fe1rx goes full spherical

[lowside67]

Originally Posted by fe1rx

I have data from 2018 (pre-spherical) to compare to 2019 (spherical). In both cases the car has a wing and a splitter, but the 2019 splitter is "improved". The track is the Mosport GP (AKA CTMP GP) and the lap times are comparable at 1:34. 2018 was cooler so had more power, but 2019 corner speeds were a bit higher, giving about the same lap time.

Plotting steering angle against lap distance reveals that the spherical car requires less total steering input, despite the fact that the cornering speeds are generally higher. Lower trace is GPS speed vs distance.

Attachment 2149118

Another way to plot the same data is as an x-y plot of steering wheel angle vs. lateral acceleration. Once again it is clear that less steering angle is required for the spherical car to produce the same lateral acceleration.

Attachment 2149119

Actual understeer can be estimated by calculating corner radius from lateral g and speed, calculating ackermann angle from wheelbase (2.66 m) and corner radius, and comparing the ackermann to the actual steered angle at the tire by dividing the logged steering wheel input by the steering ratio (16.36 near center). The method is mentioned in Bob Knox's "A Practical Guide to Race Car Data Analysis" if you want to chase down the details and the limitations of the method. Whatever its limitations, it is probably good for comparing two setups of the same car, as we have here. This method shows a reduction of understeer mid corner of up to 1°.

Attachment 2149120

My hypothesis is that going spherical (and solid RSFBs) reduces compliance steer effects and loss of camber. This reduction provides greater total grip, reduced understeer, and thus less total steering input being required.

Just wondering but what makes you draw the conclusion that the reduced understeer is as a result of the sphericals and not the increased splitter size? In the absence of being able to verify one or the other, I would have thought the larger splitter would be more likely to make an effect.

-Mark

[fe1rx]

Originally Posted by lowside67

Just wondering but what makes you draw the conclusion that the reduced understeer is as a result of the sphericals and not the increased splitter size? In the absence of being able to verify one or the other, I would have thought the larger splitter would be more likely to make an effect.

-Mark

The splitter was the same size but run with less ground clearance. That should give a bit more front downforce, although I did not detect any change in aero balance with that change alone. 2019 also had hood vents, which did move the aero balance forward and was compensated for by a tweak in the rear wing, so your point stands - I think I had more total downforce in 2019.

That said, to my eye the decreased steering angle is not speed dependant, so seems like a mechanical effect, not an aero one. The slowest corner on that track (5) is so dynamic with changes in elevation and camber that one never approaches steady state. All the other corners are longer and more directly comparable. Not that there is a huge variation in corner speeds to compare.

Also, less steering is required at every point in the corner, even before there is appreciable cornering force generated. The decrease in steering angle seems to be proportional to steering angle, not speed or speed squared. That seems like a mechanical effect to me.

[vtl]

Partly inspired by your thread, I ended up doing a project replacing most of the rear ball joints with the Lemforder 3067901 joints. I ended up a local group buy for these and the parts turned out really well.

Installed the rear M3 control arms and pressed in the Lemforder ball joints in them. The mounting face for the arms is tapered so I did a simple CAD design and we got the adapter washers CNC'ed out of 304 stainless. The ball joints pressed into the trailing arm bushing locations. The ball joints were pressed to depth taking into account the thickness of the custom washers

I already have the German Auto Solutions front monoball pressed into the M3 arms, and the rear end is now fully ball jointed apart from the inboard camber link. With this current setup I note that the rear end is a lot more stable and doesn't move around as much, less oversteer when I throw the car into a corner. Was suprised at the improvement even when not driving that hard.

Addtionally I note the rear end is more compliant/comfortable over slow/medium bumps and less comfortable on sharp bumps. The damping overall seems to be better without the rubber bushes twisting up and contributing to the overall spring rate.

[fe1rx]

Originally Posted by vtl

Partly inspired by your thread, I ended up doing a project replacing most of the rear ball joints with the Lemforder 3067901 joints.

Nice work!

[Angel67]

Originally Posted by vtl

Partly inspired by your thread, I ended up doing a project replacing most of the rear ball joints with the Lemforder 3067901 joints. I ended up a local group buy for these and the parts turned out really well.

Installed the rear M3 control arms and pressed in the Lemforder ball joints in them. The mounting face for the arms is tapered so I did a simple CAD design and we got the adapter washers CNC'ed out of 304 stainless. The ball joints pressed into the trailing arm bushing locations. The ball joints were pressed to depth taking into account the thickness of the custom washers

I already have the German Auto Solutions front monoball pressed into the M3 arms, and the rear end is now fully ball jointed apart from the inboard camber link. With this current setup I note that the rear end is a lot more stable and doesn't move around as much, less oversteer when I throw the car into a corner. Was suprised at the improvement even when not driving that hard.

Addtionally I note the rear end is more compliant/comfortable over slow/medium bumps and less comfortable on sharp bumps. The damping overall seems to be better without the rubber bushes twisting up and contributing to the overall spring rate.

It makes sense that your rear end got softer / more compliant once you eliminated the rubber bushings and replaced them with ball joints because you eliminated the contribution to effective spring from the bushings. I had poly bushings, which also eliminate the effective spring, and it was softer. I didn't like them though because (i) they were squeaking and (ii) I found the suspension was too soft in the back relative to the front and so my relative suspension frequencies were not what I wanted. I replaced the poly bushings with a combination of ball joints and Group N bushings. The Group N contribute considerably more effective spring than regular bushings, and that more than made up for the loss of spring at the positions where the ball joints went. In addition, because the wind up occurs both below and above static height (they are neutral at static height if you torque them at that height) I find that the Group N work against the metal spring when the rear end moves above static height, reducing pitch on hard braking and working to level the car both on hard braking and cornering. The suspension is now very crisp and stable and the relative frequencies are very good (about 1.6 Hz / 1.7 Hz F / R).

a

Stay tuned!

[vtl]

Originally Posted by vtl

Partly inspired by your thread, I ended up doing a project replacing most of the rear ball joints with the Lemforder 3067901 joints...

Fixed up the image links, bimmerpost has broken them all

[ajsmithvmi]

Originally Posted by vtl

Fixed up the image links, bimmerpost has broken them all

If someone wanted the conical adapters could the cad files be shared, perhaps for a nominal fee? Hypothetically of course.

[vtl]

Originally Posted by ajsmithvmi

If someone wanted the conical adapters could the cad files be shared, perhaps for a nominal fee? Hypothetically of course.

Would not be interested in making money off the community like that, attached below. We did a small run of 72 units in our group buy, which ended up being around $21 AUD for a set of 4. I elected to choose stainless, but you could do make it out of other materials if you wanted. Could have used mild steel then zinc plated but didn't want to introduce more lead time and more steps.

Anyone interested in following how the project turned out from start to finish can see in my build thread here
https://www.1addicts.com/forums/show....php?t=1302309


Installation notes

Due to the fact that the Lemforder mounts are only 1.5mm narrower in width to the stock tapered bushings, there is no space to make a tapered washer 1.5mm thick. I ended up designing the washer to be 4.5mm thick, then pressing the ball joint offset 3mm to make the geometry the same.

Illustrations here:
https://www.1addicts.com/forums/show...&postcount=293

[ajsmithvmi]

Thanks!

On a related note, will the lemforder ball joints fit in the non-m suspension arms?

[vtl]

Originally Posted by ajsmithvmi

Thanks!

On a related note, will the lemforder ball joints fit in the non-m suspension arms?

Yes it would fit, but the pressed sheetmetal design of the arms do make it harder to press the ball joints in straight. I also would hate to have to do all that effort (including making the washers) just to end up with the aesthetically challenged non M arms.

The curved upper camber arm has an additional benefit in that is provides extra clearance for the M sway bars if you ever wanted to go down that route. Otherwise at full droop the straight non M arm actually touches theM3 sway bars and certain aftermarket sway bars.

[tree233]

Originally Posted by fe1rx

I am making replacement bushings because:
1) I have the Turner parts in hand to reverse engineer the basic design
2) As I am able to measure the arms I have on hand before making the parts, I can ensure that the bushings I make will be interference fit in those actual arms and don't care about all possible arms (which Turner necessarily must).
3) I have the spherical bearings, retaining rings and spacers from the Turner parts so don't need any additional parts
4) Getting Turner to replace the part would involve substantial shipping costs both directions because I am not in the USA

Hey fe1rx, did you measure the OD of the Turner spherical by any chance?

I'm trying to decide between Turner/GAS and another option which claims it has more than 2.5x the impact & load bearing area... but I'm skeptical...

[fe1rx]

Originally Posted by tree233

Hey fe1rx, did you measure the OD of the Turner spherical by any chance?

I'm trying to decide between Turner/GAS and another option which claims it has more than 2.5x the impact & load bearing area... but I'm skeptical...

The Turner part is made by knurling a 2.726" diameter. The knurl crests produce a larger diameter than that. Unfortunately I don't have a record of the crest diameter when new.

For your info, the crests on my worn out part measure 2.742" diameter. Looking at the worn crests it is apparent that they represent only about 50% of the bearing area. It is not unreasonable to assume that when new they only provided 40% (= 100% / 2.5) of the available bearing area, although I would guess even less.



The diameter of the part I made to replace it is 2.758", with 100% bearing surface.

[tree233]

Thank you for the details fe1rx.
Did you measure the OD of the bearing itself rather than the housing?

[fe1rx]

Originally Posted by tree233

Thank you for the details fe1rx.
Did you measure the OD of the bearing itself rather than the housing?

The bearing is 47.3 mm diameter (1.862").

By the way, the bearing is p/n 33326792553, which is the camber arm outboard ball joint.

[tree233]

Thank you fe1rx!

[Atomicteal_M3]

Can anybody confirm that Lemforder 3067901 is the same as Lemforder 33326792553? They look the same but I'm unsure about the dimensions.

[fe1rx]

Originally Posted by Atomicteal_M3

Can anybody confirm that Lemforder 3067901 is the same as Lemforder 33326792553? They look the same but I'm unsure about the dimensions.

3067901 has an OD of 45.2 mm based on the attached image (although I believe it is actually 45.15 mm, to split hairs ...). It can be used to replace the rubber trailing arm bushings.

33326792553 has an OD of 47.3 mm. It is the standard outboard camber arm bearing that is pressed into the bearing carrier.

[Atomicteal_M3]

Originally Posted by fe1rx

3067901 has an OD of 45.2 mm based on the attached image (although I believe it is actually 45.15 mm, to split hairs ...). It can be used to replace the rubber trailing arm bushings.

33326792553 has an OD of 47.3 mm. It is the standard outboard camber arm bearing that is pressed into the bearing carrier.

Attachment 2445419

Thanks for the info. I'll continue to look for the 3067901