ZHP Ride Height

[shendrick]

We have a 2005 ZHP that had a RF strut leaking @ 75K miles. I didn't measure the ride height before it went in - but that might not matter since the strut had given up its gas. When the car came back today, I did verify the correct "sport" struts on the invoice (because of the part #s) - but the ride height did seem high. Besides struts and pads no other parts (such as springs) were changed. I measured 24.5" on the LF (from bottom of rim through the centerline of the wheel to the fender) and 24" on the RF. The car is all OEM, so 18" wheels and 225/40-18PS2s up front. Can anyone comment if this ride height is correct - or close to what you have?

[danewilson77]

They replaced springs as well?

Keep in mind it will settle a bit over time...say 5k miles.

Someone will measure their stock setup and be along shortly.

I thought JP posted stock measurements somewhere. I will never be able to find as I think its buried in a thread with something else.

Sent from Williamsburg, VA USA

[danewilson77]

Post #10 may give you some sort of an idea.

http://www.bimmerfest.com/forums/showthread.php?t=262384

Sent from Williamsburg, VA USA

[shendrick]

No, the springs remain the same, just new struts and pads. I do know that the coils are shorter (10mm?) - but nowhere in the manual does it give you ride height specs for the ZHP - just overall height of 330 and 325. I could meaure that and subtract about 0.4" but probably better to compare to what other members are experiencing. I do assume some settle in will occur - just trying to figure out if what I have now is close to others. I'm looking at this because when my 1999 740is had its struts replaced there were major differences in ride height that BMW could not explain.

[LivesNearCostco]

It's possible to install the strut without seating it all the way into the knuckle and that would increase your ride height. If new strut mounts are installed, they could increase ride height slightly if the old ones had sagged. And if the old ones had zero gas charge, the gas pressure might make the new one ride a tad higher. Suppose the new strut is charged at 40 psi and has a piston surface area of 2 sq. inches. That could put an upward pressure on that corner of 80 lbs compared to what the worn strut did. If the front springs have an effective rate of 200 lbs/inch, that might raise that corner by 0.4".

I don't know what the actual gas pressure charge is in a stock strut or what the real spring rate is (though I've seen some estimates of the stock spring rates), but it sounds good in theory! (And if you don't seat the bottom of the strut fully into the knuckle, it will raise your ride height.)

[midlandtech]

Just did strut replacement on mine about 4500-5000k miles ago and you are right where you need to be height wise I'm actually sitting right were you are at. Trust me I understand your apprehension with the changed ride height... I want mine lower now. If your truely concerned you can have them check to see if the springs were seated correctly as that can have an effect on ride height


~Steve
Sent from my iPhone using Tapatalk

[shendrick]

Any chance some of you could measure from the bottom of the rim to the top of the fender arch and report back what you find. Also mention rim diameter and about how many miles on the stuts so that we can adjust for that. I measured again this morning and found about 24.25" for the FL and 24" for the FR. I have 18" rims. The objective is to gain an understanding of age and ride height. With enough data point we could plot a curve and build some confidence limits around the curve to get a sense of where people are and what they can expect.

[Crickett]

Measured as requested (bottom of rim, through hub cap, to bottom of fender); I'm all stock* at 93,737 mi:

DF: 23 7/8" PF: 23 5/8"
DR: 23 1/8" PR: 23 1/8"

*(My driver-side front suspension was replaced with a used sport assembly after my accident; I have no info on how many miles were on it. It appears it's newer than my other struts.)

[shendrick]

Crikett, thanks for the #'s. Now we have 2 data points so now we have a line. As soon as someone else piles on we'll get a curve - which makes more sense.

[danewilson77]

Crikett, thanks for the #'s. Now we have 2 data points so now we have a line. As soon as someone else piles on we'll get a curve - which makes more sense.

X axis is wear, and Y is time/age?

Sent from Williamsburg, VA USA

[328ioc]

Measured as requested (bottom of rim, through hub cap, to bottom of fender); I'm all stock* at 93,737 mi:

DF: 23 7/8" PF: 23 5/8"
DR: 23 1/8" PR: 23 1/8"

*(My driver-side front suspension was replaced with a used sport assembly after my accident; I have no info on how many miles were on it. It appears it's newer than my other struts.)

I can confirm these numbers.

I am also completely stock and both fronts are aproximatly 23.75" +/- an eighth of an inch.

I did not measure rears.

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[shendrick]

X is age (mileage) and Y is ride height.

[shendrick]

328ioc, what is your mileage?

[328ioc]

328ioc, what is your mileage?

Just shy of 83,000

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[shendrick]

Let me amend the axis definition. X will be miles since last replacement of front struts and Y will be ride height.

[shendrick]

Not much variation so far, looks like we are settling in between 23-24" for the front.

[midlandtech]

4500-5000 miles on new shocks and struts ride height is 24.25 RF 24.2 (ish) LF

[johnrando]

F: 22 1/4, R: 21 7/8. Several hundred miles on an H&R Touring Cup Kit. (60K overall). Rear slightly lower due to vert rear sag, which is common unless you are on coilovers and adjust. EDIT: The ride height in my SIG is not where is sits now, that's a pic on the Race springs which I swapped out.

[danewilson77]

I thought this was a stock setup data thread?

[johnrando]

I thought about that, but then I thought someone might want a contrast just for comparison. That's why I pointed out I'm not stock.

[danewilson77]

Copy JR.........

[MrMaico]

23 7/8" both front sides. New OEM Sport/ZHP shocks and struts along with ZHP control arms installed about 12,000 miles ago. Original (currently at 101,000 miles) springs were reused with new pads. Stock wheels and tire sizes.

[danewilson77]

Just so everyone provides necessary data, only mileage on the stock springs are what will affect ride height.

Sent from Williamsburg, VA USA

[Bimmernut2]

Just checked mine...probably doesn't mean anything as it's an '05 convertible; w/29,000 miles and hardtop mounted; OEM 135 wheels; stock with full tank of gas
DFront= 23 13/16" PFront= 23 3/8"
DRear= 22 1/4" PRear= 22"

[terraphantm]

Just so everyone provides necessary data, only mileage on the stock springs are what will affect ride height.

Sent from Williamsburg, VA USA

BMW did give slightly different springs based on equipment -- I think they have something like 4 different springs front and rear based on equipment. And they weren't mutually exclusive -- as in options that added weight to the front would get different springs in the front without changing the rear or vice versa. In theory 16 combinations.

So I can imagine ride height varying slightly in those cases where some weight was added by options, but not enough to "upgrade" the car to the next tier.

[shendrick]

OK, Here is the model. This is for the front only and I combined (averaged) the left and right values for simplicity. The graph suggests an initial break-in period over the first 2,000 miles when you'll lose about 1/8" and then a very slow aging through the remainder of the stut life of another 1/8". Ride height is in inches as measured from the bottom of the rim through the center of the hub to the fender with 18" diameter rims. The equation which you can use yourself to predict your ZHP front ride height is as follows:

Ride Height = 24.157 * (1 + Mileage) ^ -.00126

I couldn't attach the plot because when I dumbed down the .bmp got hard to read. But here is the data. X = Mileage and Y = Ride Height.

X (Miles on front struts)------------Y-Averaged-------------Y-Predicted
0---------------------------------------24.1---------------------24.2
93,737--------------------------------23.8---------------------23.8
83,000--------------------------------23.8---------------------23.8
4,750----------------------------------24.2---------------------23.9
12,000--------------------------------23.9---------------------23.9
29,000--------------------------------23.6---------------------23.8

[johnrando]

Nice work. What does "^" represent?

[Hornung418]

Exponent.

From a GS3, this was sent.

[shendrick]

So my take away here is that ZHP front ride height is about 24" as we have been measuring +/- .25" based on differing configurations and age. This means that if you are more than +/- 1" from these specs you have a situation that deserves investigation. Also, for those interested in going down the path johnrando did with lowering (he's about 2" lower in front), you can get a better sense of what that means visually (although you're on your own as far as ride quality).