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      05-24-2018, 03:12 PM   #23
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Quote:
Originally Posted by ShocknAwe View Post
Only question is how to remove bind from the 128i front bar bushings.
You are on coilovers? Bump stop engagement becomes a huge limiting factor in going SOFTER, unfortunately.

Personally, I just bored out the stock bushings a bit. You can also add a small spacer (washers) the brackets to reduce the clamping effect. Or, get aftermarket bushings for the stock bar...

Reducing rake is generally not going to increase front-end grip but rather have the opposite affect. If you think the stock bar is too soft you might want to try raising the front end a bit at the same time to reduce the moment arm affect.

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      05-24-2018, 04:25 PM   #24
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Quote:
Originally Posted by bNks334 View Post
You are on coilovers? Bump stop engagement becomes a huge limiting factor in going SOFTER, unfortunately.

Personally, I just bored out the stock bushings a bit. You can also add a small spacer (washers) the brackets to reduce the clamping effect. Or, get aftermarket bushings for the stock bar...

Reducing rake is generally not going to increase front-end grip but rather have the opposite affect. If you think the stock bar is too soft you might want to try raising the front end a bit at the same time to reduce the moment arm affect.
Do I have rake backwards? I am planning to raise the front end by 1/4" to 1/2". Or is that what youre saying is opposite of what I want to do.

Yes I'm on coilovers. TCK SA front with 7" 7k swift, Bilstein monotube rear with 10" 12k swift.

I thought the stock bar was too soft with stock springs. With the coils the H&R bar was way overkill and with absolutely no bar it's just a touch too much oversteer oriented. Think it still needs some bar, but stock bar (26.5) may still be too much.
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      05-24-2018, 08:33 PM   #25
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Originally Posted by ShocknAwe View Post
Do I have rake backwards? I am planning to raise the front end by 1/4" to 1/2". Or is that what youre saying is opposite of what I want to do.

Yes I'm on coilovers. TCK SA front with 7" 7k swift, Bilstein monotube rear with 10" 12k swift.

I thought the stock bar was too soft with stock springs. With the coils the H&R bar was way overkill and with absolutely no bar it's just a touch too much oversteer oriented. Think it still needs some bar, but stock bar (26.5) may still be too much.
Based on the way I undertsand, if you put the stock bar back in and it feels too stiff you would want to lower the front end a bit to increase roll and front end grip (please correct me if I am wrong).

I measure rake from the side skirts right next to the jack points. Without knowing your front and rear ground clearance and other settings like static camber it's hard to make a suggestion. Raise the rear? Lower the front? Increase front spacers? Reduce sway bar bind and reassess?

Before you do anything I would check to see if youre bottoming out your rear struts and causing a spike in rear wheel rate. You may find that you're getting into the bumps stops like both myself and Felix found. Read through the 10 page ohlins thread I linked to and you'll see that he actually moved to a 14k spring and a bigger rear bar to alleviate the bump stop enaggement. You are running longer 10" springs though so I am guessing you have a lot of spring preload in the rear and the issue may not be as bad.

No one likes to believe in the 1:3 ratio but lower the rear of the car onto the ground and watch how you lose 3" of suspension travel when you use 700lb springs and that is just from the weight of the car lol When you have afternarket coilovers with only 4.25" of usable travel that becomes a big deal...

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      05-25-2018, 08:05 AM   #26
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Quote:
Originally Posted by bbnks2 View Post
Based on the way I undertsand, if you put the stock bar back in and it feels too stiff you would want to lower the front end a bit to increase roll and front end grip (please correct me if I am wrong).

I measure rake from the side skirts right next to the jack points. Without knowing your front and rear ground clearance and other settings like static camber it's hard to make a suggestion. Raise the rear? Lower the front? Increase front spacers? Reduce sway bar bind and reassess?

Before you do anything I would check to see if youre bottoming out your rear struts and causing a spike in rear wheel rate. You may find that you're getting into the bumps stops like both myself and Felix found. Read through the 10 page ohlins thread I linked to and you'll see that he actually moved to a 14k spring and a bigger rear bar to alleviate the bump stop enaggement. You are running longer 10" springs though so I am guessing you have a lot of spring preload in the rear and the issue may not be as bad.

No one likes to believe in the 1:3 ratio but lower the rear of the car onto the ground and watch how you lose 3" of suspension travel when you use 700lb springs and that is just from the weight of the car lol When you have afternarket coilovers with only 4.25" of usable travel that becomes a big deal...
Learning a lot. Thanks. I will remeasure height and rake this weekend.

As for preload, I have the front and rear set to where the springs are barely free at full droop. So from my understanding, there shouldn't be any preload. If I raise it a bit, yeah.

When you say 1:3 ratio are you referring to spring rate or rake?
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      05-25-2018, 09:32 AM   #27
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Quote:
Originally Posted by ShocknAwe View Post
Learning a lot. Thanks. I will remeasure height and rake this weekend.

As for preload, I have the front and rear set to where the springs are barely free at full droop. So from my understanding, there shouldn't be any preload. If I raise it a bit, yeah.

When you say 1:3 ratio are you referring to spring rate or rake?
Spring rate due to motion ratio (divorced and inboard mounted spring).

If you have a 10" rear spring at 700lbs, and it has no preload on it, you might have a pretty long shock adjustment range in the rear. Without preload I would guess that you're practically sitting on the bump stop at static ride height (~1") and your ride height is fairly low like 4-4.25"?

Crawl under there and take a look. Zip tie the strut to see how far it gets pushed into the bump stop. Maybe I am wrong but I am curious to see your results and measurements. Definitely something to rule out before you go playing with anything else.

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      05-30-2018, 03:28 PM   #28
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Quote:
Originally Posted by bNks334 View Post
Spring rate due to motion ratio (divorced and inboard mounted spring).

If you have a 10" rear spring at 700lbs, and it has no preload on it, you might have a pretty long shock adjustment range in the rear. Without preload I would guess that you're practically sitting on the bump stop at static ride height (~1") and your ride height is fairly low like 4-4.25"?

Crawl under there and take a look. Zip tie the strut to see how far it gets pushed into the bump stop. Maybe I am wrong but I am curious to see your results and measurements. Definitely something to rule out before you go playing with anything else.
Ride height isn't too low, I still have almost an inch of dead cat. Think it was ~23" to the fender panel, I'll measure the rocker panel to compare to your number.

Happy to measure the strut, but confused at what you're looking for. Shock travel without spring installed? Or suspension travel all bolted up by jacking the at the arm? Help me out here.
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      06-02-2018, 08:01 PM   #29
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Quote:
Originally Posted by ShocknAwe View Post
Ride height isn't too low, I still have almost an inch of dead cat. Think it was ~23" to the fender panel, I'll measure the rocker panel to compare to your number.

Happy to measure the strut, but confused at what you're looking for. Shock travel without spring installed? Or suspension travel all bolted up by jacking the at the arm? Help me out here.
Measure ground clearance. Wheel size will change the fender measurement and I'm on 17s.

Measure the available strut travel with the car on the ground. Then jack the car up and measure total strut travel at full droop...

I might move to a 7k/20k spring setup. 16k still seems too soft and I don't want to have to raise my ride height through spring preload just to gain a bit more bump travel.

Here is what I mean by measure the rear strut travel:

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      06-03-2018, 08:59 AM   #30
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Quote:
Originally Posted by bbnks2 View Post
Measure ground clearance. Wheel size will change the fender measurement and I'm on 17s.

Measure the available strut travel with the car on the ground. Then jack the car up and measure total strut travel at full droop...

I might move to a 7k/20k spring setup. 16k still seems too soft and I don't want to have to raise my ride height through spring preload just to gain a bit more bump travel.

Here is what I mean by measure the rear strut travel:
Perfect.

On another note, what's leading you to feel you need such a high spring rate in the rear?
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      06-03-2018, 05:37 PM   #31
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Quote:
Originally Posted by ShocknAwe View Post
Perfect.

On another note, what's leading you to feel you need such a high spring rate in the rear?
Lol I thought we were past this... 6k in front = 300 lb/in and 16k at the rear = 300lb/in. A 20k rear spring is not high... It's basically the same as a 6.5-7k spring up front. Why do I want to go stiffer? Because of the previous post about bump travel...

Look at the above picture... I put my car on the ground and I lose 2.33" of my 3.25" of suspension travel (700lb sprung weight / 300lb effective spring rate = 2.33"). As soon as I turn into a corner the car is riding on the rear bump stops. Why is that bad? Because of the exponential increase in rear stiffness when the bump stop is engaged, as covered earlier. By moving to a 20k spring I'll be able to gain a bit more bump travel (700lb/350=2). The 20k spring will support the weight of the car better.

Not all coilovers have the same travel so I asked if you could measure yours to compare. I am guessing that riding on the rear bump stops is misleading a lot of people to think their rear setup is too stiff when in actuality it's too soft and they are just riding on the bump stop.
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      06-03-2018, 06:13 PM   #32
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Quote:
Originally Posted by bbnks2 View Post
Lol I thought we were past this... 6k in front = 300 lb/in and 16k at the rear = 300lb/in. A 20k rear spring is not high... It's basically the same as a 6.5-7k spring up front. Why do I want to go stiffer? Because of the previous post about bump travel...

Look at the above picture... I put my car on the ground and I lose 2.33" of my 3.25" of suspension travel (700lb sprung weight / 300lb effective spring rate = 2.33"). As soon as I turn into a corner the car is riding on the rear bump stops. Why is that bad? Because of the exponential increase in rear stiffness when the bump stop is engaged, as covered earlier. By moving to a 20k spring I'll be able to gain a bit more bump travel (700lb/350=2). The 20k spring will support the weight of the car better.

Not all coilovers have the same travel so I asked if you could measure yours to compare. I am guessing that riding on the rear bump stops is misleading a lot of people to think their rear setup is too stiff when in actuality it's too soft and they are just riding on the bump stop.
Thanks for the explanation. So we're looking at rate over bump travel. Not sure how I missed that before, but finally on the same page. Or at least reading the same book haha.
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      06-04-2018, 09:00 AM   #33
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Originally Posted by ShocknAwe View Post
Thanks for the explanation. So we're looking at rate over bump travel. Not sure how I missed that before, but finally on the same page. Or at least reading the same book haha.
I was doing some more research and came across another post by fe1rx... This guy already measured all of this stuff! These posts need to be stickied!

Here is his assessment of the rear OE suspension and his aftermarket Ohlins suspension. https://www.1addicts.com/forums/show....php?t=1075240

You can see in his posts how the stock suspension rides on the bump stop which is exactly what I am trying to combat now myself with aftermarket suspension. This is intentional design on a street car for softening harsh bumps, but it creates a handling imbalance when stop engagement is not tuned properly from front to rear. You can see that even with 14k rear springs fe1rx only has 1" of travel before getting into the Ohlins bump stop which is the same thing as only having 1.3" of bump travel up front... (***** this is fairly blanced on an Ohlins setup but not my YCW). The linear spring rate then gets progressively stiffer as the bump stop compresses. You want bump stop engagement to happen at both ends of the car AT THE SAME TIME or the handling will shift as the suspension transitions from leaning on the springs to leaning on the bump stops.

Also, It makes sense the YCW rear struts I use would have less stroke (only 3.25") than the front since the rear struts only have move 80% as much as the front to achieve the same movement at the wheel (rear strut motion ratio is .7x? and front is .9x?). It's just a matter of getting the right bump travel distribution F:R to ensure the car stays neutral in roll. I have roughly 50/50 bump/droop distribution in front and I need the same in the rear to match. I plan to adjust the shock body shorter to achieve this. Right now in the rear I have 40% bump and 60% droop so the rear is going to get into the bump stop a bit earlier than the front causing brief over-steer characteristics as the car takes a set. I need 3/8" more rear bump travel!

*****Looking back, I was surprised to see how little the stock bump stops contribute to the effective wheel rates. It's clear that the much stiffer YCW bump stops would have a much more significant impact on effective wheel rates than the soft stock bump stops that don't contribute much until they are compressed by over 1". Also, looking at the testing felix did of the Ohlins suspension, their stroke is significantly reduced by an internal damper that begins being engaged at as little as 3" of compression up front. This may induce under-steer in many Ohlins specific setups depending on spring rates.

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      06-04-2018, 06:51 PM   #34
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Quote:
Originally Posted by bbnks2 View Post
I was
OK, so put the car up and checked. Hard for me to look at it accurately without taking the dust boot off, BUT, pinching through the boot I have conservatively 3.25 at full droop, and somewhere right around 0.75 at ride height.

//Edit: Front droop is ~ 3.3" and best I could figure about 1.25" compressed. Really tight in there at ride height so that's really more of a guess.

What I did note is that the bump stops themselves are HUGE! Between the long damper and the tall bump stops, I'm not confident that I'm not spending half my time driving just bouncing off the stops.

Ride height from floor to bottom of rocker panels is 6" front and 6.75" rear.

So, in terms of rectifying this, as I understand it: I have two things that need to be done.
1: I need to get these band-aid bilsteins off the car and a replacement set of proper rear dampers. Then once I do that, measure available droop again, and compare to the front.
2: Obtain an appropriate length and rate spring to actually support the weight of the car and preserve travel. Then I can start looking at fine tuning.
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      06-04-2018, 07:30 PM   #35
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Quote:
Originally Posted by ShocknAwe View Post
OK, so put the car up and checked. Hard for me to look at it accurately without taking the dust boot off, BUT, pinching through the boot I have conservatively 3.25 at full droop, and somewhere right around 0.75 at ride height.

//Edit: Front droop is ~ 3.3" and best I could figure about 1.25" compressed. Really tight in there at ride height so that's really more of a guess.

What I did note is that the bump stops themselves are HUGE! Between the long damper and the tall bump stops, I'm not confident that I'm not spending half my time driving just bouncing off the stops.

Ride height from floor to bottom of rocker panels is 6" front and 6.75" rear.

So, in terms of rectifying this, as I understand it: I have two things that need to be done.
1: I need to get these band-aid bilsteins off the car and a replacement set of proper rear dampers. Then once I do that, measure available droop again, and compare to the front.
2: Obtain an appropriate length and rate spring to actually support the weight of the car and preserve travel. Then I can start looking at fine tuning.
What coilovers? Stock suspension is designed to sit on the bump stops. Every coilover is different. I say all this just so you're aware of your particular coilovers design which based on your statement expects lots of bump stop engagement. They are basically used as supplemental springs.

I am just pointing out that problems arise when you choose springs that engage the bump stops at different times. If you have .75" of bump travel in the rear, you would need the front to have roughly 1" of bump travel for the front bump stop to come into play at the same time as the rear in roll. There is nothing wrong with getting into these large bump stops since they are so soft. You just need to make sure youe effective wheel rates are balanced so the bump stop engagement happens on both ends of the car at the same time. I'd need to have every detail to help you further than pointing you to this potential concern.

6/6.75 would be right around stock. You measured to the bottom of the side skirt?

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      06-04-2018, 07:55 PM   #36
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Quote:
Originally Posted by bbnks2 View Post
What coilovers? Stock suspension is designed to sit on the bump stops. Every coilover is different. I say all this just so you're aware of your particular coilovers design which based on your statement expects lots of bump stop engagement. They are basically used as supplemental springs.

I am just pointing out that problems arise when you choose springs that engage the bump stops at different times. If you have .75" of bump travel in the rear, you would need the front to have roughly 1" of bump travel for the front bump stop to come into play at the same time as the rear in roll. There is nothing wrong with getting into these large bump stops since they are so soft. You just need to make sure youe effective wheel rates are balanced so the bump stop engagement happens on both ends of the car at the same time. I'd need to have every detail to help you further than pointing you to this potential concern.

Not sure what you're measuring but 6/6.75 would be 1/2" higher than stock lol. You measured to the bottom of the side skirt?
TCK SA coils. But rear dampers on the car are currently B6. Short story is the bottom stud stripped on both rear konis. I say this to be clear that the rear dampers on the car are temporary to keep it driving while I figure out what I'm replacing the ruined ones with. I'm trying to learn what I can to make the best decisions possible going forward to stop wasting money.

Yeah I did. I'll measure the ride height again tomorrow. It's definitely not over stock height.
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      06-26-2018, 04:05 PM   #37
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Welp, I made it out to the time attack this weekend and had fully intended on doing some sway bar testing. Practice and first timed runs went great. Between first and second heat, I had planned to sway out my H&R front bar for the stock bar to get some subjective and objective comparisons. While I was trying to remove the H&R bar, though, one of the bolts broke free on the back side where it was welded? to the subframe. Now it just spins. I'll probably have to drop the subframe to get it out and replace it with a regular bolt I guess...
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      03-26-2019, 10:28 PM   #38
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Quote:
Originally Posted by bbnks2 View Post
I ran no front bar for a while. Like you said, front-end gripped like crazy but the car was also oriented toward mid-corner oversteer and the front-end felt a bit too soft relative to the rear. I found that I also had a 1.5" wider front track width than rear (big spacer sup front). So, I ended up putting the stock front sway bar back in, and I also moved to 275 wide rear tires to balance out the track width difference since wider quarter panels really aren't an option.

Through trial and error I've found my current setup to be the best and most balanced I've had:

Front:
Wheels: 17x9 ET25
Tires: 255 Z224
Spring: 6k
Sway: stock (modified bushings to prevent bind)
Ride height: 5.25"
Control arms: M3
Alignment: -2.6* camber and 0* toe

Rear:
Wheels: 17x9 ET38 (Rear quarter panels are rolled and pulled)
Tires: 275 Z224
Spring: 16k
Sway: E92 M3 (modified bushings to prevent bind)
Ride height: 5.5"
Control arms: M3 guide rod and toe arm with aftermarket spherical wishbone (used M3 hubs but kept the stock lower camber arms)
Alignment: -2* camber and .15* toe-in

***Note*** I found that even with 16k rear springs I was hitting the rear bump stops which was exaggerating the over-steer a bit. Moving to the bigger rear bar, and adding a bit of pre-load to the rear springs, helped regain some bump travel. The car handles well now (once I get heat into these tires).

As for your other questions... From what I understand, the "spring rate," or "damping impact," of bushings are important to know for a few reasons such as:

1) How does the bushing compliance affect the dynamic movement of the suspension under load (bump steer)
2) How does the bushing compliance affect the effective wheel rate (relevant for BINDING bushings)
3) How does the bushing compliance affect "load shock" as in... how quickly does load transfer through the suspension to the tires

Binding bushings, like the ones found in the suspension arms, contribute a significant amount to the effective wheel rate. A stock GTI has spring rate of 175/230 lb/in, but actual wheel rates were measured to be ~1000 lb/in on a K&C machine. Where does the 800 lb/in. come from? Binding sway bars and control arms... You would be taking a complete stab in the dark if you tried to guess how much "friction" there is in the stock 135i/128i suspension... You would need to get the car on a set of scales and start plotting suspension movement under varying loads in 1/8" increments to reverse engineer the actual effective wheel rate.

Moving to M3 controls arms, or adjustable arms with spherical bushings, can actually work to reduce the effective wheel rate since they remove some BIND from the suspension. They also significantly increase the shock load to the tires since load is transmitted more abruptly. This is generally felt as being a very positive thing for translating driver inputs to steering angle (agility) but can be detrimental to putting power down without addressing the tires. Speaking of tires, tires can actually be a source of significant sway rate... the suspension can be rock solid but the car may still roll an inch from sidewall deflection alone... time for stiffer sidewall racing tires! The suspension geometry also changes less as it is loaded due to the decrease in bushing compliance. Dampers become a much more significant part of the overall suspension and its ability to control load (most aftermarket BMW dampers seem to be lacking in this area). Again, it would be a complete shot in the dark to try to guess how much of an affect there is without doing a lot of math.

Calculating sway bar rates can be done, but, it wouldn't be worth the time to do accurately with our sway bars since they have so many curves, bends, hollow structure, and taper.
Did you ever consider increasing the front spring rate by ~100lb/in with no front bar?
Thoughts as an alternative strategy to running the oem bar?
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      03-27-2019, 07:37 AM   #39
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Quote:
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Did you ever consider increasing the front spring rate by ~100lb/in with no front bar?
Thoughts as an alternative strategy to running the oem bar?
Adding the stock sway back in is a hell of a lot easier than swapping springs. You can definitely set a car up without swap bars. It's just a matter of knowing what scenarios you might want to do that... it's good to get a it of roll resistance from the sways so you don't need to run crazy high spring rates.

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      03-27-2019, 08:46 AM   #40
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To update.

I've gone back to the stock bar, increased rear spring rate to 1:3 ratio, stock rear bar, added LSD. Definitely the best balance for oscillation and traction for the car.

At this point I'd advise a stiffer front bar if sticking with the stock Msport suspension, but if fiddling with spring rates I'd stick with stock bars all around.
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