fe1rx Ohlins Installation

[fe1rx]

Originally Posted by Kgolf31

Lowering the front more though helps front end grip though...yes?

Presumably you mean because the c.g. is lower and so there is less lateral weight transfer and so more total grip. I agree as long as the lowering doesn't mess anything else up that has more effect. For example, without enough negative camber up front (3-ish degrees) the loss of negative camber gain at a lower ride height may actually reduce front end grip.

Let me ask you this - assuming enough static negative camber up front, would you agree that a stiffer front bar will reduce total front grip? This may be why you are still struggling with getting the car to rotate.

[Kgolf31]

Originally Posted by fe1rx

Presumably you mean because the c.g. is lower and so there is less lateral weight transfer and so more total grip. I agree as long as the lowering doesn't mess anything else up that has more effect. For example, without enough negative camber up front (3-ish degrees) the loss of negative camber gain at a lower ride height may actually reduce front end grip.

Let me ask you this - assuming enough static negative camber up front, would you agree that a stiffer front bar will reduce total front grip? This may be why you are still struggling with getting the car to rotate.

Here are my specs as of now.

Front
Camber: -3.6*
Toe: 0 (maybe a bit of toe out now)
Caster: 7.5*

Rear
Camber: -2*
Toe: 1/8th total


I think I actually have too much rear grip right now. I'm still trying to play around with damping settings, but on concrete the car pushes. On asphalt, the car is fairly neutral...In early runs the car reached power oversteer very easy in the wet. As it dried out, the car came back to neutral.

Thinking about increasing front rebound while turning down rear rebound a bit to decrease weight transfer to the rear and increase weight transfer to the front of the car.

I might start to increase rear compression as well to try and break rear traction before anything else.

Thoughts?

I'm running a 28mm bar, which isn't exactly stiff when you look at the grand scheme of things that at 26.5mm stock bar is what was originally in there (granted that was hollow and middle was thinner than outside of the bar).

Here is my video from Saturday..interested to hear what you have to say. Don't want to derail, so feel free to PM me

[fe1rx]

Originally Posted by PeteA

Nice write up. I have a similar setup to yourself. Ohlins R&T with swift springs, thrust sheets and vorshlag camber plates. 7" 60NM/mm front spings, 9" 120NM/mm rear springs.

Sitting on APEX ARC-8's with Ventus RS-3 rubber. 235/40/18 fronts 265/35/18 rears. No clearance or rubbing issues on a ride height 10mm lower than stock. Was toying with the idea of 245/35/18 up front as a 20mm tyre ratio gap is a more neutral setup. I'm not 100% sure if it will clear the strut. The perch is a non-issue for me.

Will probably be pretty tight.

Given all your research, what alignment settings would you recommend as a dual duty street/track setup?

I think your choices in 245/35R18 are pretty slim aren't they? You can't get them in RS-3s.

The point of this thread is to say this is what I did, this is why, and, after some testing, this is the result. In due course, I will change something because I think it will make it better, then some more testing to validate the hypothesis. I hope it inspires a few people to try a few things.

So the ideal dual duty street/track setup? That is what I am aiming for, but it really depends on how much and what kind of each, and how much inconvenience and compromise are you willing to live with in each use. Last year on an OE suspension and brakes with M3 rear subframe bushings and M3 front bits and GC camber plates and ZII tires (225 square) I had a pretty good dual duty setup, with the only change made at the track being one more degree of negative camber added at the track. The alignment was probably not optimized for either place, but with the combination of driving I did, I wore out one set of ZII's in one season of combined driving, and all four tires wore out evenly. And when I got them down to the wear bars, I drifted them down to the cords. I got really good value out of those tires, and wore them out in 8000 km. Last year that was pretty much a perfect street/track setup for me.

This year is a very different compromise. I don't change the camber for the track (so far), but I do change wheels, tires and brakes. This is a lot more bother when it comes to getting mobilized for and demobilized from a track day, and I spent a lot of money to get to this new setup, but my motivation is different. I don't want the car to simply be fun at the track - I want it to be fast.

Regarding tire sizes - personally having driven the car with square tire sizes for five years, I would not go back, but this is a function of my driving style which is very much about managing grip and minimizing understeer.

[John_01]

Thanks for the great thread so far.

I want to comment about the issue of roll centers. With McPherson strut front suspension, the front roll center is likely to be high which reduces front grip in cornering. In my own subjective feeling, I think the front roll center is too high at standard ride height. The front roll center will move lower during braking and if the ride height is lowered. I can't prove it with numbers, but I'd love to see a technical treatment or at least some opinions and discussion.

[PeteA]

Originally Posted by fe1rx

I think your choices in 245/35R18 are pretty slim aren't they? You can't get them in RS-3s.

The point of this thread is to say this is what I did, this is why, and, after some testing, this is the result. In due course, I will change something because I think it will make it better, then some more testing to validate the hypothesis. I hope it inspires a few people to try a few things.

So the ideal dual duty street/track setup? That is what I am aiming for, but it really depends on how much and what kind of each, and how much inconvenience and compromise are you willing to live with in each use. Last year on an OE suspension and brakes with M3 rear subframe bushings and M3 front bits and GC camber plates and ZII tires (225 square) I had a pretty good dual duty setup, with the only change made at the track being one more degree of negative camber added at the track. The alignment was probably not optimized for either place, but with the combination of driving I did, I wore out one set of ZII's in one season of combined driving, and all four tires wore out evenly. And when I got them down to the wear bars, I drifted them down to the cords. I got really good value out of those tires, and wore them out in 8000 km. Last year that was pretty much a perfect street/track setup for me.

This year is a very different compromise. I don't change the camber for the track (so far), but I do change wheels, tires and brakes. This is a lot more bother when it comes to getting mobilized for and demobilized from a track day, and I spent a lot of money to get to this new setup, but my motivation is different. I don't want the car to simply be fun at the track - I want it to be fast.

Regarding tire sizes - personally having driven the car with square tire sizes for five years, I would not go back, but this is a function of my driving style which is very much about managing grip and minimizing understeer.

This is true re: RS-3. Understood though. I think -3.25 is a bit too much for street driving, the car will pull and track off center with uneven pavement far too much. I like you alignment settings for the track, but for the street its a bit too aggressive. I think -2 front and -1 rear is more suitable though you will probably disagree given your research haha

Thanks for all the info

[Bullitt]

Originally Posted by PeteA

This is true re: RS-3. Understood though. I think -3.25 is a bit too much for street driving, the car will pull and track off center with uneven pavement far too much. I like you alignment settings for the track, but for the street its a bit too aggressive. I think -2 front and -1 rear is more suitable though you will probably disagree given your research haha

Thanks for all the info

I plan to fit the R-S3 tires in sizes 255/35 in the front and 275/35 in the rear using the 18" Apex EC-7 wheels. I'll be running extra front camber as well as some fender rolling and 5mm spacers. There are some 1addicts here who've successfully fit those sizes in the 135i. There's one (blutattoo) who used these sizes in R-S3's on the track without any fender rolling or spacers. I'll report back when I try this setup with my Ohlins later this year.

Speaking of alignment settings, I could never run lower than -2.5 camber in the rear, yes rear, on the street without wearing the outer half more. This is with all M3 parts including rear subframe bushings and 0.10 total toe in. I also might need to increase my front camber to -2.5 due to outside shoulder wear and this is all on the street (backroads & canyons). But I hardly slow down for turns Apparently there are other hooligans on this forum who run -2.5 or more camber daily in the front and have even tire wear.

[Reapur]

Originally Posted by Bullitt

I plan to fit the R-S3 tires in sizes 255/35 in the front and 275/35 in the rear using the 18" Apex EC-7 wheels. I'll be running extra front camber as well as some fender rolling and 5mm spacers. There are some 1addicts here who've successfully fit those sizes in the 135i. There's one (blutattoo) who used these sizes in R-S3's on the track without any fender rolling or spacers. I'll report back when I try this setup with my Ohlins later this year.

Speaking of alignment settings, I could never run lower than -2.5 camber in the rear, yes rear, on the street without wearing the outer half more. This is with all M3 parts including rear subframe bushings and 0.10 total toe in. I also might need to increase my front camber to -2.5 due to outside shoulder wear and this is all on the street (backroads & canyons). But I hardly slow down for turns Apparently there are other hooligans on this forum who run -2.5 or more camber daily in the front and have even tire wear.

RS3 absolutely require high amounts of negative camber to be effective on the track. Its not unheard of to need -4 deg up front and -3 in the rear. This is due to the high amount of sidewall deflection in this tire under heavy cornering.

Unfortunately the e82 doesn't really give us that much room to adjust our alignment settings. I feel the RS3 isn't a good match for our cars because of this and the Dunlop z2 is far better for our application.

[Bullitt]

Originally Posted by Reapur

RS3 absolutely require high amounts of negative camber to be effective on the track. Its not unheard of to need -4 deg up front and -3 in the rear. This is due to the high amount of sidewall deflection in this tire under heavy cornering.

Unfortunately the e82 doesn't really give us that much room to adjust our alignment settings. I feel the RS3 isn't a good match for our cars because of this and the Dunlop z2 is far better for our application.

Not to throw this thread off track, but do you mean there's significantly more outer shoulder wear with R-S3 than the ZII at the same alignment? What suspension parts and settings did your car or the cars you know of have with the R-S3? Maxing out the negative camber on my Vorshlag plates is definitely the plan for the track nevertheless.

[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.

[fe1rx]

Originally Posted by Orb

One of the best suspension write ups I have ever seen.....awesome details!!

Thanks Orb. Your input is remembered and missed on this forum.

Originally Posted by Orb

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.

I did not measure this. It would have made my first-order calculations more accurate, and I wouldn't have guessed that it was quite this compliant.

Originally Posted by Orb

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.

Interesting solution. I suspect that the orientation of the spring cut ends relative to the bending axis also affects the results. The spring motion does effectively give us a progressive spring, even if our spring is linear.

[Orb]

Originally Posted by fe1rx

Thanks Orb. Your input is remembered and missed on this forum.



I did not measure this. It would have made my first-order calculations more accurate, and I wouldn't have guessed that it was quite this compliant.



Interesting solution. I suspect that the orientation of the spring cut ends relative to the bending axis also affects the results. The spring motion does effectively give us a progressive spring, even if our spring is linear.

The front spring perch does compress a lot more than one would expect. It should be noted that when camber plate vendors showing the stack up it not really correct.

Understood, that the linkage setup gives a progressive rate independent of the actual spring. Ground end spring are only linear if compressed squarely as you know. Compressing them in other orientations like one installed in our cars creates a non linear spring in practice. Pig tailed spring are subject to this non linearity as well but to much lesser degree (not really an issue and they are usually formed on a curved axis in part as well). Some investigation on my part show this is the case and some what expected for ground end springs. There are a few patents on this articulating spring perch but the one from Honda goes into some detail about application for multilink suspensions. Interesting notes where about car instability going in and out of droop travel.

Magic Number: I do not the exact number yet but these are reasonable at least for a comparison set ups. This assuming a minimum lowering (15 mm max)

CG: 22" to 24"
Front RC" 1.5" to 2.5"
Rear RC: 4" to 5"

Much appreciated for sharing all your info. I am more interested in the science and understating the information so I am hoping not to distract by adding anything....if so I will remove it.

[02rsxpilot]

@fe1rx Just curious for your impressions after having your setup for a while now. How does the car feel on the street? On the track? Anything you are looking to change now that you've got your baseline data?

[fe1rx]

Originally Posted by 02rsxpilot

@fe1rx Just curious for your impressions after having your setup for a while now. How does the car feel on the street? On the track? Anything you are looking to change now that you've got your baseline data?

The ride on the street is excellent, as others using the Ohlins shocks have reported. Given that my springs are more than twice as stiff as OE, credit must be given to the damping characteristics of the Ohlins dampers. The suspension was generally quiet, although speed bumps taken slowly produced a thump at the back, and the occasional creak at the front needed silencing with silicone spray on the camber plate bushings (GC Street). I had no noise at all from the rear spring, so the lower spring pad mod worked well.

I made one fundamental error in setting up the front of the car in that I don't have enough spring travel. This is a function of using 7" springs, which I chose for better tire-to-strut clearance and the potential to fit wider tires. I am going to stick with the same springs, but some detail changes are needed to prevent coil binding on hard bumps.

I like the GC street camber plates, but they do need regular service. I figure new bushings and steer bearings annually, and I wouldn't want to use them (or any other camber plate) if the car was winter driven. They are not optimized for my exact configuration (which is hardly a surprise), so I plan on some significant modifications to my camber plate setup. Details will follow.

Handling balance was remarkably improved based on measured understeer gradient. Steady state understeer is undetectable below 0.8 g, which means you never feel it on the street. At the same time the car still understeers at the limit, where it is very easy to drive. I think there is a bit more grip to be extracted though, by working the rear tires a bit harder. To that end, I am going with slightly stiffer rear springs and a larger rear bar. I still have the original front bar. This is somewhat counter to Forum wisdom as I don't have an LSD. I am going to work on maximizing mechanical grip before worrying about an LSD.

The big picture for the suspension this year:

1) Ride height is not being changed.
2) Stiffer rear springs and bar.
3) Fix the coil bind at the front with some custom parts.
4) Installing M3 rear suspension arms and building a custom rear toe arm.
5) Installing Powerflex rear shock upper mounts (I think that will get rid of the speed bump thump).

These are minor functional changes and amount to tweaking what I think is a pretty good setup.

I liked the Nitto NT01 track tires but wore them out faster than I expected. But then again, I did a lot of instrumented skid pad testing with them. I will likely use them again as track tires. Especially when new, their damp grip is astounding.

The Hawk DTC 70/60 brake pad combination worked well at the track (I used OE pads on the street), with front Ti shims, as did the Castrol SRF fluid. I had no pad or fluid fade problems, but did have the sense that I was getting close to their capacity on some tracks. Calipers are getting new dust boots all around, new fluid (of course) and stainless lines. I am changing the lines just because I figure 7 years is enough on the OE flex lines. I am going to consider options to improve cooling at the front, but it is not a major priority at the moment.

I am going to walnut blast the intake valves, which will be the first time for this car. I will be doing that myself as I have a blaster and the vacuum attachment. Bav Auto has a really good DIY video so the how doesn't really need to be repeated, but I will report on what I find when I get there.

[dcaron9999]

fe1rx, as you know, Im really interested in finding the proper springs to gain maximum wheel/tire clearance when I buy my coilovers.

Pardon the newbie question but, how does it feal when you run out of spring travel on your shorther 7 inch front springs? I know you are experimenting with raising the strut out of the knucle, but would choosing slightly stiffer spring rates be another viable approach for me, to avoid modifications?

Somewhat unrelated to your thread but, what SS lines are you getting?

[Bimmer-Bob]

Originally Posted by fe1rx

I presume from your pictures that you don't have camber plates and that you set your ride height pretty much as Ohlins recommends, maybe just a bit higher. This just works for the OE wheels and 215 tires. With my GC camber plates the perch is a bit higher with the Ohlins springs, and it just works with a 225 tire. I don't see this working at all with 8.5 x 18 ET45 ARC 8 wheels in any tire size.

Your posts are way over my head, so forgive me for being a bit basic, but here goes:

I just wanted to say that I'm also running Ohlins R&T dampers with the same GC Street camber plates as you. I'm running APEX ARC-8 wheels in 17 x 8.5 ET40 and Direzza ZII's in 245/40/R17 at all four corners. No rubbing in front with a 7" #392 spring. I did have rubbing with a set of 6" #400 springs that was given to me to test, but I added a pair of helper springs and that solved the issue (per a previous conversation with you, I know the 6" springs are too short, and I will go back to the 7" Swift spring when I pull the dampers to send back for their 20K mile rebuilding).

Anyway, I just wanted to say, if you really want to go to 245 series rubber and you can't get there with your current wheel, you may want to consider a 17" wheel, because it's definitely possible. I do have a 128i, but we have most of the important variables/components in common (other than wheel size, of course).

[fe1rx]

Originally Posted by dcaron9999

fe1rx, as you know, Im really interested in finding the proper springs to gain maximum wheel/tire clearance when I buy my coilovers.

Pardon the newbie question but, how does it feal when you run out of spring travel on your shorther 7 inch front springs? I know you are experimenting with raising the strut out of the knucle, but would choosing slightly stiffer spring rates be another viable approach for me, to avoid modifications?

Somewhat unrelated to your thread but, what SS lines are you getting?

There is a significant thump from the front when the spring bottoms out. My early testing of the Ohlins strut led me to believe that the bump stop was in fact a pair of internal springs. This was inferred from the force vs. displacement I measured for the stop, because it is internal and not visible. Based on that assumption I figured I was just feeling a very hard bump stop. Disassembly of my front suspension this winter revealed the evidence that the coils had been contacting each other on my front springs. I re-tested the strut with a better test setup and found that the internal bump stop actually has the characteristics of a conventional microcellular urethane stop.

Incidentally, repeated over-compression of the front spring caused them to sag in free length by 6 mm, but it did not change the spring rate of the spring. My front suspension settled a corresponding amount over the summer as a result. In contrast my rear springs were not over-compressed, and they show no change in free length.

As for the brake hoses - very timely question. I installed the rear ones today and am not happy with them. I posted my comments on these to a separate thread.

[Nugget]

Interesting, I've been running 7" swift springs on my front Ohlins for around 18 months now and I don't think I've ever bottomed it out. That includes hitting some decent sized compressions at a fair rate of speed.

This is what my ride height was set at when I got my initial alignment, I haven't measured it since though.

Centre wheel to guard
LF:330mm RF:325mm
LR:335mm RR:330

Bottomwheel to Guard
LF:580mm RF:575mm
LR:585mm RR:580mm

[fe1rx]

Among this year's changes I have manufactured new camber plates, patterned on the Ground Control Street plates. One issue with the GC Street plates is that the upper spring perch does not articulate. As a result the spring does not compress straight if more than stock camber is selected. In my case the upper spring perch was always angled 3 degrees in the camber direction, relative to the lower spring perch. My new camber plates were intended to address this by compensating for this angle. In addition, they were built approximately 5 mm taller to tweak my ride height without adding spring preload.



This top view shows the differences between the GC and my new plate. The GC plate has previously been modified by enlarging the slots to match bushings, and re-engraving the camber markings.



The new plate has a broader base, and while I was at it I made a new stainless plate to secure the attaching bolts, which are now also stainless.



A side view makes the 3° incidence angle apparent, and the difference in overall height.



This view shows the installation of the oilite bushings. These make adjusting the plate much smoother and improve the repeatability of settings.



This is a fully assembled top view.



And a detailed look at the engraving. With an M3 front wishbone, the range of adjustment is from -2° to -4° camber.



The steer bearing, upper spring perch and urethane bushings are all GC parts.



The above view makes the 3° incidence angle more apparent.

[knightarmor]

This is one of the best and most useful theads I've seen in a long time, thank you!!

[John_01]

Great work on the camber plates. They look amazing!

[John_01]

I was looking at the motion ratio calculation that was done with the spring removed. I think you settled on a figure of 0.567. It appears to me the actual motion ratio can be lower if there is too much compliance in the rear sub frame bushings. Probably with M3 bushings, there wouldn't be much significant distortion. If the stock 135i bushings are used, I reckon it would reduce the effective spring rates at the wheel. Maybe its something when analysing the factory stock configuration.

[fe1rx]

Originally Posted by John_01

I was looking at the motion ratio calculation that was done with the spring removed. I think you settled on a figure of 0.567. It appears to me the actual motion ratio can be lower if there is too much compliance in the rear sub frame bushings. Probably with M3 bushings, there wouldn't be much significant distortion. If the stock 135i bushings are used, I reckon it would reduce the effective spring rates at the wheel. Maybe its something when analysing the factory stock configuration.

You are correct about the effect on wheel rate. The rear subframe bushings act as springs in series with the rear spring (because some of the total wheel movement is accounted for by deflection of the springs and some by deflection of the bushings). Any vertical component of the wheel reaction not carried by the spring and shock which act directly on the chassis must be carried by the subframe and reacted into the chassis at the subframe bushings. Even though the OE bushings are soft, their deflection as a function of wheel deflection will be small, so their influence on the wheel rate will be small.

Assume that at a wheel reaction force of F the bump stop is reached and at that force the wheel has moved 100 mm due to the spring and 10 mm due to the bushings. The wheel rate is F/110. Without the bushings it would have been F/100. I doubt the bushing deflection is more than this under these conditions, so the OE rear subframe bushings may reduce the wheel rate by not more than 10% as a first order approximation. This isn't strictly the same as a reduction in motion ratio, although the effect is the same.

As many have reported, NVH is scarcely affected by the change to M3 RSFBs, yet if you look at the internal structure of the OE RSFB's, they are highly complex, highly engineered structures. In comparison, the M3 RSFBs are very simple, as are all the aftermarket options. That complexity is not there to reduce NVH or to reduce wheel rate but to control compliance steer effects at the rear and to produce a benign (and annoying to anyone who tracks their car) terminal understeer well before the rear tires reach their limit of grip.