AST suspension install...with rear subframe bushings

[Justin(OKC)]

I had two passenger side camber plates. That's the reason I couldn't mount the front on Saturday.

[MINI135i]

I have a question for you: Would the most rearward two (2) subframe bushings be a pretty easy install if one were using the the BMW bushing tool compared to installing all four (4) rear subframe bushings?

The reason I ask is I have heard the most forward two rear subframe bushings are the hardest and require detaching the hard brake lines whereas the rear two bushings just require lowering the subframe in the rear and putting in the bushings. So the thought is, having just the two most rearward bushings installed could provide some needed stiffness without all the hassle of doing all four rear bushings(?).

Great set up BTW, should be fun to tweak to your liking!

[Justin(OKC)]

Originally Posted by MINI135i

I have a question for you: Would the most rearward two (2) subframe bushings be a pretty easy install if one were using the the BMW bushing tool compared to installing all four (4) rear subframe bushings?

The reason I ask is I have heard the most forward two rear subframe bushings are the hardest and require detaching the hard brake lines whereas the rear two bushings just require lowering the subframe in the rear and putting in the bushings. So the thought is, having just the two most rearward bushings installed could provide some needed stiffness without all the hassle of doing all four rear bushings(?).

Great set up BTW, should be fun to tweak to your liking!

I'm not totally sure. It seems like if you've got the bushing tool to use, then bleeding the brakes is a minor issue. If you will wedge something between your seat and brake pedal to depress the pedal about 1/2" or so, your brake fluid will not leak everywhere while you are doing the install. It's a lot of work to just do two of the bushings IMHO.

[Justin(OKC)]

Update: Put the front together this evening....good and bad news again, LOL. Good news is that they are on, bad news is that the drivers side swaybar mounting bracket was backwards so we will have to take it apart and fix it. More bad news....my Forgelines hit the swaybar mounting brackets!!! I need to look into the pro/cons of using a shorter endlink to drop the mounting bracket into the barrel section of the wheel or I need about a 2mm wheel spacer.

I've lowered the car to 12.75" from the fender lips to the hub centers. The car needs an alignment; however, I took it for a bit of a drive. This thing is downright comfortable to drive. It's not too stiff, not too soft....should be better without the runflats. I'm going to try to autoX it on Sunday and start tweaking things a bit.

[arrutled]

More Pictures!

[vitig]

Thanks.you have a full mod suspension.

Do you take the e90 m3 rear swaybar or e93?.

[Justin(OKC)]

Originally Posted by vitig

Thanks.you have a full mod suspension.

Do you take the e90 m3 rear swaybar or e93?.

It's the E90 M3 bar. Since I don't have an LSD (yet) I didn't want a rear bar that was too stiff. I've compensated with heavier springs.

I am soon going to have some shorter endlinks for the anti-roll bar on the front. I removed part of the finish on the inside lip of one of my front wheels checking the fitment again Luckily it can't be seen on the car.

I'm getting it aligned tomorrow and can write a bit of a review, but with it on the runflats, it won't be as good. I'd like to figure out how to run a helper spring on the front but I don't think I can lower the spring perch too much lower without hitting the tire. Evidently I can get a helper spring that is only 10mm tall when completely compressed. This means I only need to lower the perch 12-13mm to be able to run it. I'll know more when I am actually able to mount my forgelines and make sure I have clearance from the strut, spring perch, and fender. This reminds me of the trials I went through when doing coilovers on my old Datsun 510 in 1995!! It will be worth it in the end....

[brracing]

Justin...remember that if you change and add the helper spring, your spring rates will change, as you will need to change the size of the main spring...the overall length of the compressed helper or tender springs (usually start at about 3", and when compressed end up at about 1 1/4"), but that means you have to reduce the main spring length, which means the total spring rate will need to be different ....but you're also thinking about changing the spring rate in the front any way....you're too soft right now
We did a setup this way for a customer who has 20" wheels, and it took some finesse to make this work, but is not what I would do for auto-x or track use.

[HP Autosport]

Originally Posted by brracing

Justin...remember that if you change and add the helper spring, your spring rates will change, as you will need to change the size of the main spring...the overall length of the compressed helper or tender springs (usually start at about 3", and when compressed end up at about 1 1/4"), but that means you have to reduce the main spring length, which means the total spring rate will need to be different ....but you're also thinking about changing the spring rate in the front any way....you're too soft right now
We did a setup this way for a customer who has 20" wheels, and it took some finesse to make this work, but is not what I would do for auto-x or track use.

Helper spring will not affect the over spring rate. On the other hand, assist spring will. It just so happen that the helper springs we use have a static height of just over 2 1/4", with a compressed height of about 1", so the main spring static height wouldn't have to be changed too much.

400 lb is not soft at all, should be just right for a street/HPDE set-up. Anything higher will take away mechanical grip and the ride will suffer.

[brracing]

HPAutowerks...to ensure that the suspension stays within the suspension travel with a shorter spring length on the main spring, you will need to change the spring rate...we have tried multiple helper spring setups on the spring and shock dyno, and customer cars w AST.
We would differ in the view that the spring rate of 400# front and 800# rear doesn't make the front too soft...we have run 450#, 550#, 600#, 650# on the front, and are now running just slightly softer than the 800# in the rear for our front, and to get the balance and ensure the understeer stays away both from initial turn-in and mid-turn, we have found that the balance is best w the higher ratio if the rear is 800# (which was the given by Justin) (fyi, we have 3 different 135i's with AST 5300, AST 5100, AST 4100 currently)...but this is what our current testing has shown for balance

[HP Autosport]

Originally Posted by brracing

HPAutowerks...to ensure that the suspension stays within the suspension travel with a shorter spring length on the main spring, you will need to change the spring rate...we have tried multiple helper spring setups on the spring and shock dyno, and customer cars w AST.
We would differ in the view that the spring rate of 400# front and 800# rear doesn't make the front too soft...we have run 450#, 550#, 600#, 650# on the front, and are now running just slightly softer than the 800# in the rear for our front, and to get the balance and ensure the understeer stays away both from initial turn-in and mid-turn, we have found that the balance is best w the higher ratio if the rear is 800# (which was the given by Justin) (fyi, we have 3 different 135i's with AST 5300, AST 5100, AST 4100 currently)...but this is what our current testing has shown for balance

Steet/HPDE set-up is what I mentioned, nothing track duty. I am sure Justin's car is not a track duty only car, but more of a daily driver. Anything higher than 400 lb/in F the ride will suffer and you will lose some pitch control.

[Justin(OKC)]

Originally Posted by brracing

HPAutowerks...to ensure that the suspension stays within the suspension travel with a shorter spring length on the main spring, you will need to change the spring rate...we have tried multiple helper spring setups on the spring and shock dyno, and customer cars w AST.
We would differ in the view that the spring rate of 400# front and 800# rear doesn't make the front too soft...we have run 450#, 550#, 600#, 650# on the front, and are now running just slightly softer than the 800# in the rear for our front, and to get the balance and ensure the understeer stays away both from initial turn-in and mid-turn, we have found that the balance is best w the higher ratio if the rear is 800# (which was the given by Justin) (fyi, we have 3 different 135i's with AST 5300, AST 5100, AST 4100 currently)...but this is what our current testing has shown for balance

Ok, just for clarification....what front/rear springs are you running? From what you wrote it sounds like you are running "slightly less than 800# up front" and 800# rear? Part of the reason I went with an 800# rear spring was because I selected a rear anti-roll bar that was softer than what you are running. I do believe I am probably running a softer spring up front than I should, but I'm not sure how much. I'm loving the discussion on the spring rates and appreciate the input.

[Orb]

You seem a little cloudy on how to calculate springs in series. A real helper spring (rated 20 lb/in or the like) will not effect the overall spring rate as it goes solid well before static ride height. It will however, take away a few mm of available travel from the main springs.

The sad thing here is you’re making assumptions based on? You tested but with what purpose or understanding. I’m making a few assumptions about you because your technical remarks make no sense at all.

FWIW, there been a lot of technical data posted in this forum including a load transfer worksheet so using this may help you understand what is going on and why. You need to start with the springs in series, suspension frequency, sway bar spring rate, and motion ratios. You also want to hit about 2.0 to 2.2 Hz for R compound tires to work effectively. Going over a spring rate of 500 lb/in in the front is futile as your suspension frequency is getting to high in the front so you going to lose a lot of grip.

You really can’t make a recommendation of spring selection just on the roll bars you use which are UUC. Good luck getting the car to work well with them…you will never get it even close to what it could be but you can try. The numbers don’t work nor do they perform well in practice. I can see you’re going in one direction to fix one problem only to make several more which is the nature of the beast when it comes to suspension tuning.

The setup Harold speaks of is based on e9x M3 roll bars. The spring rates are specific to this car setup. It something myself and Harold worked on for a better part of 8 months. The car vehicle dynamics was analyzed (by me) in detail and then validated in testing.

The number one thing the one series need improvement on is front track width without have a negative effect on scrub radius. The m3 wishbone does this so you change offset up to 5-10 mm.

Orb

Originally Posted by brracing

HPAutowerks...to ensure that the suspension stays within the suspension travel with a shorter spring length on the main spring, you will need to change the spring rate...we have tried multiple helper spring setups on the spring and shock dyno, and customer cars w AST.
We would differ in the view that the spring rate of 400# front and 800# rear doesn't make the front too soft...we have run 450#, 550#, 600#, 650# on the front, and are now running just slightly softer than the 800# in the rear for our front, and to get the balance and ensure the understeer stays away both from initial turn-in and mid-turn, we have found that the balance is best w the higher ratio if the rear is 800# (which was the given by Justin) (fyi, we have 3 different 135i's with AST 5300, AST 5100, AST 4100 currently)...but this is what our current testing has shown for balance

[emos325]

"The number one thing the one series need improvement on is front track width without have a negative effect on scrub radius. The m3 wishbone does this so you change offset up to 5-10 mm." can you explain this in a little more detail. Are you saying that we should just swap wish bones with the e9x s?

[brracing]

Love the discussion...
And, from our view, there is no ONE right answer here...there is no perfect suspension setup, as there are too many factors for each setup and consideration...but, we're all trying to provide input into what results we all believe work best. But, as we found in all of our racing, we often had different suspension setups from many others, but, in wining more races than all other teams, we have leaned in the direction that our suspension setups have led us (and these were w BMW race cars, not some other model like we're playing with now as well)...but the discussion here I think is helping many see the varied elements that go into a complete suspension consideration, it's not just buying a given set of springs and shocks/struts, and thinking you have THE setup..and we're not even talking about the valving in the shocks yet.....and with the 5200, Justin has the option to literally get limitless options of shock settings...such fun.

(1) trying to keep it simple for the mass majority of the audience in the discussion. The reference to the spring rate discussion in the front was based on simple math....if the original spring height that Justin is running is the 8" front spring, and it is 400#, and he wants to keep the existing ride height setting, and he wants to keep the existing spring perch location as much as possible (big assumption that has not been validated) but wants to add a helper spring, and the new helper spring is a 2 1/4" tender (uncompressed) and 1" compressed (your versions). Then, If we assume that his current corner weighting is close to 800#, then w the 400# front springs, he would be getting 2" of compression at static load, and only have a little more than 2" of suspension travel left (8" spring uncompressed, complete compression when at coil bind would be near 4"....could be slightly under 4" if using Swift springs).
Now, adding the helper spring, which will be fully compressed at static load, then was making the assumption that a different length (shorter) main spring was going to be substituted (cause, we have seen interference if you try to run the 8" main spring and the helper spring, the lowering of the spring perch to allow the combination now interferes w the tire/wheel location)...so, a shorter spring would be needed to keep the spring perch in near the original location...but, we the added helper spring, so w the load to be applied, we would not want to go into spring bind, so, therefore, we need a different spring rate in the new main spring that is being substituted (we would then be using a 7" main spring, and if the static load is 800#, then we can only allow the new spring to compress 3" w the load of 800#, therefore, the spring rate has to be different than the 400# rate that was originally used. And, because the total spring length on the main spring is shorter, we could be getting to where the shock will bottom out causing shock damage. (Justin does have the M3 front control arms, and the primary issue w understeer on the front to us is not the track width, but the tire contact patch being less than the rear, as we don't believe Justin is running a symmetrical tire setup)
The BIG assumption was all about the need to keep the spring perch in the current location for ride height and to remain out of interference of the wheel/tire location.
(2) Our 135i w the AST 5300 is running 650# fronts, 700# rears currently, and rides just fine on the street. But, it is not optimum now for the track even w the variety of shock settings that we have played with, we need to be firmer.

[Justin(OKC)]

I know both of you (Orb and brracing) are going head to head a bit, and ultimately some really good technical information is coming out that is very helpful to me. Orb has recommended that I change the offset of my wheels a bit to help solve my problem with hitting the adjustable swaybar mount on the AST's. This in turn would allow me to lower the spring perch a bit more and there would be no problem running a helper spring. (brracing, I have the part number from Orb for a swift helper spring that fully compressed is only 10mm tall.) The big question is with that offset, will it clear the fender? Luckily for me I have some 10mm spacers on the back of my E36 M3. I'm going to pull one off and test it tomorrow night. I know spacers are not ideal, but I'm not going to scrap a $5k set of wheels.

A little update...I autoX'd the car today on what is essentially a "mini" road course with some cones laid down to slow us down some. I haven't really driven in these events for about 4 years and that was in my M3 that I am very familiar with. The turn-in on this car is incredible. I did have some understeer, but honestly, most of that was driver induced. I need to work on the driver, but this supension setup provided a ton of confidence. I really only had driven the car a few miles on the highway after the alignment so I need to get used to how it feels. All in all, my first run was a 2.09 and my best was a 1.47 (5 runs total). I am most impressed with this setup and I really need to thank Harold and Orb for their advice. Although there may be some disagreement on the spring rates and such (I was skeptical about the 400# springs up front, too) it seems to work really well today. One of my friends who is a club racer and instructor rode in the car and seemed fairly impressed with the car (maybe not so much the driver). He commented that the car had some compliance and maybe didn't stay quite as flat as some cars, but he said the mechanical grip was much better. I was running on the stock runflats that were about worn out.

[brracing]

Justin...congrats on the good results. Again, I don't believe there is ONE magical right suspension setup...and while we may have some contrarian views....hopefully it helps you and others understand the bits and pieces that go into a suspension discussion and setup.
The testing we have done has ALL been done on road courses/tracks vs your current outing on a autox course....relatively fast ones (Thunderhill, Laguna, Infineon), and we keep changing some of our other parameters (adding more HP, top end speed, and the latest BBK which really allowed us to change our braking points which has affected the balance and the weight transfer right at initial turn-in (imagine if we are doing relatively light braking w the OEM setup to preserve the crummy brakes, vs now being able to put the car on its nose under very hard, but very short braking and some trail braking (depending on the corner))).
Normally, we find that autox courses induce more understeer traits or bring out understeer, as the turn in is more abrupt..so, if you are feeling good, then that is great.
We want a near nuetral setup for the three points in the turn that we measure (initial turn it, mid turn, and turn exit), as the combination of the type of turns at each track determine what we are trying to optimize for the best lap times.
Again...the proof is in the customer..and if you're feeling good about it...Woo Hoo.

We'll keep trying different setups to see what the effect is on different tracks and conditions, and happy to share what we have observed and measured.

[Justin(OKC)]

The curiosity was killing me. I popped the 10mm spacers off my M3 to test fit my forglines. Result, it works but it rubs a bit. I think the ideal offset may be about 40mm on the front for my setup. I could probably be perfect with a 5mm spacer. The thing is, I'm rubbing more in the rear than I am in the front. In the spirit of full disclosure, here are my alignment settings:

Front:
-2.1 camber
7.5 caster
-0.6 toe (out)

Rear:
-1.9 camber
0.17 toe (in)

The car drives straight as an arrow and does not dart around at all. Stable as can be. As expected the ride is even better with the 19" non-runflat tires.

[Justin(OKC)]

Here's the pics...

[Orb]

Originally Posted by brracing

Love the discussion...
And, from our view, there is no ONE right answer here...there is no perfect suspension setup, as there are too many factors for each setup and consideration...but, we're all trying to provide input into what results we all believe work best. But, as we found in all of our racing, we often had different suspension setups from many others, but, in wining more races than all other teams, we have leaned in the direction that our suspension setups have led us (and these were w BMW race cars, not some other model like we're playing with now as well)...but the discussion here I think is helping many see the varied elements that go into a complete suspension consideration, it's not just buying a given set of springs and shocks/struts, and thinking you have THE setup..and we're not even talking about the valving in the shocks yet.....and with the 5200, Justin has the option to literally get limitless options of shock settings...such fun.

(1) trying to keep it simple for the mass majority of the audience in the discussion. The reference to the spring rate discussion in the front was based on simple math....if the original spring height that Justin is running is the 8" front spring, and it is 400#, and he wants to keep the existing ride height setting, and he wants to keep the existing spring perch location as much as possible (big assumption that has not been validated) but wants to add a helper spring, and the new helper spring is a 2 1/4" tender (uncompressed) and 1" compressed (your versions). Then, If we assume that his current corner weighting is close to 800#, then w the 400# front springs, he would be getting 2" of compression at static load, and only have a little more than 2" of suspension travel left (8" spring uncompressed, complete compression when at coil bind would be near 4"....could be slightly under 4" if using Swift springs).
Now, adding the helper spring, which will be fully compressed at static load, then was making the assumption that a different length (shorter) main spring was going to be substituted (cause, we have seen interference if you try to run the 8" main spring and the helper spring, the lowering of the spring perch to allow the combination now interferes w the tire/wheel location)...so, a shorter spring would be needed to keep the spring perch in near the original location...but, we the added helper spring, so w the load to be applied, we would not want to go into spring bind, so, therefore, we need a different spring rate in the new main spring that is being substituted (we would then be using a 7" main spring, and if the static load is 800#, then we can only allow the new spring to compress 3" w the load of 800#, therefore, the spring rate has to be different than the 400# rate that was originally used. And, because the total spring length on the main spring is shorter, we could be getting to where the shock will bottom out causing shock damage. (Justin does have the M3 front control arms, and the primary issue w understeer on the front to us is not the track width, but the tire contact patch being less than the rear, as we don't believe Justin is running a symmetrical tire setup)
The BIG assumption was all about the need to keep the spring perch in the current location for ride height and to remain out of interference of the wheel/tire location.
(2) Our 135i w the AST 5300 is running 650# fronts, 700# rears currently, and rides just fine on the street. But, it is not optimum now for the track even w the variety of shock settings that we have played with, we need to be firmer.

Okay, I see now that you did no simple math what so ever. It is not a big deal but what you said is…well…nonsense. Pick the springs and I will do the calculation for you so you can see how it works. BTW, all your data is wrong.

Your wheel rates are as follows:

Front 650 lb/in x 0.96^2 = 599 lb/in
Rear 700 lb/in x .563^2 = 221 lb/in

If you assume your front un-sprung weight is 100 lbs and the rear is 135 lbs you can now find the frequency with use of the OEM manual info. At the very least you should understand why it’s an improvement but what are the trades offs as well.

Please do your homework on load transfer and track width. It not so great you don’t get it.

Orb

[arrutled]

Orb,

What frequencies would you recommend for the 135 on street tires? around 1.5Hz?

[ORIGIN M.]

Nice!