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      06-14-2020, 03:27 PM   #23
Tambohamilton
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Yeah, the spring rates I'm throwing around aren't 100% accurate. But I'd be surprised if they were worse than 95% accurate. And like you say, the rates are not constant... I'll be very interested to see how you get on with the D8 setup, especially at the front. Please get good before/after ride height measurements.

That thread you linked was about Xd stuff...what was the takeaway from it? Sorry, I read through, but didn't come across anything I didn't already know (ish).

Regarding your existing setup, I completely agree with what you said about the RSFB - made everything so squidgey that it was impossible to tell what was what back there!

Regarding the spring rates, I think upping to ~145lb/in won't present a problem in itself - you'll still have a much lower front ride freq than rear (softer front (compared with rear), as is the norm on passenger cars). And I think the front stiffness will still be around the 'sporty passenger car' realm, rather than track/race car.

I think with those additions in your front end, you'll end up with 15~20mm increase in front ride height. I could well be wrong though! And if that is the case, you can just swap back to your stock spring perches and you'll be back at stock ride height if desired.

What bump stops will you go with? I would/will switch to something much shorter if/when I do mine.


I think there's another option too...M3 front springs! Obviously the M3 strut mount is way different from a non-M one, but the spring perch rubber on the strut itself is the same part number for M and non-M: 31336764372. I think that should mean that the springs will fit our struts, with the possible exception of the top spring perch. With a suitable sleeve (M14 vs M12 shock threads), the M3 top mount could fit in our cars, but I have no idea about its stack height. M3 shocks don't fit our cars without the steering knuckle (and the lower arm for the rear)...never mind the EDC stuff.

M3 springs (could) give the option to have much firmer front end - up to about 1.5Hz ride frequency, which could match the rear end nicely...I'm working on numbers and things in the background here, but have reached a point where I need to know the front and rear roll centres, and CoG height. I may have to resort to faffing about with a tape measure on my car, and drawing the suspension geometry up in CAD...accuracy would be debatable, most likely, but should be better than a finger in the air.

Also been looking for data/specs on Alpina springs, but can't find much; I imagine they'd be a more sensible middle-ground between non-M and M items. All I've found on them so far is that they're likely manufactured by Eibach, and they have the Alpina part no 31 33 130, which seems not to exist outside dealerships. Alpina parts catalogue:
https://drive.google.com/file/d/14UT...ew?usp=sharing

Come across a searchable version of the Suplex spring catalogue, which has pretty handy notes on spring nomenclature:
https://drive.google.com/file/d/1eEW...ew?usp=sharing
Lists X and Y springs (M3), as well as L springs for Xd cars........
I've been using Autodoc.co.uk to find specs on each spring (dia, wire dia, free length).

Last edited by Tambohamilton; 06-14-2020 at 05:54 PM..
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      06-16-2020, 02:27 AM   #24
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Quote:
Originally Posted by Tambohamilton View Post
Yeah, the spring rates I'm throwing around aren't 100% accurate. But I'd be surprised if they were worse than 95% accurate. And like you say, the rates are not constant... I'll be very interested to see how you get on with the D8 setup, especially at the front. Please get good before/after ride height measurements.

That thread you linked was about Xd stuff...what was the takeaway from it? Sorry, I read through, but didn't come across anything I didn't already know (ish).

Regarding your existing setup, I completely agree with what you said about the RSFB - made everything so squidgey that it was impossible to tell what was what back there!

Regarding the spring rates, I think upping to ~145lb/in won't present a problem in itself - you'll still have a much lower front ride freq than rear (softer front (compared with rear), as is the norm on passenger cars). And I think the front stiffness will still be around the 'sporty passenger car' realm, rather than track/race car.

I think with those additions in your front end, you'll end up with 15~20mm increase in front ride height. I could well be wrong though! And if that is the case, you can just swap back to your stock spring perches and you'll be back at stock ride height if desired.

What bump stops will you go with? I would/will switch to something much shorter if/when I do mine.


I think there's another option too...M3 front springs! Obviously the M3 strut mount is way different from a non-M one, but the spring perch rubber on the strut itself is the same part number for M and non-M: 31336764372. I think that should mean that the springs will fit our struts, with the possible exception of the top spring perch. With a suitable sleeve (M14 vs M12 shock threads), the M3 top mount could fit in our cars, but I have no idea about its stack height. M3 shocks don't fit our cars without the steering knuckle (and the lower arm for the rear)...never mind the EDC stuff.

M3 springs (could) give the option to have much firmer front end - up to about 1.5Hz ride frequency, which could match the rear end nicely...I'm working on numbers and things in the background here, but have reached a point where I need to know the front and rear roll centres, and CoG height. I may have to resort to faffing about with a tape measure on my car, and drawing the suspension geometry up in CAD...accuracy would be debatable, most likely, but should be better than a finger in the air.

Also been looking for data/specs on Alpina springs, but can't find much; I imagine they'd be a more sensible middle-ground between non-M and M items. All I've found on them so far is that they're likely manufactured by Eibach, and they have the Alpina part no 31 33 130, which seems not to exist outside dealerships. Alpina parts catalogue:
https://drive.google.com/file/d/14UT...ew?usp=sharing

Come across a searchable version of the Suplex spring catalogue, which has pretty handy notes on spring nomenclature:
https://drive.google.com/file/d/1eEW...ew?usp=sharing
Lists X and Y springs (M3), as well as L springs for Xd cars........
I've been using Autodoc.co.uk to find specs on each spring (dia, wire dia, free length).
My takeaway from the Xi thread was that when the car was upgraded to the highest rate front springs it didn't raise at all. All things considered (shorter struts, etc it barely dropped at all. Obviously, not the best comparison tho. The higher rate meant nothing really, but again, strange example there.

I will absolutely be taking lots of measurements.

Bump stops - I spoke with several members and worked out a solution that was way too complicated on my own. In the end, I'm going with BMW OE sport bump stops. It seems to make the most sense to me after I over-analyzed it.

M3 stuff - the research I did here indicated this was a no-fly zone and not compatible. Certainly open to hearing differently!

The Alpina stuff... Now that's a great thought! I'd imagine that would be hard to go wrong with. Hmmm, I did not need to hear that!
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      06-16-2020, 05:32 PM   #25
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My thoughts on the M3 things are:
- springs will fit non-m struts.
- M3 top mounts will fit any e9x chassis.
- non-m strut will need a +2mm sleeve to fit the M3 top mount. Easy, if you have access to machine tools (I do).
- Discrepancies in ride/stack height can be compensated by spacers on top of the strut mount (I already own 2x OE ~3mm ones from my car), and/or spacing the strut out of the knuckle slightly (with a bit more engineering).
- the more spring rate you have, the less need there is for bump stop.
So they certainly aren't compatible, and resulting ride height is an unknown, but I think that all obstacles can be fairly easily overcome. New aftermarket springs ("Y2") can be bought for around £45 ea.

Yes, I think alpina springs would be the simplest upgrade. But they're rather rare, for obvious reasons! Can be ordered from a dealer, or a very few online sources. Also, I'd really like to get the measurements for them, at least for comparison, before laying down £$.
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      06-17-2020, 08:52 AM   #26
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Quote:
Originally Posted by tlow98 View Post
My takeaway from the Xi thread was that when the car was upgraded to the highest rate front springs it didn't raise at all. All things considered (shorter struts, etc it barely dropped at all. Obviously, not the best comparison tho. The higher rate meant nothing really, but again, strange example there.

I will absolutely be taking lots of measurements.

Bump stops - I spoke with several members and worked out a solution that was way too complicated on my own. In the end, I'm going with BMW OE sport bump stops. It seems to make the most sense to me after I over-analyzed it.

M3 stuff - the research I did here indicated this was a no-fly zone and not compatible. Certainly open to hearing differently!

The Alpina stuff... Now that's a great thought! I'd imagine that would be hard to go wrong with. Hmmm, I did not need to hear that!
Should work, if you can find parts from a B3 given that they weren't sold in the US other than the B7.
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      06-17-2020, 10:31 AM   #27
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Didn't know that! They're rare enough here in the UK!
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      06-17-2020, 07:06 PM   #28
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Can ya tell what it is yet?? (pardon my outrageous screen filter!)



Wouldn't have been able to create that with any sort of accuracy without fe1rx 's many awesome threads on 1addicts, particularly this one:
https://www.1addicts.com/forums/show....php?t=1604010
As it is, there is still a chunk of work to do to properly transpose it to show my car, and then get any meaningful data out...but now I must sleep (1am here).
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      06-18-2020, 02:42 AM   #29
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Orion's belt never looked so scripted!
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      06-24-2020, 02:30 AM   #30
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Fixed a massive error with the weight distribution in the spring rate/ride height spreadsheet last night. Also realising that the spring rates are likely nowhere near as accurate as I'd hoped...

Suspension model is nearing completion...almost spreadsheet time again!

Last edited by Tambohamilton; 06-24-2020 at 02:37 AM..
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      07-19-2020, 05:36 PM   #31
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Spreadsheet is now a reasonably user-friendly item, and seems to churn out sensible numbers. There's still something a bit off, particularly with the ride height/spring length calculation in all the spring rates, but I don't think it's miles off producing accurate results. Spring rate and ARB calculations seem decent anyhow, and the ride height has a fairly minor influence on the roll rate...

https://docs.google.com/spreadsheets...it?usp=sharing

The 'Damping' sheet is still very much a work in progress - I need a lot stronger maths before that's any use at all! Imaginary numbers give me the heebie-jeebies though, so don't expect any progress any time soon!

If there's anything that anyone particularly wants to see in there, let me know and I might be able to add it in...
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      09-20-2020, 10:50 AM   #32
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Boring update...

Oil change time came around, and I found some Fuchs Titan GT1 Flex23 5w30; 20L for £73 delivered. It's LL-04 approved, so I went ahead with it.



I had been getting a faint but definite knock that was only noticeable at low rpm (1000-1500) and on smooth roads, and with the new oil this has gone away...fingers crossed it stays away! The previous oil was Castrol Edge 0w30, which should be right for the engine, so I don't think there were any issues there...just time for fresh oil. Couldn't see any sign of anything bad in the old filter anyhow.



The old filter was a Mahle part, and the new one is an OE-spec Mann one.

I've taken an oil sample for analysis, so will also post the results of that when I have them.


Also, I've unshared my suspension spreadsheet for now. It's a bit inaccurate for the time being, and I've actually put a lot of hours into it so far, so I'm not sure I'm really ready to publicise it right now... I'll probably put it back up though, when I'm happy with it. Haven't done anything on it for a few months, but maybe that will change with the dark of winter coming up.

Last edited by Tambohamilton; 10-02-2020 at 09:02 AM..
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      05-23-2021, 06:50 PM   #33
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6 months on, and a slightly less dull update..



Driver/off/RH side spring snapped on a compression in the road. Thankfully I wasn't far from home, and could limp back like this.


Dat stance.....

This has slightly forced my hand to get on with the next stage of suspension work I've been contemplating, albeit with rather less analysis than I had planned. I've ordered up some T4 front BMW performance springs, drawn up a simple camber fix plate, and had a quick check that the D4 rear springs I have are roughly what I've been aiming for. I'll be pairing them with my existing koni special active shocks/struts (not ideal, but funds do not permit better currently).

I'll also use OE E36 M3 front, and Z4M rear bump stops. I had planned to add these to my spreadsheet to get an idea of 'magic number' Vs roll angle/lateral g, but I haven't got around to implementing that yet, so I'm fitting them on a whim and a prayer.

Let's see how this goes...

Last edited by Tambohamilton; 06-02-2021 at 06:47 PM..
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      05-24-2021, 06:07 AM   #34
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Ouch, good luck with the swap!
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      05-24-2021, 09:10 AM   #35
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Thanks! Looks like the first hurdle - actually having all the parts arrive before the weekend - is going to plan so far. Fingers crossed!
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      05-25-2021, 04:08 PM   #36
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Well, so far so good! Got a couple of deliveries of parts today. Rather stoked to have found BMWP T4 springs in stock in the UK...though I'm now less sure that they're the right part. I guess I'll find out! Now just need for a couple of ancillary tools and a pair of laser cut camber plates to show up and I'll be sorted...


Last edited by Tambohamilton; 05-25-2021 at 05:21 PM..
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      05-25-2021, 05:24 PM   #37
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Just had another look at my spreadsheet, and I'd made an error in the calculation of rate/length/etc for these T4 springs, so now I've fixed that I'm much happer they'll work out nicely!

Also fixed pics from the last few posts...again

Last edited by Tambohamilton; 06-02-2021 at 06:48 PM..
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      06-02-2021, 07:30 PM   #38
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Well, that went quite well and quite badly. I made plenty mistakes, but well pleased with the results!


Box of bits from BMW. Note that I bought the E36 dust covers to suit the bump stops, but they are not compatible with e9x struts; they'd hit the spring perch and get all messed up (they're just a plain tube, not a concertina).


My camber plates, freshly laser cut and tapped (not yet deburred!). I hadn't realised my error yet...When I initially drew them up months ago, I hadn't checked the orientation of the mount holes in the car. Between then and now I'd forgotten that I needed to check it, so these got made as they were. The end result would have been +0.33deg of castor, and -0.67deg of camber, instead of the -1deg of camber that I was aiming for. I'd also planned to reuse the Xd top mount studs pressed into the plate with their heads recessed, but without a mill that wasn't happening. So I ended up drilling, tapping and countersinking new holes in the correct orientation, for countersunk bolts to thread into and stick up through the strut tower.


Here they are with the Xd top mounts attached, along with the OE gaskets. I hadn't realised mistake #2 yet.


Note the cap head bolts I used to mount the strut tops...


2 assembled struts, nearly ready to go back in! Note the full length stock dust covers.


Gaskets to prevent creaking against the strut tower. I used 0.8mm gasket paper, but would use ~0.4mm if I did it again.

Now all that was grand to begin with. Ride height was basically unchanged initially from its previous position (~600mm, 18" rim to fender, no load in car). It dropped a few mm after a short test drive, then another 6mm ish after a longer drive. It currently sits at 593mm.

On the first drives I noticed some clunks when turning the steering. I poked about a bit, but didn't have time to figure out what was really happening for a couple of days. Turns out that the cap head bolts holding the strut tops to my camber plates were fouling the top spring seat when the strut was mounted and weighted (they were clear when the struts were out of the car)...


Oops!


All that snagging when turning the steering resulted in the springs being forced around on their seats. Not pretty.

I managed to remove the strut tops with the struts still in the steering knuckle, and replaced the cap heads with button heads; these seem to have enough clearance, though I might eventually replace those with countersunk bolts too. I reseated the springs of course, and now all is good! I've also trimmed the bottom 2 pleats of the dust covers off, because they were longer than needed.

Here's how the camber plates/top mounts look in-situ; I'm quite pleased with how inconspicuous they are!


Hopefully on Friday I'll get time to replace the rear springs to match, along with swapping in a pair of M3 arms to clear the E93 M3 rear sway bar I have back there. The rear is currently sitting at 608mm ride height, so it doesn't look right as well as the suspension not being in an ideal position.
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      06-03-2021, 09:31 AM   #39
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Thanks for sharing the mistakes and the creative suspension setup!

It will be great to get this dialed in.
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      06-03-2021, 10:50 AM   #40
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I'm already very happy with it. It's just as comfortable as the previous setup, and the car feels much better balanced; previously the rear roll stiffness was noticeably greater than the front, and the front wallowed in corners. My concern was that adding so much spring rate to the front would lose a lot of mechanical grip, hence increasing the negative camber at the same time.

Hopefully I'll get some of the back end done soon...
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      06-04-2021, 06:38 PM   #41
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Got the rear springs swapped in today Haven't had a chance to drive it at all, but so far at least the ride height is about where I had hoped it would be.


Out with the old and rusty/dirty, in with the old and clean.

I've switched from F3 (stock, touring non-sport/SE) to D4 (M-sport from an E90 335i?). They're pretty much identical in terms of spring rate (543 vs 548 lb/in, according to my calcs), but the D4 is some ~1/2" shorter.


New vs old bump stops/aux springs.

I've blindly swapped in Z4 bump stops at the same time, so I'm hoping for good things in the 'magic number' department...I won't really know without someone providing test data of these and the E36 M3 front bump stops, but hopefully this setup will continue to feel good!

While I was in there I took 7mm (37mm>30mm) off the internal sleeve of the rear shock top mount, so that the rubber parts are more compressed. This is probably a bit much really; I guess 5 or 6mm would have been a little more sensible. I also opened up the crazy tight E93 M3 rear sway bar bushings a tad, though I'm not sure if that'll have any effect on the drive/ride/noise.

Fingers crossed for the test drive!
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      04-07-2022, 12:58 AM   #42
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Ok, ok, ok. Let’s hear it. What are your final thoughts on this?

Sry to see about the spring failure. Never fun!

Wish I’d have caught this earlier so I could have goaded, errr ‘helped’ you into springing (pun intended) for some Koni yellows!

Maybe next time.

Would love to know your final ride heights. Also spring rates on the T4? I’d like to compare them to my 335i sport fronts. I haven’t measured my car since my sister took it over but to my eye the rear has seemed to settle more than the front. If the front were down 20mm it would look much better.
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      04-07-2022, 07:16 AM   #43
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Just read through all this, interesting stuff and I need to order some bump stops and shocks. I have a frankenstein setup on my wagon. Still running Bilstein B6 Xi front struts on a rwd converted car, with 335i rear springs and B6 shocks. My car is a hot mess with some clunks in the rear, crashing over potholes and the rear end and seems to pogo bounce some if I get the bounce right.

I ordered some B4 front struts and I need to get some B4 rear shocks. I was going to put it together with the 335 sedan front springs and I haven't decided which rear spri3gs to run. My wagon came with sport suspension, so I have those springs or the s35 edan springs , Ican't remember the numbers atm. The pano roof and heavy towbar hanging behind the rear axle makes me wonder if I should run the wagon springs?
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      04-08-2022, 08:12 AM   #44
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Quote:
Originally Posted by TyroneShoelaces View Post
Just read through all this, interesting stuff and I need to order some bump stops and shocks. I have a frankenstein setup on my wagon. Still running Bilstein B6 Xi front struts on a rwd converted car, with 335i rear springs and B6 shocks. My car is a hot mess with some clunks in the rear, crashing over potholes and the rear end and seems to pogo bounce some if I get the bounce right.

I ordered some B4 front struts and I need to get some B4 rear shocks. I was going to put it together with the 335 sedan front springs and I haven't decided which rear spri3gs to run. My wagon came with sport suspension, so I have those springs or the s35 edan springs , Ican't remember the numbers atm. The pano roof and heavy towbar hanging behind the rear axle makes me wonder if I should run the wagon springs?
Regarding your current rear end issues (nothing personal!), I am wondering if those B6's are worn out. Your car should not pogo or crash over potholes even when loaded up.

I would go with the wagon m-sport springs all around. I know other x-drive owners have lowered their cars, so this should not be an issue for you, especially since you have converted to RWD.

I just put a set of B4's on my '09 e91 RWD before I gave it to a daughter. My e91 has the sport suspension. I can dig out my Bilstein part numbers if you want to compare.

Sorry I do not have the spring part numbers, but mine are original sport suspension springs. I chose to re-use rather than replace because none were broken.
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