossing for a number of years.

randmness · 11-12-2020, 07:19 PM

I haven't gotten the chance to autocross my M240I, but on my previous car (ND Miata), folks generally did the front to increase the understeer (and even sometimes unlinked the rear sway bar entirely.) I'm still in the break-in period so I've mostly just been casually driving my M240I. I'm hoping to get a chance to autocross next year.

If you find the rear kicking out, have you tried lowering the rear PSI? Not sure what tires you are running.

NewWorldOrder · 11-13-2020, 03:26 PM

Quote:

Originally Posted by TACP

I am under the impression that typically a RWD car needs a front sway bar and a FWD need a rear sway bar. HOwever, I have a AWD M235i and looking at getting a sway bar but not sure to get front or rear.
I am not a super aggressive driver yet as I just started Autocross. I had the traction/stability controls turned off and only had minor issues with the rear kicking out on heavy acceleration.
Thanks for any help/advice.

Well the x drive is capable of putting most of the power to the rear wheels, so I'd assume you'd get the front done.

Aspen235 · 11-18-2020, 07:19 PM

Front vs rear is pretty chassis specific. What works on one car may not on another. I have asked this question on here but it seems there is not much experience. Too bad because it is difficult to add bars to these cars
On subarus a big front bar reduces understeer by limiting camber gain. That may work for the m240 too. At the same time most cars understeer more with a big front bar and less with a big rear.
Somebody has to give it a shot and post a review

FaRKle! · 12-09-2020, 09:04 PM

This is going to depend on what type of suspension you have.

Most coilovers boost the front spring rate massively compared to the rear. For those kits you'd probably want a stiffer rear bar to even out the understeer designed into those kits.

For a stock setup, or one with a higher rear frequency than front (not too common for coilovers, but more common on just spring kits or BMW M-Perf suspensions), you'll want a larger front bar, but you need to be careful not to go too large. H&R's front bar alone is way too stiff and causes understeer.

I've swapped multiple front and rear bars on my F31 and tested the effects on track. I settled on a Dinan front bar, which meant I had to buy the kit with both, and then find someone else to sell the rear to.

DistantTea · 12-10-2020, 10:58 AM

I would not change the bar. If you just started make no changes and just get as much seat time as you can. On the long long list of things you can do to incrementally improve a car you need to be able to feel your car first and foremost. Get experience until you can identify what your car is lacking. Then buy a miata.

My autocross credentials - Last place in DS at SCCA divisional in 2003.

11-09-2020, 01:10 PM	#1
TACP New Member 4 Rep 27 Posts Drives: 2015 M235I xDrive Join Date: Jul 2016 Location: Stafford, VA iTrader: (0)	AWD Sway bar I am under the impression that typically a RWD car needs a front sway bar and a FWD need a rear sway bar. HOwever, I have a AWD M235i and looking at getting a sway bar but not sure to get front or rear. I am not a super aggressive driver yet as I just started Autocross. I had the traction/stability controls turned off and only had minor issues with the rear kicking out on heavy acceleration. Thanks for any help/advice.
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11-12-2020, 07:19 PM	#3
randmness Enlisted Member 11 Rep 39 Posts Drives: 2021 M240i xDrive Join Date: Nov 2020 Location: MD iTrader: (0)	I haven't gotten the chance to autocross my M240I, but on my previous car (ND Miata), folks generally did the front to increase the understeer (and even sometimes unlinked the rear sway bar entirely.) I'm still in the break-in period so I've mostly just been casually driving my M240I. I'm hoping to get a chance to autocross next year. If you find the rear kicking out, have you tried lowering the rear PSI? Not sure what tires you are running. Last edited by randmness; 11-13-2020 at 09:37 AM..
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11-18-2020, 07:19 PM	#5
Aspen235 Second Lieutenant 59 Rep 205 Posts Drives: 2014 X3 35i, 2018 M240i 6mt Join Date: Feb 2016 Location: London, ON iTrader: (1)	Front vs rear is pretty chassis specific. What works on one car may not on another. I have asked this question on here but it seems there is not much experience. Too bad because it is difficult to add bars to these cars On subarus a big front bar reduces understeer by limiting camber gain. That may work for the m240 too. At the same time most cars understeer more with a big front bar and less with a big rear. Somebody has to give it a shot and post a review
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12-09-2020, 09:04 PM	#6
FaRKle! Brigadier General 4015 Rep 3,538 Posts Drives: 328d Wagon, M2 Comp, i4 eD35 Join Date: Sep 2016 Location: Bay Area, CA iTrader: (4) Garage List 2023 BMW i4 eDrive 35 [0.00] 2017 BMW 328dx Wagon [0.00] 2021 BMW M2 Competi ... [0.00]	This is going to depend on what type of suspension you have. Most coilovers boost the front spring rate massively compared to the rear. For those kits you'd probably want a stiffer rear bar to even out the understeer designed into those kits. For a stock setup, or one with a higher rear frequency than front (not too common for coilovers, but more common on just spring kits or BMW M-Perf suspensions), you'll want a larger front bar, but you need to be careful not to go too large. H&R's front bar alone is way too stiff and causes understeer. I've swapped multiple front and rear bars on my F31 and tested the effects on track. I settled on a Dinan front bar, which meant I had to buy the kit with both, and then find someone else to sell the rear to. __________________ -328d Wagon Build Log (with helpful reference links) -My YouTube Channel for some of the best DIYs and in depth information Please don't PM me for suspension recommendations unless interested in paid private consultations.
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12-10-2020, 10:58 AM	#7
DistantTea Private First Class 101 Rep 170 Posts Drives: Oops Join Date: Jan 2019 Location: Nowhere iTrader: (0)	I would not change the bar. If you just started make no changes and just get as much seat time as you can. On the long long list of things you can do to incrementally improve a car you need to be able to feel your car first and foremost. Get experience until you can identify what your car is lacking. Then buy a miata. My autocross credentials - Last place in DS at SCCA divisional in 2003.
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