TC Kline, Vorshlag, Kosei K1, Z1's and 38 lbs. of unsprung weight...

[akak1997]

Originally Posted by trboboost91

i like your wheel choice

i have the same wheels but with R1's 245/40/17 mounted.

i would have taken pics with them on but when you only make it through 3 sessions before the engine goes you forget about the photo shoot!@

Wooo! WTH happened? where's the piston? looks like the piston rod snapped..

[ridin135]

Originally Posted by trboboost91

i like your wheel choice

i have the same wheels but with R1's 245/40/17 mounted.

i would have taken pics with them on but when you only make it through 3 sessions before the engine goes you forget about the photo shoot!@

So what happend?

[MINI135i]

Further thoughts:

I think I am going to make a slight adjustment and put 600 lbs. springs in the rear of the car.

A 350/600 gives a little more oversteer with 60% ratio compared to the 50% ratio I am currently running.

F = .92 x 350 = 322 lbs.
R = .32 x 600 = 192 lbs. 60%


Because I run high compression and rebound in the rear when tracking / autocrossing I have not had any major issues with understeer. I am still trying to keep the car very streetable but at the same time optimize the spring set up. Real stiff springs can kill streetability pretty quickly. It is nice to be able to dial down all the stiffness at the end of the day with compression and rebound.

I think I can get a touch more "built in oversteer" with the 600 lb. springs and still have the adjustment through rebound/compression to keep the ride comfort good on the street and fully adjustable on the track.

I have kind of mirriored the Berk car, but with slightly lower rates:

Berk setup:
(I think they recently mentioned they were putting 450 up front compared to the current 400 to get rid of some oversteer)

F= .92 x 450 = 414 lbs.
R= .32 x 800 = 256 lbs. 62%

Also I would like to get a 235-55/275 set up instead of the 235's on all four corners in the near future to help put down more power. The bigger spring in the rear should only help with balancing the extra grip from the 275 in the rear, so as to not cause further understeer.

Still, my biggest concern with all of this is the rear subframe bushings being too soft for higher rate springs anyway. I think the M3 subframe bushings are going to be a must. Although the car feels good, a similar prepped E36 M3 feels better, and I think one of the main factors is the stiffer bushings (barring the obvious weight differences between the cars).


All the other goodies like negative camber, front sway bar, coilovers, etc. are assumed.

[MINI135i]

Ok, it looks like M3 rear subframe bushings will be installed end of next week!

The one problem I have had with this awesome setup so far is the rear end. Everytime I drive a race prepped E36, I am like, "what is wrong with the E82 rear end, it just doesn't seem as planted or predictable as the E36."

After chatting with TC we seemed to be in agreement that the rear is the most problematic and that the "mushy" stock rear subframe bushings are causing most of the issue (barring pig weight of the 135i of course). Upgraded springs and high rebound/compression dampers are just amplifying the issue.

I have had no issue with the front of the car even with the stock arms (haven't done the M3 parts). The coilovers, camber plates, and front bar have made it quite predictable.

I am excited because I think the M3 rear bushings will make a big difference with this set up and really balance the car....(?)

[bradford]

Originally Posted by MINI135i

Ok, it looks like M3 rear subframe bushings will be installed end of next week!

Looking forward to hearing your impressions once the rear bushings are done, as I'm going to be going with a very similar suspension setup to yours.

Can you attempt to qualify how stiff the ride is on the street with your spring rates? I've had 400/800 rates for the TCK DA setup recommended to me but I dont' want it to be a tooth-rattler. i will also be doing all the M3 links as well, which will remove another element of isolation...

[MINI135i]

To tell you the truth I can't imagine 400/800 being that bad as my current set up is very comfortable (more comfy than a Cooper S) when dialed down. 400/800 should be nice for the track and manageable on the street.

I might go into the 800 range also as things progress.

[Justin(OKC)]

I know exactly what you mean about the difference between and E36 and the E82. My E36 M3 (sold to my brother) was solid in the rear with the mods it had. I always felt like the stock bushings on the 1er felt like RTAB's going bad in an E36. You will be very happy with the bushings. Until I did them with the rest of my suspension, I was about ready to sell the car. Now I love it.

I am running 400/800 springs on my car now. The rates were selected based on the anti-roll bars I am using. If you have any questions about why I did what I did on my car, shoot Harold at HPautowerks a pm. It was really a collaboration of info from him and Orb that led to what I am running now. Orb thinks I should be doing 450# springs up front. This car with these springs rides so much better than my M3 on 450/600 springs!!!

[bradford]

Justin -

I know that Orb has advocated the 400/800 setup in the past, and I believe this applied to cars with the E92 M3 ARBs, front and rear. I'm interested to know why he suggested 450 int he front for you. Are you having oversteer issues?

[Justin(OKC)]

Originally Posted by bradford

Justin -

I know that Orb has advocated the 400/800 setup in the past, and I believe this applied to cars with the E92 M3 ARBs, front and rear. I'm interested to know why he suggested 450 int he front for you. Are you having oversteer issues?

He thinks the 1 series needed more spring up front than the E90/E92. I will try to look back in my PM's and find his exact reasoning for you. Yes, the rates were specific to the M3 ARBs front/rear like I have. Haven't done enough testing yet, but I was having some oversteer issues when I autocrossed it. I had some understeer issues too, but most of that was driver induced. I think with some seat time I will be pretty fast in this car!!

[bradford]

Originally Posted by Justin(OKC)

He thinks the 1 series needed more spring up front than the E90/E92. I will try to look back in my PM's and find his exact reasoning for you.

Thanks, that would be much appreciated. I've been trying to understand his posts about motion ratio and frequency and I've not yet been able to wrap my head around the way the numbers are calculated. I've seen his numbers for the E92 but I'd like to understand how the E82 differs before I pull the trigger on something...

[Justin(OKC)]

Originally Posted by bradford

Thanks, that would be much appreciated. I've been trying to understand his posts about motion ratio and frequency and I've not yet been able to wrap my head around the way the numbers are calculated. I've seen his numbers for the E92 but I'd like to understand how the E82 differs before I pull the trigger on something...

It had something to do with the spring length I had to use to clear the wheels/tire combined with how much I lowered the car. I'm not even going to begin to try to figure out how he came up with it. But, in a nutshell....the lower you go the stiffer you need to go and the shorter the spring the stiffer you need to go. Since I don't know how he is calculating it I am using his comments to extrapolate what I need to do. Right now I'm pretty happy with the 400/800 setup, but I think it might be better at 450/800 with the 7"/8" springs I'm running.

Sorry if this is a bit of a thread hijack....hopefully it helps explain some things.

[Orb]

It always amazes me when things go a stray. All the calculation I have done are based on academic vehicle dynamics which is used by BMW and most of the engineering world. The vendors who seem to don’t get this is the cottage cheese suspension industry as they typically don’t have a real engineer. The subject is no doubt difficult but it all can be explained if we account for every detail and look at the suspension as complete system. There is no black magic or anything of the sorts.

First, forget this percentage ratio that stated in this thread. It is completely worthless and has zero meaning!!!!! The only thing that has any real meaning is the suspension frequency and we can use this to make good setup judgments. The OEM car is setup with ideal text book flat ride frequency so the rear suspension is 13-15% higher than the front. As we move towards and performance setup the rear suspension frequency will drop over the OEM setup but it not linear at all as we have to consider all attributes of the car handling. In my setup the front suspension frequency is about 10% higher in the front than the rear. This is almost text book setup for my application. This is based on decades of research and development and very much well documented so there is no black magic.

The 400/800 spring I use on my car works great for me because I have hardware that no one else has and setup is very specific. In short, I am able to get considerably more mechanical grip from the rear than someone who runs 450/800 spring combo. My setup is not going to work for everyone but it is a good comprises between street and occasional tracking. With a 400/800 setup you can run less damping since you closer to ideal flat ride pitch control over 450/800 setup which also give you a better over setup in roll and the car will absolutely take set in corner smoothly and quickly. A 400/800 setup will give you a fairly neutral handling but there are other thing to consider, like pitch and corner exit traction to name a few. It is all compromise no matter which way you go but this setup just makes the car fun to drive all the time which I think matters the most.

A 450/800 setup with give you improved pitch control for high speed tracks. You have higher G forces and the suspension will works deeper in travel. Part of the problem with this car even with all the upgrades there is still some stiffness spikes in transient load conditions on the rear suspension which is of no surprise given the high motion ratio and geometry. The easy way to fix this is to stiffen the front springs which gives you more predictability or just fix the stiffness problem like I did.

A 800 lb/in rear spring is about all the M3 sub frame bushing are going to take as deflection is still noticeable but it not a big problem. If ww stick with 800lb/in rear spring with a front spring of 400, 450 and 500 lb/in then this is going to be a good working performance range but there are comprises for either on of these setups. For example, using the 400 lb/in front spring will give us really good entry and mid corner speed but we might suffer on the rear corner exit traction. Going with a 500 lb/in spring will be the opposite but a general statement but we also have better pitch control so maybe not….lots of things to consider when we look at every single condition so nothing can be scaled so please don’t try to use ratios or the like.

The first thing I would do with the 1 series is to correct the front track width so is closer to the rear like the 3 or M series car. Lucky for use all the M3 front lower control change the King Pin Inclination offset and thus the scrub radius. What this means, you can run a higher front wheel offset (5-10 mm pre side) which will not have any ill effect on handling. Messing with the scrub radius is a big deal but in this case it is working for us.

As for roll bars, the M3 bars are the only one I know of that can be used to get you even close to a neutral setup when used with stiffer spring. All the other bars on the market are just too far out of the range in stiffness to even consider.

The spring lengths and ride high is something that needs to be calculated and it is so easy to do. We know for a given load the spring will displace a given distance. We understand that with a stiffer spring the displacement will be less for the same load. For that reason we can drop the car a bit and still work with the optimal design of the suspension linkage system. If we go too far with a drop for given spring stiffness then things will go badly real fast. The spring length is calculated based on linear range of the spring which is 20% to 80% of its maxim allowable displacement. If want a smooth ride with no stiffness spiking then you need to take this in account or you will not like the feel or handling at peak loads. For example, a 60 mm 400/800 spring combo needs about 2.5” of travel from static ride height. Therefore, we need an 8” spring in the front and rear to meet the linear spring requirement. Many will run a 7” long spring on the front but it bit on the short side so you will get stiffness spike under high cornering loads. The spring lengths I used are only for Swift springs and anything else will need longer springs as almost all other vendors use a lower yield strength material.

Mini135i: It is odd that TC would say that the bushings are a problem. I discussed this with him a 1.5 years ago and the though I was out of my mind about my whole approach including the sub frame bushings. The engineering done in this industry is just a joke and then some. Tuning this car without sub frame busing upgrade was truly futile and I wasted 2-3 months coming to this conclusion.

Orb

[MINI135i]

Oh man my brain hurts...(j/k).

Orb I always appreciate your posts, they are very helpful.

I still fall in that incorrect category of price/performance compromise and autocross/track compromise, but the insight is very enlightening and I enjoy knowing the most "ideal" way to set up the car. Luckily the car feels great overall, very fast and wins me a lot of competitions. Having fun for sure. Keep up the good work!

[DBFIU]

Originally Posted by ridin135

So what happend?

What happened to the motor?

[MINI135i]

Well the M3 rear subframe bushings are installed!

I am amazed the difference in feel already! Took off the snow tires and put on the Dunlop Z1's and race wheels for a bit since we had a little warm weather to get a better idea of the difference. I won't be able to properly test them until autocross season starts or it gets warm enough for a track day, but what a difference already noticed with just toying around on empty streets!

After seeing the OEM stock bushings that were removed, no wonder the rear end slops around to and fro, those things are hideous. I can compress them with the force of my hand.

Definitely the missing link to the puzzle.

[aisthetes]

I love this thread! Thanks to Mini's real world experimentation and Orb's specific knowledge and insight, the 135i's suspension quirks are finally getting solved to unlock the car's performance potential.

Thank you both for sharing and enlightening.

I suppose the next question involves shock damping settings. Now that we have a working range of spring rates identified, understanding the optimum damping settings (with a double adjustable coilover for rebound & compression) will be the next step in rounding out the car's handling. Finding the optimum damping settings in rebound and compression to work with the chosen spring rates in a street vs. competition environment in evaluating ride quality, corner entry, pitch, and corner exit traction are key and will take some R&D due to the number of possible combinations, but I imagine Orb already has a pretty good handle on where to start...

[Justin(OKC)]

Originally Posted by MINI135i

Well the M3 rear subframe bushings are installed!

I am amazed the difference in feel already! Took off the snow tires and put on the Dunlop Z1's and race wheels for a bit since we had a little warm weather to get a better idea of the difference. I won't be able to properly test them until autocross season starts or it gets warm enough for a track day, but what a difference already noticed with just toying around on empty streets!

After seeing the OEM stock bushings that were removed, no wonder the rear end slops around to and fro, those things are hideous. I can compress them with the force of my hand.

Definitely the missing link to the puzzle.

[bradford]

Originally Posted by MINI135i

Well the M3 rear subframe bushings are installed!

Details on the install please...

[MINI135i]

Originally Posted by bradford

Details on the install please...

Had my BMW dealership do it for me....

[bradford]

Originally Posted by MINI135i

Had my BMW dealership do it for me....

How many hours did they charge? And did you have the rear M3 bar done too while they were up there?

[MINI135i]

Originally Posted by aisthetes

I love this thread! Thanks to Mini's real world experimentation and Orb's specific knowledge and insight, the 135i's suspension quirks are finally getting solved to unlock the car's performance potential.

Thank you both for sharing and enlightening.

I suppose the next question involves shock damping settings. Now that we have a working range of spring rates identified, understanding the optimum damping settings (with a double adjustable coilover for rebound & compression) will be the next step in rounding out the car's handling. Finding the optimum damping settings in rebound and compression to work with the chosen spring rates in a street vs. competition environment in evaluating ride quality, corner entry, pitch, and corner exit traction are key and will take some R&D due to the number of possible combinations, but I imagine Orb already has a pretty good handle on where to start...

Here is my start point for the track, and with a smooth surfaced local track I don't vary too much at all from the start point:

REAR:
Near full stiff rebound
Near full stiff compression

FRONT:
Near full stiff rebound
Half stiff compression

With Autocross I tend to adjust a bit more, depending grip levels and surface smoothness:

I use the rebound to balance the grip of the car whether it be front or rear bias. It is nice to be able to adjust with the twist of a knob. I like to keep the rebound as high as grip limits allow for good slalom transitions, however compromise is the name of the game depending on the course that is set up for the day.

The rougher the surface the more I dial down the compression to avoid "skipping the tires" over bumps and thus loosing grip.

Nothing really new or ground breaking here. Most of my AX National Champion buddies kinda suggest same thing, they just drive a tiny, tiny bit faster though

[MINI135i]

Originally Posted by bradford

How many hours did they charge? And did you have the rear M3 bar done too while they were up there?

It was 4 or 4.5 hours.

I have the 32mm Hotchkis front bar installed already and the stock bar in the rear. No M3 bars at all. The big bar in front is an absolute must for me as an Autocrosser and to tell you the truth I have felt no ill effects on the track. Opinions will widely vary on this issue, and I respect them all, however I know what works for me.