too large rear sway = understeer?

[mikeo]

Orb, you just about have me convinced that the methods that work for the E36 and E46 are not necessarily transferrable to the E82. Thanks for taking the time to share your testing results.

Are you or anyone else actually racing a car in sanctioned events set up per your very detailed studies and testing? I for one would like to see some track times.

[atr_hugo]

Orb - any recommendations for bringing the car back to neutral?

In the grand scheme of things the 135i with base suspension (sports package) tends to understeer too much for my taste at track out and is a bit underdamped for me. Stock spring rates are fine for my intended use (grand touring - not a track car).

I appreciate the info your post, it's always nice to see someone doing some digging. Thanks!

[sethchan]

Originally Posted by Orb

Bad idea....I have a working load transfer sheet based on Claude Rouelle (magic number) for this car now. I see about sharing more details later.

Go measure the rear motion ratio and look at what happens when you increase spring rate. The math as follows:

Rear wheel spring rate: 0.58^2 x (coil spring rate)
Front wheel spring rate: (cos 14)^2 x (coil spring rate)

The number will show that every 50 lb/in you increase in the front you need to increase the rear 130 lb/in to keep thing even. Since the stock car has 130 lb/in spring and the rear is 350 lb/in and under steers fairly bad when pushed. If you want to run a 285 lb/in spring on the front then your going to need a 560 lb/in on the rear. If you go less spring rate on the rear than this the car will under steer. You got Clubsport at 400 lb/in for the front and the rear are 570 lb/in in the rear. You’re going to need a 1000+ lb/in spring in the rear to keep it the same as stock……Side bar…car can’t handle a spring greater than 635 lb/in with out major load transfer problem due to rear bushing…..we have a problem.

The stock 135i “magic number” load transfer calculations are 17% over what neutral steer car for a starting point. H&R roll bar will put he car back within 3% of the magic number with stock springs. Once thing is very clear H&R did their homework but the bar don’t scale well when spring rate increase and heads towards under steer. BTW, the M3 has neutral steer and it matter because it shares most of the same geometry and weight distribution.

The problem with your car is load transfer and this is the first and last thing when tuning. It will be difficult if not impossible to fix the suspensions with this car without change to the M3 rear sub frame bushing. The bushings just deflect way too much with stiffer suspension and result in unpredictable handle and some very nasty transient load condition. Getting it right means you should not need more that 2 degrees on negative camber in the front so you can win the camber game but your options are limited. The calucated roll numbers support this.

The common track folklore of non stagger high profile tires and big front bar will send you 180 degrees in the wrong direction. There is very little room in tuning for maximizing the speed of this car on the track.

Orb

Sounds like the performance suspension upgrade from BMW would be worse than useless.

[mikeo]

Originally Posted by sethchan

Sounds like the performance suspension upgrade from BMW would be worse than useless.

Have you heard what the spring rates for the BMW Performance suspension are?

[sethchan]

Originally Posted by mikeo

Have you heard what the spring rates for the BMW Performance suspension are?

No, and I'm really confused.

The poster seems to be saying that a) there isn't much room to tune the suspension and b) that a stiffer front sway is counterproductive.

This bums me out since I'm scheduled to have the performance suspension (springs, struts, shocks and front swaybar) installed in a few days.

[Justin(OKC)]

Orb, I appreciate the info and am following your posts just for the education, but I must say....you are depressing me. I may not do anything to this car and just buy an M3 in a few years.

[adc]

Originally Posted by sethchan

No, and I'm really confused.

The poster seems to be saying that a) there isn't much room to tune the suspension and b) that a stiffer front sway is counterproductive.

This bums me out since I'm scheduled to have the performance suspension (springs, struts, shocks and front swaybar) installed in a few days.

I was thinking BMW Performance Suspension (with springs), junk the Perf front sway and install a set of adjustable sways front/rear (HR or UUC).

I imagine the spring rates in the Perf suspension are a mild increase over stock, so an HR set of bars (or UUC, can't imagine they are very different) should do the trick.

Of course, don't forget the M3 suspension parts (4 arms in front, 4 bushings at the rear) that Orb was so kind to post about in detail.


I think for about $2.5k (parts) you should be able to have a car that handles well for mostly street and occasional track. (And perhaps another $2.5k in wheels/tires).

[Orb]

Originally Posted by mikeo

Orb, you just about have me convinced that the methods that work for the E36 and E46 are not necessarily transferrable to the E82. Thanks for taking the time to share your testing results.

Are you or anyone else actually racing a car in sanctioned events set up per your very detailed studies and testing? I for one would like to see some track times.

I’m not sure how you came to your conclusions about e36/e46 transferable nonsense which seem to be pulled out of thin air? Going by some of your older post you seem to be clueless about even the very basics of vehicle dynamics. I am sorry if this sounds harsh but it is time to wake up and deal with it. I am not sure you even understand what I posted and it would not be a good idea to pretend you do. I would suggest you be direct if you have question and stop with the theatrical overtone.

Originally Posted by atr_hugo

Orb - any recommendations for bringing the car back to neutral?

In the grand scheme of things the 135i with base suspension (sports package) tends to understeer too much for my taste at track out and is a bit underdamped for me. Stock spring rates are fine for my intended use (grand touring - not a track car).

I appreciate the info your post, it's always nice to see someone doing some digging. Thanks!

You can improve the handling of the stock car with not to much work. The BMW shocks are not well dampened. I really did love the Koni FSD when I had them so it hard for me to not recommend them as they just well tuned. If you stiffen this car with bars or spring you do need to change the dampeners. The stock rebound dampening is not sufficient.

I don’t have the front sway bar inside diameter for your car so if some know it for sure I can calculate the rate for you. The H&R might be a bit stiff for you so I would consider doing e92/e90 sport suspension front roll bar with M3 rear roll bar. The M3 rear bar has been validated for perfect fitment. This will be you about 1% off neutral steer biased towards under steer. This is good for a steer car and you get about 0.6 degrees less roll at 0.9 G. You lose about 80 lbs of weight on the inside rear which fine for any steer car but this is at 0.9 g. and less than 17% of the overall weight. The H&R bars will put you off the magic number by about 3-4% and reduce roll by 1.2 degrees.

I am just about to by M3 front bar with fitment then cut it in half to get the real spring rate for it. I will more data on this later next week.

Orb

[Orb]

Originally Posted by Justin(OKC)

Orb, I appreciate the info and am following your posts just for the education, but I must say....you are depressing me. I may not do anything to this car and just buy an M3 in a few years.

Don't be...what I'm learned so far this car has all the potential to spank both of the bigger brothers (335i and M3). It is possible to get the car handle well but it take a lot more than springs and bars if you tracking the car.

Orb

[atr_hugo]

FWIW, here's a bimmerfest writeup of the Koni FSD shocks: http://www.bimmerfest.com/forums/sho...&highlight=fsd

[mikeo]

Originally Posted by Orb

I’m not sure how you came to your conclusions about e36/e46 transferable nonsense which seem to be pulled out of thin air? Going by some of your older post you seem to be clueless about even the very basics of vehicle dynamics. I am sorry if this sounds harsh but it is time to wake up and deal with it. I am not sure you even understand what I posted and it would not be a good idea to pretend you do. I would suggest you be direct if you have question and stop with the theatrical overtone...

Ouch! LOL! Don't think I deserved that, but sorry If the post came off 'theatrical'. Just trying to get more information.

Oh, and as a three-time SOLO regional class champ in an E36 M3 that built the car from stock to B Street Prepared I don't think I'm totally clueless about suspension dynamics, but I'd like to learn more.

[Orb]

Originally Posted by mikeo

Ouch! LOL! Don't think I deserved that, but sorry If the post came off 'theatrical'. Just trying to get more information.

Oh, and as a three-time SOLO regional class champ in an E36 M3 that built the car from stock to B Street Prepared I don't think I'm totally clueless about suspension dynamics, but I'd like to learn more.

You’re driving experience is not relevant at this level of physics and if you had a clue what I said you know this! All you told me is that you have tuned your car less badly than some other amateur which really means just about nothing. I gave you a name and term (aka: magic number) in my original post for reference so follow it through.

I’m sorry, but after reading some of your post you simply don’t have clue at some real basic level…it is just the way it is. Maybe start here at least this is the ABC… http://www.fromsteve.net/.

Orb

[mikeo]

Thanks for the link, Orb, it's a good one. I'll do some reading and try not to appear so clueless in the future.

[swiftss13]

Very informative!

[imported_TripleM]

i hv gone thru the stages of playing with ARB in my E46 M3 and that was really the last thing I would ever do again for my future car(s)

so long the car is RWD, no ARB upgrade for me. What I thoroughly enjoy more, far more in fact, is to invest in a set of coilovers with chosen spring rates, adjustable camber plate and wherever permissible, rear control arm. And of course, a slightly wider tires in the front but not all round...10mm diff front and back would be just nice. That is what I m having now with my 130 : Cross C/O, 235/245 tires set ups on 8/8.5Js of Volk Racing RE30

[turbobum]

Originally Posted by Orb

The stock 135i “magic number” load transfer calculations are 17% over what neutral steer car for a starting point. H&R roll bar will put he car back within 3% of the magic number with stock springs. Once thing is very clear H&R did their homework but the bar don’t scale well when spring rate increase and heads towards under steer. BTW, the M3 has neutral steer and it matter because it shares most of the same geometry and weight distribution.


Orb

So Orb, you're saying the H&R bar will reduce understear on a stock suspension, but all bets are off with aftermarket springs?

[Orb]

Originally Posted by turbobum

So Orb, you're saying the H&R bar will reduce understear on a stock suspension, but all bets are off with aftermarket springs?

The H&R bar number look really good if you rear suspension frequency is 10-15% higher that the front except on this car as the spring rates are very low (only seeing 1.1Hz to 1.2 Hz suspension frequency). I would just put on a e92 M3 rear bar and use the front and rear bushing and clamps and call it done.

Orb

[fourtailpipes]

using a stiffer rear bar (especially in track conditions) can be a bad way to reduce understeer... especially in cars without true limited slip differentials. a stiffer rear swaybar will make you much more likely to pick up an inside rear wheel, or at least significantly reduce the traction of the rear inside wheel. that sets the "electronic LSD" in motion, and energy is wasted. i'd go with a stiffer front swaybar and use other measures to reduce understeer, like increasing front tire width or adding negative front camber.

[Evan135]

Orb did you ever look into M3 front sway bars thickness?

I was wondering if when you recomended the stock front bar with M3 front sway bar busings and the e90/e92 rear bar/w bushings to get the 135i within 1% of neutral, that the stock front bar is thinner in the middle?

I just want to use the right front bar with the e90/e92 rear bar to get the most neutral balance. If you calculated the e90/e92 front sport bar at 26.5 and it is thinner in the middle, the M3 might be the better choice.

Thanks!

[bradford]

Originally Posted by Evan135

Orb did you ever look into M3 front sway bars thickness?

I believe Orb's rolling M3 F&R ARBs.

Details are in the suspension forum posts on 1addicts and more detail in E90post...