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      05-04-2015, 06:58 AM   #177
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Originally Posted by fe1rx View Post
Unfortunately this is a bit of apples-to-oranges comparison as the track layouts differ a bit between runs. Here is a GPS trace of my fastest race lap (blue) from last year on this track, and my fastest practice lap (red) from today on the same track, less the carousel on the returning straight. Up to that deviation (turn 10) the data can be compared.

<snip>

The data is displayed using the segments depicted below with the start line being at the top of the map and the track run clockwise.
<snip>

Speed traces are comparable, with a bit better launch through the start line in the competition. The competition was run with the Cobb tune removed. Today was run at Stage 1 - Sport, which really doesn't make much difference. I run it primarily for the linear throttle. The blue run includes a downshift to 2nd in turn 4, but is run in 3rd in the red run.

<snip>

The competition run (blue) was run with DTC 60/70 pads, which explains the higher in maximum braking g. Maximum lateral g are comparable between the NT01 R-compounds and the RE-71R Extreme Performance street tires.

<snip>

Data logging is with an AIM Solo DL, collecting chassis data through the CAN Bus. I log a math channel I call E Diff Activity, which is the difference between left and right rear brake pressures. Any difference is due to intervention of the E Diff. Not unexpectedly the stiff rear bar does increase E Diff activity in slow corners. Rear brake pressures due to E Diff are in the order of 15 bar.

<snip>

A point of interest, given that the deceleration rates are comparable between the two laps: with OE pads, maximum brake pressures are typically about 20 bar higher than for the DTC pads under normal braking. This being because the track pads have more bite.
First time reading the data in that format- corner speeds in the first few segments seemed higher? With overall speed being somewhat 'smoother'?
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      05-04-2015, 09:21 AM   #178
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The car seems to handle curbing a bit better than last year, but this is probably in part due to the fact that I am now making proper use of the front bump stops. One wheel bumps are not at all problematic, but this is not too surprising because the front total roll stiffness is still higher than the rear.
Interesting, what is proper use of the bump stop?
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      05-04-2015, 12:21 PM   #179
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Originally Posted by chris82 View Post
Interesting, what is proper use of the bump stop?
1) the car doesn't ride on the bump stop in a maximum lateral-g steady state turn (but can when a bump is encountered in a turn)
2) the bump stop prevents any part of the suspension from bottoming out (notably the springs) under the "worst case" bump event

My front suspension violated 2) last year in that it could coil bind under some reasonably probable conditions. Therefore I was not using the bump stops properly to prevent this.
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      05-04-2015, 04:07 PM   #180
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Originally Posted by _Ryan_ View Post
First time reading the data in that format- corner speeds in the first few segments seemed higher? With overall speed being somewhat 'smoother'?
I don't read it that way. Here is what I see:

1) The simple corner characterization of a turn-in followed by a constant radius at constant speed followed by acceleration and unwinding the wheel at the exit would imply that the minimum (apex) speed would be sustained for a bit before accelerating. This isn't what is shown on most corners, because I am driving them "parabolically" to fill out the edges of the friction circle. This implies a measure of trail braking on virtually every corner and it represents the true "racing line" for many corners.
2) Corner 1 (red) has identical apex speeds between the red and blue runs but the red run picks up the throttle a bit faster, then has a lazier transition to brake.
3) Corner 2 (red) is a carousel, so there is a section of constant speed. On the red run I find a way to get on the throttle sooner, which improves my run down the next straight.
4) Corner 3 (red) is driven parabolically on the blue run but as a carousel with a section of constant speed mid corner on the red run. The red run has a slightly higher apex speed which is a gain, but a slightly weaker acceleration on exit for no net difference between the two approaches.
5) Corner 4 blue run is driven with a downshift on corner entry which permits a stronger acceleration on exit and use of an upshift in lieu of a lift on the entry to the second half of this corner. This produces a gain over the red run's 3rd gear with a lift approach.
6) "Corner" 5 blue has a higher entry speed on the red run, less lift mid segment and more commitment to the approach to corner 6 for a net gain for the blue run in this section.
7) 7 blue is a true corner but 8 red is not because it can be driven flat. The blue run handles this section better with a higher apex speed at 7 which provides and enduring benefit all the way to 9, where again blue has a higher apex speed.

This is where the laps diverge to different paths but the elapsed time to this point is identical for both laps. In truth they are not strictly comparable in terms of effort. The blue run was a 100% race effort. The red run was a fast lap with a passenger. This hints at a net improvement in the car since last year.

What is never apparent in reading this kind of data is the effect of elevation change, track camber change and general track condition on the result. These factors often affect the actual speed attainable on any given corner or the braking available in a braking zone, or the acceleration available out of a corner.
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      05-05-2015, 05:28 AM   #181
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Originally Posted by fe1rx View Post
I don't read it that way. Here is what I see:

<snip>.
Thanks for the break down. That's why you're the engineer
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      05-08-2015, 12:45 PM   #182
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Quote:
Originally Posted by 135 View Post
Quote:
Originally Posted by fe1rx View Post
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Originally Posted by 135 View Post
As a side note, some Moton coilovers (such as the ones I have) come with remote reservoirs, which are nitrogen charged at 175psi, and I've been advised that the reservoir pressure can be increased to preload the springs for better transitioning.
I don't think you have that description quite right. Gas pressure results in a lifting force that will raise your car. It is equal to, in your case, 175 psi times the cross sectional area of the piston rod. Raise the pressure and you will raise the car a little bit, which actually takes load off the springs.

To be clear, when I speak of preload, I mean how much the spring is compressed when the strut is fully extended. If you are using helper springs, the preload of your main spring is zero.
I'm 99% certain that was what I was told but your description regarding gas pressure and preload does seem logical so perhaps I misunderstood. The ability to adjust the pressure was more an option rather than something that I'm likely to do. There's a lot more for me to look at before I'd consider changing the pressure.
Just a clarification about the remote reservoir pressure - the marketing material says that the pressure can be varied between 100 and 300 psi to help support the car with soft springs in high speed cornering.
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      05-08-2015, 12:46 PM   #183
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Quote:
Originally Posted by fe1rx View Post
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Originally Posted by 135 View Post
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Originally Posted by fe1rx View Post
This overestimates the ride natural frequency of the chassis, because it omits the tire deflection, which is about 0.41 inches assuming a tire rate of 2200 lb/in. Increasing static deflection to 2.85 in reduces the front natural frequency to 1.85 Hz.

...

This overestimates the ride natural frequency of the chassis, because it omits the tire deflection, which is about 0.37 inches assuming a tire rate of 2200 lb/in. Increasing static deflection to 2.88 in reduces the rear natural frequency to 1.84 Hz.

How did you calculate or approximate the tyre rate?

Tested ...

http://www.1addicts.com/forums/showp...5&postcount=17

I had previously read that post and noticed that you mentioned a tyre rate of "approximately 2000 lb/in" but in the above quoted post you used "2200 lb/in" so I was wondering how you had come to use 2200 lbf/in rather than 2000 lbf/in? And from which table did you draw the 2200 lbf/in value from?
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      05-08-2015, 12:48 PM   #184
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Quote:
Originally Posted by fe1rx View Post
Quote:
Originally Posted by 135 View Post
From my reading, there are various opinions on what the undamped natural frequency of the car should be and there appears to be general consensus that a comfortable ride is around 1.0 Hz and a race car with downforce is around 3.5 Hz+. So what's in between? It depends on how you want to define the categories but you could have:
1.0-2.0 Hz - Sports cars (street)
2.0-2.5 Hz - Dual duty street/track cars
2.5-3.5 Hz - Race cars without downforce
The problem is that it is all subjective. What one person deems harsh may be acceptable to another - within reason.
These numbers are not consistent with what I have generally read, although I think I recall a Julian Edgar article that talked along these lines. These numbers are high, not typical.

If you want to explore the upper end of the envelope, it should be based on what actually works (i.e. based on testing) not just on math. My point in raising the subject of suspension ride frequencies is that it is a tool for seeing if you are in the right ballpark. Let's say you are bottoming out your front suspension. It is natural to think you need to go stiffer up front, but if your ride frequencies are "right", the problem is actually your ride height. The Ohlins kit as delivered is glaringly out of balance, with a rear ride frequency much lower than the front. I suspect this was a necessary concession to the soft rear subframe bushings.

Speaking of which, once you go really stiff, other compliances (tires, bushings, suspension arms, chassis) will defeat your attempt to get the ride frequencies you think you are getting. Race cars are caged, ball-jointed and reinforced to reduce these compliances.

I suggest finding someone who actually races a race-prepared 135i and find out what springs they are running. Whatever it is, you probably don't want to go that stiff for a dual duty car.

For a practical street driven car I would be skeptical of any car that does not permit at least 4" of total front wheel travel. The OE 135i doesn't have much more than that. It can't afford to lose much (in my opinion).

I had built in a lot of assumptions into my calculations, some of which I know may not be as close as what is preferred but, for the purposes of my example, they would have to suffice. As an example, all my suspension components have been replaced with M3 and aftermarket and I use medium compound R-comp / semi-slick tyres on the track that can handle (or should be matched with) a higher spring rate.

I realise theory is just that and it's no substitute for real-world experiences but it's a good starting point to know in what direction I need to head. Being outside of the US, the cost involved in testing even a small range of options is exorbitant, given our poor exchange rate and high shipping costs, so theory and research play an important part in attempting to get it right the first time.

There are two or three 135i race cars in the national professional categories but I don't think they'd provide me with the details of their suspension setup. I'd think those secrets would be tightly held. Other than at a professional level, there aren't many 135s, going to the same extreme, being raced here. From my research, I have come across several other US-based 135i race cars that have published their spring rates and they were as follows:
Front / Rear
650 / 700
560 / 800+
550 / 850
700 / 850

Using the second and third spring rates, since they have the most commonality, equate to a front/rear spring rate of 100/150 N/mm, which would have a 0.45 Hz difference, which is more than my target range but it worked for these cars. To get back to a maximum 0.3 Hz target ride frequency difference, the spring rates would need to be increased to a 100/180 N/mm pairing or decreased to 90/160 N/mm.
All in theory, of course.
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      05-08-2015, 12:49 PM   #185
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Do you have anything else that you could add in reply to my posts about
static spring load,
spring preload and
stroke and spring compression?
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      05-09-2015, 08:41 AM   #186
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Quote:
Originally Posted by 135 View Post
I had previously read that post and noticed that you mentioned a tyre rate of "approximately 2000 lb/in" but in the above quoted post you used "2200 lb/in" so I was wondering how you had come to use 2200 lbf/in rather than 2000 lbf/in? And from which table did you draw the 2200 lbf/in value from?
My calculation was done to illustrate a point (a reasonable upper limit for spring rates for our street-driven cars) and the tire rate is completely arbitrary, although it is within the range I measured. If you want definitive data you should measure your own tires, and then validate the results with either an accelerometer or with shock potentiometers and data logging. Incidentally, the this tire rate calculator (thanks to Kgolf31 for posting that some time back) calculates much softer tire rates than my assumption when I input my test conditions. Any tire rate value should be considered suspect unless you have validated it for your specific wheel, tire, pressure and load conditions.

http://bndtechsource.ucoz.com/index/...alculator/0-20
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      05-09-2015, 12:20 PM   #187
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Quote:
Originally Posted by fe1rx
Quote:
Originally Posted by 135 View Post
I had previously read that post and noticed that you mentioned a tyre rate of "approximately 2000 lb/in" but in the above quoted post you used "2200 lb/in" so I was wondering how you had come to use 2200 lbf/in rather than 2000 lbf/in? And from which table did you draw the 2200 lbf/in value from?
My calculation was done to illustrate a point (a reasonable upper limit for spring rates for our street-driven cars) and the tire rate is completely arbitrary, although it is within the range I measured. If you want definitive data you should measure your own tires, and then validate the results with either an accelerometer or with shock potentiometers and data logging. Incidentally, the this tire rate calculator (thanks to Kgolf31 for posting that some time back) calculates much softer tire rates than my assumption when I input my test conditions. Any tire rate value should be considered suspect unless you have validated it for your specific wheel, tire, pressure and load conditions.

http://bndtechsource.ucoz.com/index/...alculator/0-20
Thanks - point taken.

I had also come across that link last year when I was looking to calculate contact patch area and factors that could impact its size and shape.
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      05-11-2015, 09:40 PM   #188
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AIM Solo DL V2

I have previously documented the installation of my AIM Solo DL data logger:

http://www.1addicts.com/forums/showp...0&postcount=60

When I did this, I didn't bother connecting it to power as the Solo has an internal battery with a decent battery life. I have run the battery flat a couple of times though so I decided to make that connection in the fuse box using a Littelfuse "Add-A-Circuit".

http://www.littelfuse.com/~/media/co...fhm02fha02.pdf

That process has been documented elsewhere on the Forum, but I want to add a few details.

My original installation located the Solo beside the LH A-pillar. What I noticed was that the off-center location showed up in the data when doing skid pad testing as an error in path radius of half the car width. Although this might be splitting hairs, the device should really be located on the vehicle centerline. So while relocating the wiring and connecting to power, I moved the harness to the center of the car. That required a small notch to be filed in the center air vent.

Name:  AIM Solo CL Install.jpg
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I took power from the switched power circuit "8" in the fuse box behind the glove box, using an Add-A-Circuit device.

Name:  Circuit Tap.jpg
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As there are no convenient grounding studs in the vicinity, I added one to the steel dash support structure.

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It is worth examining the internal wiring of the Add-A-Circuit to understand the right and wrong way to insert it into the fuse box. If you are adding to an existing active circuit the device will work in either orientation, but the correct one keeps the original and new circuits isolated from each other. The other orientation does not. If you are inserting the device into an empty space on the circuit panel, it will only work if inserted properly. When using circuit "8" as a power source, the bottom pin in the box is the live one and the top one the load, so the new circuit wire should be on the top side of the Add-A-Circuit when it is inserted.

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      05-30-2015, 05:36 AM   #189
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I am very happy with the change. The car corners flatter, takes a set quicker, and handles transitions better. More important, I have definitely not gone too far aft in terms of roll stiffness distribution because the car is easy to drive with nannies off (my normal mode). With them on, intervention seems much more subtle (although I didn't fully explore this). My hypothesis is that the improved balance and perhaps by reducing the nasty transients due to excessive body roll may result in the DSC seeing less need to intervene. I will try a faster few laps with DSC on today to see if this is in fact the case.
Forgot to ask- have you had any fitment issues with the H&R bars? Some of the e90 members reported clearance issues and went to the M3 bars.
Did you end up fitting the matching front bar?
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      05-30-2015, 06:53 PM   #190
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Quote:
Originally Posted by _Ryan_ View Post
Forgot to ask- have you had any fitment issues with the H&R bars? Some of the e90 members reported clearance issues and went to the M3 bars.
Did you end up fitting the matching front bar?
I had no issues with the rear H&R bar fitment. I am still on the OE front bar. I feel I have enough total roll stiffness with this arrangement, and I like the handling.
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      09-10-2015, 12:40 PM   #191
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How is everything performing? Are you making any adjustments?
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      09-03-2016, 09:34 AM   #192
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Just found this thread linked from an autocross forum, lots of great testing going on here!

I especially love the swaybar testing you've done. I tried something similar because I didn't trust the equations I found online, but my resources for doing the testing were not nearly as good as yours, and I wasn't able to get good data over a few hundred pounds of force, because the wood bench I had it bolted to would twist!

You can read about my journey here, if you have some time:

http://www.bimmerforums.com/forum/sh...-STX-330-Build

Some thoughts on what you're up to, based on extensive autocross testing on my E46:

1. Coil bind or even too much bump stop engagement is death for grip. You seem to know this intellectually, but I'm not sure you're focusing enough on measuring whether and how much that's actually happening on your car. A shock pot tied to your data logger is the best way to do that, but a really cheap/easy way to measure the maximum travel of the strut is to just use a tight zip tie on the strut shaft

2. Tire tech is moving very quickly, and those RE71R's can generate a LOT of grip. The ride frequency ideals that you read about in books assumes a certain level of grip that is a lot lower than what you're working with today. The more grip you have, the more the car will roll, and the more likely you are to see coil bind or bumpstop.

3. It's easy to assume that if your front outside wheel can accommodate all the weight of that end of the car without coil bind, you should be golden, because you probably won't transfer 100% of the load of the front end, and that's true, but often you're braking going into that turn, and so you get some weight transfer from the rear as well, and then you hit a bump and you're screwed. So test, test, test!

4. I'd recommend some testing days where you bring extra springs and bars, test one change at a time, and keep a lot of records of the results. Test the ride height too. You're correct that too low is no good, but too high and you're giving up grip as well. Gotta test to find the right balance.

I ended up with 600lb springs and a 30mm bar up front on my car, with older tires that didn't generate as much grip as your RE-71s and a lighter car. (though wider tires and wider wheels) You might not need that much on your car due to strut travel differences, that's hard to say, but I'd just encourage more real world testing. I'm quite sure you can manage more than 1.2 G's in that car.
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      09-14-2016, 12:48 AM   #193
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Quote:
Originally Posted by Orb
One of the best suspension write ups I have ever seen.....awesome details!!

I was looking at the CG plated when I came across this thread. I will defiantly will make my own. They obviously did no testing or calculations.

Question for the poster:
Did you account for the CG OEM spring perch deflection under load. I measured about 10 mm for the OEM spring perch. I suspect this came out a wash or close to it.

As for the rear spring compressing on a curved axis. I did a non linear analysis in Ansys and the spring rate does increase anywhere from 15-40%. This is dependent on spring wire diameter, spring length and stroke position so not a straight forward answer. I resolved the issue with the a sealed articulating spring perch placed between the helper spring and main spring. The soft helper spring works well at taking up translation by deforming as well. This made a very noticeable improvement and ride quality was a night a day difference especially over rough roads.
Curious about what type of articulating perch is that.

Any info is appropriate.

Great job to op
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      09-18-2016, 01:38 AM   #194
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Quote:
Originally Posted by Orb
One of the best suspension write ups I have ever seen.....awesome details!!

I was looking at the CG plated when I came across this thread. I will defiantly will make my own. They obviously did no testing or calculations.

Question for the poster:
Did you account for the CG OEM spring perch deflection under load. I measured about 10 mm for the OEM spring perch. I suspect this came out a wash or close to it.

As for the rear spring compressing on a curved axis. I did a non linear analysis in Ansys and the spring rate does increase anywhere from 15-40%. This is dependent on spring wire diameter, spring length and stroke position so not a straight forward answer. I resolved the issue with the a sealed articulating spring perch placed between the helper spring and main spring. The soft helper spring works well at taking up translation by deforming as well. This made a very noticeable improvement and ride quality was a night a day difference especially over rough roads.
Does anyone know any info on these perches
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      09-18-2016, 06:33 AM   #195
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Probably Genesis hydro perches.
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      10-25-2016, 09:54 AM   #196
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fe1rx

So I've read through this thread, and I was wondering if you could reiterate a few points. Stock front camber is approx -.5*. I've installed m3 front arms and removed the strut alignment pin allowing me to get -1.5* up front. I zeroed out front toe. According to what your saying, when my coilovers arrive, and I move to -2.5*, I should dial in .1* toe out per side to maintain steering feel due to tire construction? Does dialing in that toe out offset also come with the typical effects of running toe out such as less stable straight line stability?

Also, I have no idea if MFactory took anything you've come to realize as limiting factors of mass produced suspension setups into consideration when they developed thier e90/e82 coilovers. I'll have to look into tire fitment/spring perches/and top hats once they arrive.

When you moved to a shorter spring did you end up limiting your overall strut travel as a side effect?

Last edited by bNks334; 10-25-2016 at 08:43 PM..
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      10-26-2016, 06:22 AM   #197
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Quote:
Originally Posted by bNks334 View Post
fe1rx
So I've read through this thread, and I was wondering if you could reiterate a few points. Stock front camber is approx -.5*. I've installed m3 front arms and removed the strut alignment pin allowing me to get -1.5* up front. I zeroed out front toe. According to what your saying, when my coilovers arrive, and I move to -2.5*, I should dial in .1* toe out per side to maintain steering feel due to tire construction? Does dialing in that toe out offset also come with the typical effects of running toe out such as less stable straight line stability?
I am saying that you can do that without much net effect on stability (not that you should). More negative camber is stabilizing so it can be offset by a bit less toe in. On the other hand, more negative camber may cause more tramlining.


Quote:
Originally Posted by bNks334 View Post
fe1rx
When you moved to a shorter spring did you end up limiting your overall strut travel as a side effect?
By careful selection of the spring and preload I was able to avoid coil binding that could have become the travel limit. I have a very narrow range of acceptable preloads though. This is something you need to look at carefully with a short spring.
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      03-04-2017, 01:06 PM   #198
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Dear fe1rx

I am tracking my 135i e88 twice per month.
I have the same MI00 system, and i am about to order my swift springs.
My semi slick tyres are 255 35 8.5" r18 front and 265 35 9" r18 rear.
Will go for a square setup with 245 649 r18 slicks soon.

My camper plates are from Vorshlag.

Would you recommend the 60nm in front and the 140nm in the back for my car as well?

Thanks in advance for your reply and detailed work!
Appreciate 0
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