Perfromance, real, not so real, balance in the middle?

[03whitegsr]

The motion ratio in the rear is 0.64. Square it and multiple by the spring rate to find the wheel rate. The shock mount has a motion ratio of 1.02...

950lb springs in the rear comes out to 390lb at the wheel. A 400lb coilover setup is stiffer then the 950lb spring in the stock location.

I'd put driver ability above even tire selection. I had fun 2 seasons ago with the stock 17 year old suspension beating up on cars with slicks and built suspensions in my class. And I'm not a good driver by any means...

FWIW, a stock 318ti will 2-wheel on 215 wide R-S3 tires.

[Breticus]

They run 200ish in the rear on the full setup

[raamaudio]

200 is a very light spring rate on coilovers!

I have built many cars into being far faster than one would expect, being the underdog and taking 2nd and 3rd place finishes against "superior" big bucks, more powerful, etc...cars was always far more rewarding than having the best car in class setup the best and winning all the time, something I have also done. Even then it was not money as I did not have much, it was about making things work as a balanced package. I beat up on the same cars as mine as well no matter how much money they threw at it because it was just buy stuff and put it on or have it put on, no thinking involved. I had to dig in an learn, tweak, make parts, etc.........it was rewarding to win but not as fun as being the underdog

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I just sold a different kind of project, 95 M3 I wanted to make the fastest one ever around a race track, after $80k into it, built in house, at least $20k more to go, a few more thousand hours into developing the best aero ever done on one, the hard way, best suspension ever used, etc...........I realized I was building a car well beyond my abilities to drive to the limit anyway. I just sold a few more parts off it, another $10k and it will be gone, at a bit loss as it is the way of race cars.....

The plan was to meet up with top drivers at all the tracks of my dreams and sort the car out for each track and let them go set the track record for the E36. It would not be an offical race record but would be on MyLaps, good enough for me. I would then run the car to my best abilities but I know I would be much slower, I have never driven that fast a car on course.

2300lbs target weight, best suspension, best LSD, best aero, LS1 with 500WHP, more if needed, best most everything except without a sequential box as just to much money but a 4 speed dog box can be quite fast.

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Now building the street/track ti and going back to my roots a bit. Not the fastest ever, just superbly sorted out and very competent, reliable, very very quick and easy to drive fast. I will shock many car owners I come across with it as it is not an underdog car but getting my best effort at a reasonable cost, well sorted out car....and it is a BMW

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I have two wheeled in quite a few cars, I love using the curbs at the track, when you can use them and keep the wheels on the ground it is ever faster

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This is a very fun thread but has strayed quite far from the original intent, trying to help others see what real performance is, but I am fine with it

Rick

[MINIz guy]

Originally Posted by raamaudio

200 is a very light spring rate on coilovers!

Well, I am assuming Breticus is still on about the GAZ full coilover conversion in the rear suspension. I too have been recommended 250 lb/in springs in the rear if I did the full coilover conversion.

Going by 03whitegsr's motion ratio of 0.64 to find wheel rate and 650 lb/in springs, which is what I've been recommended without going to coilovers in the rear, gives me 266 lb/in (I'm assuming these are the rights units and motion ratio should be unitless). 250 lb/in springs at the shock mount, with a motion ratio of 1.02, gives me a wheel rate of 260 lb/in. These two wheel rates are very similar and makes sense if I would want the rear of the car to react the same way with two different suspension setups.

[raamaudio]

I left it up to GC and they chose 700 for my springs, not coilovers so I will see how it works out with the dogs, groceries, wife, me, etc on the street and then empty on the track

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When I was going to do coilvers I was going to built an STB/Xbrace with welded plates to stiffen the shock mounts.

Not quite as intense on the M3 race car we were building:

[raamaudio]

First one of these I ever made, for the X door bars, I want to incorporate some dimples into the rear subframe mount braces and trailing arm braces on the ti.

[03whitegsr]

More off-topic but oh well.
FWIW, the BMW has pretty decent arm angles up front compared to a lot of other Macpherson strut cars. With my current ride height, it is ~2.25" lower than stock in the front. The LCA pivots are flat with the ground right now. For comparison, my EVO with about a 1.5" drop has the arms pointing at the ground by a pretty fair amount. While a 1" extension on the spindle would likely correct any amount of lowering I could ever hope to do on the BMW, the EVO would take a good 2" or more just to correct a moderately aggressive drop. The roll center is in reasonable shape on the BMW even with a decent drop.

As for optimizing what you got, that is what I'll be doing next year. Going to modify the OEM swaybar to make it adjustable, probably revalve my rear bilsteins (make them digressive) and spend lots of time playing with the alignment. From there, I'll decide which direction to go on my spring rates and if I'm going to convert to a coilover.

Currently, the biggest issue is the car picks up the inside rear on low speed tight corners. It wouldn't be a major concern if the OEM LSD had any real lock up, but it doesn't so it's wheel spin central. I gotta see if I can get this under control with my current spring rates and if not, I’ll be going to a coilover.

As for coilovers, I'm not sure how significant it is, but the OEM spring setup causes the spring to be bent instead of it being linear motion. This will undoubtedly make the spring rate non-linear with the OEM spring setup and a coilover would correct this issue. However, at the current ride height, the spring pads are fairly parallel so at nominal height, it's not trying to bend the spring too much. Ground control has a solution to this for the standard E36 rear suspension and was working on an E30 setup last time I talked to them. I have no idea if they have released anything though. On the trailing arm suspension setups, it will require modifying the trailing arm where on the standard E36 is just bolts in to the unmodified arms.

[MINIz guy]

So I'm probably a little off topic, but I've been trying to do some research and figure out suspension stuff.

I've found that the motion ratio for the Ti is .94F and .64R after some digging through regular E36 stuff. I've also been using this calculator to figure out springs rates: http://farnorthracing.com/autocross_secrets16.html. I'm guessing my corner weights at 700 lb for the front and 650 lb for the rear. I'm guessing my unsprung weight at 40 lbs for the stock wheels and tires. There is an old post here saying that M-tech springs at 200 lb/in front and 380 lb/in rear. I've also set the natural frequencies to 2.2Hz in front and 2.5Hz in the rear. I went slightly higher than the 10% increase over the front.

When I throw all that into the calculator, I'm getting ideal spring rates at 450 lb/in front and 650 lb/in rear. Now that does seem to go along the lines of what most suspension companies are suggesting.

Now I'm also looking towards creating custom coilovers by playing with adjustable spring perches/sleeves. For the rear, I know I can get the IE adjustable perches. In front, I will be using Bilstein Sports with a 36mm diameter strut tube. I've found these sleeves for them: http://www.summitracing.com/parts/bs...0187/overview/. Is it possible to get these to work with my struts without needing to hack the original spring perch up?

Also, does anybody know what spring rates the valving of Bilstein Sports are capable of handling? I know you can get them revalved for not much money, but I'm just curious on what they are optimized for out of the factory.

[03whitegsr]

Self-plug...
http://www.318ti.org/forum/showthread.php?t=38847

The biggest issue with the bilsteins is the length if you want to get the car low. The sports are 20.04" in length when compressed and 22.81" extended. Bilstein seems to be a little erratic on how they measure the collapsed length though, sometimes it is first contact with the bumpstop and others it is with the bumpstop fully compressed. I would guess in this case it is first contact with the bumpstop based on the small amount of travel. This means you probably have another inch of usable travel then advertised and a collapsed length of probably 18.5-19".

By comparison, the setup I built has an extended length of about 19.5" and fully compressed of 15.5". I will say, they are too short IMO and a more ideal length would probably be 16.5" fully collapsed and 21.0" fully extended.

A potentially better way here would be to modify the Bilstein strut. Depending on your abilities though, this might be cost prohibitive. Bilstein will modify struts for you, inlcuding shortening the body (internal and external) and putting in a shorter shaft. You would likely need to shorten both bodies, which is something that can be done on a manual lathe. However, without having taken apart a bilstein sport for the E36, I can't say for sure what would need to be done. You also have an issue with the fact that OEM Bilsteins don’t have a Shrader valve on them so you would either need to have them rebuilt by a shop that can rebuild the OEM stuff, or you need to convert them into take aparts. Converting a strut however is a little more involved.

Also, you'll have to remove the OEM spring perch either way as it's going to sit right where you would want to put the perch for an 8" spring. You could possibly use a 6" spring and make it work, but I wouldn't count on it.

Second option is to look at the shortened Konis...
I'm a Bilstein fan, but Koni makes good stuff too.

[03whitegsr]

Hum, actually...
Z4 M struts are looking pretty good for a moderately lowered car.

http://www.ajusa.com/Bilstein-35-141...ly-ab06b2.html

The Z4 M PSS10 kit looks potentially usable too.
http://www.motorsport-tools.com/bils...48-141635.html

For $2200, it's pretty reasonable considering the quality of shocks/struts you would be getting.
http://www.ajusa.com/Bilstein-48-141...em-ab071c.html

[MINIz guy]

There is a post on bf.c of somebody using Z4 struts on their E36 M3. I do recall it being slightly shorter than the E36 and probably the length you're describing.

I am a bit disappointed that I can't cut the adjuster super short and place it on the space between the stock perch and the top of the strut. Oh well, guess I was expecting too much. And about the adjustable valving, I planned to just take care of that by getting the shocks revalved by Bilstein once I know a range of spring rates I plan to use.

Sent from my SAMSUNG-SGH-I537 using Tapatalk

[JFMBMW318i]

My 318i has the stock suspension and my 328i has been lowered 2" front and 1.75" in the rear. The shocks are new front and back, a no name brand I don't
even remember. They aren't performance shocks but slightly thicker than stock.
I like the lowered look and how it handles. It is a little harsh over bumps.

The 318i is the stock height. The ride has a little more "float" to it but def more
comfortable over the bumps. I am looking for a good cheap set up. Maybe something similar to what I have on the 328i. They both are daily drivers and
will never see the track unless someone drives one of them to the track to see my ride my GSXR (crotch rocket) lol.

Any suggestions on a good CHEAP set up for the 318i?

Thanks

[raamaudio]

Find a good used set of Bilstiens and some lowering springs, it will make a big improvement. My ti came with some and Bilstiens springs and though one rear shock was blown it rode quite fine and handled great even on crap tires......

I have those listed for pretty low, can help on that a bit more, then find one more used shock......

Others have sold some good used parts as well, best to get good parts used instead of general stuff new......far better as long as the used parts are still good.

Rick

[MINIz guy]

Ok, I'm still reading about suspension setup and have a few more questions.

In regards to the rear suspension setup, what is the cheapest adjustable spring perch available for our cars? Are there generic perches available that we can use? I am trying to search it up on eBay or even some speed shops like Speedwaymotors but cannot find the right kind that is similar to IE or TCKline ones.

Now, I keep on reading that the rear needs a 5" spring and that a 6" spring is too long. Now what happens at full droop with a 5" spring? Does it loosen up, and would a helper spring be needed to assure that the spring doesn't come out of its perches? Eibach does make some nice springs with an integrated helper spring to help out what I'm worried about.

For the front suspension, I'm still seeing many people use generic sleeves mounted over where the original perch was cut off. They didn't weld on a new flat perch but used what was left of the original perch. Is this safe practice?

[03whitegsr]

Link to the integrated helper springs? I'm not an Eibach fan at all, but that feature would almost make me reconsider. The droop travel is something I am trying to address now on my car as yeah, with a high spring rate, you have very little travel in the rear before the spring goes loose. I have added internal spacers on my shocks to limit droop travel but you could also do it with more typical steel cable travel limiters.

I've been playing with the idea of basically gluing a helper spring to a 4" spring to get the added travel. 3M makes some pretty serious adhesives for metal so it may or may not work. I came across a post from one of the guys from GC and he mentioned that the original BMW race springs were two springs welded together to pull off this same feat. You'd have to re-heat treat the springs though IMO for this to work out.

Welded Eibach Spring

Another option I have considered is possibly trying out some of the J-stock rear springs as they are basically a 900 pound spring with a built in helper. I'm not sure it will get the car down to the ride height I want though.

Depending on the rate and desired ride height, you may need a 5" spring. Here is my car with the Ireland Engineering E30 spring perch, urethane isolator, and 950 lb/in springs on a car that is ~300 pounds lighter then stock. The adjuster is all the way down and is basically just a spacer at this point.


The urethane pad is about 3/8" thick and the adjuster is about 1/2" thick so they add ~7/8" to the spring height. If you dropped to the ~700 pound spring most people use and the car is full weight, a 6" spring with 1/8" isolators top and bottom would put you about the same height as my car is. A 600 pound spring and 1/4" isolators would be about the same too.