Updated: Lowering my 2.5si by a negative amount

[smorris_12]

From the day I bought my Z I was scraping the living hell out of the front splitter. I was used to the idea that it's a low 2-seater but it was ridiculous. Almost any shaped speed hump would grind. I did some googling and found that 2.5si's seemed to be prone to sitting low. I came across the BMW figures for ride height (and then lost them again - repeatedly. I could never seem to locate them reliably when I actually had the time to do some reading. Grrr) and eventually broke out the tape measure and got outside.

With 18s, BMW state 602mm rim to arch, +/-10mm when loaded up. Mine were 585 (driver's) & 590 (passenger). Somewhat low. The springs weren't broken but the top mounts weren't in the best of health with a couple of tears in them. I bought some new top mounts and tried to work out if they were responsible for any of the height loss while being too lazy to remove the strut. I came up with a figure of 5/6mm.

From this, while not in a drunken stupour, I decided, yes, I will, I shall raise the Titanic!..... No, wait, I mean suspension strut. By about 12mm. Or half an inch as Farage will have it. To do this I needed a disc of metal between top mount and chassis leg to keep the two apart. So I went and bought some lovely, tasty aluminium (best 150mm diameter x 17mm) from eBay and proceeded to run it through with a hole cutter in my pillar drill and tidied it up in the lathe:

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I marked off the three mounting holes (8mm) and the alignment hole (10mm) and then drilled them through. The new top mounts had their press studs removed forcibly by hammer so I could put longer plain bolts through the whole assembly while the mounting holes are partly threaded so that I could attach them to the top mount to make one assembly that would go into place nicely. Trying to manoeuvre multiple loose bits inside the strut tower seemed like it would lead to insanity.

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The ring was put in the lathe to reduce the outer diameter to match the top mount and thin it down from 17mm to 12 and bolted to the top mount with 10.9 set screws (which I bought too long because stoopidity.)

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I pulled the struts out and removed the old top mounts using a home brew spring compressor that, while it looks like it's made out of angle iron and random bits of scrap by Dr Frankenstein after a hard night in the tap room of the Lightning Rod and Hunchback, is infinitely superior to those damned spring compressors they sell in Halfords.

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I put it all back together and I got 600mm & 605mm, exactly 15mm up on where I started. In hindsight I wish I'd made them a bit thicker but I had visions of it looking like it was on stilts if it did turn out that the top mounts were much flatter. As you can see, they'd lost about 5mm.

What does this translate to? Before:

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After:

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It's hard to see the difference as the photos are crap as I'm up against the fence for these; the drivers side pics all ended up in shadow and out of focus. Did I mention my appalling phone camera? But the wheel now looks more centred in the arch and, best of all, I've not scraped a single thing in the month since.

[srhutch]

Your avatar pic clearly shows your car has been lowered, it’s wasn’t on standard springs.

[smorris_12]

The front springs are pukka BMW so, unless they've been replaced and the wrong ones put in, it ought to be correct. As I said, I've read several comments of the 2.5si sitting low.

Edit: just fetched out the code from another picture (31336760621) and they seem to be correct for a 2.5si (according to a Suplex part) or, at least, 6-pots going by an eBay advert.

Just to add complication, the rear seems to be on non-sport springs as it sits as per SE specs, although they feel equally as hard as the front ones.

[srhutch]

Something def not right.

This was my 2.5si and you can see it sits much higher. I’ve never read about them sitting low.

viewtopic.php?t=20315

[smorris_12]

Lovely wheels. There's nothing else that controls ride height and springs don't normally deform much. I must try and find those posts I found about them sitting low.

[Smartbear]

Lovely wheels. There's nothing else that controls ride height and springs don't normally deform much. I must try and find those posts I found about them sitting low.

I’ve read a few posts about si models scraping their chins, they were all blamed on worn out dampers & a consequent lack of compression damping
Rob

[MrPT]

Pretty odd. I haven’t heard anything about 2.5si’s being low at the front either. This was mine on stock (Sport) springs -

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[smorris_12]

It was on other forums somewhere, my Google Fu is letting me down again. It was perhaps more comments about scraping too often. It might be that the whole car has tended to sit lower and age and wear on both springs and top mounts contrived to give me trouble.

I could replace the springs but without going to BMW that can be a lucky bag. I redid my 320d SE with sports spec suspension based on the Sachs spring and damper catalogues and that came out about 10mm lower than I expected.

Maybe gravity is higher round here? (I'm which vein, I'm only 10st8 so it's not my pie count!)

[skelters]

3 fingers between the tyre and wheel arch = SE Suspension
2 fingers = Sport
1 finger = it's been lowered.

Either it's on the wrong suspension or the suspension is knackered.

[Zedebee]

Either way, you can’t knock the engineering solution, even if it may have been unnecessary. I expect that was a very satisfying project.

[Mr Tidy]

Definitely!

Whatever the issue(s) those spacers look great - lovely job OP.

[smorris_12]

I have sat, stood and laid down stewing over this since last September (it's now June) wondering if I've made myself look silly[1] with all the machining, the mildly amusing language and the rest of it.

Am I, I would ask at 3am to passing burglars, just looking at saggy springs? And why didn't I waste my money on new ones instead of several quids worth of ally? Should I have just listened to the posts saying it's obviously been lowered and be a man and lift your skirts when going over sleeping policemen?

The back being high bugged me and with the front suspension being firm enough to shake the fillings out of passing pedestrians, I thought something must be done so, in a rush of blood to my PayPal account, I sprang for new springs.

I dug thru the Suplex catalogue, looked up M-Sport alternatives for a 2.5si with optional equipment (I've got cup holders and map lights) and found the world's slowest car parts supplier[2] to provide them. Part numbers 06248 front and 06231 rear.

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They arrived. I made a thing to lift the back of the car in one go (there I go again, see: viewtopic.php?p=2010083) because I'm too lazy to move the trolley jack side to side, and set about the rear springs. First thing of note, the new springs are already longer than the old ones which, going by ride height, appear to be SE spec. Cue much swearing. Although, for my blood pressure, I kept telling myself that the ones on the car are not original and not BMW so I'll just hope it's a spring rate thing. I think they have Sachs code numbers on them from some idle Googling.

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Moved to the fronts, dug out the Iron Maiden (strut version) and pinged out the spring. Original BMW spring, the part number agreeing with the car apparently and... it's exactly the same length as the Suplex replacement I've bought. I kick at the cat, curse at the postman who's just arrived and throw things about a bit while searching for my Spring Rate Hypnotherapy tapes.

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Now, of course, we're back where we started. Do I take the lifting plates off, assuming that the springs have merely been compressed over 17 years or do I leave them in place in a state of paranoid panic? Well, I left them on because I'd rather come back to it at leisure and take them off than have to spend the next day putting them back in before I destroy the bumper.

So, the results:

The back is sitting lower than it did before by about 10mm but still about 14mm higher than the spec says when I sit on the bootlid (my logic being that most of the passenger weight is on the rear axle rather than the front.)

The front is sitting about the same as it was before and about right against the spec but this is still with the spacers in. Which leaves me confused. Is the spec wrong (although the scraping was all too real before)? Am I failing to identify domed out strut towers (they don't look it and it's nice and even left to right)? Am I so heavy that the suspension sags when I merely stand next to the car?

I'm completely bemused. But I'm happy with the ride height and the ride feels slightly less spine shortening so we'll call it a win, I suppose.

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[1] Well, sillier.

[2] I really don't want to leave them crap feedback on eBay or name them but they must have missed the memo about the cut throat prices and delivery times in the world of car parts.

[enuff_zed]

I’ve read all this and think I’ve found the solution. Your car is fine but your drive is too high.

[j3nks79]

The front looks like it’s sitting very high. And it looks like the caster is off as the wheel looks to be sat closer the to front bumper.
Which adding a spacer would do this.

[smorris_12]

I’ve read all this and think I’ve found the solution. Your car is fine but your drive is too high.

Ha. That's only half of it; the exit is uphill and quite steep with a bit of a hump at the top so I was paranoid about driving down it first time and grounding out! My E46 can scrape when loaded and a stock E39 Sport Touring didn't like it at all.

The front looks like it’s sitting very high. And it looks like the caster is off as the wheel looks to be sat closer the to front bumper.
Which adding a spacer would do this.

The camera/angle/lighting is making it look worse than it is. I've just tried taking another photo and had similar results. It's slightly further forward than back but by the same amounts as my E46 (all I have for a yardstick.) I'd agree about the spacers altering the geometry excepting that the ride height is nearly bang on book figures which means the strut length is "correct". The front is sitting 603/607mm unloaded while the official BMW figure is 602mm with various weights in various places.

The only thing I'm left with is that the oft-quoted table of heights is pre-facelift and BMW did something aggravating to the facelift (unlikely.)

I also think the ride height is right as a) the wheel's centred vertically in the arch and b) srhutch's comment about my profile pic looking lowered.

I think I'll take up something easier like international politics.